Increasing power output in the engine.

[ace.cafe]

Well, it's a lazy Sunday morning, and i felt like writing something.
So, considering spring is coming up soon, and people may want to "perk up" their Bullets for this year's riding, I thought I'd devote a little time to the subject.

What is "power"?
In an engine, "power" is basically divided into two aspects.
These are "torque" and "horsepower".
Strictly speaking, "torque is the "torsional force" or rotating force around the center axis of the crankshaft. Just like if you put a torque wrench on the crankshaft nut, and used the leverage of the torque wrench to turn the engine.
Horsepower is the work done by the torque, including time, which is usually described by rpms. And horsepower is a mathematical function of torque and rpm, specifically torque x rpm, divided by 5252(a constant).
Looking at this function, we can see that since the dividend in the equation is 5252, then torque will always be higher than horsepower up until 5252 rpm, and horsepower can then go higher than torque above 5252 rpm.
So, in our Bullets, it's easy to see that torque is the main aspect of power production that we will use in our daily riding. We cannot use rpms that are much higher than 5252, because of the strength limitations of the parts in the bottom-end of our engine. However, we can go a little above that, and usually 5500-6000 rpms would be considered the safe maximum limit for us.
And given this function of torque and horsepower, we can now address power production with these things in mind.

How do we increase torque?
Torque in an engine is the result of 2 things primarily. Those things are the leverage exerted on the crankshaft, and force exerted on the piston.
The leverage exerted on the crankshaft is dictated by the stroke length in our engine design. Specifically, it is the distance from the centerline of the crank, to the centerline of the crankpin. This distance is 45mm. But, you say that our stroke is 90mm? Yes it is. The 45mm goes up and down around the centerline, so the distance of 45mm is multiplied by 2 to get total stroke. But the actual distance involved for torque production is 45mm, because that is the distance of the crankpin from the crank center. This leverage is increased with longer stroke, and decreased with shorter stroke. It is fixed by the engine design, unless you change to a stroker crank.
The force exerted on the piston is the combination of the combustion pressure in the chamber, times the area of the piston crown. So you can increase this number  by enlarging the bore/piston size, or increasing the compression pressure, or both.
And this is commonly done with a big-bore kit and high compression piston.

Anytime you increase torque, you automatically increase horsepower, due the the nature of the mathematical function. But only at the points in the rpm range where that torque has been raised. It is entirely possible to gain torque in one part of the rpm band, and lose some in another part of the rpm band. So we want it to be broad enough in the torque curve, to provide good useful riding results. Some racing engines make power only in the highest rpms, and are very poor at low or midrange rpms. Conversely, some other engines pull like a tractor at low rpms, and can't reach high rpms very well at all. It's all part of how the engine designer picked the parts for the application.

Horsepower on the other hand, always follows torque. You can't have hp without torque. BUT, there is a special circumstance, where breathing efficiency allows torque to drop slightly, and the rpms can still cause horsepower to increase, as long as the engine can continue to pull in sufficient air/fuel mixture to increase rpms.

The "knee" in this curve is known as "peak torque rpm". It is the point where the engine is operating most efficiently for torque production. Everything is coming together just right at this rpm. As we accelerate from idle to peak torque rpm, the torque continuously increases until we reach peak torque rpm. Then it may hold on to the peak torque figure for a while, or it may begin to drop off at higher rpms.  Most times it will slowly decrease for about 1000-1500 rpms, and then drop off precipitously when breathing capacity reaches the limit. Even during the decreasing slope of the torque, engine rpm can increase and thus still produce higher and higher hp, until the breathing capacity of the engine is reached, and this is "peak horsepower".  The longer the engine can provide breathing capacity to rev higher, the longer the area from peak torque to peak hp will become.
So, there you have your 2 curves in power production of the engine, with the critical rpms for peak torque and peak hp. The rpms between the peak torque rpm and the peak hp rpm is commonly known as the "max power range".

