Does higher compression ratio raise TQ off boost?

[Halon]

I don't have a ton of first hand experience, but the theory I've basically accepted is:
- It does increase off-boost torque
- It does not affect spool (or not enough to really notice)
- It will make the car feel as if it's spooling quicker because of the increased off-boost torque/response, but if full spool was at 4k RPM at the lower CR, it will likely still be 4k. You'll just get to 4k quicker because of the increased off-boost torque.
- More power at the same boost level, if done properly.


Also the other thing that I'm learning a lot about on the 2JZ platform that I rarely ever heard with the 4G63 platform, is to consider quench area is as ideal as possible. I'm not an expert what so ever, but I've heard some individuals whom I'd consider to be experts, say that quench pad area/design should be as important and thought out as CR is when building a motor.

[Shane@DBPerformance]

Magnus was always big on designing his custom Ross pistons to try to take full advantage of the quench area.

Higher compression will add power/torque when not making boost or on an NA car, so it will make a car feel stronger during normal driving. Higher compression doesn't create more exhaust though, so it doesn't help spool a turbo faster, but it will make more power with less boost, so it can feel like it's spooling faster. As you go up in compression ratio, the gains become smaller and smaller though, so going from 8.0:1 to 9.0:1 is a much larger power gain than 12.0:1 to 13.0:1.

[Halon]

Yep, Magnus is the only one I ever heard pay any attention to quench on 4g63's.

[Goat Blower]

It's not apples to apples, but I was VERY happy with the 10.5 to 1's I put in my Evo, that thing spooled at idle, or at least felt like it. When I rebuild my current DSM motor someday, I'll definitely be going higher compression. For a street car, I think it makes a noticeable difference, if it's a drag car, lower compression and higher boost might be better.

[Murlo26]

For most of us locals who run strictly e85, I don't see a downside to running higher compression.

We all run our turbos at MAX boost anyway since we are on E85, so if you are building the motor anyway, mind as well do higher compression.

If you are in fact doing a straight race/drag motor then yea you might be better off with lower comp more boost, but us street guys it seems like a no brainer.

[turbotalon1g]

I'm planning on 10.1:1 instead of 10.5 on wiseco HDs, but this was for a guy with a 2.3 9:1 motor.

I'm pondering AL rods vs. howard HDs now

[Halon]

Have you considered talking with Magnus about their pistons with (marketed) improved quench design? No idea where those land price-wise though...

10:1 (stock CR) is what I'm running on the SC300.