Compression Question
Thread Starter
2nd Gear
Joined: Oct 2013
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Compression Question
This is my first post please forgive me i've missed a obvious answer, i've been looking to buy a 911 my whole life and recently i've set my eyes on a 911 sc. I've read the faq, and know there isn't much to be done to the motor. So what keeps the compression so low on these motors, huge piston dish? Big combustion chambers on heads?
Drifting
Joined: Nov 2011
Posts: 2,526
Likes: 116
I have no idea why some of the earlier SC's were designed in that manner.
There is an issue with Hemi heads and flame front that can be addressed with dual plugs...that allows raising comp considerably if that is your focus.
There is an issue with Hemi heads and flame front that can be addressed with dual plugs...that allows raising comp considerably if that is your focus.
RL Technical Advisor
Joined: May 2001
Posts: 11,870
Likes: 75
From: Portland Oregon
This is my first post please forgive me i've missed a obvious answer, i've been looking to buy a 911 my whole life and recently i've set my eyes on a 911 sc. I've read the faq, and know there isn't much to be done to the motor. So what keeps the compression so low on these motors, huge piston dish? Big combustion chambers on heads?
Porsche kept the CR low to deal with all kinds of low octane fuel around the world as well as help contain oxides of Nitrogen.
Porsche's race cars, not being constrained by fuel issues nor emissions concerns, varied from 10.3 (3.0 RSR) to 12.7:1+ (GT-3 RSR). Turbo cars, naturally, were less.
Depending on where you live, you can makes some significant changes. Just remember that CIS limits how far you can go due to insufficient fuel delivery.
Thread Starter
2nd Gear
Joined: Oct 2013
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I live near a drag strip, airports, and a race track so 93, 110, and 116 are plentiful to me lol. I've been looking at a 80-82 911 my main focus is a mountain carver with help from the FAQ. But i would like some extra grunt, if i ever (or should say whenever) i have to or want to tear into motor.
Rennlist Member
Joined: Jul 2002
Posts: 16,556
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From: Bend, OR
I live near a drag strip, airports, and a race track so 93, 110, and 116 are plentiful to me lol. I've been looking at a 80-82 911 my main focus is a mountain carver with help from the FAQ. But i would like some extra grunt, if i ever (or should say whenever) i have to or want to tear into motor.
PS, at one point, I had my car set up to run on high octane. It is a pain to deal with, when you go afar. When I went to twin plug, I could go with the 91 super we have in Calif.
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Drifting
Joined: Nov 2011
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On the 930-10 the fuel head is different delivering more fuel and the runners on the '83 row are the larger earlier runners too. The CIS looks the same tho until you notice the runner diameter.
The Dizzy is also different (as is the procedure for setting advance) from the US 930-16 and colder plugs are specified.
I think that's about it.
The Dizzy is also different (as is the procedure for setting advance) from the US 930-16 and colder plugs are specified.
I think that's about it.