Compression

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F21

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So, what if I decided not to do any change to the current build, except change compression
Let’s say I went from 9.5 to 11.5 what would you really gain as far as horsepower and or torque? As well as quarter-mile time
 
That is a totally open ended question:
I can change my lawnmower compression from 9.5 to 11.5 and it will go from 3hp to 3.2hp.
But in a 440 bored .040” it could change 350hp to 500hp.
More info needed!!!
 
It will run a hell of a lot better. Many times people add a bigger cam and hurt the performance. Compression is the what you need unless your adding boost.
 
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F21 said:
So, what if I decided not to do any change to the current build, except change compression
Let’s say I went from 9.5 to 11.5 what would you really gain as far as horsepower and or torque? As well as quarter-mile time
Click to expand...
Should be around 5-8% gain in power across the powerband.
 
Rule of thumb is 3% per point of compression.
It’s not a great rule since SO much depends on everything else.
So I can jump to 5% or more.

If the cam is a sizable one and the compression ratio is low for the cam, you’ll gain efficiency with the power as well.
 
It will make a difference, but not enough of one to justify all of the work.
 
The gain is a lot less than most people think. The HP gain gets less as the CR increases.
Going from 9.5 to 11.5 gains about 5%. Going from 11.0 to 13.0, also a two point increase, is about 4%.
 
I don't see this being a plausible question without more specifics. Cam profile comes to mind.
 
Errr, what build?

Compression and cylinder trapping efficiency, start there and optimize for the fuel you plan on running, then increase flow and fuel to reach for the horsepower attainable for the torque you have produced with your combination.
 
Well fellas, general question, general answer.

I’d call this one done.
 
F21 said:
So, what if I decided not to do any change to the current build, except change compression
Let’s say I went from 9.5 to 11.5 what would you really gain as far as horsepower and or torque? As well as quarter-mile time
Click to expand...
What all is 'the current build'? Every detail you can give is important to get an accurate assessment.
 
If you don't have headers, start there.
You won't get full improvement with any addition till you can get rid of exhaust, the choke point.
It's the most cost effective h/p improvement short of nitrous.
jmo
 
On a street/strip car you'll surely notice it in the low/mid range. It will sound better and be a lot more crisp as long as your fuel and timing can keep up.
 
Compression [ & cold air ] have a benefit that many other power producing changes do not have. They increase power everywhere from idle to max rpm.
 
F21 said:
So, what if I decided not to do any change to the current build, except change compression
Let’s say I went from 9.5 to 11.5 what would you really gain as far as horsepower and or torque? As well as quarter-mile time
Click to expand...
That is an impossible question to answer. It hinges entirely on what You are starting with, directly & specificly, there is no way to tell You w/o knowing.
Stock 360 w/iron heads & small(260°'s adv.) cam..?..You'll likely gain detonation, popped head gaskets, or the bearings banged out of the bottom end..
Hot 360 w/forged slugs & cam in the mid-high 290°'s & Al-U-minimum heads..?...humongus gains.....
 
The thing i notes the most, going from 9.4 to all most 13:1 was when i let of the gas at the end of the track.........Way better engine braking going on. as far as power.......went from a mostly stock 340 to a stroked 408 hard to compare in that way.
 
F21 said:
So, what if I decided not to do any change to the current build, except change compression
Let’s say I went from 9.5 to 11.5 what would you really gain as far as horsepower and or torque? As well as quarter-mile time
Click to expand...
I wonder if some of you guys mighta dropped the ball on this one.
How many 9.5 engines can you actually jump to 11.5
"with no other changes"?
I know OP didn't say, but if an SBM,
11.5 has the potential to quickly run the pressure up near to 200 psi;
Which I have run BTW, and it was fantastic!
Ima thinking 33IMP/ post #6, hit pretty close to home.
Ima thinking the 9.5 engine would have, had to have been, a less than exciting build to start with.
 
I don't think anybody 'dropped the ball'. The question asked was hypothetical & the answers given were in that context, mine certainly.
 
Yes, it was a hypothetical question me and a guy at work were discussing if the cam and heads could support it
 
AJ/FormS said:
I wonder if some of you guys mighta dropped the ball on this one.
How many 9.5 engines can you actually jump to 11.5
"with no other changes"?
I know OP didn't say, but if an SBM,
11.5 has the potential to quickly run the pressure up near to 200 psi;
Which I have run BTW, and it was fantastic!
Ima thinking 33IMP/ post #6, hit pretty close to home.
Ima thinking the 9.5 engine would have, had to have been, a less than exciting build to start with.
Click to expand...
Since you said this , I'll say this, that's the reason I didn't reply & no details and a anemic start.
 
F21 said:
Yes, it was a hypothetical question me and a guy at work were discussing if the cam and heads could support it
Click to expand...
What are you building a Chevy, Is that why you're not giving any details at all ?
 
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