Thread: 6-71 supercharged 302 help needed

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I am looking to build my first supercharged engine. I have a 302 out of an old 4 door Fairlane and I am wanting to build a Roots 6-71 supercharged engine out of it. Can anyone suggest some reference materials on specs that I can use as guidelines for this build? I bought a book by Bob McClurg "How to build supercharged & turbocharged small block Fords", but this book isn't much help. I need specs, not theories, so any help would be greatly appreciated. Thanks.

I'm certainly no supercharging expert, but I think the 671 might not be the best fit for a 302, both physically and boost wise. If you do the math, the 71 portion refers to the per cylinder volume this supercharger is designed to handle, so 6 x 71= 426 cubes. On the other hand, a 471 mathmatically would be 4 x 71=284 cubes, much closer to your engines size.

On the physical end, 671's are externally huge by comparison and take more HP to drive. Once you get all the info you can from some of our sharp engine guys, I would call Blower Drive Service or Dyers and talk to one of their techs. I could be way out in left field on my suggestions, so it will be interesting for both of us to see what we can learn.



Don

Whats your intended use for this engine /ride........

4-71's are cool but arent worth it alot of times. a 6-71 is fine. i know a guy who put a 8-71 on a 350

if you want genuine performance then go with the vortec or paxton type blowers so many guys today use .. much more knowledge in that direction .. if you want the 671 for apperance then just build a greatly undertuned motor for looks ..

And on top of that, bottom ends of SB Fords with the OEM cast steel cranks, bearing webs witout enough meat (except the Mexican or Aussie versions) leave something to be desired. Particularly with being overboosted. Now....if you were to use one of the new SVT blocks, and with a billet crank - that would be worth the effort. And, yes, a 6-71 is too much for a street driven small block of any brand.

Originally Posted by V8juggernaut

I am looking to build my first supercharged engine. I have a 302 out of an old 4 door Fairlane and I am wanting to build a Roots 6-71 supercharged engine out of it. Can anyone suggest some reference materials on specs that I can use as guidelines for this build? I bought a book by Bob McClurg "How to build supercharged & turbocharged small block Fords", but this book isn't much help. I need specs, not theories, so any help would be greatly appreciated. Thanks.

I not sure what you are asking.
I will tell you that above about 450 hp the 302 blocks become very un-stable.
I would start by under-driving the blower by 30% to be on the safe side.

Originally Posted by IC2

And on top of that, bottom ends of SB Fords with the OEM cast steel cranks, bearing webs witout enough meat (except the Mexican or Aussie versions) leave something to be desired. Particularly with being overboosted. Now....if you were to use one of the new SVT blocks, and with a billet crank - that would be worth the effort. And, yes, a 6-71 is too much for a street driven small block of any brand.

The 6-71 is fine on a a 4- bolt main 350.
As long as you keep the boost to 8 lbs. it will be fine.

I wasn't planning on running any more than 8-10 lbs of boost. More than that would be dangerous. I like the Roots blowers better than the whipple or screw types. I'm sorta old school in regards to the way I want it to look. I already have a cruiser with my big block T-bird, I just want a hot rod that will boil the hides when I get the urge. It won't be a drag race car, although I might take it to the track just to see what it does. I appreciate all of your advice. Keep it coming, guys.

Originally Posted by V8juggernaut

I wasn't planning on running any more than 8-10 lbs of boost. More than that would be dangerous. I like the Roots blowers better than the whipple or screw types. I'm sorta old school in regards to the way I want it to look. I already have a cruiser with my big block T-bird, I just want a hot rod that will boil the hides when I get the urge. It won't be a drag race car, although I might take it to the track just to see what it does. I appreciate all of your advice. Keep it coming, guys.

8-10 lbs. of boost I.M.O. would be to much for a stock 302 block plus I don't think at 10 psi. it will run on pump gas.

Well, as I said, I've never built a supercharged engine before and all your input is helpful. I can't afford an aftermarket block at this time, so I guess I'm stuck with the FoMoCo block. As far as the 6-71 being too big for any small block, with the proper cam, heads, carburetion and under-drive pulleys, wouldn't I be able to get a streetable engine out of it?
I may have been too hasty throwing out boost #'s. Sorry, still learning about boost.

Originally Posted by V8juggernaut

Well, as I said, I've never built a supercharged engine before and all your input is helpful. I can't afford an aftermarket block at this time, so I guess I'm stuck with the FoMoCo block. As far as the 6-71 being too big for any small block, with the proper cam, heads, carburetion and under-drive pulleys, wouldn't I be able to get a streetable engine out of it?
I may have been too hasty throwing out boost #'s. Sorry, still learning about boost.

yes you can under drive it alot but this would have to do with how sealed up the blower is and the cr and cam .i am building a sbc383 with a 871 littlefield on it just going to under drive it and it as a good bottom end with a bigger cc intake port

I am not sure about what cam to use, but I figured on keeping the compression ratio in the 8:1 - 8.5:1 range. I have heard that this is an ideal range for a blown engine. Do you have any suggestions on a camshaft?

Originally Posted by V8juggernaut

I am not sure about what cam to use, but I figured on keeping the compression ratio in the 8:1 - 8.5:1 range. I have heard that this is an ideal range for a blown engine. Do you have any suggestions on a camshaft?

I would either run a cam that has 112 or 114 lobe seperation.
You would need to run 10 degree's more exhaust duration.

just fill the block part way and go ahve fun with it. if it blows salvage the internals and start over