How does the engine continue to make more power after it reaches the torque peak? Why doesn't it just stop there, if it has passed the place of best efficiency?
It's because the engine has capacity to breathe in more air/fuel mixture, at a rate which can be multiplied by rpms, even after max efficiency(peak torque) is passed. And it can continue to do this as the torque slowly declines, until that breathing capacity is limited enough to not be able to overcome the torque decline any more.
So, what we'd like to do is reach a high peak torque figure, and hold onto it as long as we can while the rpms rise further. And we'd like to place this range within the ability of our engine's structural integrity, so that we can access it without blowing the crank or rod. And in our case, this might be a torque peak of 4000 rpm and a hp peak of 5500 rpm, or maybe even a torque peak of 4500 rpm and a hp peak of 6000 rpm. The latter is pretty high, and probably reserved for a sport rider who likes to push the limits.

What can we do to help raise torque, keep a broad and useful curve, and increase hp too?
Well, we are pretty much limited in mechanical leverage by the stroke, unless we get a stroker crank. So that's about set in stone.
But we can get a big-bore kit and hi-compression piston pretty easily, and that can help out all thru the entire range.
But, those are only parts of what we can do.

How can we go further?
We can increase the breathing capacity of the intake and exhaust systems, and also increase the breathing capacity of the cylinder head. We know that a somewhat bigger carb, and a free-flow air filter can help, and many of us have done that. So does removing the very obstructed exhaust system, and replacing it with one that can let the gases out of the engine with less impediment.
This seems to make sense, right? We can bring more air/fuel mixture in, and get the exhaust gases out, better. And it works. To a point.

What is this "point" of which I speak?
Remember a few paragraphs back, when I mentioned that it's possible to gain torque or hp in one rpm range, and lose it in another. That is the issue that I'm referring to.
It's possible to set up the engine breathing so that it is very big, and flows alot at higher rpms, but this makes it flow slow and lazy at lower rpms. And that means that at lower rpms, not alot of air/fuel mixture is getting in, because of slow lazy flow that was created by making it all big enough to flow at much higher rpms, and that's what makes racing engines do poorly on the street. Conversely, if we make the breathing small enough to give us really high flow speeds at lower rpms, giving us great low-rpm torque, our ports(or carb or manifolds) can't flow enough mixture at the higher rpms to develop the power at the high rpms. So, for street work, we need a balance.

What is the "balance"?
The balance is to have breathing which can be fast enough to give good flow and good torque down low, and still be able to breathe well enough to allow the engine to access the high rpms. This means not going too far in either direction. Not too small, and not too large. So, we don't want an overly large carburetor, or overly large intake manifold, or over large ports. Nor do we want them too small.
We want it to be like "Goldilocks". Just right!
So, we select are carburetor size, manifold size and port size, so that we are good for our intended range of use, which is about 2000-6000rpms. It does us no good to set up the engine to do 9000rpm. We'll never get there without blowing up, and it will just wreck our low-speed running.
Happily, our India-made head has an intake port which is very nearly sufficient for our highest rpms, and doesn't really need enlargement. But, the shape of the port is poor, and while it may be able to pass enough air, it doesn't do it with good velocity. So what we need in our India-made intake port is improved shape, and not necessarily bigger size. The size"could be" bigger, IF the shape is improved sufficiently to get good velocities with that bigger size. That's not easy to do, but with the poor shape that we have in there, it could be possible, IF you really know what you are doing.
The same goes with the carb and manifold. If the carb is too big, then it just slows everything down, and you can't get the overall flow you need because velocity suffers. So, putting a big 38mm carb on our stock ports isn't going to help us. But, going bigger than the 28mm carb might certainly help us, because our ports are 32mm, and that makes the carb a restriction.
The whole idea is to get more air/fuel mixture in, which means sufficient volume, AND sufficient velocity, which combine to get most mixture in during the time the valve is open. And do it well enough at all our rpm ranges, so that we don't suffer weak spots in our riding range.
The more mixture that enters the engine at any given rpm, the more the combustion pressure is going to be exerted on the piston crown, and the more torque is going to result. So, it stands to reason that we want to get as much in as we can, at all the rpms that we plan to ride. Since this increases torque, it also increases horsepower, and everybody's happy.

