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[-nick]

I came across this ebay listing, the engine shot looks omniously familiar-



Those are the remains (at least in cylinder #3) of forged JE pistons. Mine melted down in a similar way. The factory pistons may not be perfection, but they certainly don't do this...

[bass gt]

Nick,

Did you get to the bottom of why yours self destructed?? I am about to buy some new slugs, and this doesn't fill me with optimism!!!

Regards,

Steve

[-nick]

I never came up with anything conclusive. I was running 10psi and premium fuel on the 8.5:1 slugs, and basically stock everything else. Fuel system seemed up to par, but the fuel dizzy could have had variations between cylinders which lead to the demise. It's a bit of a long shot, and it must have really been lean to cause a piston to melt entirely. It's possible that my head/block had been decked too much in the past (never checked it very thoroughly) raising the compression up. It was certainly detonating. Either my ears weren't trained well enough to detonation, or the sound was masked by the catless exhaust note.

I think the jury is out still on the VW flattops. Racing has had great luck with them. The questionable compression ratio with those makes me leary. Racing reported hogging out his cylinder head volume from 21cc to 28cc to lower the ratio, plus a slightly thicker headgasket. I think he still ended up with a bit more compression than he anticipated.

I'll let the cat out of the bag - I have a rebuilt engine coming my way with new factory pistons / new cam / crank turned 10 over / headjob / etc. I got lucky on an ebay listing, but I have lots of faith in the 100% factory configuration. Add EFI/dizzyless igntion & the intercooler and I'm hoping for a long trouble-free ride. Finally

[Raceboy]

I hope to give some report on VW pistons in a couple of weeks as I installed the engine and now finishing my intake. Most important thing is to find out the maximum advance that don't cause detonation, hope to do it without trashing the engine (with stethoscope, it's possible).

Steve, what's your advance curve looks like? What's the advance in WOT near redline and in what boost?
_________________
'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

[924RACR]

As a counterpoint, I've been quite happy with my JE pistons - running them in my NA racecar, 9.5:1 compression, and about 40-42 degrees max advance, 93 octane gas. Haven't had the head off to look, but they've run solid so far...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[AFRICA DEE]

I am also in the process to rebuild my track car's 931 engine. It is the 1980 model, so no DME with TPS etc. This is the first time the motor is opened. Has only done 50k but previous owner was a bit negligent in maintenance area and it stood for a very long time. To get it up and running again the previous owner had fitted a new KKK26 (1981+ model), new injectors, exhaust manifold and new fuel pump and the sold it 600 miles later to recover his cost. Since then she has done less than a 1000 miles, but is pushing fair amount of oil through breather and definitely needs new valveguide seals.

My engine is the ROW spec. 7.5:1 compr. motor with standard boost. (I think 0.6 bar?) It is quoted as the 170hp engine.

If I have the need to go up in piston size if the barrels have got some damage I need to decide on pistons. I was thinking the VW flat tops as they are not expensive over here. Std piston rings over here alone are more expensive than the VW pistons.

I have bought over the FMIC from Outofthebox and is busy fitting it. We have also 95 octane fuel in SA.

Now my question: If one would use standard compression ratio pistons, with 1 bar boost with I/C or use the VW flat tops, say 8.5 to 8.7:1 compr. depending on work on head, with I/C but with standard boost, which set up will have more bhp/ and also which should be in theory have less reliability problems. eg detonation, or is it much of a muchness?

What would you guys recommend to go with either these setups to "guarantee" reliability.

Your comments will be appreciated.
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1980 924 N/A Ex-931 Track car: My cash guzzler
2004 996 4S: My Weekend plaything
2012 VW POLO GT: My daily commuter