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Author Topic: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?  (Read 3215 times)

ace.cafe

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Okay, I thought I'd approach a technical subject here, which often comes up early in conversations about modifying the performance of the Classic Iron-Barrel Bullet engine.
This pertains to 500cc Bullets, and not the 350(which is different).

Alot of people get to thinking about doing performance mods to the Bullet to "perk it up" a bit more. Of course the exhausts and carb re-jet and filter come first. but many then wonder about getting "a little more" and think about pistons, cams, and "porting".

What is "porting"?
"Porting" in terms of cylinder head modifications is simply the concept of changing the shape of the inlet port and/or the exhaust port, in an effort to allow more mixture into the engine, so it can burn more, and thus increase power. That's the concept.

The "traditional" way of thinking about porting is to make the ports larger. After all, it stands to reason that if the ports are bigger, they can let more air in. And in many cases that is true, and this is done as common practice in many engine modification procedures for performance.

However, we need to look at all the things surrounding this "porting", to determine how much, if any, work needs to be done in this area. And it totally depends on the exact design of the particular engine that is undergoing modifications, as well as the goals for the modifications.

So, you say, "I want it to go faster". Sounds simple enough.

Ok, let's look at our Bullet engine design parameters and see what we have to work with.
First, we can look at the limiting factors which will define our boundaries for our goals.
This is a basic set of goals, based on the idea that you still want to ride your Bullet on the road, and not just be strictly a track bike.
We have the displacement to feed, which is defined by our bore and stroke for the cylinder that we want to fill.
We have a stroke length which is very long, in comparison to most modern engines.
We have a goal of good street powerband with increased power over a fairly wide range of rpms.
We want to maintain decent reliability, and not have to rebuild the engine very often.

Now, for optimal filling of the cylinder, knowing the basic cylinder displacement already, we need to look at how many rpms we are going to be seeing with this engine. And in our case, it is generally about 5000 rpms, with a possibility of going to 5500 rpms on occasion, and certainly never going over 6000 rpms. This is so we don't blow up the engine bottom-end from revving beyond its capability.
So, that's a limit. And now we need to feed that 500cc's, from 0-5k rpm ,or maybe up to 6k rpm.

Now, when does the port get into this? Right now.
Ports are a transport mechanism for our air volume to enter the engine.
The air flows in with certain air mass, and certain air speed. If we want to maximize our fill, we want to get as much air mass into the cylinder as we can, in the time allotted by the intake valve's open time.
So, now comes the "garden hose analogy".
If we are watering the lawn, and we have a hose of a normal size, we get a certain flow rate of a certain mass and a certain speed, and this adds up to the volume that comes out in an allotted time. If we make the hose bigger, but don't change the water tap setting at the faucet, then what happens? The water comes out slower, doesn't it?
But, even if it comes out slower, if more comes out over the time period, we get gains because the diameter was previously restrictive. And if less comes out, we get losses because diameter wasn't restrictive, but flow speed dropped. Similarly, if we make the hose narrower, the water comes out much faster. And if it comes out faster, and still can flow more water over the time period, we get gains.  But, if it comes out faster, but is restricted to the point that even though it's moving faster, we get less overall water coming out over the time period, then we get losses from the restriction.
So, there are boundaries in both things. Faster flow can help, and larger size can help. But,  only to the points where they create lesser volume flow by either restriction or insufficient speed.

And this is why ports have a certain size. They don't just cast a hole in the head and hope it works.

So, where does this leave us with the Bullet?
Well, the Bullet ports are not very well designed for performance purposes. They are mostly "backwards" in design, because they get wider from the manifold joint to the valve head. A performance port would get slightly narrower from the manifold joint to the valve head, because the ideal would be to force the volume of the larger opening at the manifold to speed up just as it enters the cylinder at the valve, this getting the volume we want at the highest speed.
Unfortunately, we cannot do this with the Bullet head, and this is primarily why porting the Bullet doesn't work as people expect it to.

Engineering practices have shown that air speeds around 300ft/sec is a good flow rate for an intake port to keep flow going into the cylinder real well. The Bullet in stock form with an Indian-made cylinder head can do that, but it requires a very high rpm to do it. 32mm port is big for this engine, at the rpms it can generate. It's actually about as big as it can get, without causing weak areas in the casting, so we can't even really enlarge it much, even if we wanted to. So, we'll never get the ideal port shape, within the flow rate boundaries necessary, because we're already too big to start with for low rpm benefits that we can use with this engine. And casting sizes preclude us from really ever getting the ideal shape anyway.
All this really means, is that we can't enlarge the Bullet ports for beneficial effects at the rpms that we can run it on the streets. Enlarging is not the answer for the Bullet.

