Anyone knows what would be the increase of CR when shaving 0.3mm off a 2.7 head?

 

You'd have to cc it to get the exact change, but roughly, on a 104mm bore, 88mm stroke motor, starting with 8.5:1 compression, it would bring it up to about 8.523:1 by my math. That assumes the combustion chamber in the head is shortened by .3 across the full area of the bore, which I don't think is actually the case -- so, the actual change is probably even less in the real world.

 

I bet he rounded up from 8.5225:1….

 

or in the Australian metric measurement the difference will be four fifths of five eighths of StrekStrekStrekStrek all

 

Thanks.

The thing is that the 2.7 head I use was shaved a bit beyond the limit stated in the WM so use a 1.4mm thick headgasket.
I was just wondering if it would be ok to fit a headgasket with the "normal" thickness of 1.1mm without having to redo major tuning.

 

Bumping this thread as I will replace the headgasket soon.

If a difference of 0.3mm doesn't make any real world difference, why does the WM mentions the two headgasket thicknesses?

The Cometic is available in both thicknesses, the widefire isn't...

 

Go with the thinner gasket - don't worry about it.

 

What is you compression ratio with a standard gasket? How much thicker is the thick MLS gasket?

I've never tried to figure out the impact on cam timing from surfacing the head, so don't know if that also motivated Porsche to make the thicker gasket. Maybe it was just a "specs are specs" thing back in West Germany...

 

Tom, I wish I knew what the exact compression ratio is on my engine.
The head came from the machine shop with perhaps 0.1mm past the lower limit mentioned in the workshop manuals, so according to Porsche I should bin the head

If I go for a headgasket with the standard thickness I might get away with the potential CR increase by retarding the timing, but I just might. Not sure where I'm treading, I suppose I just have to test and see what happens.

 

Why is the head off? Were you having hg problems? If you are running Andial 104.5 turbo pistons (per the 3L registry) with stock length rods, then your compression is higher than 8.5:1. I cc'd mine and posted the results a while back. If you are not running o-rings, then maybe worth trying a thicker gasket--can't hurt.

 

I would worry more about the change in the cam timing.(im saying its not enough for you to worry about the compression difference) but I would certainly invest in an adjustable cam gear and set it back to zero.-well, whatever gets you the best curve.