DLS

I was recommended 120nm because i run E85 and higher boost and compression to not get head lift.

Duke

I have had sucess with 400+ rwhp on 2.5l engines with 120 nm using Raceware bolts. But it might be a bit safer to stop around 110 nm. 120 nm is pushing the limits of the block thread.

Hmmm strange that you have the same problems now even with a different block and head?
What studs do you use?

DLS

Thats why i haved helicoiled all the studs in the block
I read on this forum a while ago that the block threads breaks around 135-145nm (when the block is fresh)

I use oem studs.

Duke

If everything else is checked out (flatness and no cracks etc), I would change to ARP or Raceware.

DLS

hm
i will do the co2 test and the cooling pressure test first, then we will see if i should buy arp

dlr944

Has there been resolution to this problem?

DLS

For my part, I solved it with arp studs and o-ringed block.
but I believe that the key is to have the right mapping in the first Place.

michaelmount123

Bless you DLS. I believe you're on the money suggesting the issue is mapping (tune)! All this effort to determine where the coolant is going... The HC test showed combustion in the coolant after hi boost runs. How did it get there? THE HEAD IS LIFTING. Further, many are addressing the symptoms rather than the cause (different studs, o-rings, more torque). Detonation! You'll never seal a head when there's detonation. Once you get on the dyno with someone who knows how to tune the Motronic, the head won't lift - as DLS subtly suggested.

A couple of other comments:

-Cometic had issues with their gaskets years ago (when this thread was started). The embossing was too stiff and the gaskets wouldn't compress/seal properly. It's fixed now by going to a wider embossment. I have first hand knowledge of this.

-When using Cometic, use a torque setting you like, and after you finish the torque pattern in 3 steps, go through it one more time by backing off each stud in sequence and torquing it to your final spec. Otherwise, the center studs will be loose.

-Neither ARP nor RW have any idea of the torque to be used, and no clue what the clamping force is at a particular torque with their 944 studs. Porsche does. Don't waste your $ on the aftermarket stuff without doing your own sophisticated clamp force testing on the 944 with whatever gasket you choose.

-Run a pressure gauge into your cooling system to alert you to a combustion leak. If you put it in the block, you'll see that the water pump generates around 30psi of pressure at full song. When it goes substantially over this, the HG is leaking into the coolant passage(s). Simple as that.

333pg333

What about when you're running E85 and there are no traditional signs of detonation and nothing much coming up on data Michael? Agreed that tune is paramount but if that is ok and there is still headlift, what then? We have found that the O ring and copper gasket has worked well so far. We've been running over 1.5bar at the track for short duration but still clearly enough time to see coolant losses.

michaelmount123

E85 is a great way to go since it eliminates many of the issues with boosted engines. In your case, I will never argue with something that's working (if I understand that you're head is not lifting with o-rings and copper). I don't suggest you change anything, but if your tune is good, you may be able to run with a standard or more likely a Cometic gasket and go up to 1.5 bar too. Just making a point, no suggestions here.

I do believe there's value in extra insurance, like you've done. I had some special head studs made in the UK that increased clamping 40% (IIRC) for the same purpose. There's always the occasional case where a hot spot in the head will generate some air, or you're tucked up behind someone and your intercooler is not getting the air it wants. Insurance is good.

I chased a lifting head (with a good tune) in my own car for way too long. Turned out it was the coolant thermostat. The thermostat would close on a long straight because cooling conditions were so good, then take a while to open up again (watch the lazy opening in a pan of water on the stove). So I'd come out of the next turn WOT with a closed thermostat.... detonation, head lift! Think about that one - it may apply to you and others.

The pressure gauge in the cooling system is easy, cheap, and will tell you without question when the head is lifting. Connect it to data and the trace may surprise a lot of folks.

333pg333

Yes, good idea re the gauge. Simple insurance. Ran the Cometic for some years. Best thing was being able to drive home from the track if you had some coolant transference. Once we moved to a full blown trailer car that wasn't such an issue but having to replace the Cometics after each event became tiresome. Run Motec ECU and knock protection. Not much sign of ping/knock. Big studs at higher tq values, deck plate, race grade E85 but still we were getting the embossed part of the crush ring separating in layers and loosing the seal. Possibly block flex. Not sure.

Since going to the O ring / copper gasket setup we've only had one occasion where we've seen any loss of coolant and it was a very small amount. Nothing to worry about seemingly.

dlr944

I had the exact issue explained in this thread. I put a pressure tester on the coolant system and found that the water pump was leaking around the drive roller.