A Quick History of the GMC 6-71 Blower

[Richard Bartrop]

A little background on an iconic piece of hot rod hardware,  From Mac's Motor City Garage by way of Hemmings.

https://www.macsmotorcitygarage.com/a-quick-history-of-the-gmc-6-71-blower/

includes a short bit on why it's apparently not actually a supercharger, even though it's used for supercharging.

[TransAmMike]

Great interesting post Richard. After all my years, I now have a better understanding about this well used piece of hardware on drag cars and hot rods.

[Jon Haigwood]

I worked in a Diesel Injector Rebuild shop for many of my younger years. The owner liked to surplus lots and had a few 4-71 blowers on the back shelf. These always interested me to put on a motor. I was told that there was a lot of work to make them usable on a car motor.

[Jon Haigwood]

Looking thru a copy of Customs Illustrated from 1964 , I ran across this picture this morning. It shows a different way of mounting a 671 blower. Gives me some ideas for a future build.

This close to the way they were mounted on the GM 

 

[GLMFAA1]

The  AMT double dragster kit had the front mounted 'blower' unit for the front engine drive. You could build it with a single or double engines. My favorite dragster kit when I was young. Nice frame to fit the Allison engine in.

greg

Edited April 18, 2021 by GLMFAA1
grammer

[Ace-Garageguy]

5 hours ago, Jon Haigwood said:

Looking thru a copy of Customs Illustrated from 1964 , I ran across this picture this morning. It shows a different way of mounting a 671 blower. Gives me some ideas for a future build.

Crank-driven GMC blowers were popular for a number of years. A famous company by the name of Potvin built them by the truckload...as did some others.

The attraction was the elimination of the early chain-drives necessary in the days before the Gilmer belt became de rigueur.

The downside is length, obviously, and the pumping (and efficiency) losses associated with the two big curved pipes.

You can still get a Potvin setup new...

https://www.mooneyesusa.com/product-p/potvin2009.htm

.Some very well known cars ran them. Below is the Mooneyes dragster.

Below again is Brian Chuchua's Bonneville-record-setting Corvette.

http://www.superchevy.com/features/1508-1958-chevrolet-corvette-sets-record-at-1960-bonneville-speed-trials/

Edited April 18, 2021 by Ace-Garageguy

[Fat Brian]

There's also a Potvin setup in the Orange Crate kit.

[GLMFAA1]

The AMT 61/62 Buick special wagon had the set up.

greg

[Greg Myers]

[Jon Haigwood]

Found a different setup with a couple S.C.O.T. blowers in a  Rod Handbook mag from 1961

 

[Ace-Garageguy]

3 hours ago, Jon Haigwood said:

Found a different setup with a couple S.C.O.T. blowers in a  Rod Handbook mag from 1961...

That's one I've never seen. Pretty crazy...and dig that wicked chain drive.  

[Richard Bartrop]

In the 1930s, you had carmakers like Bentley and MG offering cars with crank driver blowers they just let poke out in front of the radiator.  A really cool look, IMO.

It would actually look pretty neat on something like a Deuce roadster, though I imagine trying to thread the intake under the radiator and over a V-8 might get a little unwieldy.

[Rocking Rodney Rat]

There is a front mounted (Potvin style) blower that's for the Hemi in the reissue of the MPC Cosmic Charger dragster.... -RRR

[Reegs]

On 4/18/2021 at 6:29 PM, Ace-Garageguy said:

Crank-driven GMC blowers were popular for a number of years. A famous company by the name of Potvin built them by the truckload...as did some others.

The attraction was the elimination of the early chain-drives necessary in the days before the Gilmer belt became de rigueur.

The downside is length, obviously, and the pumping (and efficiency) losses associated with the two big curved pipes.

 

 

And you can't monkey with the compression by switching to a different length drive belt.

[Ace-Garageguy]

23 minutes ago, Reegs said:

And you can't monkey with the compression by switching to a different length drive belt.

You change the over- or under- drive ratio (and the pressure developed) on a Gilmer-belt setup by changing the relative diameters of the crank and blower snout pulleys (or the sprockets if it's a chain drive), sometimes requiring different belt or chain lengths. Not too difficult, obviously, because everything is right there in the open.

Some of the front-mounted blower setups did actually have a provision for changing drive ratios by changing internal gearing; obviously a royal PITA because you have to take everything apart to get to it.

 

 

Edited May 20, 2021 by Ace-Garageguy
CLARITY and ACCURACY

[Reegs]

Thanks for 'splainin' it better, Ace.

The same article told of how the design, combined with a hung-open valve, led to some entertaining blower explosions.

Wish I could remember where I read all this stuff. 

Edited May 21, 2021 by Reegs