So, what can we do?
We try as best we can to improve flow rate marginally, because we already have enough mass capability for our needs. And we can't idealize the shape, really, because of the previously mentioned limitations.  So, we work on general smoothing and improvement of the shape of the port at the downward turn to the valve, and the area just prior to the valve seat.
We can't "change the size of the hose", but we can make sure that the hose is real smooth inside, and has least ill-effects from flowing out the nozzle by optimizing the shape of the nozzle. So to speak.
Our "hose"(port) has alot of rough casting flaws and marks inside it that can impede flow speed, by causing turbulence in the airstream. So, we smooth them down as smooth as we can, without doing any significant enlargement. We just sand down the protrusions, and smooth the surfaces, but don't try to smooth out all the little pits and pock-marks. They don't really matter much. It's the things sticking up into the port that we want to knock-down, and smooth into the general shape of the port.
No "high polish" is needed, nor wanted in the intake port. 220-grit sandpaper finish is just fine in the intake.
That's about all we need to do in the general "tubular area" of the intake port.

Then we come to the bend in the port, after the valve guide location. This is where we can do some good. The casting usually gets pretty rough around this bend. Sand off all the big  casting flaws that stick up here too. And make a nice smooth shape around the outside of the valve guide support hump(not the valve guide itself. leave that alone).

Now we come to the "transition area" where the port changes shape into the "bowl" around the valve guide, and you'll notice that on the floor of the port, there's a pretty sharp turn down to the valve. This is an important area. DO NOT LOWER THE FLOOR OF THE PORT AT THE TURN! Just lightly radius any sharp edge at the peak of that turn, VERY LIGHTLY, so it's not a "table edge", but instead is a a very small radius "bullnose" edge. JUST A LITTLE!

Then work the bowl area with your 220 sandpaper, to smooth the bowl into a nice bowl shape, and try to smooth out the crags and craters as best you can, and blend it very nicely to the joint where the port meets the valve seat insert. If there is a mismatch at the valve seat insert where the bowl is narrower than the seat insert, blend that to match the seat insert, so the flow is smooth from the bowl to the seat insert.

When doing this, make sure that you don't scratch or sand the valve seat insert unnecessarily, and certainly do not even touch the actual valve seating angle cut onto the insert.

Then, take the head to your automotive machine shop, and have them do a 5-angle valve job on the valve seat. This is where most of your gains will come. A good 5-angle valve job, blended to the port bowl, will give more result than all the other stuff you did.

So, here's what we accomplished.
We used the already large diameter port size to keep our air mass levels, without enlarging it any, so as to not have a negative impact on our port speeds.
We helped the port speeds to reach their maximum capability, within the framework that we could work in, to remove obstructions and smooth the pathway into the engine. We rounded any sharp "table edges" on the short-radius turn to help the air hang on to the port as it goes around the bend on the floor. And we shaped the bowl and transition to the valve seat insert to remove obstructions, and generally smoothed the shape. And we got the right kind of valve job to assist the air to hang onto the turn at the valve seat into the cylinder.

This is the best you can do with an Indian-made Bullet cylinder head.
You don't need to do jack-shit with the exhaust port, because it's already so big that we actually want the restrictions in there. You can actually leave the exhaust port just as it is, or if you want to knock down any big mountains or ridges left by the casting process, you can do that.

If you do all this correctly, it can be good for maybe up to 15% improvement in power.

And this is why, if you buy the "ported head", it is done just like this, except they put in big valves(which aren't needed for a street Bullet), and do a real nice beadblasted finish, and use top-quality valves and valve guides..
And don't get me wrong, the Stage 1 and Stage 2 heads are really well-done. And they are very good for those who don't want to do the work themselves. But, they are done very similar to what I just described. They are not "hogged out" giant ports.

If you "hog out" the ports oversize, you will KILL the flow in this head, for the engine rpms that we will use on a street Bullet.  Do NOT enlarge the ports.

I hope this has been helpful to those of you seeking more power levels out of your Bullet Iron-Barrel 500 engine.
Please feel free to ask specific questions about this procedure here, and I can help you with those, or clarify things that I perhaps didn't describe as well as needed to be fully understood.

« Last Edit: December 10, 2008, 05:51:02 PM by ace.cafe »
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Cabo Cruz

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #1 on: December 10, 2008, 04:57:33 PM »
Ace, what a great lesson!  And, you explained the process so well that even an old Cuban like me understood every single phase!  WOWZAA!!!
Long live the Bullets and those who ride them!

