C2 Turbo head gaskets on 3.0?

Lukesportsman · 11-18-2005, 03:40 PM

I know that Protomotive offers a stage II 3.2 with the idea of lowering compression by using C2 965 Turbo head gaskets. I think they qoute something like .5 point reduction.

Does anyone know if this can be used on a 3.0? I realize bore is different and that is the detail I'm curious about. Does anyone know if this or other gasket can be used to take a little compression out of a fresh 3.0 without swapping out new pistons? I know enough about engines to know what this is doing to squish area and is NOT ideal.

I'm most concerned with will it work, will it seal, will the space left behind due to the larger bore be suspectible as an issue with detonation due to small but possible steps at the cylinder to gasket interface.

Does anyone make thicker standard bore gaskets? You know, like all the Import Racers use when bolting on a turbo to a Civic?

THOUGHTS???

WERK I · WERK I's Garage

Why not use thicker cylinder to spigot shims? This would increase your deck clearance, lowering compression. Probably in the order of .3 of a point for each .25m increase?

Lukesportsman · 11-18-2005, 06:09 PM

Dave, thanks for your input.

Where would you get these spigot shims? This make better since to me, kind of like shortening the rod length just a smidge.

What do I spec out? What do I ask for? Where could I get these?

DonE · 11-18-2005, 06:39 PM

EBS sells shims from .25mm to 1mm

Lukesportsman · 11-18-2005, 06:57 PM

Thanks, Don

Pelican comes through with the answer as always.

KobaltBlau · 11-18-2005, 11:27 PM

Luke, note that you are raising up the cylinder relative to the piston at TDC with these base shims. this has a detrimental effect on squish just like a thick head gasket does on a "normal" motor.

note that a 3.0 is actually the same bore as an early C2 turbo. I don't really know if the head gaskets interchange but the base shims are what you were looking for anyway.

Lukesportsman · 11-19-2005, 05:04 AM

I agree, Andy that this will reduce efficiency of combo in that I'm changing the squish area and that for a given compression ratio the smallest squish is the best.

But, I'm looking for the best "band-aid" fix. Does anyone know what difference there are between stacking base gaskets and running shims? Is it simply the benefit of running one component versus stacking? I will have to call EBS next week, couldn't get their website to work. I'm sure I can the base gaskets at our host or maybe the shims too?

BIG FAVOR: Can anyone calculate how much of a shim I would nee to loose a half a point? I found that it has Alusil pistons so I don't think JE pistons are an option (correct ?).

WERK I · WERK I's Garage

There have been a couple of threads of the subject of stacking vs. single shimming. Either will work just as well as the other. I use Curil T to improve sealing on the shims.
Porsche engines are notoriously liberal on their compression ratios, but 2 (.25mm) should bring you down to where you want to be. When removing your cylinders, measure the shims that are currently there. Ideally, you should measure your deck height before you pull the cylinders. That way you'll know if it's close to factory specs. Has the engine been torn down before? It may be a case where the engine was modified in a similiar manner to raise the compression by decreasing the deck height with reducing the shim height.......ya' know in the days of plentiful cheap high octane gas?!

Lukesportsman · 11-19-2005, 09:50 AM

I will check, this is Tony G's engine that I'm hoping to purchase from him. It has been recently rebuilt fully. I'll ask him if he has any knowledge of changes. Thank you Dave for the answer on shims. That surely doesn't sound horrid. I didn't want to open her up 1mm or so due to combustion changes, but an additional .25mm doesnt sound too bad to me.

I'm new to the Boxster world, but have a reasonable grasp of performance engines.

I will measure deck height like you suggest before going deeper. That is a sound recommendation. Shouldn't take anything for granted even though I'm opening up tolerances. We all check valve clearance when going bigger, but who would going smaller even though ramp angles or overlap could result in less clearance with a cam as an example.