eyeball 3.0 piston compression ratio?
 

Is there a way compression ratio can be determined by looking at a piston?
All I know is that these came out of a 79' SC, but they are not original.
Anyone here see enough of these that can tell by looking at one? If there is a number or marking anywhere on the piston that can determine this I will ask the seller

I appreciate the help
http://forums.pelicanparts.com/uploa...1149127989.jpg

They sure look like stock CIS pistons. I wish I had my book with me, but I believe most CIS motors ran about the same CR. Whatever it is, it is going be low when compared to a high perfomance piston. If you don't get any responses, bump the thread to remind me and I can look in my book when I get to work.

CIS motors ran a couple of different ratios. I think the early ones were 8.5:1, and the later ones were around 9.1:1. I agree with Kenik, yours look like stock pistons.

sounds good

I believe N/A 3.0 CIS could be one of three CR's
8.5 which would be standard in 79' (but this car had them replaced- but possibly with the same)
9.3 USA 80-83
9.8 ROW maybe 1980 and up. Not sure there

I don't believe the higher CR came in until the 3.2 Motronic cars (in the USA at least). Correct me if I'm wrong. You could cc the suckers (obviously); it's pretty easy to do.

My 1983 USA car has 9.3:1 smaller intake 180hp
The later euro SC's had the higher 9.8 and 204 hp with the big intake runners

Copy and paste from our host

Piston & Cylinder Set of 6, (95mm bore, 8.5:1 comp), 911 3.0 (1978-79)


930-103-962-05-SET $3144.00
Piston & Cylinder Set of 6, (95mm bore, 9.3:1 comp), 911 3.0 (1980-83)


930-103-977-03-SET $4171.50
Piston & Cylinder Set of 6, (95mm bore, 9.8:1 comp), 911 Euro 3.0 (1980-83)

SWEET!

I think from your picture that you have 9.3 or 9.8 pistons. If the "flat" area is dished down (concave) then they are 9.3. If the "flat" area is really flat then they are 9.8.

-Andy

Andy-

Thanks for the great reply.
Is it safe to say they are definitly not the 8.5 pistons?

I appreciate it
Vinny

It's been about 6 months since I did the same thing you are doing but I'm 90 percent sure of what I see in your picture. If you can find some pictures of 8.5 compression pistons you'll see the difference. I looked at ads for 8.5 and 9.3 pistons in the for sale section to make my determination and got the concave vs flat info from Henry.

If you look at 8.5s you'll see a larger "flat" area that is not round like in your picture.

-Andy

Thanks Andy

I did a search on this BBS and agree with you. There is no way those are 8.5's.

I really appreciate the help
Vinny