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Location:
Adelaide
Registered:
June 2003
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Re: compression...how low is to low (boosted engine)
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Sat, 05 March 2005 00:08
 
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Yeah, I was speaking to a well respected engine tuner about the same thing, he said that 7:1 is very seventies. The engine is pretty flat until the boost comes on really hard, then it's time to change gears.
You won't get anywhere near the linear curve that makes for the best drivability.
If you want a really good kick in the back, low compression will do it for you.
I have run some figures for you through the "Compression ration calculator".
Note, this quite theoretical, but takes into account head cc's (72ml), head gasket dimensions to suit pistons and deck clearance (piston distance below deck)
88.5 bore = 7.085:1 with 18RC pistons.
89 bore = 7.15:1 with 18RC pistons.
92 bore = 7.19:1 with $600 Forged VW 311 Bigbore (non stroker)
90.5 bore = 7.05:1 with $600 Forged VW 331 Bigbore (non stroker)
Note: the VW pistons come as a kit with rings etc, 22mm pin, Cylinders (aircooled). It is suggested that you get teflon gudgeon pin hole blockers.
Note 2: The VW pistons come in two compression heights:
- 39mm (non-stroker kit) will give you a .5mm deck
clearance
- 36mm (stroker kit) will give a 3.5mm deck clearance
and therefore shit all compression (and I mean shit!)
For US$600 plus ~US$60 freight (~$850AUS), Toysport will do you up some forgies that have an 18RGEU dome on a 92 bore (ends up being about 8.7:1) These will also have big valve releifs (2mm wider, 1.5mm deeper if I remember correctly.
I hope that helps.
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| | Subject | Poster | Date |
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compression...how low is to low (boosted engine)
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people100 | Wed, 02 March 2005 10:49 |
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Re: compression...how low is to low (boosted engine)
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4agte | Wed, 02 March 2005 10:53 |
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Re: compression...how low is to low (boosted engine)
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people100 | Wed, 02 March 2005 11:18 |
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Re: compression...how low is to low (boosted engine)
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4agte | Wed, 02 March 2005 11:37 |
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Re: compression...how low is to low (boosted engine)
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thechuckster | Wed, 02 March 2005 12:43 |
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Re: compression...how low is to low (boosted engine)
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4agte | Thu, 03 March 2005 08:14 |
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Re: compression...how low is to low (boosted engine)
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thechuckster | Fri, 04 March 2005 06:31 |
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Re: compression...how low is to low (boosted engine)
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4agte | Fri, 04 March 2005 07:16 |
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Re: compression...how low is to low (boosted engine)
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Cool1 | Wed, 02 March 2005 12:48 |
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Re: compression...how low is to low (boosted engine)
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people100 | Thu, 03 March 2005 07:41 |
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Re: compression...how low is to low (boosted engine)
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Norbie | Thu, 03 March 2005 11:21 |
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Re: compression...how low is to low (boosted engine)
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THE WITZL | Thu, 03 March 2005 23:24 |
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Re: compression...how low is to low (boosted engine)
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Mr DOHC | Fri, 04 March 2005 06:22 |
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Re: compression...how low is to low (boosted engine)
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oldcorollas | Fri, 04 March 2005 07:39 |
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Re: compression...how low is to low (boosted engine)
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YelloRolla | Fri, 04 March 2005 08:51 |
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Re: compression...how low is to low (boosted engine)
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people100 | Fri, 04 March 2005 09:48 |
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Re: compression...how low is to low (boosted engine)
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sideshow | Fri, 04 March 2005 11:43 |
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Re: compression...how low is to low (boosted engine)
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Norbie | Fri, 04 March 2005 15:19 |
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Re: compression...how low is to low (boosted engine)
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fatmr2 | Fri, 04 March 2005 21:15 |
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Re: compression...how low is to low (boosted engine)
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4agte | Sun, 06 March 2005 08:12 |
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Re: compression...how low is to low (boosted engine)
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Steve M | Sat, 05 March 2005 00:08 |
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Re: compression...how low is to low (boosted engine)
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people100 | Sat, 05 March 2005 11:09 |
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Re: compression...how low is to low (boosted engine)
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people100 | Sat, 05 March 2005 12:06 |
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Re: compression...how low is to low (boosted engine)
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MS-75 | Sat, 05 March 2005 11:57 |
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Re: compression...how low is to low (boosted engine)
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YelloRolla | Sun, 06 March 2005 06:54 |
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Re: compression...how low is to low (boosted engine)
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people100 | Sun, 06 March 2005 09:44 |
