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AFRICA DEE
Joined: 16 May 2006 Posts: 48 Location: JOHANNESBURG, SOUTH AFRICA
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Posted: Tue May 16, 2006 8:46 pm Post subject: HELP NEEDED:PISTON REPLACEMENT |
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Have a 80 924 turbo euro spec and has seen reference to using flat top VW pistons as replacements.
Is it from the VW Van's with Air cooled Boxer motors or is it aftermarket performance parts?
VW parts are relatively inexpensive in SA!!
Please advise all details on this piston, and tech. changes, like do you have to change small end sizes etc.as I want to change injectors etc for more fuel flow .
I have an aftermarket ecu etc. and have a huge intercooler installed. Also 1 bar wastegate spring and boost controller. We have 95 octane fuel locally, plus octane booster helps. Intercooler sits in place of battery, has removed some of the wall between motor and original battery box, I/c gets air through original NASA duct with hood duct on top. Battery now in boot area! makes for very short plumbing between turbo and inlet.
Thanks Africa Dee _________________ 1980 924 N/A Ex-931 Track car: My cash guzzler
2004 996 4S: My Weekend plaything
2012 VW POLO GT: My daily commuter |
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endwrench
Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana
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Posted: Wed May 17, 2006 4:17 am Post subject: |
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Most are using the Type 1 87mm piston. Preferably forged. The rods will need rebushed to 22mm.
Todd |
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Peter_in_AU
Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia
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Posted: Wed May 17, 2006 1:18 pm Post subject: |
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A set of 87mm forged type 1 VW pistons and barrels will cost you US$180 plus shipping on ebay. _________________ 1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)
Learn to love your multimeter and may the search be with you |
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Motorheadmike
Joined: 22 Feb 2006 Posts: 25 Location: missoula, montana
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Posted: Wed May 17, 2006 1:18 pm Post subject: |
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Endwrench is correct, 87 mm Type 1 are the most affordable. I just redid the bottom end of mine And everything fits great. FYI, the mod will bump your compression up slightly. the pistons I ordered from bug auto, I think, 199.99 for the forged ones. the piston pin bushings are from EBS, they stock them. You will need some machine work done, and you will have some VW bug jugs left over. Defently worth the price.
Mike _________________ 1981 931 series2 |
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AFRICA DEE
Joined: 16 May 2006 Posts: 48 Location: JOHANNESBURG, SOUTH AFRICA
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Posted: Fri May 19, 2006 5:56 pm Post subject: HELP NEEDED |
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Thanks Guys.
The info on the pistons helps a lot!!! _________________ 1980 924 N/A Ex-931 Track car: My cash guzzler
2004 996 4S: My Weekend plaything
2012 VW POLO GT: My daily commuter |
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koolkarateguy
Joined: 16 Dec 2005 Posts: 108 Location: Nova Scotia ,Canada
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Posted: Sat May 19, 2007 6:00 am Post subject: |
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Will the 87 mm VW pistons work on a 1979 N/A 924 ? _________________ 1979 N/A 924 |
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endwrench
Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana
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Posted: Sat May 19, 2007 12:45 pm Post subject: |
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koolkarateguy wrote: | Will the 87 mm VW pistons work on a 1979 N/A 924 ? |
Well, making a few assumptions because I can't seem to get answer that I totally believe, if you are making 8.5:1 compression with a 931 head then according to my calculations you would have nearly exactly 12.0:1 compression with an NA head and stock deck height. You could probably mill or lathe .050" off the top of the piston fairly safely and end up with 11.0:1 or so. Pump gas? Don't know. Better have some sort of progammable ignition at the least.
Todd _________________ '79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!.... |
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-nick
Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA
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Posted: Wed May 23, 2007 3:15 am Post subject: |
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I got the shop to measure out the volumes. It seems that my caliper was a little off. This is what it really looks like -
VW piston - to - deck = 5.44mm (not 1/4" that I measured previously!)
Headgasket compressed = 10.6cc
931 head = 22cc (approximately, mine came out to 25.2 after opening it up)
For a 931, the CR comes out to be 8.7:1 with 87mm bore and 8.8:1 with 88mm bore. The N/A would come out to 12.7:1 for an 87mm bore. I don't know if you could get away with much over 10:1 on pump gas.
