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spuggy spuggy is offline
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Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 2,825
Originally posted by 125shifter
Twin plugging on a 930 isn't as much of a benefit because the piston doesn't have the dome that blocks the flame travel. It's my understanding that 98mm and larger pistons on a 930 benefit from twin plugging because the combustion chamber is so large.
Thanks for the clarification! It had just seemed a little counter-intuitive to me, taking a simplistic view, that a 97mm wouldn't get much of a benefit, but the larger sizes would - because, in percentage terms, there's obviously only a small delta between a 100mm cylinder and a 97mm cylinder...

But in Real Life, things often aren't that simple..

Originally posted by DRV2FST
I had mine twinplugged and wonder if I should have. On turbo's there is real doubt if it is worth it or not. There are some downsides, more plug cables to buy, more plug cables to come loose, more plugs to buy, more plugs to install in awkard angles (like behind the turbo), custom drilled valve covers, ...
Heh. I had the old-style 930 valve covers on the motor. I noticed some 964 covers for sale, guy selling them told me they were "different studs, won't fit". Bought his late-style 930 covers instead.

Mentioned this to my wrench when I dropped them off. He looked at me like I was trying to wind him up, and said "yes, the 964 covers are M6 instead of M8, you would need to drill them out slightly".

I had thought it was a different stud pattern, rather than merely a smaller diameter hole...

Originally posted by briankeithsmith
100 octane. Don't run 93 or lower fuel in it if you are gonna run 8.0:1 static compression + 1bar of boost.

It has been tried, and its not gonna work.
Ah, now that's almost precisely what I was looking for, thanks!

This is a street-driven car, and I don't want to tow a bowser of octane booster on road trips, casual adjustment of boost levels on a CIS car (i.e. on race gas) having been covered elsewhere.

If I'm understanding what I'm hearing correctly, although there's some benefit, twin-plugging still probably won't make enough difference to let me run 8.0:1 compression with higher boost levels and pump gas on CIS.

In which case, twin-plugging isn't cost-effective for me at this time, and the money will be better spent elsewhere...

Thanks everyone.
'77 S with '78 930 power and a few other things.
Old 03-09-2007, 09:49 AM
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