Keep the shiny side up, the boots on the pegs and best REgards,

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geoffbaker

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #2 on: December 10, 2008, 05:28:11 PM »
Ace,

Good analysis.

I talked to several machine shops about my diesel engine, and I ended up doing the following mods to improve performance. (I should add that my goal was NOT speed, but efficiency; but in truth there is not much difference - more efficiency can translate into either higher speeds or more torque or more mpg, depending on other factors including your driving habits).

The diesel head was ported much the way you describe, with the intent not of enlarging any particular surface, but to SMOOTH out the surfaces to reduce turbulence. 

Additionally the head was coated with a ceramic coating which disperses heat. The theory behind this is that the better the engine throws off heat the less energy it has to expend mechanically removing it via the exhaust chamber, or by the oil cooling system. Therefore the entire internal area of the exhaust port was coated to "throw off" heat back into the exhaust itself, rather than absorbing it into the head for the cooling system to remove. Additionally, the coatings made both intake and exhaust ports micro-smooth.

Thirdly, the piston, bearings, crankshaft and flywheel were all balanced to witin a couple of grams. Again, any eccentricity in weight distribution not only damages the engine over time (by ovalling the bearings and machine surfaces themselves) but also is energy that is transferred into unnecessary vibration, instead of being channeled into the power output itself.

I can't comment on the result in any way except to say that the engine seems to run exceptionally cool (max temp so far is about 170 degrees, but I'm not pushing it hard) and, for a diesel, very smooth. Although noisier than the gas engine, it does not offer significantly more vibration.

Ace, you may want to comment more on these areas; I'm no expert, merely following the opinions of a couple of machine shop pros.

ace.cafe

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #3 on: December 10, 2008, 05:39:55 PM »
Ace,

Good analysis.

I talked to several machine shops about my diesel engine, and I ended up doing the following mods to improve performance. (I should add that my goal was NOT speed, but efficiency; but in truth there is not much difference - more efficiency can translate into either higher speeds or more torque or more mpg, depending on other factors including your driving habits).

The diesel head was ported much the way you describe, with the intent not of enlarging any particular surface, but to SMOOTH out the surfaces to reduce turbulence. 

Additionally the head was coated with a ceramic coating which disperses heat. The theory behind this is that the better the engine throws off heat the less energy it has to expend mechanically removing it via the exhaust chamber, or by the oil cooling system. Therefore the entire internal area of the exhaust port was coated to "throw off" heat back into the exhaust itself, rather than absorbing it into the head for the cooling system to remove. Additionally, the coatings made both intake and exhaust ports micro-smooth.

Thirdly, the piston, bearings, crankshaft and flywheel were all balanced to witin a couple of grams. Again, any eccentricity in weight distribution not only damages the engine over time (by ovalling the bearings and machine surfaces themselves) but also is energy that is transferred into unnecessary vibration, instead of being channeled into the power output itself.

I can't comment on the result in any way except to say that the engine seems to run exceptionally cool (max temp so far is about 170 degrees, but I'm not pushing it hard) and, for a diesel, very smooth. Although noisier than the gas engine, it does not offer significantly more vibration.

Ace, you may want to comment more on these areas; I'm no expert, merely following the opinions of a couple of machine shop pros.

Geoff,

Yes, the street Bullet would have similar goals for porting as your diesel, with both requiring to maintain or increase lower and midrange torque, along with any hp increases. And port speeds are directly related to torque production.
The coatings in the ports, especially in the exhaust port, are helpful for the reasons you mentioned.That coating in the exhaust port will keep engine temps lower, and assist in a faster exhaust speed by keeping the heat in the exhaust gases, and not transmitted into the head. The other coatings also help, but IMO the exhaust port is where you are getting the most benefit from those coatings.

Certainly a properly dimensioned and balanced bottom-end is crucial for best engine life, and least vibration. No question about it. That's a maxim.
« Last Edit: December 10, 2008, 05:47:10 PM by ace.cafe »
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REpozer

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #4 on: December 10, 2008, 05:47:28 PM »
Ace, thanks for all your input, I enjoy the reading . Even a lean- burn guy can benefit. .
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Rick Sperko

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #5 on: December 10, 2008, 06:08:52 PM »
Last night I took off my intake manifold and saw how rough it was just inside. I was thinking about the turbulence. I was trying to come up with a way to smooth it without taking the engine apart. I guess I will learn how to take it apart and find a good machine shop. Thank goodness for the manuals (Snidal, Service, & Parts).

Thank you,
-Rick
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ace.cafe

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #6 on: December 10, 2008, 06:19:15 PM »
Last night I took off my intake manifold and saw how rough it was just inside. I was thinking about the turbulence. I was trying to come up with a way to smooth it without taking the engine apart. I guess I will learn how to take it apart and find a good machine shop. Thank goodness for the manuals (Snidal, Service, & Parts).

