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Martijnus
Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands
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 Posted: Tue May 29, 2007 12:44 am Post subject: Which compression ratio? |
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I'm a little confused what to do. I'm rebuilding my engine and I want to raise the compression ratio.
The engine is a euro spec one, 9.3:1 compression ratio.
I've calculated how much the cylinderblock has to be machined to get to 11:1 compression ratio, but if I do this, and it runs bad because of the compression ratio I have a big problem because there's no way back.
It's a stock 924 head which isn't very wonderful...
anyone tried this? A stock 924 head with raised compression? Or is it smart to get 10.5:1 or something like that...
Hope the gasket will hold too...
edit:
I will be using MS1 v3 for the fuel and the spark, combined with knock sensing. I'll use 98RON fuel. Anyone think it's possible? MS will automatically retard the ignition when knock is detected...
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment  |
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Raceboy
Joined: 01 Mar 2004
Posts: 2326
Location: Estonia, Europe
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| Posted: Tue May 29, 2007 1:25 am Post subject: |
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I recently completed a 924 racecar and it's engine has 2mm take off the block. Right now it runs with NA head and VEMS engine management. With 98 gasoline no detonation.
But I'll be changing the NA head to 931 head soon (hence the massive block milling).
And BTW, taking 2mm off the block results in barely tensioned timing belt, not sure you want to change the timing belt in every couple of months on street-car  Of course, elongating the belt tensioners bolt hole allows some compensation.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche |
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Martijnus
Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands
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| Posted: Tue May 29, 2007 3:07 am Post subject: |
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| Raceboy wrote: | I recently completed a 924 racecar and it's engine has 2mm take off the block. Right now it runs with NA head and VEMS engine management. With 98 gasoline no detonation.
But I'll be changing the NA head to 931 head soon (hence the massive block milling).
And BTW, taking 2mm off the block results in barely tensioned timing belt, not sure you want to change the timing belt in every couple of months on street-car Of course, elongating the belt tensioners bolt hole allows some compensation. |
The timing won't be a problem, but you're talking about the belt tensioning... thought of it. 2 mm lower means the belt is 4mm 'longer'.
Haven't looked at the timing belt overall... but if you say it's possible to fix it, I can do it 
The car you're talking about has the same pistons and stock head gasket?
If so, I'm worried for nothing, especially since I'll be running MS for the spark.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment |
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