TRBOMP5

Ok, I have a machine shop that has done alot of work for me (my header flange, turbo in and out flanges, downpipe to stock exhaust flange) plus an assload for my work. I talked to him about making a head spacer to lower our compression to whatever we wanted it to be. I heard about this from a Civic guy, and also there is a write up in European Car (sorry japanese guys, but I got the S4 too) about a BADASS GTI that has it done to it too.
Basically you just pull off your head and sandwich this between 2 headgaskets. and voila 8.5:1! (or whatever)
He said if I bring him a head gasket he could make it from that. But it will probably be a chunk unless I can get a pretty good size group buy going (maybe 10 plus)

Ok but here the questions start:

1: Does anybody know all the specs on our cylinders to come up with the proper thickness to lower it to the right compression? (dont forget to add in for the extra head gasket)

2: What all else do you have to do because you've lowered the compression?
(I'm sure just a little tuning on your Stand Alones for all you lucky asses with them)

3:What is the sugested material it should be made out of?

dude ina mirage

With a stock compression of 9.0:1 I don't see the need to lower the compression anymore than it already is unless you plan on building a drag only high pressure turbocharged vehicle (in which case it would probably be more stable to just have custom pistons made to lower the compression ratio).

Problems: Your cam timing will be slightly off necessitating a couple of adjustable cam gears to get it back to stock timing. You will need two headgaskets and now you introduce an additional potential area of weakness (two headgaskets). You will need to specify new head bolts (or head studs dependant upon what the protege engine uses) with the extra length taken into account.

How to calculate necessary thickness: Take stock stroke * stock surface area (piston radius^2 * pi). Then you know stock compression ratio is 9.0:1 so that means there is 9 times the volume at its lowest point compared to the highest point (so combustion chamber volume (unknown) + the volume swept by the piston = 9 * combustion chamber volume). Now that you have all the info you need just plug in the new compression ratio and you will find what the new combustion chamber volume should be. Subtract the combustion chamber volume you found with the stock engine. The resultant will be a volume equal to the volume of the decompression plate. You will then divide out pi and divide out the radius^2 number from above and be left with the thickness required (which should be small...less than 1mm in most cases). A slight change in thickness (say for example an in-exact material that is .9mm on one end and .8mm on the other end) will result in a few tenths difference in the compression of your cylinders.

TRBOMP5

our stock compression is only 9.0:1? thats sort of pathetic for a NA motor isnt it? I figured it was around 10-10.5:1 so if thats the case your right untill i hit a lot more psi there is really not a point