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3.6 twin turbo motor


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Hi there, I'm a new member so I hope I am posting this in the correct category!

We race a 917 replica which has a 3.6 litre air cooled motor, ex 964. We have a twin turbo set up on the car, and have experienced a number of rocker failures with the motor. On the latest occasion, we had an overboosting problem and would like some expert input as to whether this would have been the main cause of the breakages or if there may be an underlying problem as well. The car is limited to 7200rpm - would it be wiser to drop this to, say, 6500 or 6750?

Any advice would be much appreciated!

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Hello

Rocker failures are mostly based on oilproblems (wear) or overload (shear) best would be to contact the engine builder/tuner. Most 964 Biturbo upgrades where based on TTP Development. (Lotec/Turbo Technik Pietz)

Factory stock engines are built to 6800/min rev limt on the Hardware side.

The weak point in the stock engines are the 7mm Rod Bolts. While they will survive 6800rpm at 100%load at fulltime, higher revs cause higher failure rates and abouve 7500/min the fail risk is higher then the survivaliance rate.

However Turbo Kits came with lighter Pistons adding additional save rev margin.

Now if you realy RACE that 917 with that engine you should find al local expert on race preperation and building race engines. If you can´t find one in the US would be Steve Weimer or Andial a good start point. On any Porsche Club Race weekend you can find local experts or Advice from Drivers.

Grüsse

Edited by IXXI
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Hello

Rocker failures are mostly based on oilproblems (wear) or overload (shear) best would be to contact the engine builder/tuner. Most 964 Biturbo upgrades where based on TTP Development. (Lotec/Turbo Technik Pietz)

Factory stock engines are built to 6800/min rev limt on the Hardware side.

The weak point in the stock engines are the 7mm Rod Bolts. While they will survive 6800rpm at 100%load at fulltime, higher revs cause higher failure rates and abouve 7500/min the fail risk is higher then the survivaliance rate.

However Turbo Kits came with lighter Pistons adding additional save rev margin.

Now if you realy RACE that 917 with that engine you should find al local expert on race preperation and building race engines. If you can´t find one in the US would be Steve Weimer or Andial a good start point. On any Porsche Club Race weekend you can find local experts or Advice from Drivers.

Grüsse

Thanks for your interesting input. You made us think about the oil - we're going to look at some other options here as a precaution. After doing quite a lot of research on the net and speaking to various people, I think it makes sense to turn the revs down to around 6750. We DO really race this car! It's an awesome car with loads of potential, but we need to get the reliability sorted. Our engine builder is a very good Porsche man, but this twin turbo set up we have is something of an unknown quantity. We've had the car a year but because we've been busy with other racing, we only got around to racing it in January. We ran it once when we got it, but it broke rockers then and we basically rebuilt everything after that. We've now installed a Turbosmart wastegate and boost control unit to take care of the overboost problems, too. We're really trying not to upgrade everything at great expense - I would much rather run it at a lower maximum rpm and keep it reliable. I have attached a pic of the car - it really is a beauty!

post-65941-0-24869100-1297349783_thumb.j

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