rev limit for 302?

[Jim Rosenthal]

I asked a lot about this because we have just started the buildup of the engine for my GT40. We are using a 68 302 block with an .030 bore, Mexican mainbearing caps, forged internals, AFR heads, mechanical lifters/cam, and likely a new 3x2 Weber setup from Pierce that they are keen to get dyno numbers on. The point on which everyone seemed to agree was that it is revs, not power, that explode SBF lower ends, and that increased horsepower capability also gives you the opportunity to rev higher- and blow out the bottom end of the motor.
Bottom line on the bottom end? I'm going to use a main girdle, AND limit the engine to 6500 revs electronically. That may be overkill, but I don't want to overrev the engine and have it grenade on me. When I picked up the block (literally) I was impressed by how thin everything is- and this is an older block where the webs and rails are beefier. On a modern stock 5.0 block, I'd be sweating it past 6000revs.

 

[Adam C.]

Don't be so scared. We have a late model 5.0 with a cast crank, stock chevy 5.6" rods, and hyper Keith Black pistons. The balancer and flywheel are stock, but we did have it balanced (mandatory in my opinion) and the rods are bushed.

This thing routinely sees the far side of the 6200 RPM EFI fuel cut off limit and we've had no problems.

On the other hand, I've blown up two Boss 302's at 8,000 RPM so go figure.

I think one of the most important factors other than the materials is how well it is put together. If I had a limited budget, I would concentrate on balancing, machining, and good fasteners than in blocks and cranks. You should definitely get the best rods you can afford.

Adam

 

[Ross Nicol]

Lynn
That is a good point you've made. I was assuming GT40 Guy was able to rev higher than a self imposed limit from the way he worded his post.

Jim
Electronic rev limiting only works when your under power,however a lot motors blow on an over rev on change down. so if your going to race watch out for that one.Can you imagine the revs I pulled in my 240z when going down the straight pulled 3rd gear instead of fifth.

Regards Ross

 

[Jim Rosenthal]

Gosh yes, I can imagine. Mostly the rev limiter is to keep me from getting too enthusiastic on acceleration. I realize on downshifts it won't protect the engine.
Lynn is right about the fasteners; I think they are one of the most cost-effective ways to spend money when building a hipo engine, as they really do protect a lot of vital parts. And we will balance everything carefully.
Does anyone here have an opinion on whether a hi-pressure oil pump is needed if I plan to use an external oil cooler?

 

[Guest]

Jim,

The high pressure would be more involved with the tolerances of bearings, etc and RPM you will run at. But, you might want to consider a high volume pump. This is what I put in and I am seeing close to 100lbs at cold idle with plain 40 wt dino break-in oil.

 

[Jim Rosenthal]

Hi Lynn:
One of the source books I have, I think, suggested using a high-pressure pump if there was to be an external oil cooler on the engine. Perhaps this has to do with pressure drops encountered through the oil cooler system, I am not sure. I wondered if anyone else had heard similar advice or knew of this. I will use a high-volume pump unless I get advice otherwise.