6-71 supercharged 302 help needed

[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.

[Itoldyouso]

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

[shawnlee28]

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

[gassersrule_196]

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

[HOSS429]

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 ..

[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.

[erik erikson]

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.

[erik erikson]

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.

[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.

[erik erikson]

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.

[speedy55779]

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.

7.5:1 compression max 12psi and run 91 octane. it will run fine. if you run 87 octane it'll ping at higher rpms do to the boost pressure. its alot of work tuning it in to the way you want it with adjusting carbs and timing and your boost but can it be done.

[erik erikson]

7.5:1 compression max 12psi and run 91 octane. it will run fine. if you run 87 octane it'll ping at higher rpms do to the boost pressure. its alot of work tuning it in to the way you want it with adjusting carbs and timing and your boost but can it be done.

12 psi on a stock 302/5.0 block???
Your kidding right??
I have built many a 5.0/302 block and we where breaking them at the 475 to 500 hp level.

[speedy55779]

12 psi on a stock 302/5.0 block???
Your kidding right??
I have built many a 5.0/302 block and we where breaking them at the 475 to 500 hp level.

he'll be lucky if he even see's 400hp out of it if its a stock motor plus lowering the compression to 7.5:1, but i can see where your coming from if he builds it up for the strip she'll pop. plus i said a max of 12 psi.

[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.

[pat mccarthy]

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