redmill

87 944 turbo, fitted with turbo S bits - running SP3
Has fresh conservative tune, use 100octane only, everything else is stock

had blown head gasket 4 years ago during early stage of ownership

went in for a pre season maintenance, coolant in cyl 4.... UGH

I assumed that the 100 octane and tune would prevent a lean condition.

The last 4 days the car ran were on cool days in Late Sept/October.
Started the car for the first time in a long time on Saturday, cold garage - 30degree, no antifreeze, fired up but a bit clanky, put on the trailer after warming up, noticed a recently caused bit of a vaccum break on hose feedign the KLR


Any ideas what else can be causing the head gasket to pop? injectors, goofy head?

Tom M'Guinn

Tell us more about the motor. What chips/tune are you running, and how much boost? Have you confirmed AFR's across the range on a dyno or with a wideband? Did you have the head machined flat last time it came off?

Unless you have a later two port intake, both the FPR and KLR hoses are fed from the same banjo bolt. As a result, I leak in the KLR line can have a big impact on the vacuum/pressure that gets to the FPR (much bigger than if you had a small vacuum leak elsewhere in the system). So it's possible you just ran lean under boost due to that line. 100 octane is great, but is no match for a really bad mixture under boost. I once blew a head gasket while running 100 when the hose got disconnected to the FPR, and that was on a street car.

redmill

i replaced turbo in the spring, so again it went to an east coast tuner called behe, who put it on the dyno, running stock boost and a 'conservative' tune
( running in a stock class, im not cheaty and didnt want to have ANY chance of another head gasket popping for more $$)

I even put an AFR gauge in this year and that kept showing 12.9 ish which BEHE said was good and was matching the dyno/computer.

Head was machined when it came off last time and they presurre tested it, but they didnt disassemble it.

do you think a casual trip around the block, with a big leak next to the klr line would be enought to pop the head gasket?

i have teh service records from PO.... head was 'reconditioned' in 2011....

Smudo

AFR of 12.9 under full boost is not conservative for these cars when you chip them. Did you use new head studs or not? They can stretch after couple cycles.

lart951

12.9 there you go that's why. Under boost at high rpm 11:7 max

Tom M'Guinn

Hmmm... 12.9 AFR is not conservative on these cars. In the old days, common wisdom was to keep the AFR at or below 12.5 under at full boost, with anything approaching 13 getting into the danger zone. These days, I'd say most folks shoot for high 11's, as that adds a bigger margin for error (more cooling fuel) without any real reduction in power. As for timing, you have to wonder what your tuner thinks is conservative, given his AFR approach. I'd get yourself a V-knock unit from Vitesse Racing or just a simple Curtis Counter (search here, both cheap), so you can see if your car is knocking. I'm guessing it is, and that's why you are having HG problems. No guarantees of course, but odds are... You really have to be careful with both ignition timing and AFR to keep the HG in place.

And, no, a casual drive around the block with a broken KLR hose shouldn't pop a head gasket if you didn't get on the boost, etc. I thought you meant you had raced with it that way, my mistake.

Paulyy

adding a steam vent? I know that was suppose to prevent HG failures in cylinder 4.

Unless it's an actual tune issue.

redmill

All,
thanks for the info ..
I suggested the steam vent with the mechanic last time...... not sure why not embraced, he is very familiar with 944 race prep....

FWIW: to clarify the tune was done with 93/100 in the tank, but subsequent refueling was only 100 octane

AFR Captured during dyno
RPM / AFR
4000 / 13.08
4200 / 12.77
4400 / 12.63
4600 / 12.42
4800 / 12.39
5000 / 12.42
5200 / 12.07
5400 / 11.58
5600 / 11.86
5800 / 11.93
6000 / 12.15
6200 / 12.38

im also thinking I should hook the PLX AFR Gauge to one of the Traqmate digital ports just to keep an eye on things. Frankly I seldom look at the gauge while driving flat out...haha flat out..

Mechanic suggested the injectors should be looked at...
Anything else to suggest as root cause other than tune?

This was luckily caught at the shop during leakdown/compression tests.

