How to tell CR on CIS pistons?

mike95125 · 07-28-2004, 05:35 PM

How can I tell what the CR is on my CIS pistons. I want 8.5:1, but on the 74 CIS I think that the stock was 8.0:1. Anyone have a good used set of 8.5:1?

Thanks!

2.7RACER · 07-28-2004, 08:02 PM

Mike,
I have a set of mahle pistons that I removed from my '76 2.7s. The numbers inside are 90L58+ AND CO11. I replaced these pistons with some JE 9.5:1 last year.
I notice from reading in Bruce Andersons book the '74 and '75 911 CR was 8.0:1, while the 911s was 8.5:1. In '76 he shows all the 2.7's at
8.5:1.
For 1974 he shows motor type 92 with 8.0:1 and motor type 93 as 8.8:1.
I hope this helps.
If you are interested in my mahles let me know.

2.7RACER · 07-28-2004, 08:08 PM

Mike ,
typo, the type 93 motor is 8.5:1

mike95125 · 07-29-2004, 11:40 AM

I may be interested, thanks for the info. I need to see what my numbers are. will the numbers be inside the piston, and will it be like yours "90L58+" only with a 93 or 92? What arew you looking to get for your pistons if I need them? What size are they; 0,1,2..? I have size 0 jugs and the class (? number in the triangle) is 6.
Thanks again, Doug!

2.7RACER · 07-29-2004, 02:35 PM

Mike,
Essentially what I'm saying is if your motor type is 92 then it is likely the pistons are 8.0:1 CR.
I do not know what your pistons will read inside.
My pistons are standard size, not oversize. I'm sure they are 8.5:1 CR.
I suppose my question is what are you trying to accomplish?
The higher compression will improve your torque and power. I don't know how much.
When I installed the JE 9.5:1 pistons I got some gain, maybe 10HP. My problem was high altitude. In Albuquerque, we are at 5,000 feet. So we are down at least 15% HP compared to sea level.
I don't know if just these pistons are the difference between the 911 and a 911S.
To really bring my motor to life I replaced the CIS with Webers and a Solex cam. I'm looking at around a 25 hp increase.
I don't have to deal with smog issues where I live.
Bottom line these are good pistons and you can have them cheap if you want them.
Good Luck,

mike95125 · 07-29-2004, 07:00 PM

Doug,
What I am trying to do is get 8.5:1 with SC grind cams for a flatter tourque curve and about 15 more ponies. I figure that this is the least that I can do and still stay with the cheaper pump gas.
Thanks,
Mike

2.7RACER · 07-29-2004, 08:34 PM

Mike,
Looks like you have a sound plan and reasonable expectations.
Let me know if you want the mahle pistons.

mike95125 · 07-29-2004, 08:43 PM

Hey Doug,
How do I figure out if my engine type is a 92 or 93?

2.7RACER · 07-29-2004, 09:26 PM

Mike,
The engine serial number is located just to the right of the cooling fan on a vertical flat, near the oil pressure sender.
The engine type is just behind the serial number on the horizontal flat. You may need to wipe the surface to see the numbers.
Let me know if you have trouble finding it.

mike95125 · 07-29-2004, 11:14 PM

Well,
The case is th 911/92 so it is the one with the 8:1, but it has had work done in the past so its anybodys guess what I actually have. I will attempt to find out and then will contact you. Send me an email at mike95125 at yahoo dot com about the price for yours so I can plan accordingly. Thanks!