cwigg66

Hey all. Getting started on the new monster engine and have a few technical questions. First off, what is the standard thickness of a stock head gasket, and what is the ACTUAL bore? I have read a million posts of everyone arguing about it, but what I need is for someone to sit down and measure the damn thing!

Secondly, what is the dish volume of the stock pistons in the 951 (say an 88' if there was any difference).

Lastly, how many CC's is the head on a stock 951 (also assume and 88').

I need the specs so I can figure out what to have JE make me. I am still figuring the details but I need these few pieces of info first. I'll keep you posted on what I get and what not. Thanks all,

Chris

cwigg66

PS. I just became your newest member!!

ilikemy944

:P
Hey - driving to the mts. this weekend, you should go
- Oh yea, I have no idea to above questions... :P

Tom M'Guinn

Standard bore dimension is 100mm for group 0 blocks, 100.01 for group 1 and 100.02 for group 2. Actual measurements will vary from block to block, depending on wear, etc., so any measurement reported here may or may not be close to your block. Usually, machinist will take the pistons and bore the block to match -- if you are planning to bore and re-hone the motor. I trust you know that JE pistons are not compatible with the alusil cylinders, according to Porsche (although I have spoken to at least on engine builder who swears he's done it without problems). There are some companies out there that claim to be able to coat them to work however.

cwigg66

Yeah, I have heard that the JE's are not compatible with the Alusil bores, but I am getting around that problem. The block is getting sleeved with cast iron up to 106mm as of right now I believe, unless I change something.

As for the bore dimensions, I meant the bore on the head gasket. I am trying to figure out the exact combustion volume and compression ratios. Sorry for the vagueness in my original question. Thanks all
Chris

Chris White

106mm on a 2.5? I hope that s a street only set up….
Personally I think you are better off sticking to a 104mm max and running slightly higher boost than you were going to run with the 106mm set up. Not much cylinder wall thickness left with the 106mm bore.

Chris White

cwigg66

Not dead set on the 106 yet... I am still running through the calc and looking at everything. I am trying to get the most bang for the work, avoiding the use of an S2 crank like the plague.
Chris

dand86951

The stock head gasket bore is 102mm for the 100 and first over size bores. The 2.7 litre head gasket bore is 106mm for the 104 mm bore. The head gasket thickness was 1.1mm (uncrushed) and the stock pistons for 86 model year had 25.7cc dish and the stock head, again for a 86 model, had 56.6 cc (measured) of volume.

I put a small simple spreadsheet together that you can use to look at what happens to compression ratio as you change the variables like bore diameter, piston dish, deck clearance etc. Like Chris White said the liners get pretty thin when you go to 106mm. Depending on liner OD the wall is probably only 1/16 thick.

Dan

cwigg66

Hey thanks for the info.... that is exactly what I was looking for. If anyone can verify those numbers, feel free. Otherwise, I will take your word for it.
Chris