Thank you,
-Rick

Rick,
One of the quick and easy things to do is to match the manifold gasket to the manifold.
Very often, the hole in the manifold gasket does not perfectly align concentrically to the hole in the manifold, when it's installed on the engine. Sometimes the hole is a little too small to match, or it is off-set in some way, which forms a partial barrier to flow going thru from the manifold into the port. Sure, the manifold bore itself is smaller than the port hole, but this is not the issue right now. I'm just discussing making sure that the manifold gasket isn't making the manifold hole any smaller than it's supposed to be for that carb.

With the carb off the bike, stick your finger into the manifold, and see if you can feel the gasket itself sticking out somewhere in the hole. If you can, this is a restrictor plate, acting to choke-down your airflow.

Very simple to remove the manifold, get a new gasket, and temporarily put the manifold on with the gasket(don't tighten it down hard), and determine where the intrusion of the gasket is occurring.
Then remove it, and use a small round file to shape the hole in the gasket to not intrude into the port hole.
Many times the bolt holes have a lot of slop, and this allows the gasket to move its position when you install it. Sometimes all it takes is to use your finger to hold the manifold gasket in the correct position when you bolt the manifold on, so it doesn't slide on its slop enough to interfere with the port hole entry. Other times it needs a little filing to match it to the hole.

In either case, making sure tha manifold gasket isn't acting as a restrictor plate is always beneficial.
Smoothing the manifold internally wouldn't hurt anything either.
« Last Edit: December 10, 2008, 06:24:53 PM by ace.cafe »
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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Rick Sperko

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #7 on: December 10, 2008, 06:34:36 PM »
I meant that I noticed the roughness in my inlet port. I like the suggestion about cleaning up the gasket too. I was trying to come up with a way to smooth the inlet port without taking the engine apart. It is a black box to me right now. But then many other things were too.

Thank you for your technical input ace. I enjoy reading your posts.

-Rick
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ace.cafe

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #8 on: December 10, 2008, 06:48:52 PM »
I meant that I noticed the roughness in my inlet port. I like the suggestion about cleaning up the gasket too. I was trying to come up with a way to smooth the inlet port without taking the engine apart. It is a black box to me right now. But then many other things were too.

Thank you for your technical input ace. I enjoy reading your posts.

-Rick

Glad to help, Rick.
Ya gotta take the head off and the valves out, to do port work.
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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Vince

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #9 on: December 10, 2008, 07:02:17 PM »
     Ace, I always enjoy your analytical discourses. I do have a question about this. It is my understanding that on the intake side one does not want a mirror finish. At low  RPM that mirror finish will not provide enough turbulence to keep the fuel in suspension. This will cause puddles of fuel, an inconsistent mixture, and poor throttle response at low RPM. Certainly, as you mentioned, any large flashing or sharp angle that will disrupt flow should be removed. You mentioned using 220 grit paper. I guess my question is: Can you quantify the right amount of "rough" finish needed in the intake tract? Would your answer be Enfield specific or of general application?
     On the other (exhaust) side it is my understanding that a mirror finish will aid exhaust flow and minimize carbon build up. How much does this apply to the Enfield specifically, or for general application?

ace.cafe

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #10 on: December 10, 2008, 07:47:55 PM »
     Ace, I always enjoy your analytical discourses. I do have a question about this. It is my understanding that on the intake side one does not want a mirror finish. At low  RPM that mirror finish will not provide enough turbulence to keep the fuel in suspension. This will cause puddles of fuel, an inconsistent mixture, and poor throttle response at low RPM. Certainly, as you mentioned, any large flashing or sharp angle that will disrupt flow should be removed. You mentioned using 220 grit paper. I guess my question is: Can you quantify the right amount of "rough" finish needed in the intake tract? Would your answer be Enfield specific or of general application?
     On the other (exhaust) side it is my understanding that a mirror finish will aid exhaust flow and minimize carbon build up. How much does this apply to the Enfield specifically, or for general application?

Thanks Vince! :)

Regarding the finish of the intake port.
From a perspective of drag on the incoming air, it has been found that the slightly rougher surface, about 220-400 grit finish, is best. You could bead-blast to this grit also, if you want. It's not to make it "rough",in that sense, but just enough to create the desired effect. Tests have shown that this finish has the effect of forming a slight aerodynamic boundary layer over the port walls, which while very minimally reducing effective port diameter(only a couple thousandths of an inch), actually provides less drag on the incoming mixture than the mirror-polished port wall would have. It effectively eliminates the "skin-drag" that happens when the air runs right on the port wall.
As far as fuel puddles from insufficient port turbulence, I haven't heard about that, but I suppose it's possible. However, the sandpapered finish isn't to provide general port  turbulence, but conversely, it is to reduce it. But, the boundary layer  is a form of very thin  turbulent layer that is only along the walls, and will keep the fuel off the walls, so it might be less likely to condense on the walls. Perhaps that's what they meant?