So, in summation, we must strive to modify the engine within the expected range of use(rpms) to provide the best breathing possible in the bulk of that rpm range, and use that to produce more force exerted on the piston. And we can combine that with a piston that "squeezes" that mixture with more compression, to improve the result. And we can use a slightly bigger piston to give more area for that pressure to work on.

Of course, we could discuss how cams assist this, and the exnaust extraction effects, but I think we've bitten-off a pretty good chunk here, so we can chew on this one for awhile.

[ScooterBob]

ACE - Bravo!! .... Very well done, my good man .... A couple of questions tho ....

1). How strong IS the coffee that you drink on Sunday morning?
2). Just when are we going to share a pint or two and discuss port velocity and rotational force over time ..... ?? Hahaha!! You have a "bit better than average" understanding of this stuff .... I love it! I LIVE there when I am not buried up in other endeavors .....

I'm bettin' that there is some untapped torque in the old Bullet - I'm also guessing some of my work in getting nearly 650ft/lbs out of a normally aspirated Olds engine at 2800rpms might apply. Port velocity SEEMS to be the factor here - as long as it isn't supersonic! I'd LOVE to make a Bullet pull like an Unlimited Class John Deere diesel at a tractor pull .... 

[ace.cafe]

Hi Bob,

Yeah, I make the coffee pretty strong! And I drink alot of it!

I do think there's some "untapped torque and hp" available left in the old Bullet.
But it has to be carefully tapped, so that we can keep the nice midrange that we all love about our Bullets.

Since you're an Oldsmobile enthusiast, I'm sure you are familiar with a guy named Joe Mondello.
I've got quite a surprise coming up for you and all the Bullet faithful here.
But I'm not quite ready to discuss the details just yet.
You can ask Kevin about the details.

We'll have to see how it goes along.
Here's my train of thought.
I think a well-prepped 535 Bullet can reach the power output levels of the  612 performance kit.
If I can find 3 extra foot-lbs of torque in the 535 somewhere, and hang on to it reasonably well, into the upper rpms, then it can produce just a hair under 40hp at 6000 rpm, with about 35-36 ft/lbs of torque peaking around 4500 rpm..
And do it with a crisp and punchy midrange and low-end too.
On pump gas.
35 foot-lbs x 6000 rpm , divided by 5252 = 39.98hp @ 6000 rpm.
That's my goal.  A 10% torque boost out of a 535, with a 6k rpm redline.
612 power out of a 535, which gives lower piston speeds, and better durability.
Basically like a Fury that doesn't blow up. Very close to a Gold Star DBD34.
And totally streetable and reliable, with good road manners.
We'll see if we can hit it.

You know, this Mondello guy knows a thing or two about heads.

[ScooterBob]

Uh, yeah .... Joe Mondello IS the "head master" when it comes to Olds stuff ... It was his stuff that inspired me to further tinker with the buddy's drag car to get "fasterness" out of it. I'm really intrigued by your Bullet project - but I'm really thinking that there is even five MORE torques in there than you are hoping for .... I'm thinking "cylinder charging" and burn time vs. crank rotation .... You know the old 340 Dodge trick of switching the offsets on the pin holes to effectively get more dwell at TDC and all that - why not increase the length of the rod (plenty of room!) on the Bullet for the same net effect? The OTHER thing on the old Bullet IS the intake port .... a fellow needs to DevCon the poop out of one and do some "spare-uh-mintin'" on it to get the velocity (and therefore the torque) up a bit in the middle range. Just food for thought .... The worst thing of all of it is trying to get it to run on that miserable azeotropic bag of crap they call motor fuel these days! I have tested some of it - and "Inconsistent" is its name .... I'd LOVE to build a powerhouse, torque-bastage Bullet ... but I'll be pretty happy just to get to RIDE one after THIS winter in Minnesota!! Hahaha!! Perhaps the bug will hit HARD this spring ... we must share a note or two ... perhaps we can make each other go faster!! Hahaha!!

