jmj951

Update 11.28.2008: Posting a pic of the fire ring failure. Notice all of the corrosion on the gasket - is this normal?

I just had a head gasket failure with a spectacular smoke screen while I was on the track yesterday. I was not running hot, and I don't think there's any serious damage (don't even see coolant on the dipstick or in the oil fill cap, and the oil level is right where it should have been). 1986 944 Turbo, 138k miles. Here's a summary of significant engine-related maintenance done to it:
Head gasket job and valves were redone at 65k miles due to a timing belt failure.
Timing belt was just replaced at 129k miles and retensioned at 131k.
Front Engine Seals at 88k miles
New intake manifold gasket at 135k miles
Rebuilt turbocharger at 130k miles
Oil cooler resealed and P/S pump replaced at 132k miles.

No mention of a water pump replacement in the maintenance history, and I don't think they replaced the timing belt rollers when they replaced the belt, so I guess this is a good time to do those. Anything else you recommend? I will not be seriously modding this engine for big HP gains beyond upgrading to a K26/8 sometime in the future if/when the K26/6 goes out - I'd like to do more, but after reading months of posts it looks like it needs a very expensive engine build from the ground up, or else it's a neverending problem chasing the next point of failure, and that won't be much fun. That said, do you think I need to replace the head studs or any other main hardware?

Also, the head gasket replacement kit I'm looking at comes in two versions - standard/stock and widefire. Any significant advantage to the widefire on a mostly stock engine?

Thanks in advance for all your help. I've replaced a few head gaskets on stock Chevy and Ford engines before, but this will be my first time doing any signficant work to a 951 engine.

dillon410021

a widefire head gasket is said to handle higher boost settings.... it is well worth it

reno808

mls

95ONE

I have a stock head gasket and it is holding 360whp (minimum) 420whp high boost. I've been beating the crap out of it a lot lately. Still holding.. oh god. Now I've done it.

what kind of boost on what kind of tuning do you have? if it's some sort of Autothority chip, toss it. If it's Russell's or Vitesse, I'd look further into the motor.

Bri Bro

Take the head off and see were the gasket failed. Check the head for true, replace the seals and replace the springs if you want to go above 6K rpm. Have the injectors flow tested and replace the engine harness to the injectors, speed and reference sensors. Get an O2 wide band and check your AFR. Then run it like you stole it and it will bring a smile to your face.

Then start to modify the setup one step at a time.

jmj951

I have Russell's chips, nothing too fancy. They're tuned for the basics, 3bar FPR, boost enhancer, 15-18psi of boost, rev limit at 7k RPM. I'm regularly going over 6k RPM at the track. Stock gearing just isn't optimal for running Laguna Seca. Turn 3 is terribly slow and going into turns 5 and 6 I barely use 5th gear, it's so much easier to leave it in 4th and go to high 6k's.

Forgot to mention it because I don't know the exact mileage or date - injectors were sent off and flow tested and matched...some time within the last few years. Also, I'm using 100 octane at the track, which Russell said would push the limits of the chips I currently have and probably result in high exhaust gas temps.

I'll tear it apart and post pics as quickly as I can... may not be until this weekend though.

Thanks for all the replies so far!

blown 944

you really need a WB or at least and AF gauge to keep an eye on things. Or if you do what was it reading??

jmj951

I have a wideband Autometer Phantom AFR gauge and it reads lean at idle or low RPM's, stoich/centered at speed or high RPM's, but it jumps around a LOT and I was never sure if that was normal or if it was a problem.

Bri Bro

The WB will jump between 14-15 AFR in closed loop (low throttle) to support the cat reducing and oxidizing the emissions. At WOT, it should be around 11-12. If you are seeing lambda of 1 with boost and RPM's above 4K, I would suspect it would cause a gasket failure due to detonation even with high octane fuel.

FRporscheman

I've driven Laguna with a 6-speed NA, and it's perfect. Maybe a shorter 5th or slightly smaller wheels will help you there.

I've heard nothing but good things about the widefire gasket.

cas951

Check and make sure it's the head gasket before you tear it down. Just because you have smoke while driving it means you have a head gasket failure. From reading your post you say your oil level is where it should be and no sign of coolant. What about your coolant any sign of oil? Just validate.

Next test would be to see if it smokes all the time as soon as you start it. If it takes awhile before blue smoke starts to burn it's probably your turbo.

TurboTommy

"Also, I'm using 100 octane at the track, which Russell said would push the limits of the chips I currently have and probably result in high exhaust gas temps."

That doesn't really seem to make sense.

"stoich/centered at speed or high RPM's"

What does that mean exactly? It's not clear where your air/fuel is under load.

Willard Bridgham 3

Wide fire ring gasket is designed to be used on o-ring head/block engines.

The stock head gasket has higher clamping force and will let you run higher pressures than the wide fire ring.

Use the stock gasket.

jmj951

I had my 996 out there a few times and it was definitely easier to find the right gear.

Regarding the first part, here is what Russell said, verbatim:
"Realistically running anything higher than 100 octane with my chips will become detrimental, as the AFR curve changes drastically using fuels with higher than 100 octane. The higher the octane, the lower combustion pressure, that is the basic rule of thumb. On these boosted cars, anything over 100 octane would require a timing advance well into the danger zone to optimize combustion and keep exhaust gas temps at an acceptable rate, under 1400 degrees F. Otherwise your headers will glow at idle and you head gasket will be screaming for its life."
So, I'm not running more than 100 octane, but I interpret his statement to mean that by running 100 octane, I am right about at the limit of what his chips are programmed to manage.

I don't know how else to describe it. I don't have tuning equipment or a programmable ECU so I don't know exactly where my AFR's are, the only thing I can see is the feedback on a gauge that simply goes from lean to rich.

jmj951

It was definitely very white smoke, not oil, and I checked the oil level again and it's exactly where it was before my last run. No coolant left in the reservoir now, despite being mostly full before my last run, so I'll have to drain the radiator before I know what it looks like.

I did try to start it after we got back to the paddock, but it didn't finish one revolution before it made an evil sound, and then I couldn't get it to turn over at all. The sound almost sounded like metal-to-metal, except that there was a hiss to it. It reminded me of another Rennlist post where coolant got into one of the cylinders, and they learned the hard way that coolant won't compress like air. I should have remembered that and at least removed my plugs before attempting to turn it over the first time. I'm hoping that since I didn't get any ignition yet, that there wasn't enough force from the starter to do any damage.