As for the exhaust port, you are correct that the mirrored finish is good for that, in a general sense. The Bullet being an exception, only because to get a mirror finish on the Bullet exhaust port would require opening it up wider to get that finish on it, and would be counterproductive for us, because our exhaust port is too big already.
However, in general, mirror finish is good in exhaust ports because it reflects the heat well, and reduces the amount of heat transferred into the head from the exhaust. This keeps the heat in the exhaust, keeping the exhaust gases at maximum expansion, and thereby speeding exhaust flow, which assists scavenging effect during cam overlap periods. And it also helps to keep the head from getting too hot. And the mirror finish is less prone to pick-up and hold carbon deposits on it. So yes, in general the mirror finish in the exhaust port is a good idea.
For the Bullet, it would probably be better to use the Ceramic-Metallic reflective thermal-barrier coating in the exhaust port, because we could narrow the exhaust port a few thousandths with that, and also provide the same effects on the exhaust gases.
I'm currently doing an experiment with a torque-cone, like they use on Harleys, to see if I can get a low-rpm torque boost out of the Bullet with it, and still not lose any of the top end because the Bullet revs so low anyway. We'll see how that goes. I might get around to that this week-end, if the weather permits.
The Bullet is woefully lacking in exhaust gas speeds, and it really needs a smaller port and a narrower header pipe. I'm hoping I can get partway there with this torque cone project.
« Last Edit: December 10, 2008, 08:09:04 PM by ace.cafe »
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Vince

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #11 on: December 10, 2008, 08:17:27 PM »
     Thank you, Ace! Nicely put- clear and concise. A pleasure to discuss these things with you.

geoffbaker

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #12 on: December 10, 2008, 11:11:39 PM »
I would imagine, ace, that the ceramic thermal coating in the exhaust would be particularly effective on the Enfield head, as it tends to run pretty hot. As I said, it is keeping my diesel ridiculously cool...

ace.cafe

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #13 on: December 10, 2008, 11:22:20 PM »
I would imagine, ace, that the ceramic thermal coating in the exhaust would be particularly effective on the Enfield head, as it tends to run pretty hot. As I said, it is keeping my diesel ridiculously cool...

Yes Geoff, I agree.
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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #14 on: December 11, 2008, 12:56:39 PM »
Something I noticed when I ported my 04 is the rubber flange connecting the carb to the manifold.  Inside is a internal flange that protrudes into the air flow (its there for the carb and manifold to mate up to).. I used my 60 grit "flapper" wheel to turn it down to match the complete intake diameter.  Seems a shame to match all ports and leave this sticking out into the intake trac.  Just my two cents.

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #15 on: December 11, 2008, 02:35:55 PM »
Something I noticed when I ported my 04 is the rubber flange connecting the carb to the manifold.  Inside is a internal flange that protrudes into the air flow (its there for the carb and manifold to mate up to).. I used my 60 grit "flapper" wheel to turn it down to match the complete intake diameter.  Seems a shame to match all ports and leave this sticking out into the intake trac.  Just my two cents.

Yep! You did good!

The idea that we're aiming for with flow in the head, is to create conditions for the flowing air to "see"  a path with the least obstructions and least changes in diameter  and direction as possible.
The air doesn't like obstacles or abrupt changes in direction, or abrupt changes in diameter. It just wants to go straight in a nice comfy tube that is constant, We have to make it turn a bit, but we want to assist it to make any turns as much as we can.

Now, regarding the obvious question about the fact that the stock carb is 4mm smaller diameter than the stock port.
Yep, this is a problem for max flow. But, there is an advantage to the smaller carb in starting and idling steadily. The smaller carb has a stronger "signal" from the vacuum in the engine, and will give better results in starting, idling, and even some low-speed running in most circumstances.
However, as we start to move up the revs a little, then the bigger carb starts to "come into its own" and outperforms the smaller carb. This is when the air is really starting to flow, and can begin to take advantage of the larger port and carb size.
The 28mm carb was spec'd in the original Redditch model, but it's not very common knowledge that the Redditch Bullets had 29mm ports in their heads, and not the 32mm ports that the Indian-made Bullets have. The Indians changed the head ports, but kept using the same carb. Not a terrible choice, because the 28mm carb is still a decent "all around" carb for general use, but is small for performance purposes when used with a 32mm port.
The typical "rule of thumb" for performance is to use a carb with a matching-size throat to the size of the port. In our case, 32mm.  And in some cases, the carb can be a little bigger, if the shape of the manifold and port is suitably designed. But in all these cases, the larger carb will not start, idle, or have low-speed running quite as good as the smaller carb.  But, often this is only a small difference, and the Bullet starts, idles, and runs at low speed quite well with the 30mm or 32mm carb, and some report even the 34mm carb works good.

