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930 Piston rings/cylinders
We are rebuilding our first Porsche Motor, of course it had to be a turbo, that has been sitting for 15 years.... We've gotten it apart, sent necessary parts to machine shop, for cleaning, polished crankshaft, replaced studs, valve job(replaced one valve for poor seating), everything else looked good.
Cylinder #6 had 2 broken rings, no damage to the cylinder, piston or the like. Cylinders don't even look worn. These cars had Mahle rings/piston sets factory, the only place i could locate the factory chrome rings was from Porsche. Is this a sound investment? Does it matter if we go with the Goetze sets? Trying to keep the car as stock as possible. The car will be fittted with high flow exhaust and updated turbocharger/intercooler. We just don't want anymore trouble than we've had to make this car as right as possible! Hilarious, I know.
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When the common bond is a Porsche, the people who own them are even more interesting than their cars. |
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11-23-2012, 12:24 PM
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Join Date: Oct 2008
Location: Nash County, NC.
Posts: 8,503
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Goetze is the factory, Mahle or KS supplier.
Bruce |
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11-23-2012, 03:28 PM
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Really, I did not know that.
It's been presented to me however that the rings from Goetze are cast and the factory rings were not. Does this make a difference, or cause any problems going back together? We don't want any smoke!
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When the common bond is a Porsche, the people who own them are even more interesting than their cars. |
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11-23-2012, 04:46 PM
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Join Date: Jul 2001
Location: Portland Oregon
Posts: 7,007
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Your rings broke due to detonation and I'd strongly recommend you determine the cause before running the engine again.
This will help prevent an "encore performance".
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Steve Weiner Rennsport Systems Portland Oregon (503) 244-0990 porsche@rennsportsystems.com www.rennsportsystems.com |
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11-23-2012, 05:17 PM
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I did notice that the tell-tale boost gauge in the car was at 1.2bar at it's highest reading.... would this be a factor? I drove the car for a bit before we embarked on this journey, car ran great, believe it or not, and there was no smoke, noise, misfire, or anything of the negative nature.... This all began with a broken headstud
 .... it's been an expensive and interesting ride from there on out. The spark plugs looked to be about 20 years old, but I cannot say with any certainty what the cause of the detonation would be. Fuel issues? Where should we start?
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When the common bond is a Porsche, the people who own them are even more interesting than their cars. |
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11-24-2012, 07:01 AM
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Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 4,184
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Your car may not have seen 1.2 bar, the tell-tale could have just been set/left there. Only the previous owner knows for sure...
930's often seem to run fine with broken rings, I'm told. Many factors are in play for detonation; timing, fuel, overboost are all suspects, the lower you can keep the temperatures the better - so intercooler/shrouding is a factor as well. My car had no broken rings - but showed the tell-tale tiny pockmarks when apart for a re-seal. I fitted a J&S Safeguard, mostly to protect against a clogged injector or a bad tank of gas. It instantly showed when my dizzie stopped returning from full advance (giving me 28 degrees at idle) months later and it had to work for a living pulling timing... Seems to be a very sound investment to protect a CIS (or even Motronic) motor. even if you keep everything entirely stock; all my knock is below 3500 RPM, even on the track. When I reverted to my original RoW distributor with the Safeguard fitted, it was also very noticeable how much more knock was detected/prevented, even with stock timing. RoW springs have a much more aggressive advance curve. You can also use it to run more aggressive timing than stock to enhance cruise economy/off-boost response, bleed timing off as boost comes in, and still provide adaptive per-cylinder knock control/protection. My 930/60 currently runs 34 degrees mech advance @ 4000, and uses the Safeguard's boost retard to bleed off timing back to RoW spec (28 degrees) at full (.8 bar) boost, keeping 20 degrees in-hand for knock retard if necessary (it usually isn't, but it sometimes pulls as much as 4-8 degrees @ ~2800 RPM climbing hills, before the boost retard threshold - mine is set to 0 PSI - is reached). Low to mid range response seems considerably improved. There's a Safeguard unit designed for coil-on-plug; I'll be getting one when I go that way.
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'77 S with '78 930 power and a few other things. |
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11-24-2012, 08:13 AM
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Okay, Ill look into the SafeGuard unit.... I have a local Porsche guy who's going to help with assembling the top of the motor for timing, cam, valve overlap purposes(we are taking no chances here). Should this car be dyno tuned once completed? Any suggestions on where to go? We have 2 shops with dynometers here locally, but like I said before, it needs to be spot on..
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When the common bond is a Porsche, the people who own them are even more interesting than their cars. |
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11-24-2012, 10:55 AM
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First "one"
Kremer 930
