Can a 6-71 be used with a flathead?

Hey Gang,
I have most of my blower back , it is a sbc set up and i am wondering has anyone used one on a flattie? If so what manifold is used, is the nose drive the same? Any issues?

Thanks
Leon

 

I've never seen a factory made manifold for that combination. Most folks will modify a SCOTT or 4 barrel manifold with a plate or box to mount the blower.

In my opinion a 6:71 is physically to large for a flathead and will eat up as much horsepower as it will make. A 4:71 would be my choice.

 

I agree, Pat Akins once ran a 6-71 on his flathead dragster, and often pushed the head gaskets out like mush...I think that a 4-71 or even a 3-71 (if you can find them) would work better.

 

I have a 4-71 in my shop some where......hummmmm.

 

Wouldn't a serious flathead have copper head gaskets and be o-ringed? Lippy

 

Only one problem . . . the 'O' part of the O-ring . . . that combustion chamber makes it a bitch! There are people who have setup CNC programs to mill a wire receiver groove . . . but I've not seen one done in years. Anybody on the HAMB ever do one?

Like the others said, for the displacement of a flatty - either the 3-71 on a smaller cube motor or a 4-71. If you want a much more efficient blower, than consider something like an Eaton - they take a LOT less horsepower than an old jimmy. You see a lot of the guys at BVille running more efficient styles of blowers these days -- Eatons, Pro-charger, Vortex, etc..

 

A 6-71 eats up about 40 to 50 horses just spinning it at boost speed, (high idle).........go with a 4-71 or even a 3-71........alot smaller.....less heat buildup.....less parasitic loss......just looks cooler on a flathead...

 

The challenge is sizing - with a 6-71, you'll have to spin it so slowly to keep the boost down at the higher RPM ranges, that the rotors will actually be turning slower than if vacuum was pulling the air through them causing a restriction.

One school of thought is that a blower's displacement should be about 2/3 the size of the engine.

Smaller blowers turned faster are generally more efficient than larger blowers turned slower. Look at what factories do when supercharging...

 

Sell your 6-71 an buy on of Joe Abbin's setups. Uses a Wieand blower and sized perfectly for anything orther than a race car. If you want to go racing get a 4-71.

IMHO

 

Sorry - couldn't resist, but it seems like similar overkill to me. This blower was from a locomotive and story was it blew out the head gaskets and would barely turn over with the starter motor.

 

Steve McGunnuis in Australia , ran a 6/71 blown 286 flatty called flathead express .It ran high 8s all day on alcohol .Did eventually snap his fancy billet crank!

 

got this picture from coverage of the CHRR 2009. Does anyone know anything about the car?

 

Wasn't there a baby blue 32 chopped highboy sedan running one? I used to see it at Macungie Pa. several years ago now. It has been done. I haven't a clue how he did it.

 

I'd love to know more about this car! Can't say that I've ever seen a 6-71 blown and injected flatty in what appears to be a Willy's coupe . . . cool shit!

 

Both Tom Sparks and Freddie Owens ran blown flatty powered Willys. Tom Sparks was Tony Nancy's mentor. Freddie Owens sold the Willys to the Grist Brothers minus the engine. The Grist Brothers installed a 364 Buick and then a 430 Lincoln I think.

 

It depends on what you want to achieve. Small, fast blowers generate more compression heat at high rpm, so mixtures can get rarefied to the point of negating the advantage of the blower. Factories nevertheless tend to go that route because they're looking to augment low-rpm flexibility for the engine size, and they can always bodge any unwanted high-rpm effects out with electronics.

On the other hand, big, slow blowers leak pressure at low rpm (though I wonder how much) but they suffer less from compression heat effects. They're associated with seriously hairy engines, but they more closely approximate pure mechanical compression. I'd think the whole blower capacity/engine capacity/static CR/cam profile equation would be a bit simpler and more predictable with a big slow blower scenario.

