APKhaos

Don't worry too much yet. Remove the plugs and crank the engine. Don't be surprised if you see coolant spouting from #4. I've had a total of three gasket failures around #4 over several years of race duty on my engine, which is PCA Stock spec running stock boost. The #4 area seems to be a weak point in these engines, and there are various after market tweaks that try to improve cooling at the back of the head. I'm not sure they make a bit of difference.

The head gasket R&R is straightforward, expecially since you have some experience with other engines. If you haven't already discovered Clarks Garage, click Clarks Garage then click Garage Shop Manual for clear step-by-step procedures. Follow them religiously, use new hardware, and it will be an easy job.

lart951

Yeap, finally someone who knows the stuff.

Luis de Prat

Good to see some of the wisdom that's been tried and true still alive and well on this site!

jmj951

And I appreciate that VERY MUCH! This forum has no doubt saved me money and unnecessary trouble. Still pending teardown, I'll post pics then.

dand86951

If you have the head off you might want to put a Lindsey coolant vent kit on.

Bri Bro

Autometer does make a wideband but the picture you posted matches the picture in the link and it is a narrowband O2 meter. You really need the wideband to get accurate data.


http://www.customcarscentral.com/ame...all-makes.html

jmj951

Thanks for catching that - so I guess I need a wideband O2 sensor and a wideband gauge as well. I didn't install and wire up the existing gauge so I didn't realize the difference. Not sure if the wideband O2 sensor would require any chip changes, guess that's another question for Russell.

TurboTommy

jmj951;
The deal with the higher octane gas causing less combustion pressure; I've never heard of that before.
Higher octane fuel resists detonation, which is like overly rapid pressure spikes in the combustion camber, but that's only at the very threshold of detonation. At any lesser engine loads flame speeds (which can determine combustion pressure time) have nothing really to do with octane.

TurboTommy

So, if you say that under some load your aif/fuel meter was "centered", then you were running lean and that definitely caused your head gasket failure

jmj951

Any good references for this? Meaning once I have the wideband O2 sensor and gauge, what I should expect to see under various loads?

Bri Bro

THe transfer point for the NB is around 14.7 to 1 (lamda=1) which is very lean when on boost. The voltage is above 0.5V when rich, below 0.5 when lean. The switch point is very sharp. The WB sensor has a more linear voltage vs Landa curve and is calibrated.

Highest HP is developed around 12.4 to 1. You want to run a little richer to cool the mixture and as a safety net. Around 11.3 to 11.8 to 1, lots of posts on this.

Chips stay the same but you need to weld a bung on the down pipe near the starter...lots of threads on this. Do not put it in the stock location of the NB, it is too hot and has too much pressure for a WB.

special tool

I personally have had good luck with the Cometic gasket forthe 944 turbo.

APKhaos

Good intel on the stock gasket vs the widefire. I have been using the widefire, but sounds like I was wrong on that.

There seems to have been a lot of thread space taken up with sealing problems using Cometic gaskets, although many of these were high HP engines where the stock gasket was just not going to do the job.

Is there any real advantage in using the Cometic gasket on a stock race engine?

jmj951

Tonight I finally got a chance to remove the spark plugs and crank it. A few of the spark plugs (front two cylinders) were wet with coolant, but overall the spark plugs look really good. It turns over 'fine' when cranking with the starter, but it seems to have a light jingling sound to it as it turns over that I never noticed before. Not a serious banging like a valve dropped or anything, but something that is not normal. I tried to figure out where it was coming from, but can't make it out - too much echoing in the garage. Sounds exterior to the engine though. On to the teardown next.

Willard Bridgham 3

I had a cometic o-ring gasket and it blew and not under racing conditions.

I replaced it with a stock gasket and it does fine under racing conditions.