Tech Talk: Should I, or Shouldn't I "Port" my Bullet's Cylinder Head?

[ace.cafe]

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.

[coinzy]

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.

[ace.cafe]

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.

[jonapplegate]

 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]

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

[jonapplegate]

  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]

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.

[Rick Sperko]

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

[ace.cafe]

 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.

[stw]

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.

[jonapplegate]

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.

[jonapplegate]

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]

Here's another.

[ace.cafe]

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.