dand86951

Have someone you trust and who has the experience mic the bad piston skirt and the pin boss ID to check for deformation. Compare that to the good pistons. If the skirt has collapsed and/or the pin has oblonged then you probably got into detonation that was more than the 968 piston could handle in #4, and once it deformed a skirt it caused some galling that led to further galling over a period of time.

If you had good success for a while and then started blowing head gaskets, I would think the tune changed or number 4 injector quit flowing. A very experienced non Porsche engine builder looked at a set of 968 pistons for me and made a very definitive statement that the piston would not hold up in a boosted application. He also thought they would be great for a high revving normally aspirated engine.

Now that you have a Motec, I would also suggest a 4 cyl EGT. I found it to be very helpful in tuning and keeping a boosted engine healthy for a lot of miles.

gt37vgt

Doh!? well the coolant in my engines go's that way at least with electric pump

Chris White

You will find that the center 2 cylinders run about 50f hotter than the outer two...BTDT.

Chris White

Davies Craig?

Chris White

If you had detonation bad enough to wipe out the piston you should see a flat spot on the top of the rod bearing – typically the rod bearing will fall out when you remove the rod (instead of staying in the connection rod).

gt37vgt

Yeh Davies criag and the install is reasonably strait forward well it was ..
the pump is just on top of the low mount alternator kind of replaces the steel tube that was there and pumps "into" the head the bypass port in the pump is epoxied up impeller out thermostat out .
But it will have to be all redone as my 17 kg supersizehearstopperheavylift turbo is now moving forward to take that space .. probabaly end up with it all over the right side with castom rad to suit and i guess i will make a proper plate to replace the pump and get a short belt ..

Dubai944

A few marks, but nothing in the way of actual deformation.

95ONE

makes sense considering firing order.. but you noticed this on a stock car with EGT probes at each cylinder on a 16psi or higher psi car with Motronic? Good info IF that's the case.

George D

Chris,

Then why have all my head gaskets over....15 years of 951 cars blow the gasket at number four? Just curious. I've always been the driver/owner. When **** hits the fan, I get others to do the dirty work. I'm too busy at work to spend late nights/weekends working too much on my cars. Know I do work on my stuff, but not when things get out of my comfort zone. I know when to hire professional help. I do have interest in knowing why all my head gaskets in my 951 cars have blown at number four.

Know, I've only had two gaskets blow in 15 years of ownership with three of these cars. One was a complete meltdown going to San Diego on business. I was cranking tunes, and didn't notice the redzone on the temp till....

The other was when a cheap Turbonetics wastegate didn't open at the track. I was pulling away out of the corner and had this grin.....Saw 30psi....Oh **** PPPFFFFSSST......Not in that order, but it happened quickly. Quick release of pressure and no damage. Just a new head and gasket. Head was fine, but since it's out why not upgrade?

This is the only turbo car that I've blown gaskets. I've owned EVO's with 28psi boost on 91 gas with no issues ever. My Saab Aero with 25psi was a killer sedan. My...same story. Why in the hell do I spend money on these 951 cars....oh yeah...driving them is a f****** blast.

Chris, tell me why we blow at number four? Is the edge just the easiest escape? Less pressure from the studs in that location?

Thanks for the cliff notes in advance.

Kindest regards,

George

gt37vgt

so what is behind the statement "a 968 piston cant candle boost"" but can handle heaps of NA revs"
sit down and calculate the loads of increased cylinder pressures V increased RPM and also cosider is tensile V compressive load .I guess you can spend years building Porsche engines read clean and measure everything well do a good job but not understand the physics..

Dubai944

So maybe this can be simply traced back to the original lean tune which did the damage and led to progressively worsening piston distortion each time out. First the car was tuned lean following the rod install and run on a dyno for an hour or so like that - maybe that started some no4 overheating and piston distortion. Then each time it was run on the track it overheated quickly from piston friction more than from lean tune which was now corrected. Overheated cylinder 4 probably led to some detonation and blew out the gaskets first two times out. Last time out the piston finally had it and the bore damage reached failure point....

Will definately look at individual cylinder tuning for the next motor, which will also have a much better piston in it. Has anyone ever setup individual cylinder AFR sensors, rather than EGTs?

George D

I'm doing this as I type. I'll be running full sequential using my TEC stand alone setup utilizing a cam sensor along with the standard flywheel/crank sensor from Chris White. We'll be able to tune each cylinder bank with timing and fuel. I don't want to have another "money pit" setback.

We should be done in a few weeks.....OK a month.

My understanding is that John at Vitesse has software that works with your factory software. I don't know if he has sequential software for your factory setup to allow tuning for each cylinder. But know batch tuning is fine, as long as you have a good tune. You should PM John at Vitesse or PM Chris White.

Chris White can provide you with a stand alone system that will allow more tuning ability with full sequential software.

It's a matter of how much money you want to spend and whether you are willing to tune a stand alone system.

95ONE

well.. my #4 also.. everyone elses #4.. so.. yes, absolutely. always. (99%) number 4 gasket. Rob's and Genes here in Houston (Observed) also.. 2xs minimum each.. number 4. there is a real "cheap"- relatively 4 readout EGT gauge for airplanes out there. $250 for the gauge and you buy 4x $40 probes.. . ONE gauge is nice. maximums and everything. pretty cool stuff..

Click on the INFINITY guages.

TC-1 is what you're going to scroll, or click the pic of after clicking infinity page... check the price.. Do the math... 1/2 price of anything else. Waaaaaaaay cooler too. Oh.. yeah.. thank me now. \\

http://www.mglavionics.co.za/ <<<<<<<<--------------CLICK HERE

Tons of other goodies to oogle over on that website also.

Dubai944

I'm running Motec stand alone, sequential injection already.

gt37vgt

yeh George try n keep up please