How many hours before rebuild them?
I heard that OEM crank has narrow journals and will fail Rod bearing journals

 

Where are you getting your info from??

 

It is funny because plenty of 3.8's over here. No one mentioned anything. How many hours on your car?

 

Not necessarily a given for street use cars or those with occasional high power blasts. You won't see issues with 3.8s as many people run them without problems. When my shop built my 3.8 they insisted on using an RSR crank which has wider but smaller diameter journals compared to the stock TT crank. The smaller diameter of the journal slows the speed between the crank and rod. The RSR crank also has twice the oiling capability vs the TT crank (every 180º vs 360º) and is designed for 9000rpm use in Porsches race cars. My engine sees extended high RPM use (7500-7600 but I've seen 7800 on data) with repeated redline shifts for 30 minutes at a time. The RSR crank is also quite a bit lighter than the TT crank and it's always a plus if you can reduce rotational mass. Using the better crank was a no brainer for long term longevity. Another benefit of the RSR crank is the fact that you do not have to clearance the oil pump for use with Carillo rods. Surprisingly you can still get these cranks from Porsche for around $2500. Well worth it during an engine rebuild. I anticipate 100hrs track hours between an engine refresh on my 3.8

 

Interesting info
Isn't RSR has 80.4mm stroke ?

 

No, RSR has 76.4mm stroke just like all 3.6/3.8 Mezgers. The RSR crank is dimensionally the same as all the 996/997 GT3 3.6/3.8 cranks. The 4.0 crank is 80.4.

There are several benefits of the GT3 crank over the 996/997TT crank. The GT3 crankshaft is fully counterweighted whereas the TT crankshaft is not. The GT3 crank is about 2lbs lighter. The GT3 journal diameter is smaller resulting in a slower bearing speed. The GT3 has racing bearings available. The GT3 has a wider bearing area over the TT. As previously mentioned, the GT3 crankshaft has oiling every 180º of crankshaft revolution vs. 360º of the TT crank to prevent oil starvation at higher RPM. There is also a larger internal oiling passage to prevent oil starvation at higher RPM. Again, none of these improvement are really going to be relevant for a street 60-130 engine but much more so for a race motor operated continuously at high rpms. Porsche is not dumb. There is a reason they use this crank in all their race and high rpm applications. Hope that helps..

 

Very interesting Pwdrhound and the way to go in my opinion.

 

Great info powder!

 

john as always i learn something invaluable from your posts. great research that you do

 

I'd love to take credit but I'm not the smart one here. I'm still very much learning. I am just very fortunate to have a friend that is not only one of the fastest Porsche race drivers I know but also an incredibly talented and knowledgeable mechanic / engine builder. He has never steered me wrong and most of what I know regarding these these cars comes from his years of shared knowledge and long history of racing and setting up some of the fastest Porsche race cars out there. He's always hit the bullseye with his recommendations...

 

tell him to write a book ill buy 2!

 

agree on pwdrhound and depth of his acumen. incredible base of knowledge and his posts like these, i always need to at least read twice. i hope a 3.8 build ( by CHOICE ) is in my future and is ANYthing like his, since i have his build sheet framed ( well...) almost. brilliant.

 

cant think of a single post about rod bearing failure that was not due to something else before hand like loosing a timing chain.

 

i think it really boils down to how the motor is done. with layinbacks motor which is a 3.8 i found thru research that the motor has been apart twice. the first time for a head gasket and had rods and headbolts installed. doesn't look like the blowout in the cylinder housing was ever addressed.nor were the coolant fittings addressed. shortly after the engine came apart again for pistons and liners and a full race setup. again nobody addressed the coolant fittings and the cases were never split to replace bearings or anything below the rods. going from a 416 hp to 900+ and not replacing any crank , main or layshaft bearings on a 106,000 mile motor is a recipe for disaster imo. I'm having the motor gone thru from top to bottom and the 3.8 should be as reliable as any 3.6 i have seen.

I'm betting unless you spend some time doing the research and speaking directly with the builder you may not get exactly what you think your getting

 

Is there a reason you think that Porsche used the 997tt crank over the GT3 crank for what they had to assume was going to be a street driven car? Are some of those benefits of the GT3 crank negligible or actually detrimental in non race motors? Do you have the part number for the crank you are referring to?

I know...back from the dead, but just trying to do my hw this time around.