And as Sewerman points out, the manifold should also be matched, just like anything else in the air path, so that the air has a consistently shaped flow path from carb throat to valve head. Or, at least as consistent as we can get it to be, anyway.
« Last Edit: December 11, 2008, 02:38:34 PM by ace.cafe »
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coinzy

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #16 on: December 12, 2008, 01:48:45 AM »
Ace,i've noticed where the bowl meets the seat it is under cut slightly,any blending would need to be made on the sea itself,however that  would turn the flow back slightly.Can epoxy steel be safely used on the Alloy to build it up so it blends in a nice straight line with the seat?
the coinz.

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #17 on: December 12, 2008, 03:07:47 AM »
Ace,i've noticed where the bowl meets the seat it is under cut slightly,any blending would need to be made on the sea itself,however that  would turn the flow back slightly.Can epoxy steel be safely used on the Alloy to build it up so it blends in a nice straight line with the seat?
the coinz.

Hi Coinzy!

Yes, occasionally this does happen.
If we had a water-cooled engine which held head temps more stable, I think we could use forms of epoxy products to do just that.
It is fairly common practice in water cooled engines.
However, in our air cooled alloy head, I am skeptical about whether something like that would hold up.
Even if the epoxy steel itself is rated to temps that would be high enough to withstand the actual heat encountered, I'm concerned that the repeated expanding and contracting of the alloy head in those temperature changes would cause the epoxy repair to let loose over time.
It certainly would make me nervous about it.

In my experience, for aircooled alloy heads, any port repairs are done by alloy welding, and then grinding and shaping the weld down to the proper result.

I know that probably wasn't the answer you wanted to hear, but I don't think that the epoxy steel repair will stay in place with time, and if it drops off in one piece and goes into the engine, it could do damage.

So, I'm playing the cautious angle, and recommending against that type of epoxy repair.

If I was in your shoes, I'd do what I could with the port and ignore that one area for now. When the time comes that you need/want to replace your valve seats, you can have the weld job done at that time after removing the seat, then install the new seat, and match the port to the new valve seat.
Or else you could go for the big intake valve, have the bigger seat installed, and the port bowl will need to be enlarged and re-shaped to suit that new bigger valve seat, and the current  depression you see now would disappear with the newly re-shaped and enlarged port bowl for the big valve.
I realize the big valve isn't needed for street use, but its a way around having to do a weld job.

I hope that helps you.
« Last Edit: December 12, 2008, 03:23:38 AM by ace.cafe »
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jonapplegate

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #18 on: January 02, 2009, 04:23:18 AM »
 Lets see. To paraphrase what Ace and Vince have talked about. INTAKE. Knock down large casting imperfections, port/gasket match, bowl blend and five angle valve job.I would add a modest intake extension between carb and head. Longer runners improve low speed torque and our machines engine fits the bill. These are available from at least one supplier of flatsides whose name escapes me right now. EXHAUST. Smooth and port match, Ceramic coating to control heat. I don't recall if it was mentioned but this is also a very good idea for the combustion chamber and piston top, to carry this step all the way. I imagine that this is what was done and I missed it. Thats about it.
  An old rule of thumb amongst some engine builders is this, "build the intake for torque and the exhaust for horsepower". You want a strong signal at the intake so the carb works properly and you want the exhaust to have very little restriction so you can move gases out of the chamber so the incoming charge is as unpolluted as possible. Moderation in everything though. Taking any of these principles too far will kill flow rate.
 I know I haven't really added anything to this thread but its nice to talk this stuff. None of my everyday acquaintances could care any less. Eyes glaze over...   

Rick Sperko

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #19 on: January 02, 2009, 06:27:44 AM »
add a modest intake extension between carb and head. Longer runners improve low speed torque and our machines engine fits the bill. These are available from at least one supplier of flatsides whose name escapes me right now.

About how long would you suggest? I am going to put a 32mm flatside carb on and all I can find so far is a short rubber mikuni manifold. Everything I find seems to be 2" center-to-center and the bullet seems to be 60mm center-to-center.

