Turbo crank question

[turboaz]

Anyone know if an 83 turbo crank is the same as the later ones ? I've been trying to look it up, but am getting mixed answers. Thanks, Paul

 

[UncleDave]

Supposedly, and someone may correct me, all original cranks in the turbo 3.8L from 1978 thru 1989 (and n/a 4.1L from 1980 thru 1984) had rolled fillets. They may or may not be the same part numbers but I recall reading that they're identical.

 

[GNeric]

I have seen different part numbers but dimensionally the same, same double rolled fillet, AND there are 2 different crank/balancer bolt sizes.

 

[charlief1]

All of the turbo engines from 78 to 87 and the TTA use the same rolled fillet crank. The only differece is the TTA has a cross drilled mains and the rest of them are aren't.

 

[bison]

I ran a crank from a 78 regal for 6 years around 500hp. Now that same crank is in whitettype89's engine that dynoed 550whp. It has over 8 years on it over 500hp

 

[wickedtt]

All of the turbo engines from 78 to 87 and the TTA use the same rolled fillet crank. The only differece is the TTA has a cross drilled mains and the rest of them are aren't.

Why did the factory take the time to cross drilled the mains on the TTA cranks? I guess the benifit wasn't that great because the aftermarket cranks didn't follow suit.

 

[charlief1]

Why did the factory take the time to cross drilled the mains on the TTA cranks? I guess the benifit wasn't that great because the aftermarket cranks didn't follow suit.

My best guess is that the Buick V6 engine has suffered from spun rod bearings to some degree and this was a fairly cheap way to reduce the problem. I remember that Kenne Bell had 360 grooved main bearings to help reduce the bearing issues as well. It makes sense to provide full oiling to the rods by cross drilling the mains and keep the oil flowing.:smile:

 

[turbofabricator]

I personally do NOT agree with the 360* oiling groove bearing theory. The main bearing acts as an oil pump to pump HIGH pressure oil to the rods by way of the cresent shaped clearance between the crank and the main bearing. By cutting a groove in the bearing to supply oil, you reduce the load carrying capability of the bearing, AND reduce the pumping action by giving a secondary path for the high pressure oil. There is also controversy surrounding the cross drilled crank theory, too. Oil passage "timing" is critical to supplying the high pressure oil to the rod journal. There is ALOT of engineering that goes into a crank oil holes, they're not just hap-hazardly drilled. Think about having the oil hole timed so high pressure oil transits when the rod is at bottom dead center. Then the high pressure oil is not there when it is needed the most. By cross drilling the crank you risk having a second opening at the wrong time for the high pressure oil to back up through. Food for thought.

Now I DO agree with the cranks all being the same, though.

 

[novaderrik]

I personally do NOT agree with the 360* oiling groove bearing theory. The main bearing acts as an oil pump to pump HIGH pressure oil to the rods by way of the cresent shaped clearance between the crank and the main bearing. By cutting a groove in the bearing to supply oil, you reduce the load carrying capability of the bearing, AND reduce the pumping action by giving a secondary path for the high pressure oil. There is also controversy surrounding the cross drilled crank theory, too. Oil passage "timing" is critical to supplying the high pressure oil to the rod journal. There is ALOT of engineering that goes into a crank oil holes, they're not just hap-hazardly drilled. Think about having the oil hole timed so high pressure oil transits when the rod is at bottom dead center. Then the high pressure oil is not there when it is needed the most. By cross drilling the crank you risk having a second opening at the wrong time for the high pressure oil to back up through. Food for thought.

Now I DO agree with the cranks all being the same, though.

i think GM might have had access to some pretty smart people in house and within all the race teasm they work with on a day to day basis, and they wouldn't make a change like that in a production engine unless they saw some benefit from it.