Originally Posted by IcemanG17

guys.....you might be making this far more complicated than it needs to be...... There are many variables that affect the crankcase pressure, blowby is just one.. Yes there takes a certain amount calculations to make it work correctly.....Yes, and if you do not calculate properly, you will be off target..and boosted cars making high HP or cars with larger bores....Revise the calculations to suit the load if boosted..

Keeping things "smog" legal gets insanely complicated as well....It depends on what the goal is in modifying, my dual 3 inch stainless exhaust with cats has passed smog just fine. A stroker with a stock intake tuned properly should also pass just fine. A lot of this depends on what is done to the car. I have a significant preference of a clean running motor that is not wasting fuel, running out of tune, and makes power. Maybe that makes me a greenie, but I like clean air..

the two single most important issues that make our 928's so sensitive to crankcase pressure are a horribly designed breather system than became more and more un-engineered as the cars "developed" The early breather setup was "okay" at best....it only got worse....So, if the design was horrible, why not redo it to improve the situation if you can? On any car that is race only, why run any oiling system other than a dry sump?

Another HUGE issue with any 100mm+ bore is ring flutter.....I do not think that this is a case dependent on bore size. There are too many other variables, some of which include side clearance, compression ratio, static and dynamic, ring tensions, cylinder material, fuel used, cylinder pressures, I could keep going, but I think you get the idea..even slightly worn rings can flutter significantly at anything past say 5000rpm....by 6000 its VERY risky..... Keep in mind our ring-pistons were designed in the 70's....not exactly high tech by today's standards.... The OEM pistons from Mahle and Kolbenschmidt are pretty good, Mercedes used some, and in the 944 they are fine as well. There are several manufacturers that used similar pistons, and the engines run just fine. Maybe you have also forgotten that in the same '70's, BMW made formula 1 motors that were about 2 liters, turbocharged, and produced 1200+ HP......

Keeping the crank counterweights so close to the oil pan doesn't help either....

One interesting lesson I learned this weekend was it IS possible to kill a 928 engine with extreme overheating....You will kill any engine by extreme overheating....previously I had overheated the Estate engine to above 230F with no ill effects.....another 16V 928 engine was overheated to the point that it nearly stopped running from a busted lower radiator hose This demonstartes the point I made earlier that the cooling hose cooling hose would be a more serious concern that the vacuum pump failing..(no steam to see)....while the car runs and seems fine until 3000rpm...anything above that it spits oil at insane levels.....rings are GONE.....near 100psi per hole.... in 8 minutes on track it spit 1 GALLON into our improvised catch can

Originally Posted by blau928

If you are running a race car and overheating the engine, you obviously have cooling issues. Running the motor like this without addressing the cooling issue is only playing russian roulette with the motor. It should not surprise you that it grenades. that would be no fault of the engine, just the crew chief..

Brian,

Sorry, but I have to disagree with a few things here.. Nothing personal.... In addition, I am surprised you run the race car on track with cooling issues without resolving them..

Originally Posted by IcemanG17

Rich
Not my car........Seans car driven by another driver......it didn't help that electrical issues made the coolant temp gauge not work either Sorry to hear... Gauge/sensor problems really suck..!

Casper runs super cool.....the new little vent-ducts in my bumper help A LOT....Casper ran cool before, but I would guess 15F cooler now once at speed.....During my race yesterday it was about 90F......once moving I never saw above 1/2 on the gauge.....at full race pace....let up a bit and it drops to just above the 1st line