HP Per ci

[headcase]

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)?

[skatinjay27]

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

[MattO]

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).

[headcase]

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?


Hmmm.

[Steve Chryssos]

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.

[DTM Racing]

Originally Posted by streetfytr68

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.

[Matt@BOS]

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

[IMPALA MAN]

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.

[headcase]

Thanks for the feedback.

I know I want 10.5:1 compression. We have 98 Octane fuel here at every pump. May as well get the compression up. I know it will produce more efficiency.

My car is basically a street car but I want it to hammer through the RPM's. If light goes green, I want those 600 HP ferrari's behind not in front. THose cars hit 0-60 in 3.0 seconds.

I know Torque is good there, but My purpose to car is to make it handle so it can keep up to those cars on a track to in corners. So I wondered what is the happy middle here.

Im happy with how ferraris drive on the road, no drama with them, but the RPMS fly up when they start to kick the power. I can see a big cube (small or big block) leaving them dead right there. How would more cubes effect a cars road course speed though and why would it be bad (if at all) when it has more to get out of the corners... or is that the actual problem as the car would spin out.

[Flash68]

Originally Posted by -George-

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)?

George,

The 428 would clearly be better at that 650 hp level for street cruising and longevity vs the 360. As others have mentioned, the 360 would also need tons of rpm at the sacrifice of low and mid range power to hit that number.

The acceleration and flatter torque curve questions cannot be answered with the lack of info provided.

Originally Posted by ratman67

my 540 bbc makes 1.5 hp per c.i. single four barrel, big hyd roller, 10.7 comp, trick full cnc heads.... i think the motor made 100 more hp from the full cnc port job...

Yep, 1.5 hp/cube can be easily done these days with good parts and stuff that is not too radical or on the edge.