crank hub / balancer question for a blower

I was told I needed a 2 keyway hub and machined crank on my blower project.
This is a 20% underdriven 30 T lower 37 T upper 6-71 setup on a stock 8.5 to 1 400 small block chevy.
Is it okay to just get a steel hub and run just the single woodruff key, or am I asking for big trouble? Motor is already in the car and if I dont have to pull the motor, I'd like to get the blower on it sooner rather than later. thanks. jim

 

Small block crank snouts are small, they key is small, you might have problems. Boost and rpm will put quite a load on it. If you don't make much boost, and you don't rev it high, it will probably live for a while. Or not.

Big blocks running mild boost seem to be ok without the extra key. They have a much larger, full length crank snout.

 

If the motor is still externally balanced you'll most likely run into vibration issues if you try and run it with the hub and without its specific balancer. 400s are externally balanced motors, unless its been internally balanced and uses a neutral damper and flywheel you may already be at a roadblock.

You may need to do more homework.....

 

Hopefully he's planning on using a 400 specific steel crank hub, they are available.

 

I looked up the BDS catalog and they do have a 400 hub. So if I do this, im going to run the 400 hub. jim

 

I ran a 6-71 blown 400 on the street for about 12 years,using a stock damper.I have had various blower setups on small block chevys,and have never used anything but the stock damper.I am talking street driving,not drag racing or other abuse. I had a 6-71 blown 327,with a pressed on damper (no bolt) that I ran for a couple of summers on the street. Common sense is the key.If you plan on hammering it hard,go for the hub setup,otherwise just put it together and drive it.

 

Just do the machine work now. If you don't, it'll eat at you. It's easier to do it right the 1st time. Repairing the crank & replacing the hub is a pain in the *** after it comes apart. Ask me how I know haha!

 

I understand your situation but, you would be wise to add the 2nd key. of course, you really cannot do it without removing the crank and having a keyway added. Usually a 1/4" keyway is machined in 180 degress from the stock key.
I guess you can try it with a single key but, it may bite you in the **** at the worst time. You know Murphy's law?
Best of luck with it.

Steve
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Sunday April 11, 2010 8th annual Nostalgic Show & Go! Phoenix www.nostalgicshowandgo.org

 

I got a email back from Don Hampton, of Hampton blowers, he says for a mild, (5psi) setup for the street without racing or hammering on it, it should be fine with the stock key, but I am buying the steel hub ($179 OUCH). This motor has issues trying to rev to 4500 right now. With 3.07 gears in the 12 bolt, I dont plan on reving it much. (Im 47 and pretty much done beating on my car Ive had since 1978).
I plan on taking another crank and have it properly machined and build a decent little 350 as cash allows. jim

 

The blower belt will remove some vibrations from your motor, however; I would not run just a hub with a single keyway on the street...

Remember a blower actually robs the engine of horse power at lower RPM's (before boost is created, motor still has vacuum) when the blower is "under driven"... The blower belt actually tightens as you drive your rod which obviously places stain on the hub/balancer. The first time you hit the throttle, and you will just to experience the feel of the blower, may be your last time as you may spin the crank inside of the hub with the single keyway...

Is the motor internally balanced as noted above?

I would not run just the hub on the street... Just my 2 cents as I run a blower on the street and at the track, two seperate animals....

 

motor is externally balanced, Like I was saying pretty much stock 400 out of a 74 caprice, Would you suggest a steel something like a ati balancer? jim

 

My engine was built for the blower. I'm running a 4:71 and I get 8lbs boost any time I get on it. It's one to one on the drive. Oh I'm running 383ci sbc, blanced, blower pistons (KB), etc.. I'm 71 your 47 if you can keep your foot out of a blower motor, at least every now and then, tell me how. That instant horse power and getting slammed back is the seat is a rush. Double key the crank and you get to do it more often.

 

Exactly, run an ATI balancer. Keep your boost down, you'll be rebuilding your motor with proper pistons, etc. some day as you are aware....