[t120rbullet]

The OTHER thing on the old Bullet IS the intake port .... a fellow needs to DevCon the poop out of one and do some "spare-uh-mintin'" on it to get the velocity (and therefore the torque) up a bit in the middle range.

Or get a 350 head and machine it to fit on the 500 cylinder spigot and go from there.

[ScooterBob]

Hmmmmmm - I think there is one of those on my desk!! ..... 

[ace.cafe]

The OTHER thing on the old Bullet IS the intake port .... a fellow needs to DevCon the poop out of one and do some "spare-uh-mintin'" on it to get the velocity (and therefore the torque) up a bit in the middle range.

Or get a 350 head and machine it to fit on the 500 cylinder spigot and go from there.

The original Redditch 500 heads had 29mm intake port, so they can be opened-up to the proper diameter, but the shape is still "backwards.
However, it's less work that using a 350 head.

[Alaroyal]

Anybody ever create a four valve head for a Bullet?  Lots of folks think 4 valves only work at high RPMs but that's not the case, they can be VERY efficient at low AND high RPMs.  They are small enough to keep the air flow speed high at low engine speeds, but have enough combined area to give good breathing at high RPMS.

The Ford and Dodge pickup diesel engines each went to four vave heads and got a noticeable power bump, and Ford kept pushrods.  Detroit Diesel's Series 60 engines for road tractors have four valve heads and rarely see more than about 2100 or so RPM.

Jim Feuling (and others)  developed four valve heads for Harley Davidsons and they worked great.

Overhead cams might be out for RE's, but I'd LOVE to see a 535 with a nice four valve hemi head, with dual ports for intake and exhaust, two exhaust pipes, a  sparkplug in the center of the combustion chamber,  and two carbs or fuel injectors.

If you're gonna dream, make it in technicolor !

[ace.cafe]

Uh, yeah .... Joe Mondello IS the "head master" when it comes to Olds stuff ... It was his stuff that inspired me to further tinker with the buddy's drag car to get "fasterness" out of it. I'm really intrigued by your Bullet project - but I'm really thinking that there is even five MORE torques in there than you are hoping for .... I'm thinking "cylinder charging" and burn time vs. crank rotation .... You know the old 340 Dodge trick of switching the offsets on the pin holes to effectively get more dwell at TDC and all that - why not increase the length of the rod (plenty of room!) on the Bullet for the same net effect? The OTHER thing on the old Bullet IS the intake port .... a fellow needs to DevCon the poop out of one and do some "spare-uh-mintin'" on it to get the velocity (and therefore the torque) up a bit in the middle range. Just food for thought .... The worst thing of all of it is trying to get it to run on that miserable azeotropic bag of crap they call motor fuel these days! I have tested some of it - and "Inconsistent" is its name .... I'd LOVE to build a powerhouse, torque-bastage Bullet ... but I'll be pretty happy just to get to RIDE one after THIS winter in Minnesota!! Hahaha!! Perhaps the bug will hit HARD this spring ... we must share a note or two ... perhaps we can make each other go faster!! Hahaha!!

Ok, here's the trick.
You need  to get enough CFM going in to make the power, so you need some decent port volume.
And you need to get it in at good velocity.
We need to have enough port to not choke at full lift, but still flow well at low-lift.
And we are very lift-limited.
Seemingly at odds with each other.
It's all in the shape.

Regarding the other stuff, definitely the long rod will give us the dwell time, and we have a stroke/rod ratio of nearly 2 right now. Plenty of dwell to use the late intake valve closing timing for extra cylinder charging, and that will be involved. Got one of the leading cam grinders on board for this task.

I think that there may be more to be had than my goal, but I don't want to aim too high, particularly since I'm working within a limited rpm range for street use, with a low redline dictated by piston speeds.
If more can be gotten, we'll see about it. It has to be streetable.

[ace.cafe]

Anybody ever create a four valve head for a Bullet?  Lots of folks think 4 valves only work at high RPMs but that's not the case, they can be VERY efficient at low AND high RPMs.  They are small enough to keep the air flow speed high at low engine speeds, but have enough combined area to give good breathing at high RPMS.

