Potvin style blower set-up/Flathead

I've been working on a Potvin style blown flathead project. I had a couple of questions...
1. Open car or closed car?

2. Is anyone using unmodified(stock)bearing plates on their GMC blowers? Are they holding up well?.. By definition the blower will turn crank speed, around 4800 rpm max.

 

no problem with mine, plus the blower should be ok to those revs, I know originally gmc wise they didnt turn that quick but the pulleys on mine near look to be 1:1 ratio. cant say I have counted to be honest. but I know that its over driven upto about 12 lbs.

 

Pulley drive observation: I found an old feature/semi-tech article on Tom Cobb's GMC blown flathead racecar, probably one of the first few GMC blown flatheads. His was top mounted, but used the same '40 Ford type pulley as the basis for the drive system at first. He said the pulley reached its limit at about 5 pounds boost, and beyond that a stronger fabricated drive was necessary.

 

I'm hoping that I won't have that problem. The front drive should only impart torsional loads. But it wouldn't be the first time I had to collect broken parts and start over......

 

wow, keep this post going....

 

Depending on what end you are driving from, the opposite end plate is lubed by packing the bearings with wheel bearing grease with just a flat cover over the end to clean things up a bit .Potvin ,Moon and Reath had finned covers with drive flanges cast in for injector/ or water pumps that drove off the end of the internally splined rotor . If you use good quality bearings and seals , should be no problem with the R's at 1 to 1 . Have fun !!

 

*****in, maybe this site will help with ideas?

scroll down a bit until you see their potvin setup for the flathead

http://www.uncommonengineering.com/catalog.html

 

...I was thinking about the stress on the front drive bearings...the only thing I could come up with negative is the unit recieving a little thrust loading from the coupler if it trys to separate itself while it turns. (pushing the drive into the blower??)...but I dont think it will be any major issue, if any at all.

The fact that you dont have to tighten a belt up and pull on the unit should be a big plus.

Are you thinking of mounting the carbs in a draw thru design, or you mounting the carbs on the intake and pressurizing them?

Looks good!
--reed

 

That uncommon engineering site is awsome. How about that big blown Hudson in an A.

 

I've got a front mounted Italmechanica (SCOT) blower for a flathead. Some people don't beleive this thing exists but it does. Mine is chain driven off of the crank. It's a very short chain. The crank drive and blower drive are right ontop of each other.

Here's a couple pics of it. I could count the teeth on the drives to give you an idea of under or over driven if that will help.
Clark

 

I can only imagine owning something so cool and so rare for a flathead.

Danny

 

That SCOT is really a rare piece ! Neat !--- I have a front cover and 471 cover that were on a boat ,kind of a backyard deal but it worked at the time . It used a marine front cover with a GM 471 cover bolted to it and used a chain/double sprocket type coupler that was modified to press on the end of a SBC crank , the water pump was driven off one of the accessory drives in the front of the blower. I bought it from a guy I work with for $10 because the 471 was junk.

 

I think that the original Potvin set-up used the same double row chain drive/twin sprocket set-up.. I'm actually using a pump drive from a jet-ski. It's not really period correct, but it allows for some mis-alignment, and I hope it will absorb some harmonic vibration...I am also thinking about using the original detroit water pump. It sure makes the overall ***embly LONG...

 

I think I am going to hard mount the blower to the engine. I'll eliminate the stock water pumps and use a front engine plate to mount the blower and as the engine mount (to the frame). I'll fabricate a " halo" around the front blower cover, and attach the two with some plate... I know it is hard to visualize, I'll try to get it mocked-up in the next couple days and post some pics...

 

I'm planning on running 2 or 3 94's in a draw through set-up.. Of course a two port hilborn would be cool....

 

I have always been intrigued with the Potvin styled blowers. Why did they never take off like the 6-71 upright? Is it because of manufacturing costs?

 

I would imagine the reason the top mount was so attractive was the ability to change the drive ratio w/pulleys and belts, and it would fit in a p***enger car..

 

O.K. here are some pics of the blower mount I am fabricating.. I might get it finished today, I'll post more pics...........

 

damned nice work man...you must have a mill, or access to one...

 

I got the mount welded up... Not as pretty as I would like, but I can clean it up....Starting to take shape!

 

Im in love!

 

The only bad thing about these is the Drive ratio is not easily Changable, if its adjustable at all... Clarks could be changed but its not direct driven off of the front of the crank.

1:1 Drives make alot of boost, as you cxant underdrive them much. You had better have a good bottom end and extra head studs for that flatty, or run really low compression.

that Chevy Roadster that was on the cover of Hotrod, with the Potvin blown SBC, and the Pantera Transaxle, isnt really driveable at all, cause it gets hot Real fast, nainly due to the heat of the 1:1 blower drive.

 

Standard 8BA bore with 1CM heads will give 6.4:1 compression. Thats not even taking into account relieving the block and or heads. I think bottom end would be an issue before compression

Danny

 

I'm gonna run Ross flattops, H-beams and 1 1/2" main cap "straps" on all 3 mains w/studs. Hand built pan.. I had Crower grind a cam special for the application... I'm looking for a couple of large SU sidedrafts.... I am worried about too much boost, But I will relieve the block and open up the heads to lower mechanical compression.. If I have heat problems, there is always Ethanol/Methanol

 

Hi Stank,

Could you run some sort of heat exchange/intercooler to lower the intake charge temp? Maybe you should mill some fins into the piping from the blower to the intake!!

Danny

 

A Roots output is dependant on several things , blower speed , internal clearances and intake area . OK , you are stuck with a constant 1 to 1, Small venturi area and/or looser rotor clearances would help kill some of the output . On the engine side , something that isn't discussed much is dynamic C/R vs. static C/R . A camshaft can have a big effect on the **** and squeeze before the bang and blow , talk to your cam grinder on this one before ordering anything . The inlet air cooling is a plus , whether an air to air/water exchanger or water/ alcohol injection . Detonation is the killer here .

 

I've been thinking about that some. The cam I had ground has an LSA of 110.. The blower was a swapmeet find that measures a little big on end clearance. Rotor to rotor clearance was good, as well as rotor to case.. I am planning on putting high speed bearings in it and running it the way it is.. I really had not thought about venturi area up to this point, but it adds another tuning tool.. I guess if the cylinder pressure is too high, I'll stick another cam in it. One with a tighter LSA and more duration... I sure as hell don't want to melt it first time out

 

You have the idea ! --Ever wonder how the 60s muscle cars could run so much static C/R ? The secret was in the overlap and lobe centers , they bled the dynamic at low RPMs , rumppity -rump and usually had very fast idles for the day . Just another tip ,a boost retard control for your dizzy in conjuntion with a H20 injection , MSD or Crane make a nifty adjustable box but you'll probably use their other **** too, too chainey ? Anyone that has come as far as you have on this project can , I'm sure, finger out sumthin' !! Good luck !!