Increase comp ratio?

Speedwagon · Apr 6, 2009

Can a 2.5 crank go in a 2.3 engine to increase the compression ratio? I noticed on the tech pages, that the 2.5 crank gives a longer stroke, but the comp ratio on the 2.5 is only 9.1, whereas later 2.3 engines are at 9.2. So I'm guessing this is caused by the pin location on the piston? Any comp ratio experts out there to clear this up?

4b316 · Apr 6, 2009

You are correct,different pin location.Need to cut the head to increase comp.We usually wack the head 80 thousandths for the race truck with EFI.Some of the guys with carb systems are cutting them so far they leave in the intake bolts and mill halfway thur them,almost 200

Beanmachine7000 · Apr 6, 2009

Why would you want to increase your CR from 9.1 to 9.2? Or maybe you want to go higher? You building a race truck, I hope?

Speedwagon · Apr 6, 2009

Beanmachine7000 said:
Why would you want to increase your CR from 9.1 to 9.2? Or maybe you want to go higher? You building a race truck, I hope?

Not a race truck... I'm thinking of going high comp ratio, adding a turbo, and running E85. If done correctly, should give me tons of extra power for the rocks.

Beanmachine7000 · Apr 6, 2009

Cool... I'm not sure if I'd have E85 as a preferred fuel in mind for that set up though...

Speedwagon · Apr 6, 2009

Beanmachine7000 said:
Cool... I'm not sure if I'd have E85 as a preferred fuel in mind for that set up though...

Well it's cheap 105 octane. No way I'm going to try and use race gas. I'd like to be able to run premium as an alt, if I can't find E85, but that isn't an issue right now here in Denver.

rurouni20xx · Apr 6, 2009

to be honest id like to see the gains on raising the compression to 11 or 12:1 n/a, if they are decent (say from 100hp to 145hp) i may consider doing it myself. add that, port the heads and headers/ported intake you might just have something w/o boosting. hell if the internals could take it id almost try a 100 shot of nos w/ dual rail injection to richen her up.

skyy_4life · Apr 6, 2009

yea i planned on doing a 2.5L crank in my new motor for my ranger. are they direct bolt up or is there some modifications required?

Beanmachine7000 · Apr 6, 2009

If I was building up a 2.3, I'd do a low compression 2.3 with a twin turbo set up... Although it would be neat to see a high compression 2.3... E85 actually has less energy per molecule than gasoline, so the increases you would get from raising your CR up will be less than what you would see with gasoline... Imagine what you could do if you could figure out a way to reverse cool the engine... My LT1 has 11:1 CR and it runs 87 just fine, because the coolant goes to the heads first... I think it's a neat idea... Wish you could adapt it to something else...

Speedwagon · Apr 6, 2009

Beanmachine7000 said:
If I was building up a 2.3, I'd do a low compression 2.3 with a twin turbo set up... Although it would be neat to see a high compression 2.3... E85 actually has less energy per molecule than gasoline, so the increases you would get from raising your CR up will be less than what you would see with gasoline... Imagine what you could do if you could figure out a way to reverse cool the engine... My LT1 has 11:1 CR and it runs 87 just fine, because the coolant goes to the heads first... I think it's a neat idea... Wish you could adapt it to something else...

Some of the stuff I've read, has indicated that E85 would like 13 or 14:1 CR for best results.

99RangerBoss · Apr 6, 2009

the other apprentice at my work is going to be running e98 which hes ordering from the states to use in his race truck even though it will run richer he can crank that timing right up there!

shadetree · Apr 8, 2009

Speedwagon said:
Can a 2.5 crank go in a 2.3 engine to increase the compression ratio? I noticed on the tech pages, that the 2.5 crank gives a longer stroke, but the comp ratio on the 2.5 is only 9.1, whereas later 2.3 engines are at 9.2. So I'm guessing this is caused by the pin location on the piston? Any comp ratio experts out there to clear this up?

Anytime you increase cylinder volume, and you use the same piston configuration as the original,(flat top, dished, etc.), the compression ratio(cr) will increase.

If you reduce combustion chamber(cc) size, say with pop up pistons, replacing a dished piston with a flat top, replace the cylinder heads with cc's of reduced volume, etc., you will also raise the cr.

Same result if you increase cylinder volume by stroking.

The reason, cr is determined by the space in the cc above the piston divided into the cylinder volume with the piston at bottom dead center. Ex: Cc volume = 10cc, and the cyl volume is 100 cc. Divide 10 into 100, and you get 10 which results in a 10:1 ratio. This is the static ratio.

Cam timing also affects compression. Wide duration cams will bleed off compression at lower rpm, and the compression will return at high rpm.

Supercharging has the same effect as raising the cr. That is why high static cr's are not good when supercharging as it increases the probability of detonation.

shady

Speedwagon · Apr 13, 2009

So how do I determine where I will end up, given a certain mod to CR?

Beanmachine7000 · Apr 13, 2009

shadetree said:
Ex: Cc volume = 10cc, and the cyl volume is 100 cc. Divide 10 into 100, and you get 10 which results in a 10:1 ratio. This is the static ratio.

Speedwagon · Apr 13, 2009

Beanmachine7000 said:

But for things like the cam and whatnot, how do I get there? And how do I obtain the Cc(combustion chamber?) of the engine? From the tech page, I can get bore and stroke, but that seems about it.

Increase comp ratio?

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