The Ford and Dodge pickup diesel engines each went to four vave heads and got a noticeable power bump, and Ford kept pushrods.  Detroit Diesel's Series 60 engines for road tractors have four valve heads and rarely see more than about 2100 or so RPM.

Jim Feuling (and others)  developed four valve heads for Harley Davidsons and they worked great.

Overhead cams might be out for RE's, but I'd LOVE to see a 535 with a nice four valve hemi head, with dual ports for intake and exhaust, two exhaust pipes, a  sparkplug in the center of the combustion chamber,  and two carbs or fuel injectors.

If you're gonna dream, make it in technicolor !

That could be done.
But it requires a new head casting, or a CNC billet head to be made.
I think it is cost-prohibitive for our market.
In fact, I'm a little worried about the modified head being cost prohibitive.
We don't have a huge market to absorb large numbers of these things, so that has to be taken into consideration.
I'd love to do a project like that, but I think it would end up with the heads costing thousands of dollars each.

RE had Dr. Stuart McGuigan prototype a 4-valve head for the Bullet, but as a diesel engine, during the 1990s. It was pretty cool. Never saw daylight, though.

[BigDon]

Ace you are killing me with the little blurbs here and there lately!

When man when!!!!!

[ace.cafe]

Don,
All in good time, sir.

Actually, I'm expecting to have my first one in my hands within a couple of weeks.
Then I"m gonna put it on my bike and test ride it.
After verifying that all is good, I'll get some prices listed.

I've contacted Kevin about it already, so that he has the first opportunity to list them in the CMW catalog, if he wishes to do that. I suppose that it all depends on whether he feels it hits a price range that he considers right for him.

I'm expecting that the mods will be done on the customer's own head that he sends in. This will help to keep the price down a bit, because you don't have to buy a new head casting. If your head is damaged, then you need to send in a new casting, or we can procure one for you.
But since this is premium work done by the world's best head porting expert, it isn't going to be a cheap item. My instructions were to try to keep the retail price as close as possible to the Stage 2 head currently offered. We'll see how close he can come to that. I think it will cost a bit more, but I don't know exactly how much more.

I understand that the Bullet market is generally a very cost-conscious market.
However, I expect the market to understand that I'm bringing something in that has never been done before, in attempt to raise the bar of performance for Bullet owners.

[Cabo Cruz]

Well, Brother Ace, all this deserves, you can easily guess, a huge:

                            WOWZAA!!!

                                       

[cyrusb]

Do you think the added poop will cause the head to leak? Some stock bullets have that problem at 22 hp. The stock bullets have some pretty slim studs holding the head-jug assembly down.

[ace.cafe]

Do you think the added poop will cause the head to leak? Some stock bullets have that problem at 22 hp. The stock bullets have some pretty slim studs holding the head-jug assembly down.

No, I don't think that's a problem associated with the power production issue.
It mostly comes from a mismatched spigot height on the barrel, which is a little too tall for the recess in the cylinder head. Then it doesn't compress the gasket well, and oil leaks at the pushrod tubes.

Many people are using the hi-compression pistons, and not suffering oil leaks at the head joint. But, it is a very good idea to match the spigot height to the recess in the head, so that leaks can be avoided in any case. Also, if you have too little spigot height to make a good compression seal in the recess, compression can leak out and blow the gasket.
The whole central theme of good head sealing in the Bullet is to get a good match in the spigot/recess joint, and still be able compress the gasket to seal the pushrod tubes. I think that "ideally", the spigot should be about .010" taller than the recess in the head. This leaves room to use a .015"-.020" thickness head gasket, and be able to compress it to seal the pushrod tubes, and also still seal the compression well at the recess.

The "cheesy" studs can be an issue sometimes, but I don't think they are the main offender. It wouldn't hurt to use better studs if you want to, though.
But watch out for the next link in the chain, which is pulling the stud threads out of the crankcase.
I actually use about 10% less torque than the manual specifies on the head studs.