By the way, you can buy the pistons without the cylinders for $80/set -
http://www.924board.org/viewtopic.php?t=21021&start=45
Just don't use the rings they give you. Folks using the Mahle rings seem to be ok. You can call up totalseal and buy rings for these pistons and have them replace the top ring with a nitrided part which seems to all the craze for turbo rings at the moment. Plus they'll let you know exactly what stone to use to hone in the cylinders for them. _________________ 1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet |
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endwrench
Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana
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Posted: Wed May 23, 2007 4:01 am Post subject: |
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Allright! This I believe Good info Nick!!
Todd _________________ '79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!.... |
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R924T
Joined: 17 Sep 2007 Posts: 3 Location: Sweden
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Posted: Tue Oct 09, 2007 4:19 am Post subject: |
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Gathering parts for at N/A engine built on an 931 engine and have been keen on using 88mm flathead vw pistons.
Have read a lot about them in the forum but can you shave the block and get enough compression for a race n/a engine without hitting the valves with the flattops. Or should i get custom pistons? I belive 2mm is the most you can shave the block.. remember this will be a race-only engine and cheap rebuilds is a big+. |
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simsport
Joined: 06 Nov 2002 Posts: 573 Location: UK Warrington
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Posted: Tue Oct 09, 2007 9:26 am Post subject: Pistons |
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Hmmm.
So, just for clarity. the vw pistons are forged and ok for use in the 931 engine?!!
And they come in at 199 dollars!!
Eeek!....has anyone run a car in anger with these pistons in??
Cheers
Simon _________________ Blown is always best! |
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leadfoot
Joined: 11 Dec 2002 Posts: 2222 Location: gOLD cOAST Australia
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Posted: Tue Oct 09, 2007 10:00 am Post subject: |
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Depends on your cam lift...I run slightly reduced lift. Can someone with a 931 head measure the valve protrusion out from the face of the head, if it's anything more than 4/5mm then it would be close, possible valve recesses needed. You would need to make sure the block has not been skimmed before. Mine wasn't and the piston to deck clearance was 6mm.
I would consider 87mm pistons then or you won't be able to get another bore out of the block without going to custom forged, I went 88mm because I will never rebuild the block again.
Nick has your block been skimmed at all??
My calculations all fell between 8.7 and 8.9 comp as there is also gasket crush and gasket bore size to consider.
The stock gasket bore is 90mm on the turbo gasket FYI , OMV
Simsport, I making 10psi now on these pistons... and they are hyperutectic, and yes maybe once or twice...
Leadfoot _________________ 1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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-nick
Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA
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Posted: Tue Oct 09, 2007 10:09 am Post subject: |
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They're actually $80 for the set! $200 includes the aircooled cylinders, which you'll just throw away.
My shop measured the piston-to-deck height and got the 5.44mm number. He also has a ~6ft tall graduated cylinder setup to measure chamber volume where the other numbers come from. I have plenty of confidence in those measurements. My block hasn't been skimmed by much, if at all. I didn't measure that though...
I'm hitting 12psi now and showing 180rwhp according to my g-tech-esque software. I think I'm getting limited by my airfilter volume and placement (sucking hot air), and I expect to see a bit more hp at 12psi. Pistons are performing excellent so far.
I believe there is _plenty_ of room between the valves and pistons. No chance of collision even with a big lift cam. Although you'll want to measure before you try of course! _________________ 1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet |
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R924T
Joined: 17 Sep 2007 Posts: 3 Location: Sweden
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Posted: Tue Oct 09, 2007 6:44 pm Post subject: |
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Thanks for the info! Im going to talk to a pro enginebuilder this weekend so i will do some measuring then..
and i have 2 euro 931 engines in my garage so i have some spare blocks and so.. |
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Raceboy
Joined: 01 Mar 2004 Posts: 2326 Location: Estonia, Europe
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Posted: Tue Oct 09, 2007 9:19 pm Post subject: |
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R924T wrote: | Thanks for the info! Im going to talk to a pro enginebuilder this weekend so i will do some measuring then..
and i have 2 euro 931 engines in my garage so i have some spare blocks and so.. |
In Sweden, Jesper Karlsson aka Racing used those pistons first on his yellow 931 and with success. _________________ '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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