Discussion: GM Recommended Crankshaft mods

[XLR8ING]

According to the Chevrolet Power Service manual, 1987 and later cranks have lead in grooves to the main bearing journal oil feed holes. Well, I don't have these grooves on either of my cranks. One crank is a 1993 and one is a 1996.
Now I'm wondering if there's a reason the grooves aren't in there. Were they stopped later on for some reason?
It also says to cross drill the center two main bearing journals for extra oil flow to the rod bearings, and to drill extra holes in the upper main bearings.
What the opinions on these three mods? Are they worth it, or is it just old information?

[smilinguy99]

About the cross-drilling. This is a good question. When I first read that in the book I took note and didn't really think much of it. I figured they came up with this after doing some destructive testing on the dyno.

I've read some things more recently from David Reher and he is absolutely adamant about not cross drilling cranks. He says it will lead to problems with oil starvation at rod journals. I don't quite know what to think. Here's his article:

http://www.rehermorrison.com/techTalk/51.htm

So, I'm not sure what I'm going to do. Get a third opinion? I'd really love to sit down with the engineers that did the early development work on this motor and hear them explain what is going on here.

Reher-Morrison-Shepherd were a big deal back it the 70s and 80s. Shepherd and Morrison have passed on. Their current focus is monster mountain motors, but I remember reading of their very unorthodox approach way back then. The tech talk articles are kind of interesting.

sg99

[Guest]

RE: Discussion: GM Recommended Crankshaft mods

I put the lead in grooves in Chris' crank (z2 4cams), it was a '95ish crank.

Mine (in the Franken60) had them from the factory.

I have not performed the other modifications....yet.

I would definatly put the lead in grooves in the crank. The extra oil holes would probably help, for some reason I'm thinking that either we drilled the extra holes in Chris' bearings or they were already there, when he bought them.

[XLR8ING]

RE: Discussion: GM Recommended Crankshaft mods

Thanks for the link SG. Interesting read.
Raven, I just took a look at my upper bearings, and it's got 2 holes per bearing. The manual is saying you can have up to 5 holes per bearing, except the rear. I'm just wondering if there's gonna be any down side to the extra holes, since this isn't a "race only" car.
The lead in grooves is what I was thinking about machining too, but it just makes you wonder why they would stop putting those in.
Thanks for the info so far guys.

[donk_316]

RE: Discussion: GM Recommended Crankshaft mods

Cross drilling your crank is old school move for getting more oil to the rods isnt it? I cant see how it would be a bad thing. I had my 454 crank cross drilled. No issues. Hell MILLIONS OF GUYS run cross drilled cranks. I have never heard it being related to rod journal failures.

[Fiero11]

Moldex did a crank for me:

1. Lead in grooves
2. Straiten crank
3. Balance crank
4. Nitride crank

Cross drilling was not recommended. Most cranks now come with rolled fillets, but if not have that also done. Also, lightening of the crank was not recommened because they are not strong enough. 3.4L can take about 350hp if preped. The 3.9L cranks are much stronger, so they my be lightened.

[SappySE107]

Who told you it will only take 350 hp? What proof is there of this?

[TurboZ24]

That's what I was going too say, my stock TGP crank has held up fine, from 7 psi and 310 wheel HP too 16-20 psi and well into the 400's wheel HP.

[SappySE107]

Yeah, tim has 325 at the wheels on a 3.4 DOHC crank.

The 3500 and 3900 cranks are heavier than the iron cranks as well, so they better be able to be lightened:P

[Fiero11]

Moldex-350 HP for reliable road racing engine, severe service, hours of high RPM, on off throttle, etc.

[SappySE107]

Who is moldex? Have they done any testing or are they just guessing? There are people pushing more than that at the crank already. Hours of high rpm? So they are recommending 350 hp peak for oval track?

[bszopi]

IIRC, Moldex did the crank for the Indy Pace Car.

EDIT: I always screw this one up. It was the twin turbo Beretta prototype...

[SappySE107]

You remembered that? Wow, well thats good to know, though it would be nice to know how they have come up with 350 hp.

[TurboZ24]

I wonder what was done too that 5-speed so it wouldn't explode constantly..........

[smilinguy99]

Who is moldex? ...

Moldex is a low-volume producer of racing crankshafts. They've been around a long time making cranks for every major and minor racing series. They will make anything for any motor you have any way you want it. When last I spoke to them, they made only two custom crankshafts per week and there was a 10 week lead time. They are familiar with this engine.

They have no web presence, but you can call them. This is the most recent information I have on them:

Moldex Tool Co.
25229 W. Warren
Dearborn Heights, MI 48127
313-561-7676