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CR? 3.2 crank and 964 pistons.
So that's what I'm wondering now...
 I am planning on using a 100mm cylinder kit for my 3.2 liter engine, using the stock 3.2 crank. (74,4mm) And, because I can get them cheap, I am thinking of using 964 pistons. (CR about 11,3:1?) What would the compression ratio be with that setup? Am I calculating it right when I get around 9,65:1? Guru's; chime in... 
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08-03-2012, 11:03 AM
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Stock 964 pistons run under the advertised 11.3:1. I believe they average around 10.7 to 10.8 to 1...
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Steven 1995 - 993 RS Tribute - 4.0l Engine plus other stuff... 2005 - Touareg V8 Tow Vehicle |
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08-03-2012, 11:05 AM
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Really? Static CR?
Will that mean that the CR for my intended setup would go below CR 9:1? After all, I will "subract" the piston travel toward the head with 1mm. That relates to lower CR. But by how much? Thanks |
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08-03-2012, 11:15 AM
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Yep, some are as low as 10.6.
Unfortunately I am not an expert in calculating compression, I am sure someone else will chime in...
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Steven 1995 - 993 RS Tribute - 4.0l Engine plus other stuff... 2005 - Touareg V8 Tow Vehicle |
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08-03-2012, 11:29 AM
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Hmmm...
OK. And is this down to the volume in the heads being larger that they should be? Or the deck height being larger that is should be? lower pist dome? or a mix? I guess I can get away with a lower volume in my heads, since they are 3.2 stock, and will need to be machined slightly. Chime in gurus! 
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08-03-2012, 12:05 PM
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I guess what I should be asking is this:
Has anyone done this? (964 pistons on a 3.2 crank, using 100 mm Barrels) Experience appreciated. |
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08-04-2012, 04:44 AM
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Join Date: Oct 2008
Location: Nash County, NC.
Posts: 8,500
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The 3.2 and the 3.6 use the same rods, how do you handle stud spacing for the cylinders?
Bruce |
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08-04-2012, 04:59 AM
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I know that the rods are the same. But the stroke is different. The shorter stroke will make the pistons designed for a longer stroke, stop 1mm lower than with the 964 crank. This will give me more "headroom". I think I got my numbers right, and this setup should give me a CR of ca 9,3:1. This is assuming that the CR is lower than stated for the 964 pistons.
I will either buy a finished cylinder set with the correct stud spacing, or I will machine some 964 cylinders to make them fit. I'm also going to machine out the spigots for the barrels. This will mean there is no need to twin plug, although I might do it anyway, when the heads are at the shop. |
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08-04-2012, 01:37 PM
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Black bastard
"The Red Rocket"
