HP Per ci
 

Hi

I was wondering about fuel consumption and other factors after looking at different engine ci - power possibilities.

Eg:

2 identical cars, both at 650hp.

Car 1: 428ci (stroked 351 small block) = 1.5 hp per ci.
Car 2: 360ci ---------------------------- = 1.8 hp per ci.

Which of the 2 will be a more efficient engine in terms of street cruising and which would be more efficient under wide open throttle (racing)?

Which would have better acceleration (flatter torque curve)?

You cant know with just the displacement and power numbers... Need more info ie: compression,cam profile...

There's too many factors to make a judgement based on that. There's just so much that goes into it. Yes, hp/ci can be a measurement of efficiency, but again, alot goes into that. I remember a bunch of Honda S2000 fanboys saying that, at the time, the motors in those cars made more hp/ci than any other n/a motor produced at the time. Problem: You didn't really make any power until the VERY top end of the RPM range. Down low, the cars were pigs by comparison. Same deal with the rotary cars I've driven (Mazda RX7/8).

So there is many ways to get a 351 at 650 hp with different cams etc and still produce same power even though the bits were all different?
:confused18:

Hmmm.

The 351 (C or W) is not known as the world's most efficient engine. As such, 1.8 to 2 HP per cube usually requires a lot of race-only design elements including high compression, and aggressive cam and revs.
You might be happier with goals in the 1.2 to 1.3 HP/cube range with a carb and 1.4 with EFI.

DISCLAIMER: I'm talkin' real horsepower, not internet horsepower.

Wait you mean I can't take my engine builder's word for it? But he SAID my 225cid Slant Six should be good for 650HP with this 3/4 cam!

I love taking cars to the Dyno. Complete heartbreaker for some folks. A customer of mine swore up and down that there was no way my Road RUnner only made 400rwhp, since my car was way faster than his "600hp" 383 Stroker 350. We spent the day tuning his car on the dyno...256rwhp.

I can't imagine that 360 engine would be any fun to drive on the street.

George,
Building / specing an engine is no different than a car. To a degree, the limits are endless. The question you ask is like asking which car would be better for setting a land speed record, a Charger or a Gremlin. The answer is.... Whichever one you choose. Keep this in mind. The Speed Demon that set the record for the highest horsepower for a piston engine was a 4 cylinder. Why, because it was built for it. How would it run on the street? Probably not too good.
The answer to your question lies in the answer to what you want. A Flathead Ford can be built to provide you whatever you want. Yes including a land speed record.
Step 1. Figure out what you want to do with the car.
Step 2. Go to a reputable engine builder and ask him for his suggestion.
Step 3. Ask a few owners that have that type of engine.
Step 4. Get it built.

If you continue to ask on the forum, you are more than likely to end up with way too many reccomendations than you can digest. Personally, I like 383 stroker (GM) engines. They are the best all around for what I like to do. If I was building a 32 Ford, I would use a Flathead V8. Why because it looks cool and I know it can make the power if I need it to. A Buick Skylark, a Nailhead. Etc, etc. I hope this helps.