| RKDinOKC |
02-12-2013 06:57 AM |
My 944 turbo story...
Bought a 944 Turbo from a guy that was a Boeing mechanic. He had rebuilt the motor and installed a new turbo. It was running way lean not under load in higher rpms, but was not only just fine, it was very very quick under full boost and full throttle. He had done all the go fast things to make it really quick, except for fuel management, which was why it was lean under partial throttle at higher rpms and no load.
At 10K miles on his rebuilt it got some rod knock. On disassembly found he had nikasiled the cylinders (a great thing) but put in stock rings (a bad thing with nickasil.) Turns out after about 10K the stock rings start chipping away the nikasil and a chunk got in the crank and started eating rod and main bearings. Luckily I noticed before the block crank, and rods were toasted. However the running a bit lean, even under partial throttle had enough predetonation that the girdle was warp and the wrist pins were bent. So much for the skills of an airplane mechanic when applied to a Porsche.
Rebuilt the 2.5 with a lightened 3.0 liter 968 crank and had custom pistons made to re-use the lightweight rods the previous mechanic had installed making it a 2.8 liter. I also upgraded the MAF and turbo for the larger displacement. The builder tuned the car and gave me specific break-in instructions which I followed. Went back 3 times at different mileages to retune the car and raise the maximum boost. The motor was built and tuned to run 18 psi boost. After almost exactly 4500 miles the head gasket blew decelerating coming off a leisurely cruise down the highway. I basically coasted the 2 miles from the off rap to my house. They claimed I cranked the boost up hungry for power and would not stand behind their build and tune. The turbo had way too much lag and I was running only 16 psi because even then the turbo would hit so hard at 5800 rpm you couldn't keep the rear wheels hooked up.
After I found the local shop had no intention of ever touching my car again, I sold it as is. The new owner sent me pictures and description of what he found when tried to fix the car. First half the bolts holding the thing together were either broken off or loose (no torque wrench). Next the turbo was much larger than the one I asked for (no wonder it had so much lag and hit so hard at higher rpm.) Looking at the head gasket it looked like someone had cut a hole in it with a torch. Mechanics tell me that is sign of the head lifting from loose head bolts instead of busting a chunk out when under too much boost. Understand that instead of retorquing head bolts after some break-in heat cycles, they used infrared heat to head cycle and retorque, a practice used on race engines that don't see over 4500 miles. And the clyinder walls were all scratched up on both sides like the pistons were sized to small for the bore.
90 944 Turbo, parted out and scrapped.
http://www.zipbang.com/Cars/944T.jpg |
