Hemi crank

ordering a new crank this week and one of the options was standard BBC pin size or standard hemi. Has anyone tried a BBC pin on a hemi crank with any luck? Application is close to pro mod engine 540 ci with 1471hh 45 percent.

 

Any reason why you would want to go with the Chevy journal? We’ve been quick with a stand big Chevy crank in a 481x. BBC mains, rods and rear flange. The only issue with the Chevy stuff is you can’t buy a sleeve of uppers like you can with the Hemi rod bearings and you end up with a bunch of spare Lowers if you lean on it. Theoretically a larger bearing can carry more load; The way I see it that’s what they run in top fuel and it seems to carry the load OK, so it’s fine for anything below that.

Not to derail, but the other day I was having a conversation about journal size and actual bearing speed, it was a little over my head, and not something that I had previously thought about so if anyone would like to chime in on that I’d like to hear what you have to say.

 

Those were the exact reasons I was asking. My tune up must not be that strong to where I am changing bearings often enough to buy sleeves. My thoughts were if the smaller size was strong enough the surface speed would be less and so will the amount of oil needed. Also the bearing weight and big end of the rod should be lighter lowering the rotating mass weight.

 

been running bbc b/e for years. advantage = yes less bearing speed and slightly wider rod - just buy a couple of sets of bearings

 

Anyone have a formula for figuring out what the bearing speed would be? I am curious of the difference. At what point does the smaller bearing fail to carry the load? At 2”, 1.88”?

 

Determining The Surface Speed of Your Shaft

In order to choose the right babbitt metal, you will need to calculate the surface speed of the shaft. You can do this by multiplying the diameter of the shaft in inches by Pi (3.14) and the RPM and dividing the result by 12 (Pi*D*RPM/12=Shaft Surface Speed). This will give you the shaft’s feet per minute.

 

This method of calculation would be true of a main bearing, where the main journal of the crank is simply rotating (spinning) but not mot moving (translating) at the same time. Calculating the true instantaneous surface speed of a rod bearing is a lot more complicated as the rod journal is both spinning and translating at the same time. The difference at the end of the day though would be small'ish, but still calculable, when comparing the two approaches.

My thoughts on rod bearings is this........

Go with the bearing that has the most load capacity and best availability in terms of materials, sourcing, sizes, and other order options. If Top Fuel finds an advancement, then that will all trickle down to you as well by default.

I really wish I knew how to post a picture here. Several years back I read an SAE paper which broke down the actual frictional, mechanical, and pumping losses inside a well developed race engine.

They put all the areas of examination into a cool little bar-chart, ranking each area's effect (or opportunity for improvement). The effect from rod and main bearings was so miniscule that they barely even showed as a blips on the bar-chart versus everything else.

Follow the lead of the Top Fuel Guys, and maybe get them coated, and you will be a happy camper IMO.