For me, I have decided not to port it or do the valve job yet, I want a reason to take the head off. Like maybe to celebrate 3,000 miles.

Thanks,
-Rick
Rick in Milwaukee, WI

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jonapplegate

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #20 on: January 02, 2009, 07:04:23 AM »
  rsperko, let me find the site that has the manifolds and i will send it to you. I would suggest the shortest just because that would be an improvement over having the carb bolted straight to the head. Otherwise, if I was really just looking to build the engine for low end torque, I would get the longest possible. From a practical perspective, just go with the next step up whenever you are doing anything for the street. I know.
   I used to be heavy into Muscle cars and my first I really went to town on taught me the lesson. I had a 68 Firebird 400 i was "restifying". I didn't want to mess with that already scary handling beast so when a Ford Maverick came available to me, I jumped. Having a family friend who raced small block fords at the strip, I started buying used parts off him. Only the biggest, gnarliest parts for me. I ended up with a ride that was constantly out of commission. When it did run reliably it was so high strung that it was miserable to drive. Fun for a block, or a quarter. Other than that i had to fight the thing all the way. Unless you got real low gears you dont want an engine that only runs well between 5 and 7 THOUSAND RPMS! I thought I had had scary moments in the Firebird with the back end whipping out.
  Anyway, the moral to the story is you will be much happier just bumping up everything a notch unless you really plan on racing. I still have the bug to just go nuts with my Bullet.
 I have a flatside carb. Low restriction exhaust and of course low restriction filter. I am going to start doing little things to increase efficiency and added together will be a nice increase eventually. Stay away from the cams that are available right now. Too hot for enjoyable street riding it looks like. If your power band doesn't come on until 3500 rpm in a machine that probably shouldn't be pushed past 5500 you arent going to enjoy it.
  Sorry to ramble but I want every one to have a great time with their bikes.
GOOD LUCK!

ace.cafe

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #21 on: January 02, 2009, 01:52:22 PM »
add a modest intake extension between carb and head. Longer runners improve low speed torque and our machines engine fits the bill. These are available from at least one supplier of flatsides whose name escapes me right now.

About how long would you suggest? I am going to put a 32mm flatside carb on and all I can find so far is a short rubber mikuni manifold. Everything I find seems to be 2" center-to-center and the bullet seems to be 60mm center-to-center.

For me, I have decided not to port it or do the valve job yet, I want a reason to take the head off. Like maybe to celebrate 3,000 miles.

Thanks,
-Rick

Rick,
There's very little room to extend the intake manifold length, before you can't fit the carburetor under the tank anymore. Very little room to extend.
I tried it with a longer rubber hose, and I forget the exact amount, but I think it could only get about 3/8" to 1/2" longer, before the throttle cable adjuster was hitting the tank. Unfortunately, that small of a change isn't going to do anything noticeable.
If you try to extend it way out past the end of the tank, and use a long cable, such as 72westie's race bike has, then the carb is hanging out where your knee normally is, and you have to sit back further and use rear-sets, because the carb is in your way.

The next best option is to do the stack.
The max stack length that can easily fit where the airbox was, is about 6" long. And that's an unusually long-looking stack from an appearance viewpoint, but it is still visually acceptable. Anything longer than that starts to look pretty odd.

Chumma7 is getting very good results from his 6" stack on his Amal 32mm. In fact, he had a similar issue with it getting lean and "hitting a wall" in revs, and is having to go alot richer.
I pulled my plug after running that really long extension, and it looked quite lean.
You will have to keep an eye on your plug when you do this stuff, to make sure you aren't leaning out from the mods. Re-jet as needed.
It will get more air in, and if it's working as intended, it will need more fuel.

I've already got to the point where my clutch is slipping from the additional torque in the midrange, and I need to do something to beef up my clutch. If I give it a twist at 3500 rpms, the clutch starts to slip.

Regarding manifolds, you can go to the Sudco website and look over their selection of Mikuni manifolds. They should have something there.
I just bored my stock manifold out to 32mm. This leaves a very thin manifold wall left for supporting the rubber hose and carb. So, I epoxied a metal sleeve over it, using hi-temp epoxy, so it would strengthen it back up. Then your rubber hose will have less difference to account for on each end, because your 32mm Mikuni has a 40mm connection stub leading to the manifold, and your stock manifold is smaller. Enlarging the outer diameter of the manifold stub helps when using a straight hose. I tried to find a sleeve diameter which had a close sleeve-fit onto the manifold stub, so that I didn't rely totally on the epoxy for strength and integrity. It's just a bonding agent if you get the right size sleeve fit.
« Last Edit: January 02, 2009, 02:07:19 PM by ace.cafe »
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Rick Sperko

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #22 on: January 02, 2009, 02:47:21 PM »
Thank you all for the great feedback. I tend to overthink things a bit sometimes.

