dark mephisto

I was wondering if anyone has tried putting a 4:71 or 471 GMC Supercharger in a 1981 mazda rx-7? I'm thinking about putting one in, but don't know what to expect.

mwatson184

Nobody has done it yet, but if you are mechanically inclined and have access to somebody who can fabricate (or you can do it yourself) I don't see how it would be too hard. There are a few decisions you have to make, mainly whether you will blow through or draw through the carb. If you draw through you will need a much larger carb, but if you blow through it will need to be modified for boost.

Good luck,
Marques

rototiller1

There is an aussy car with a 6:71 on it . I saw a video of it at the track, it sounded great right up to the point it blew up.

I was thinking the same thing, about using a 4:71 on mine.

dark mephisto

yeah, i'm becoming a mechanic, and my dads been one for over 40 years so I think I can handle it. But yeah, i'm gonna have it sitting underneath the carb so I don't have to put a new one on, but I do have a holley 650 cfm double pumper 4-barrel sitting on my floor next to me... hmmmm. sugestions?? Does the carb need to be modified if its drawing from the carb into the supercharger? If so how would i modify the original carb for more boost??

FB II

if you're drawing through, you mainly just need to worry about fuel pressure.

dark mephisto

yeah, i had already planned on putting in a new fuel pump.

dark mephisto

Is there anything else I have to do besides connect an oil hose to lubricate the supercharger, get a new fuel pump, and make templates to put the supercharger on the intake manifold, and one to put the carb on the supercharger. Also i would need to put a pulley on it, and connect it. Is there anything else that i'm missing?? thanks.

dark mephisto

can someone help me??

rototiller1

the carb will need to be mod'ed to use a blower, mainly the power valve circut will need to get its vacumm signal from the manifold below the blower. Peterson's makes a great book on supercharging

mwatson184

^that would be for holley/carter/demon carbs only, not with edelbrock, or the stock nikki carb.

I think you have everything that you need to do planned out, but I think you should think more about your carburetor choice. When drawing through a carb for a roots style supercharger, there is vacuum while under full throttle, this can cause some strange problems with getting progressively richer as rpm increases. Holley makes some specific supercharger carbs you might want to look into.

Marques

dark mephisto

k, thanks. I'm looking into putting a Holley 650 cfm 4-barrell double pumper on if I do this. I have it sitting right next to me now so I wouldn't have to buy a new one.

dark mephisto

I jsut thought of something, will my clutch be able to handle the supercharger??? If i'm lucky the new one I just put in should last but it was meant for a normal 12a. Any thoughts on this??

mwatson184

Just don't shift/launch too hard, it should hold up ok.

I recommend getting an SC holley, not an ordinary 650 dp, it will just cause you problems.

Marques

dark mephisto

umm, sc holley??

dark mephisto

umm, sc holley?? What kind of clutch would you recommend for this kind of setup??

dark mephisto

can i put a clutch from a t2 on my tranny without having to swap tranny's??

mwatson184

SC holley, a holley build specifically for draw through supercharger applications. http://www.holley.com do a bit of research.

Nope. Just get a performance clutch built for the 12a from racing beat if you find it necessary. The stock clutch should hold up fine for quite a while, if you take it easy on the shifting/launches like I said earlier.

Marques

dark mephisto

sweet thanks, i'll have to check out this out and see. But i don't really want to put a new carb on, how would I modify it?

mwatson184

I think somebody said it earlier, the power valve will have to get its signal from the intake manifold. You can't have the power valve signal come from the base plate because in drawthrough supercharger applications there is still vacuum between the throttle blades and the supercharger (usually at high rpm), even under WOT. There are also other suddle differences, larger air bleeds etc... You could tune around that though.

Marques

dark mephisto

sweet, thanks. I think thats all i need help with.

82streetracer

iTrader: (1)

your going to have to figure out the belt routing and such also,

should be cool, I wanted to do a atkins blower just so I could have it sticking out the passenger side of the hood. That would be sick.

82streetracer

iTrader: (1)

your going to have to figure out the belt routing and such also,

should be cool, I wanted to do a atkins blower just so I could have it sticking out the passenger side of the hood. That would be sick.

Bitchn7

We had a 471 on our 13B. Unfortunately i cant give a good indication of tuning as we only had the engine int he car for a small time

We used a s4 13B custom tubular manifold (for sale at moment) 650 dp spread bore Holley carb and electronic 12A turbo distributor.
We never realy got a chance to tune this set up well. had a couple of small fires then came winter so took the car off the road. We are now going to a 20B with intercooler and injection, may step up to a 6/71 blower yet
i would suggest injection and someform of intercooling if you want to make any real power with reliability without detonation issues.



hope you like the pics

Bitchn7

also you dont need to have any form of oil lines to the blower, just fill it up with good gear oil to the over flow and close it up.

rototiller1

afb carbs need to be mod'ed also, the metering rods are controlled by vacumm and spring pressure on the rods, they are for cruise and part throttle metering