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Join Date: May 2001
Location: Juncos, P.R.
Posts: 84
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Lowering Compression
Hi Guys:
Why the compression in Porsches can't be lowered by using copper head spacers or shims under the cylinders like the VW engines? Is it because of the lenght of the chains and cylinder head studs? Thanks, Francisco Soto Puerto Rico |
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03-02-2004, 11:35 AM
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Join Date: Nov 2003
Location: Southern California
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Francisco,
I don't know if they are made for Porsches but in my old Chevy blower motor we used dished pistons. Lar
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2001 Turbo |
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03-02-2004, 01:43 PM
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Join Date: Dec 2003
Location: Arapahoe County, Colorado, USA
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Francisco,
The performance reason is that the cylinder-to-head minimal clearance provides what is known as “squish.” This causes almost all of the air-fuel mixture to be forced into the combustion chamber at TDC compression. This has important advantages: 1. It causes more turbulence in the combustion chamber, allowing better and more complete combustion. 2. It prevents small volumes of combustible gasses from being available for detonating. If you just add spacers under the cylinder you reduce the CR but you also reduce/eliminate squish, with bad results. If, for some reason, you need lower CR, get different pistons but keep the squish. Lar, Yes, some Porsche Turbos have flat and dished pistons. They still have “squish” around the perimeter. Best, Grady gradyclay@hotmail.com
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03-02-2004, 02:21 PM
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Join Date: Jul 2003
Location: morro bay, california
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I've always thought that you could use an additional copper cylinder base gasket with no disadvantages. However, this would only lower your compression ratio but a few tenths.
Clint
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_____________________________ Clint Smith www.RebelRacingProducts.com 1970 911T ----> RGruppe RS/R (mexico blue) 1995 993 becoming an RS (gran prix white) |
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03-02-2004, 08:27 PM
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Join Date: Mar 2002
Posts: 3,563
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U can use a 0.5mm head gasket and a 0.5mm base shim without upsetting cam chain geometry at all.
It's what Protomotive/Prototech do with their Stage 2 (&3) Turbo-systems to drop from 9.5:1 C/R, to 8.8:1 C/R, for a bit more boost and a better cylinder -> head seal.
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Merv '89 911 Turbo Cab Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition 
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03-02-2004, 08:39 PM
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Join Date: May 2001
Location: Juncos, P.R.
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WydRyd:
What did you do to your AC condenser? Did you relocate it under the car? Thanks, Francisco Soto |
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03-03-2004, 06:47 AM
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Join Date: Mar 2002
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Francisco, I *will* be installing a "sub floor-pan" static condensor soon. I'm just awaiting the shipment to come in from the USA.
Why do u ask? Are u thinking of a similar upgrade?
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Merv '89 911 Turbo Cab Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
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03-03-2004, 06:44 PM
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Registered
Join Date: May 2001
Location: Juncos, P.R.
Posts: 84
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Hi Merv:
I think I am going Juan Ruiz route and install the OEM condenser under the car. He did it and looks good. About how it works, don't know yet. Francisco Soto |
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03-04-2004, 02:54 AM
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