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Drop compression ratio for Turbo

944 Views 31 Replies 9 Participants Last post by  Funkycheeze
Hi all!

I have a 2zz Spyder that needs a headgasket replacement and I intend to go turbo before the summer.
Heres my thinking and I would like someone to correct me if I am wrong.

Cause the high compression ratio on the 2zz stock is 11.5:1 it cannot take much more than 8psi.
So to gain more power (into the 300s) reliably i've read you need to drop compression ratio.
So what I thought I needed to do was get myself mahle forged pistons 10.5:1 as it's in the range from 5-15 psi that i am looking for.
However I saw that cometic has a headgasket that is 1.3mm thick (stock is 0.5mm) and drops compression by one full point (from 11.5:1 to 10.5:1) according to MWR. Which is significantly cheaper and does exactly the same as forged pistons.

Link to both items:
Cometic head gasket – Toyota 2ZZ-GE 82.0-82.5mm 0.052″ (1.3mm) | Monkeywrench Racing
Mahle Piston Set – Toyota 2zz – 10.5:1 compression 82mm | Monkeywrench Racing

Am I being dumb or will this actually work?
1 - 3 of 32 Posts
You're not wrong. I run timing on the VERY conservative side and stay well away from any knock. I probably leave 30 HP on the table just to protect the engine.

300 hp is way on the low side of what the unopened 2ZZ engine can do. 300 crank is only like 8 PSI on most builds and maybe even less. You can do that without an intercooler! Heck, you can even manage that supercharged with no intercooler (see Lotus TVS builds). I have done that with my 71mm turbo even without active knock control from the ECU.
On the other hand, the more you retard the spark the hotter the exhaust gets, unless you go richer in fuel/air.
That's not exactly the case. I can make no more power at 10.5:1 than 11.5:1 with more timing in most of the map.

I go back to my point I was making earlier though. A 500HP 2ZZ does not make a whole lot of sense if you are running a C-series transaxle. Seriously, look at what the power to weight would be (if the transaxle didn't explode). That is an insane car. Trust me. IMO it is not worth building the 2ZZ for that kind of power.

Power/Weight LBS
Cayman GTS 4.0 = 0.123
FAT Spyder 2200lbs @ 500 HP = 0.23
Huracan = 0.188
There is a direct relationship between spark timing and exhaust temp. As you retard from MBT (Minimum spark advance for Best Torque) at a fixed speed and load, exhaust temp goes up. This is basic engine science.
Yes, but my point is that adding fuel does not actually help protect the engine beyond a point.
Right, but it can reduce knock tendency all the way to almost the smoke point.
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