Here is another overthinking on good fuel air flow: In this thread on porting you mention that the rough walls of the intake mess up the flow, doesn't putting a rubber hose between the manifold and carb cause two relatively large steps that would mess it up? Is it insignificant? I am thinking about filling in the gap with high temp silicon.

I called Sudco last week, they have the gall to take time off and spend with their families right now while I want to work on my bike! They will be back on the 5th. They do show a spacer with their manifold, I just wondered why and how long.

Happy New Year everybody,
-Rick
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'66 Chris Craft Cavalier Cutlass 26'
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ace.cafe

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #23 on: January 02, 2009, 03:46:27 PM »

 doesn't putting a rubber hose between the manifold and carb cause two relatively large steps that would mess it up? Is it insignificant? I am thinking about filling in the gap with high temp silicon.


-Rick

Yes it does cause a disruption in airflow, and that's why there is a molded reducer in the stock manifold hose, which keeps the manifold at a relatively constant diameter inside.
It's not very precise, but they make an attempt at it.

I wouldn't recommend using silicone in there. From my research, silicone is not very resistant to the volatile components in gasoline or ethanol additives, and I'm not certain it would hold up for long, and would probably wind up going into the engine.

The best bet would be to use a short aluminum ring that fits inside the hose, which has the 32mm inside diameter, as a reducer ring between the manifold stub and the carb stub. That way it's a solid single piece inside there that won't dissolve or break loose, and can't go anywhere. If you look around enough, you can probably find a piece of aluminum tube that has the required inside diameter, and the wall thickness to approximate the O.D. of the carb stub, so it will fit in the hose and give the proper flow.
The narrow gaps left inside there then are probably the minimum that we'll be able to get without a solid manifold.
The rubber does serve to isolate some vibration from the carb, so that it doesn't jiggle the fuel in the float bowl so much, and keeps float level from being constantly disrupted. So, keeping the rubber hose in the joint serves some purpose.

For normal street Bullets, it's not really an issue, because they are low performance enough for alot of this stuff to not be noticeable, but if you are trying to maximize performance, then it makes sense to look at all the little things that might help. Each one thing, by itself, might not set the world on fire, but if you add enough of the small things together in harmony, they can add up to a decent improvement that you can feel.
« Last Edit: January 02, 2009, 05:42:03 PM by ace.cafe »
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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #24 on: January 02, 2009, 05:30:15 PM »
Didn't want to post this at first since it's not about RE but the extension between intake and filter is something that I learned about with Jeeps.  There was a year in the 90s when Jeep moved the filter from very close to the intake on the left side, all the way across the engine to the front right side.  Many Jeep tuners (yeah I know it's goofy to tune Jeeps) thought this was a bad compromise to deal with engine space and moved the filter back to the right side to be closer to intake.  They got bad results (less torque).  I also got bad results when I moved the filter to make room for my air compressor on the right side.  Eventually, smarter engine tuners, and a Jeep engineer, explained to Jeep tuners that the reason for the long pipe to the filter was the same reasons described by Ace:  a steadier supply of air for the intake, and a long smooth passage that smooths out and steadies the air supply before it gets to the intake.
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jonapplegate

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #25 on: January 05, 2009, 02:17:16 AM »
Hey all, I have got a flatside and as you know these bolt right to the head. So if you have one an extension is a good idea. If for nothing else than to isolate the carb from heat. You could get an extension that caused interference with the cable but if we are going this far then why not custom length cable?
  I am still looking around for the source of those manifold extensions for flatsides. I thought I bookmarked it but perhaps they are not made anymore? I swear it was JRC.

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #26 on: January 07, 2009, 05:59:25 AM »
Thanks and no, I dont have the new and improved. I haven't had any problems yet other than having to be more intelligient than i am accustomed to when putting the carb on! I will check it out.

Chuck D

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #27 on: February 18, 2013, 12:24:53 AM »
Here's another.
2006 Bullet Sixty-5 w/ Ace "Fireball 535" Kit (#10)
Ace "GP" head in the works.

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ace.cafe

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Re: Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?
« Reply #28 on: February 18, 2013, 12:42:22 PM »
Coming back to see this several years later, I would caution that if you ever plan to have the professional porting job done, that you leave the ports alone, other than the most minimal reduction of obvious casting flaws that are sticking up.

If you remove metal that we need to be there, then our job won't come out as well as if we had the metal remaining in the right places.
So, that's a decision you have to make if you are going to try to do something to your own ports.
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