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HELP NEEDED:PISTON REPLACEMENT
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AFRICA DEE  



Joined: 16 May 2006
Posts: 48
Location: JOHANNESBURG, SOUTH AFRICA

PostPosted: Tue May 16, 2006 8:46 pm    Post subject: HELP NEEDED:PISTON REPLACEMENT Reply with quote

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
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2012 VW POLO GT: My daily commuter
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endwrench  



Joined: 07 Dec 2002
Posts: 1629
Location: Victor, Montana

PostPosted: Wed May 17, 2006 4:17 am    Post subject: Reply with quote

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: 2742
Location: Sydney, Australia

PostPosted: Wed May 17, 2006 1:18 pm    Post subject: Reply with quote

A set of 87mm forged type 1 VW pistons and barrels will cost you US$180 plus shipping on ebay.
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Motorheadmike  



Joined: 22 Feb 2006
Posts: 25
Location: missoula, montana

PostPosted: Wed May 17, 2006 1:18 pm    Post subject: Reply with quote

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
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AFRICA DEE  



Joined: 16 May 2006
Posts: 48
Location: JOHANNESBURG, SOUTH AFRICA

PostPosted: Fri May 19, 2006 5:56 pm    Post subject: HELP NEEDED Reply with quote

Thanks Guys.

The info on the pistons helps a lot!!!
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koolkarateguy  



Joined: 16 Dec 2005
Posts: 108
Location: Nova Scotia ,Canada

PostPosted: Sat May 19, 2007 6:00 am    Post subject: Reply with quote

Will the 87 mm VW pistons work on a 1979 N/A 924 ?
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endwrench  



Joined: 07 Dec 2002
Posts: 1629
Location: Victor, Montana

PostPosted: Sat May 19, 2007 12:45 pm    Post subject: Reply with quote

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
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"simsport" said....superchargers are better than turbos its official!....
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-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Wed May 23, 2007 3:15 am    Post subject: Reply with quote

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.
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1991 964 C4 Cabriolet
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endwrench  



Joined: 07 Dec 2002
Posts: 1629
Location: Victor, Montana

PostPosted: Wed May 23, 2007 4:01 am    Post subject: Reply with quote

Allright! This I believe Good info Nick!!

Todd
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'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

PostPosted: Tue Oct 09, 2007 4:19 am    Post subject: Reply with quote

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

PostPosted: Tue Oct 09, 2007 9:26 am    Post subject: Pistons Reply with quote

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
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leadfoot  



Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia

PostPosted: Tue Oct 09, 2007 10:00 am    Post subject: Reply with quote

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
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-nick  



Joined: 16 Nov 2002
Posts: 2699
Location: Cambridge, MA

PostPosted: Tue Oct 09, 2007 10:09 am    Post subject: Reply with quote

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!
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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

PostPosted: Tue Oct 09, 2007 6:44 pm    Post subject: Reply with quote

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: 2321
Location: Estonia, Europe

PostPosted: Tue Oct 09, 2007 9:19 pm    Post subject: Reply with quote

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.
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