Tony

What is the block deck hgt for 32v S4 engine?

(center of crank to top of deck)

Joe Ricard

HMM. I have always measured deck hieght from the top dead center of the piston to the edge (surface) of the block.
No rings when measuring personal preference. measure on the same axis as the wrist pin (no piston rock).

Tony

Hey Joe,
Isnt that called Piston deck height/deck clearance?
A lot of this terminology is new to me, so i could be wrong.

Ive got all the other variables to figure it out, just havent measuerd the deck clearance...which usually aint much! Anyone know the deck clearnace off hand? Im waiting on a dial gauge to measure all this stuff.



S4 PISTON COMPRESSION HGT 56 MM = 2.20472 Inches
S4 ROD LENTGH 150MM = 5.90551 Inches
S4 STROKE 78.9 MM/2 = crank throw of 39.45mm = 1.55315 inches

I figure it has to be pretty close to ....... 245.45 MM= 9.66338 ............
from the numbers above and the picture below.

BC

I think I remember ATB said that the deck height was like 9.6,so I think your on.

LT Texan

Tony, tha's a question from a man that needs to see a man about a stroker!!!

atb

Got a chance to do some measurements above using a 968 piston. I am assuming my 928 Int'l Crank has a stroke of 3.75", and have been advised to use a rod length of 5.850". The block deck height spec came from documents that Porsche submitted to NHTSA for importation of the GTS.

H (Compression height 968 piston) = 1.412"
L (Connecting Rod Length) = 5.850"
T (Crank Throw) = 1.875"

Total = 9.137"

Block Deck Height Spec for GTS = 9.134"

So, given the above measurements, the assembly is too tall by .003", and that's with zero deck height clearance. The stock head gasket will provide some, but probably not enough deck height clearance. Options? A thicker head gasket? Machining the piston crown? Go with a slightly shorter rod, say 5.845"?

In Smokey Yunich's Power Secret's book, he states that .038" is the minimum deck height required for piston rock in a chevy small block running .007" piston/wall clearance. This doesn't even come close to Porsche clearances, which I would imagine means we could run even less deck height, but how little?

Input anyone?

Tony

Probably machine the crown. How much material is there to work with?


Intresting numbers. Perhaps someone will chime in...with the strokers running around now, there are a few folks in the know.

atb

Tony wrote:

I'll be able to measure it out this weekend and will post the results.

I'm also taking various 104mm pistons out to get weighed today and will post those weights. It's interesting that the pistons for the 968 and 944S2 have different part numbers, but the Mahle pistons I have appear to be dimensionally the same. I've read that the 968 pistons were forged, but the Mahle set from the 968 and the Mahle set from the 944S2 look identical. I'm going to weigh a Mahle piston from each set to see if there is any difference there. I also have a set of Kolbenschmitt (sp) pistons out of a 968 which are partial skirt. I will weigh those as well.

Anyone have any clues to unlocking the mysteries of the difference between the 944S2 and 968 pistons? The part numbers are not on the pistons. I'm wondering if the factory just used what was available, and that all of the Mahle's were cast and all of the KB's were forged, or visa versa.

slate blue

The 968 and 944 s2 pistons are different and the 968 is the lighter one of the 2 @ 700 grams.

T_MaX

Need a tool made or an idea of what is used to do this job?

http://www.frontline-equip.com/bhjtools/bhj.html

atb

Greg Gray wrote:

Can you elaborate on that a little Greg? Are they dimensionally different? Or is the difference that one is cast and the other forged. (Just talking about the Mahle variants here).


T_Max, thanks for the website. I've sent in an inquiry for a price on their sonic tester. I didn't even do a search before because the "how to blueprint" books I've been reading put these devices into the thousands of dollars. Then again, the copyrights on the books I'm reading are in the '80's so hopefully prices have come down some.

atb

Just got a price check, $1750. A little too rich for me, but it sure would be nice to have one around the shop.

T_MaX

Adam, ask BHJ if there is someone in your area that they have sold one to. You may get lucky and find that there is a machine shop or custom motor builder close enough to you that will do what you need for a few bucks.

wildguy

The comp height I got for the 968 was 1.42". I do know the deck clearance is REAL close to zero.

Anyone need a set of (8) new Porsche 968 pistons?

Jay Wellwood

Seems as though I recall in a ddiscussion with Mark Anderson that the 944 S2 piston skirts required abit of trimming to eliminate interference with the stroker crank. I may very well be remiss here.