That is, don't think in terms of boost; rather, you're splitting the job of compressing the charge between the blower and the pistons on their compression stroke. The compression work you're taking away from the pistons you're giving to the blower - and the fact that you're sitting with about the same overall pumping losses per unit of charge mass means there's little or no real loss of efficiency. Only now you're dealing with a greater charge mass, possibly a much greater charge mass, than was the case with the naturally aspirated engine. A small, fast blower is a boosting device. A big, slow blower is an alternative to cubic inches - or rather an additional source of cubic inches.

At least that's my purely theoretical understanding. How does that compare to experience?

 

But for a flathead, a 6-71 would have to be underdriven so much to keep from overboosting at high RPM that it actually becomes an impediment to flow at low RPM. So, for a street-driven flathead, a 6-71 is a very poor choice.

My point was there are efficiencies to be realized (depending on type of blower) by turning a smaller blower faster. There is a point of diminishing returns for each scenario...if you're trying to build big boost, then yes, a smaller blower faster is not as efficient due to heat...we were talking street though.

I should have caveated my statement with: "For street use,..."

 

Now THAT'S a blowjob!!!!

 

4-71 works the best! 6-71's are too big and you'd have a helluva time getting it to idle or run. Especially on the street.

 

There is no hard and fast general rule. Supercharger sizing is typically based on size of the engine, application, blower efficiency and required lbs of boost.

On a street flathead, there are very few that are going to be running much over 6 lbs of boost. Given this and a flathead below 300 cubes, a 4-71 is probably a good fit. However, if you're running a big 324 cube stroker, and need 12 lbs of boost for B-Ville, then a 6-71 is probably a better choice. Most street flatheads are not huge-cube motors . . . one of the most common configurations is a 4" stroke and 3 5/16 bore (276) cubes - with this combination, you'll easily achieve all the required boost you can handle on the street with a 4-71 - heck, a 3-71 would work for a 239 - 255 cube motor! Other things that come into play for race situations are rotors with teflon strips (better sealing and more boost), different rotor designs, etc..

If you have any questions, talk to a major blower supplier like BDS, Dyers, etc - they'll know exactly what you need (at least for GMC style blowers).

 

Seems like it would be overkill to me, too, like Dolly Parton's tits on a 3 foot tall midget (or whatever the more PC term for that is).

Although maybe you could get it to work, there was that little girl in Total Recall with the three boobs.. special effects and all but it seemed to work.

 

3-71 is fine for most street flatheads, and, race flatheads too - Navarro set most of his records with a 3-71. 4-71 "looks" better and can be made to work on the street well enough - like a 6-71 on a SBC. Not the most efficient setup, but works well enough.

 

Or run a ridiculously low static CR. If all things (e.g. cam profiles) were equal one would need a CR of 3.4:1 to run a 6-71 on a 255 and achieve the compression characteristics of a hypothetical 840 cu. in., 9:1 naturally aspirated engine. But think of the valves you'd be able to get into that thing!

 

The ideal set up would probably be the 4-71 with a high helix rotor. same look on the outside, but the rotors that have more "twist" to them (140 degrees as opposed to 70 deg.), which would make less heat, and have less parasitic loss, at the same RPM. The possible reason some of the above 6-71's, may have been okay in race applications, are that they have been run on alcohol, which has a cooling effect, which prevents detonation and cools the intake charge and the rotors. This is the reason the modern screw blowers, like some of the modern blowers like the Eaton street blower (think Ford Lightning), and Whipple and PSI are so popular in Drag racing (where legal). The screw blowers have such a low parasitic loss and don't build heat. Moving Violation,go with that 4-71 and save that 6-71 for a Nailhead or Hemi project, in the future.

 

But now you lose out at low RPM due to extremely low and inefficient compression ratios...

Everything is a compromise. The question is WHERE do you compromise?

 

We ran a 6-71 on the XF/blown gas roadster for 1 season.It actually went slower than with the 4-71,took too much HP to spin it.But it sure LOOKED cool!

 

Pete Keyser ran 144 at Loring ME with a 6-71 on a flathead in a 33Plymouth Coupe

 

one nice flathead out of Conn.

 

Hey, I'm not arguing with you ...