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Drop compression ratio for Turbo

945 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 - 8 of 32 Posts
Forged pistons are stronger and will make the engine more knock resistant. Plus just a thicker head gasket makes the quench area (cylinder volume with the piston at the top) a very non ideal shape. Go with the pistons. Might want to go down to 9.5 or 10:1 depending on what fuel you plan to use.
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Can always order custom pistons with a spec compression ratio. Just a little more $
It's true. My Cayman has 350 HP (known for being close to that at the wheels) and weighs just over 3000 lb and is very quick. My Supra is just under 3000 lb and 475 wheel (in the higher gears) and is frightening. Even my cammed non FI 2ZZ MR2 is quick.
You get in a bit of a corner between knock, spark retard, and too rich. Only way out if you want more power is better fuel, lower CR, more inter cooling or water/meth (which cools the intake and improves the fuel quality)
Yeah I'm in a similar situation with my Supra - I'd need to go to a larger turbo or better fuel etc. as I'm getting close to my EGT comfort limit, don't want to go richer than 11:1, and can't really get better intercooling without a lot of work (or water/meth injection). But that all being said I don't need more power. I've got 475 wheel in a car weighing 2900 lb, I can't even use full boost until 3rd gear which if you rev it out starts at 110 km/hr!

And it's nice to be able to just use 91 AKI pump gas (93 or 94 on the track) and not need to worry about any other consumables like meth.
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Yeah I usually drive around at 11 psi which is about 360-370 wheel and it's still tons. In 'high boost' mode activated by a switch it runs the same 11 psi in first, 15 or so in second and 18 in 3rd and above to limit the amount of work the traction control needs to do (if I have it turned on). It's actually a 8 setting progressive slip setup which is really ideal.

For me if I can make the power I need with pump gas alone, and have it reliable on the track, that's the ideal.

And yes it has big brakes. Wilwood 4 pot with 12.15 x 1.25" rotors front and 12.12 x 0.81" rear. Plus ducting to the front spindles from the bumper.
EMU black. It's actually cable throttle - the traction control is spark cut so you don't want it working too hard, thus the boost by gear. It does do E throttle but the car is old and originally cable throttle so it'd be hard to change and I'd lose cruise control unless I did a lot of work to implement it in the ECU.
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Yeah but after a point it's better to run less boost so you can keep the mixture a bit leaner.
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