Now that the head is coming out possible reconditioned, what are some other things to do 'while your there' (within financial reason)..


This was already on the list:
Inspect/Replace as needed balance shaft and roller bearings
flush cooling
new spark plugs

Tom M'Guinn

I added a steam vent when chasing my HG issues. If nothing else, it makes venting the system self-executing and cleaner. Those AFR numbers aren't terrible, but still leaner than I'd use overall. Ignition timing is also a HG killer, so that data is equally important. I'd go for some way of monitoring/logging knock and AFR on the track. Dyno tuning numbers are great, but things change over time (and on the track at speed) and it's best to see the actual data as you drive it. Carbon deposits and burrs on the piston or head can act as glow plugs, so worth looking at that. For the track, I'd move down a range on the plugs as well, to WR6DC or similar. I'd take a precision flat edge to the deck and head and check it ten ways to Sunday. Raceware head studs (if legal) torqued to 90 ft lbs has always helped me too. Temps are also important -- if it runs on the hot side at the track, see what you can do about that, the head can over-compress the gasket when super hot and leave it too skinny when back to regular temp. E86 or water injection does wonders for HGs too, if legal...

jerome951

Which cylinder experienced the failure? If #4, then the steam vent kit might help. If another cylinder, then your shop needs to perform more troubleshooting.

Certainly have the injectors checked while the head is off.

fast951

Running stock boost should not blow a head gasket even with 93oct fuel. On 100oct, there is something wrong! Fuel, Ignition or mechanical issues.

Under boost, you want to be in the 11.5-11.8:1 AFRs. However, reading the AFRs on the 951 can be misleading. You couls have 1 injector running lean, while the remaining have to dump extra fuel to get the desired AFRs. This is something your tuner should spot, as he'll have to enrich the AFRs in his tune outside of the norm.

I would check the injectors and the harness. Also check your fuel pump, if original or questionable, I would replace it. The fuel pump can be fine on the dyno, however on the track it can run hot and will not support the flow. It's difficult to observe AFRs on the track, data logging (AFRs, fuel pressure) may be needed.

If the AFM or TPS are faulty, or become faulty when hot, you could be running off the wrong maps in the DME. I have seen a TPS that tests perfect, however when it heated up it failed.

If the cyl head or the block's mating surfaces are not true, or the headstuds are not holding you will blow a head gasket.

If your ignition is too far off, you can get knock. Best to monitor knock! Examine the pistons and head for any sign of detonation. There will be marks if you know what to look for.
If someone moved the Sync set screw on the flywheel, your ignition will be off. Way back (when DME tuning was illegal), racers moved the set screw to advance timing. However, since your car was dyno tuned, I would think the ignition is setup to match your engine's configuration. If the flywheel is different than what you used on the dyno, make sure you investigate the position of the set screw.
Of course, you must run the engine with the same octane rating (or higher) as what you used on the dyno.

If the cyl head or the block's mating surfaces are not true, or the headstuds are not holding you will blow a head gasket.

If your intercooler is heat soaked, it will no longer do its job. Hot air induces knock which can lead to a blown headgasket. Check the ducting to the intercooler.

George D

Thought I read your obit a few years ago - you've always posted - great "free" information towards remedy.

333pg333

All good advice. ^^

Humboldtgrin

You may have a small coolant leak and air would enter the coolant system, the air will find its way to the #4 cylinder coolant area which will heat up the head and bock which crush the head gasket. I recommend pressure testing the coolant system and check for leaks. Also installing a steam vent kit is a good idea. I have found every 951/944 I've owned has had a leaking stock radiator. But they are 29-30 years old plastic end cap tanks. It's a good idea to pressure test the coolant system after every major engine service.

redmill

broke 2 rocker arms too... not sure what causes that

while there:
the lindsey steam kit installed
new cam rollers and belts
had head refreshed......

sounds much better, valves were a little sticky when cold . holding breath for this season

will run afr data feed into traqmate to capture AFR rates during break in day...

at some point i will need to find a good used turbo down pipe, crossover and manifold, hopefully it can wait a few races