TonyG

Who has actually measured and cc'ed a 968 ro S2 cylinder head?

Also, I'm looking for the cc of the 968 piston.

Thanks,

TonyG

Ski

Tony, there was a thread not long ago, something like "my 3.0 project" or something like that; there was much discussion on the 968 head volume, where it could be increased to lower compression, where to do it, what to do with the pistons. Not sure of the knowledge of the people who were discussing it but one of them did seem to have a good past in machine work and calculations. If you can't find anything there, you might place a phone call to Bob Norwood,,maybe he would help for free...

RajDatta

Piston volume is 27cc from some recent posts. Maybe someone can tell you on the combustion chamber volume.

Bengt Sweden

Displacement is 748cc and CR is 11.0:1, so compressed volume should be 75cc.
75cc-9cc (1mm head gasket) -28cc (piston relief)=38cc
The 28cc are my measurement and could be off by I guess 1cc.
I will measure the head for you.
Cheers
Bengt

TonyG

Ben

Where did you get the 1mm compressed thickness on the head gasket?


And did you cc the pistons and come up with 28cc's?


What is the deck height of the piston at TDC?


I've not had a chance to do this yet... I'm just trying to do some preliminary calculations...

TonyG

fast951

From memory, S2 head is 41.6cc

Bengt Sweden

Well, I measured the head gasket, but not compressed. I don't think you can compress it very much.
The pistons turn at deck so the clearance equals the head gasket. Could be some minor difference but I don't think so.
My cc ing wasn't perfect but yes I got 28cc for the pistons.
If you would want 8:1 you would need 748/7=107cc total i.e 32cc more that is 3.5mm more head gasket or shorter rods.
I assume you will double check the figures.

The CR of S2 was 10,9 so there should be a difference of .75cc to 968

if 27 and 41.6 and 9 are correct then CR would be 10.6. and it is stated 10.9

we need 75.6 total for an S2 and 74.8 for a 968.

Bengt

dand86951

Tony, I don't know about the 968 block but the 2.5 has a positive deck height. I.e. the piston is proud of the block deck at tdc. Mine measured at .076 mm.

dand86951

Tony, I put together a spreadsheet that does a pretty good job of predicting compression ratio based on bore, stroke, head and piston dish ccs and amount of head and block machining. If you want it I can email it to you.

TonyG

dand86951

I know the 951 pistons come up out of the hole... and although I've never measured it.... it looks a lot more than .076mm More like 1mm or more.

But that was just looking at it.

Are you sure of this measurement? Are you sure you were at TDC?

Thanks,

TonyG

TonyG

dand86951

Thanks... I'll take a look at it. I've got my own I made... but I'm always looking for better tools.. physical or virtual :-)

Thanks..

TonyG

Jay Wellwood

dand86951-

I would also like an email with the spread sheet if you don't mind.

TIA-

dand86951

Jay, what email address and I will send it to you.
PM me that if you want.
Dan

dand86951

Tony. I will do some digging through the old papers, but I am pretty sure that it was the .076mm. It may take a day or two for me to get through them. It was measured accurately at the machine shop.

Dan

Bengt Sweden

.076mm gives .65cc
For sure not 1mm. It would hit the head.
B