SBC crankshaft hub w/6:71

[George]

I am putting a 4.125 X 3.48 SBC together. We have a RCD girdle but I'm concerned about the wall thickness of the available hub. I have a 3/16 and 1/4 keyway on the crank. Should I look for a BBC OD hub? The timing chain cover is a cast Hilborn so cutting it for a larger seal is no biggie. I am also wanting to run my MSD crank trigger . I spoke with Randy @Good Vibrations today and left a VM with John Lane at ATI. Thanks. George

OH, also got a question on "burndown breathers" . Are they all for 1.25 hose? I'm looking at the cast units with the quick connects. Pretty pricey! Any other options or parts available.

[dreracecar]

By all means go with the BBC OD hub, There is not enough material between the .250 keyway and the SBC hub OD and you will split the hub and rotate the key out the crank snout even with the support. If you already have the SBC hub then you can shrink a piece of moly material and machine down to BBC OD that way if the hub does crack it will hold because the crack stops at the ID of the over tube. How do I know this--myself and 4 others racers I know of have all gone thru it.

As far as a crank trigger, is that for standard ign or a magneto?

[George]

The only hub I have has no snout. The crank trigger is for the MSD 12lt mag.

[dreracecar]

The only hub I have has no snout. The crank trigger is for the MSD 12lt mag.

Missing somthing here--- "snout" is the end of the crank, "hubs" have pulley registers, "girdles" support the crank and pulley under load while using a blower on a SBC because the crank snout does not stick out far enough and puts a load on the hub,streching the 7/16 crank bolt, losening up the hub,causing the hub to flex and crack along the 1/4" keyway,rolling the key out of the crank and really messing up the crank seal, pukeing out oil all over the front of the engine and on the track.

By going with the ATI hub or shrinking material over a standard SBC blower hub, you eliminate the hub itself flexing and will not crack along the keyway. But even with the girdle I have seen the standard blower hubs split apart and do the same amount of damage.

[George]

So there is no one making a crank hub with a SBC I.D. and a BBC O.D. long enough to be carried in a outboard bearing?

[dreracecar]

No, not enough market and takes too much material to machine. I couldnt even get Leach at RCD to make a sbc id to bbc od blower hub even tho I had sent him 3 blown-up hubs(So, would you like to buy another?) thats when I added an over tube to the hub and machined it for a bbc seal myself.

  What is made is a post that has a SBC register on one end and the other end has a register for the support bearing. The post is bored for a long stud that threads into the crank and a nut tightens the post and hub to the crank. Now you shim the front plate to the block adapters allowing some crank endplay. Get your overdrive combo figured out so you will leave the bottom pulley alone and just change the top one. On my 375 SBC I run a 64 bottom and a 1440 belt and by changing the top I can go from 2% to 25% over.
   I dont run a girdle because I had my crank built with a BBC snout and a 3/4" hub bolt---zero flex with that combo

[Paul New]

I run a Bryant 3.625 stroke BBC snout crank in my SBC with a 3/4" bolt 6.60's @ 206 mph 24lbs of boost. One of our other engines ran a Cola 3.48 stroke double 1/4" key way with a RCD crank support and hub 7.20's @ 190mph. We also have a BRC 3.48 stroke with BB Chrysler snout, 3/4" bolt, Milodon gear drive, and a RCD hub that may be for sale

[George]

The BBC crank snout is the best way to go for sure but I am using what I have. It looks like ATI has a hub that will do the job. From there I will have a piece built to bolt inside the pulley and into the ATI hub. I'm going to need to make the bottom pulley size compatible with the MSD crank trigger ring.