Read the above post from the "71 year young" hot rodder (Blown Mopar) with a blown motor.... That is experience talking to you.....

 

My problem is I get impatient and want to get this thing done yesterday. I talked to a guy thats got a wieand 144 miniblower that needs a rebuild for 500 bucks, and thinking of maybe going that route and put the 6-71 on the back burner. But ive already got the 6-71 setup so I may just go ahead and buy the pulley,belt, V belt pulleys at least I'll have everything if I decide to just go for it. Here's a pic of the setup, Ive got a new manifold thats not in the pic, just have to pull the trigger and spend a few more bucks. jim

 

i ran a 390 ford(i know not chevy but ) 20 under like you. it was all a stock engine with 9.5 to 1 compression and all.when gary dyer set it up when i bought it, he need my bottom pulley to make one so the 2" drive pully would be able to bolt to it.ran the car for 5years on the street(every day during the dry warm days.) with only one key way.if you can look around for a used bottom pulley. but for what you said you want it to do one key way should be fine (imo).here the stats and how they get them for the pulleys(might be able to make one yourself.

 

I may just go for it in the next week or two. If the thing does have issues, I do have a rebuilt 350 with vortec heads and stuff on the stand ready to install. jim

 

If you are under driving a 6-71 and only getting 6 psi or so boost there is no need for double keyways and keys.

I have never run a stock damper on any of the blower motors I've built and never had a problem. I just run a steel hub. Actually on my current blown SBC I run a complete Hampton drive...and steel hub. I put over 1k miles on it in the last 6 weeks of drivable weather of '09. Purrs like a kitten.

BTW I'm 68 and well know where WOT is.

 

If the motor is already together, is there an option like drilling / threading holes for set-screws rather than a key? It wouldn't be as good as a second key but better than just one, and not hard to do... just guessing, never ran a blower myself.

 

a customer had a 406 with a 6/71 single key and would split the hub until I made him a bigger hub and installed a big block seal in a modified timing cover and has been running for 10 years

 

To be absolutely correct it needs the 2nd key. BDS, Weiand, Enderle, etc will all tell you you need it but, if you have a back up motor and are so impatient you don't give a **** if you blow up the 400. Cool.

 

heh...I have driven a LOT of 500 mile days on the blower motor in my 55.

Steel hub, one key, but it's a big block with mild boost.

 

i spent saturday nite in a small town trying to repair tossed ballancer ..not a lot of fun double key is a must

 

I guess I don't understand having a blower on your motor and not hammering it. I'm only 38 though, maybe I'll figure it out when I grow up?

 

Yeah, kinda like having an 18" **** and not being a **** star.

I would listen to DW and do the keyway NOW. You will regret it later.

 

Three things enter into the equation...diameter of the crank, how much/hard you jump on it, and % over/under driven the blower is. The larger the crank snout diameter, the less likely the key is to fail...both other factors included. The smaller the crank blower pulley is in relation to the drive pulley on the blower (under driven), the less likely the key is to fail...both other factors included. And the less you WAIL on the engine, the less likely the key is to fail...both other factors included. As the crank drive pulley gets bigger and the blower drive pulley gets smaller, the greater the strain on the key gets and the greater the chance that the key will shear...

 

I have single keyed on my 471 with a steel hub and thousands of miles on it. Its seen 6000 + rpms many times!

 

I believe this all may have gotten started years ago, when guys started cramming 6-71's and 8-71's onto SBC's and ran them at the Drags. I ALSO know that if you don't torque the damper bolt down on the crank snout, that that contributes to the sheared key syndrome...

 

Well we can debate this to death, why do street driven hot rods with blowers shear off the crank pulley/balancer/hub. Answer - they only had ONE..... Probably driven hard, why wouldn't you if you have a supercharged car !

If you are going to build the motor, why wouldn't you cut a second keyway for the hub? Spend $$$ on a blower and not cents on a keyway...

 

I'm curious as to the guys that have lost single key set ups were they steel hubs or stock balancers?