compression ratio for a tuboed 2.5l

[erfnick1]

a while ago i posted a thread about turboing my car. I have been reading alot about the forged interals but i could not find any thing that shows any guidance on the compression ratio's that is need to run the trubo. cause i know i don't want to much copression in the piston chamber or boom but to little you will have an undriverable car.. any words of wisedom???:confused:

[SpookSVT]

It would depend on cam selection and chamber design.

Example, I know of a supercharged B16 Civic with a 11.2:1 static CR and 24lbs of manifold pressure that makes 487BHP on pump fuel.

[20COUG00]

usually you dont want to go over 12:1 air to fuel. The lower compression pistons you have the more air/fuel you can give it.

[jrak123]

huh? what does air fuel have to do with this? I hope you misstated and meant compression ratio.

These engines like to run 13.2:1(maybe as low as 12.8:1(any more than that and you are running pig rich and your car will loose power)) A/f at full load WOT and 14.6(stoich) at part loads. Most of the RPM range is very happy between 14.0:1 and 13.5:1

BTW this is coming from the person that did the baseline calibration work for the contour/cougar for Ford.

[Blackcoog]

huh? what does air fuel have to do with this? I hope you misstated and meant compression ratio.

These engines like to run 13.2:1(maybe as low as 12.8:1(any more than that and you are running pig rich and your car will loose power)) A/f at full load WOT and 14.6(stoich) at part loads. Most of the RPM range is very happy between 14.0:1 and 13.5:1

BTW this is coming from the person that did the baseline calibration work for the contour/cougar for Ford.


I think he was referring to a Contour/Cougar under boost. NA you'd want around 12.7-13.

[gamiller]

Since he's talking about forged internals, I think he really was asking about compression ratios. Stock is 10:1 IIRC. Some folks (i.e. DemonSVT, Warmonger) say you can run mild boost on the stock internals. Others recommend going with forged pistons that allow for lower compression (and more boost!) like 9:1 or even 8.5:1 like I am reportedly running.

Honestly, though, doing a search on "compression" should have given you hard numbers.

[SpookSVT]

Here's the thing; Many already assume they need to drop the STATIC CR way down when they run boost. Static CR means absoulutley nothing. The dynamic or actual CR takes into account when the intake valve closes (when compression actually starts). A later IVC will lower CR and an earlier will be higher.

Another thing is that when lowering the CR, many remove the optimum 'quench' height that adds 'artificial octane'. This 'quench' increases the knock threshold. Chamber, port, and piston design have a big affect on mixture quality. A more homogenous (evenly mixed) A/F mix will tolerate higher CR.

Hence why I say, cam selection and chamber design will tell how much is tolerable.

[erfnick1]

so since i will be turboing my car in the next couple of months i think i will go with the 8.5 to 1. Do you have any idea on the cost and where to get them on both the pistons and the rods?? what is the daily drivablity on your car since you have the ratio? also i will be putting a 75 shot of nitrous as well have any idea or comments??:cool:

[gamiller]

As stated in a PM, all that info is here; just poke around a bit. custom pistons are made by Diamond. forged rods are made by Pauter and another company. originally, rods and pistons were ~$1000 per set. I don't know what they are going for now.

the lower compression doesn't affect me at all, but that's because i've got a three liter block installed.

guys have had nitrous setups before, including FastCougar and ILoveMyCar. checkout the N2O FAQ.

[pgtatx]

so since i will be turboing my car in the next couple of months i think i will go with the 8.5 to 1. Do you have any idea on the cost and where to get them on both the pistons and the rods?? what is the daily drivablity on your car since you have the ratio? also i will be putting a 75 shot of nitrous as well have any idea or comments??:cool:

I'm not sure how to put this... Unless you are going to build a motor and setup for a turbo, and you never install the turbo, then run it NA... you will have no daily driveability problems.

My car runs an 8.2:1 compression ratio... everything is relative.

Also, why do you want to add a 75 shot of N2O? A basic turbocharged setup will create more than enough power. In fact it will create more power than the platform can even handle. Just my opinion...

[gamiller]

the usual reason to have N2O in addition to a turbo is not to increase power at the top end but to have power on tap while the turbo is still spooling. i'm guessing he wants to spray from ~2000 RPM until the boost comes full on.

[pgtatx]

I understand the reason to want ot use N2O in addition to a turbo... either used as a way to compensate spool time (lag), or to fill in a gap of the powerband (top end). Or of course, just to push the car farther when the turbo just runs out of steam...

Using a 75 shot to help spool is overkill... a mild 35 shot, or better a progressive shot is all that's needed. A 75 shot on top of a turbo setup on a cougar is overkill too if you want "more power". Plus by the questions asked, I'm not assuming anything by the poster.