Where do you gain the most HP

[1969zeitler]

Thinking about how you take a 40hp engine and get 60+ out of it while staying within the FV guidelines. Where does the majority of the gain come from? Also, what makes the engine go from a 5000 max RPM in factory stock form to 6500+ and still not fly apart. I know it is a combination of all of these and more, but what is the most gain for the work/money spent? Given the restrictions on the class, what is the highest to lowest gain in the following areas.

Intake manifold
carb changes (venturi, jets )
Exhaust
Lightening (flywheel, rods, pistons, lifters etc)
Balancing crank, rods, pistons, flywheel)
Compression/ piston height
Head work (smoothing and port matching)
Ignition and timing changes at the cam

Did I miss anything?

[SR Racing]

*Intake manifold

Quite a bit. Typical flow increase from stock to race prepped is in the 30% area.

*carb changes (venturi, jets )

Same here. Flow increase comparable (jets don't improve HP per se', but they must be changed to keep a/f ratios proper for the venturi change

*Exhaust

Not much, but it depends upon what you are comparing to. If you are comparing to stock, quite a bit, but from one decent exhaust system to the next not a lot. (maybe 2 hp from best to worst)

*Lightening (flywheel, rods, pistons, lifters etc)

Very little measuable static HP, but significant in ah inertial run. For example at a steady state 5100 RPM, there is no HP increase. However at an inertial run of 300 RPM per second it can be 2 HP. Keep in mind that lightening pistons by cutting the tops is primarilly to move the top ring closer to the top of the piston. This effectively increases compression ratio.

*Balancing crank, rods, pistons, flywheel)

Can be lots. Assuming a poorly balance rotating assembly could cost 2+HP and put signicant loads on bearings, saddles, etc.

*Compression/ piston height

(See above)

*Head work (smoothing and port matching)

Another big hitter. Only less important than carb and intake.

*Ignition and timing changes at the cam

Ignition timing obvioulsy has to be right for the engine but within +/- 2 of the 36/35 wont mean too much.

Cam is retarded to get maximum efficiency at higher RPMs. It moves the peak Torque point to a higher RPM point. It MIGHT decrease torque slightly at lower RPM points. But since HP= T x RPM / 5252, it is worth the decrease.

It all adds up to get from 40 to 60 HP.

Since we are pretty much stuck with the displacement, CR and VE we were born with, most all of the above things are done to move the peak torque point up higher in the RPM band. While our torque doen't compare favorably with a stock VW engine we do it at a much higher RPM, thus the work (HP) that we can do is more.

As far as being able to get 7000 rpm instead of 4000 it is primarily the induction work. (carb, manifold and heads) Other than external plumbing and windage work the Unversal 1600 case with stock oil pump provides plenty of lubrication. Actually a "HD" oil pump is only required for LOW RPM engines when the bearing load is quite heavy and th eoil pump is turning slowly. We are turning our pumps much faster than VW planned. So if bearing clearance and plumbing is good, we get more lubrication than even needed.

[fvracer27]

Thinking about how you take a 40hp engine and get 60+ out of it while staying within the FV guidelines. Where does the majority of the gain come from? Also, what makes the engine go from a 5000 max RPM in factory stock form to 6500+ and still not fly apart. I know it is a combination of all of these and more, but what is the most gain for the work/money spent? Given the restrictions on the class, what is the highest to lowest gain in the following areas.

Intake manifold
carb changes (venturi, jets )
Exhaust
Lightening (flywheel, rods, pistons, lifters etc)
Balancing crank, rods, pistons, flywheel)
Compression/ piston height
Head work (smoothing and port matching)
Ignition and timing changes at the cam

Did I miss anything?

Send it to a FV engine builder and write a check and save yourself time and money. They do it all the time and know how to get the HP Legally and the key word is "legally".

Mark

[brian]

One must think of an engine as a total system and not address individual components. Durability is critical and must be done before increasing hp and stress. I have seen engines with full weight and unbalanced lower ends make great hp and live. The Germans weren't that far off when they made these engines so all the fancy stuff downstairs is marginally measured. From my experience, the heads kinda lead the charge to hp land. In addition to port flow, spring pressure and compression can and will really improve hp and rpm range. Obviously, if the carb isn't tuned it will cost you a ton but it won't have a significant effect on increasing eveything else until you get closer. If the carb is clean and tuned, simply removing the venturi or buying a machined one, will give you 90% of what a carb will do. Same thing for the intake, there will be a gain but not a lot without good heads and tune. Like most things, the last 10% will envolve 90% of the effort.

[SR Racing]

I have seen engines with full weight and unbalanced lower ends make great hp and live.

Brian, The typical stock Vee rod set was +/- 10 gr overall and probably that much end to end out of balance. They did no end to end and only spec rods to about 10 gr overall. That is what I would call a VERY unbalanced engine at 6000+ RPM. The cranks were just as bad. Ok for street cruising but hardly 6000. I have seen stock cranks that had computed 500+ lbs of stress on a journal at 6000 RPM. In regards to full weight (not lightening), try an inertial run on the dyno at 600 rpm / second and see what happens to HP vs. a lightend one.

the heads kinda lead the charge to hp land.

??? Comparing stock pieces to race prepped, carb and manifold are far more important. We broke a head one time and replaced it with a pure stock one (with HD springs). HP loss was slight. Try that with a stock intake or carb. Due to the allowed rules you can increase (from stock) flow on a manifold and carb 30%+, You can't get close to that with head work.

Obviously the induction system is a stereo system (A $500 amp with $29 speakers won't work well.) But he was asking about individual components.

His question doesn't have a lot of practical use since as you say it is a system. But from stock vs "race prepped" components those is the facts..

Jim

[smsazzy]

I love it when engine builders argue. (Now, the following, is not the opinion of an engine builder, but rather my own)

I agree with both, however with some caviats.

I agree with Jim that the carb and manifold are more important to changing a 40HP motor into a 57 HP system. However, I am going to assume Brian was presuming those are in place and agree with him as well. The difference between a 57 HP and 60 HP motor is in the heads (and rings).

There is (as with everything) a trade off. Ideally, you want a low drag set of rings. However, too low drag and they won't seal. Blow by will commence and you'll burn oil instead of gas, which will cost you power.

Another critical piece is the valve job. A good valve job alone is probably worth a couple hp....

I also think the balance is very important, but not for huge power gains. There certainly would be some HP, since any unbalanced component is technically robbing a fraction of a HP by moving in a direction of flex, rather than in the direction that actually makes HP on the crank. However, it is likely hard to measure. It WILL effect the life of the engine, as the bearings will go out of round.

[brian]

No arguement here. Jim's right about factory specs. What I said was a motor will still make HP without being balanced. Would I ship a motor without balancing, hell no cause it will eventually hurt itself.