996 3.4 l cylinder head replaced with 3.6 l cylinder heads

Most likely my 996 01 cylinder heads are cracked and will need to fixed or replaced. My local Porsche mechanic has a set of 3.6l cylinder heads in good condition. Can these be fitted on my 3.4 l. What adjustments need to be done? What types of problems could I get? Should I have my cylinder heads replaced with the ones for a 3.4 l? Thanks for your help

Saw your earlier thread, just wondering what makes you think your heads are cracked at this point? You can also send them out for repair, much cheaper than new or even second hand. Maybe have your mechanic have a good look at the cooling system, pressure test it, flush and properly refill before dropping the motor.

The 3.4 used Variocam...the 3.6 uses VariocamPlus. I don't think it would be a simple matter of changing the heads...I think the whole system is different...cams, tensioners, chain drives IMS shaft and bearing.

If your mechanic can't give you a solid answer to this then get your car out of there and take it to someone that knows the answer.

These are incompatible. The chain well area is completely different, and on top of that the entire va;love train is different, your timing chains are also too short. Don't go there.

I don't know if "don't go there" was directed at the proposed repair, or the shop of the person who proposed the repair. Works just fine either way.

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If the person that proposed this swap doesn't know better, then I most certainly would not go there. Originally I was making my comment saying "don't go there" mechanically. If someone doesn't know the component interchange any better than this, I'd not listen to much that they said.

It seemed appropriate for both eventualities.

Thanks for all your comments. Definitely noway I will consider having a mechanic replace the 3.4 l head cylinders with 3.6l. I have a bad feeling that if there is really compression gas in the coolant system as I have been told, it is not the cylinder heads the problem but worst the cylinders. In that case, a total rebuilt could be expected. I am doing a last attempt to check if it is only an air bubble in the system before having the motor repaired.

Yep, its an 01, of course one of the heads is cracked! I bet I can find the crack in about 5 minutes :-)

The question that came to me after reading your threads is this, wouldn't the expansion tank cap just vent any excess pressure past the 15 or so psi it's rated for?

Yes but the ven't cap doesn't know the difference between gas or liquid. It will vent anything that's pushing on it.

Well that's my point exactly. The earlier thread was about the coolant level mysteriously disappearing then coming back. I would think it would remain fairly constant other than the expected rise when at operating temp.

I have been told by the mechanics that with gas compression the hose may expand ( like a balloon) which explains the fact that coolant disappears when the car is running and reappears when the engine is cold. Now are we talking cylinder heads or cracked cylinders? Or we will only know if we open the motor? How can we tell the difference for sure with some tests?

No test will tell you due to where the cracks occur. They are NOT in the combustion chambers, but rather on the opposite side of the head. Test the oil/ coolant heat exchanger; if it is good, then tear the engine down- don't waste any more time.