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SBC and 471 gm blower

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SBC and 471 gm blower

Postby BrazilianZ28Camaro » Sun Oct 04, 2009 3:27 pm

Hello fellows

I'm thinking if a "old school" combo would do some steam (worth the trouble) since good condition SBC 350-400 are hard to find and expansive here in Brazil. :x

283-307-327 engines are more easy to find in good conditions, then I ask if the following parts can do 500-550 horses on 100 octane gas.

SBC 327ci forged rotating assemblie 8.5 CR
AFR 195 heads
lunati MFT 242-252 at .050" 112lca .540/.560 lift
1 3/4 headers
rebuild 471 gm blower overdriven to boost 16 lbs
Mallory unilite dist
Mallory 6al box
super victor intake
1.6 roller rockers
4 bolt mains
dual side mounted Holley 750 carbs

Any reply is apreciated! :wink:
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Postby Ron C. » Sun Oct 04, 2009 4:17 pm

Are you sure you can get the 16 psi boost out of that 4-71??

If you can you'll probably have to overdrive the heck out of it and that would concern me about the intake temps to run 100 oct gas.

A true 16 psi would certainly reach your goal.

Blessings.........Ron.
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Postby BrazilianZ28Camaro » Sun Oct 04, 2009 4:31 pm

Ron C. wrote:Are you sure you can get the 16 psi boost out of that 4-71??

If you can you'll probably have to overdrive the heck out of it and that would concern me about the intake temps to run 100 oct gas.

A true 16 psi would certainly reach your goal.

Blessings.........Ron.


It difficult to be "sure" about the blower pressure because there are several variables, but I believe that to get 16psi , that little blower would turn 40-50% more than the engine...

My main concern is about its low adiabatic eficiency (55-60%) versus power production...

Intake temps should be a problem on street, strip or both?

Thanks Ron
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Postby Ron C. » Sun Oct 04, 2009 5:16 pm

It difficult to be "sure" about the blower pressure because there are several variables, but I believe that to get 16psi , that little blower would turn 40-50% more than the engine...

My main concern is about its low adiabatic eficiency (55-60%) versus power production...

Intake temps should be a problem on street, strip or both?

Thanks Ron[/quote]

I've had no experience with a 4-71 blower so not sure what kind of overdrive it would take. I do have some experience with a 6-71 or 14-71 and ProChargers and turbo's. Most likely the 4-71 is not going to be very efficient at 50% or even 40%.
The 327 chevy motor was a very happy engine and responded very well to making power. I don't think you would need much more than 10-12 psi of boost to make that 500hp level. A lot will be dependent on how well the 4-71 is prepaired.

I've been to your country and spent some time in the Belem area (lower amazon) . Have you been to the States?

Blessings..........Ron.
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Postby BrazilianZ28Camaro » Sun Oct 04, 2009 5:53 pm

Ron C. wrote:


I've had no experience with a 4-71 blower so not sure what kind of overdrive it would take. I do have some experience with a 6-71 or 14-71 and ProChargers and turbo's. Most likely the 4-71 is not going to be very efficient at 50% or even 40%.
The 327 chevy motor was a very happy engine and responded very well to making power. I don't think you would need much more than 10-12 psi of boost to make that 500hp level. A lot will be dependent on how well the 4-71 is prepaired.

I've been to your country and spent some time in the Belem area (lower amazon) . Have you been to the States?

Blessings..........Ron.[/quote]

About prepairing the 4-71 to be more efficient, I can hard anodize the rotors /case or crome they to tight up the tolerances a little and hopefully increase it efficiency...the clearances are on the high side on those blowers...

A friend of mine have a 69 dodge Dart with a blower 4-71, 50% overdrive 318 ci...the car weight 3600 lbs and ET is 11.9 @ 110 with drag slicks.It blow some head gasket once a while :shock:

You are welcome, my State is Rio Grande do Sul, south of Brazil.
Belem is at north...my State is different from Belem (colder climate, arquiteture), and we have a couple of dragstrips here. The dragstrip I run is called Velopark and it is certified by NHRA.

I never had been on USA mainly because I have a fear:

Go to a dragstrip and see all that awesome machines and never go back to home :lol: :lol: :lol:

Here 80% of our drag cars are 4 cylinders :x , and as I love V8s USA is a Dream land to me...

Try to build a fast american car like mine (Z28 71) here is a life project to a regular worker like me... we have 77% taxes on import parts and our money worth about half of US dollar...

Thanks for reply
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Postby Tokyo Torquer » Sun Oct 04, 2009 8:40 pm

A 4-71 GMC blower is 280ci.. you would have to overdrive by 40% to reach 16 lbs of overheated boost on a 327ci engine. That is far too much for pump gas and 8.5:1 compression. More reasonable is 12.5% overdrive which would give you ~10lbs boost on the 327.

That cam is awefully big for that little engine.. are you looking to winde that blower motor past 7000rpm?

You dont mention whether this is mostly street or track.

Dual 750 holleys is far too big for that engine. Dual 600s will do just fine even at that high boost, and never bigger than dual 650's on that 327.

Big Al's Toy Box can sell you an adapter plate to convert a real (6-71) blower intake for a 4-71. You will get better fuel distribution than with the converted 4-barrel intake.

A 355 with a 6-71 would be much better to work with.

mike
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Postby BrazilianZ28Camaro » Sun Oct 04, 2009 9:14 pm

Tokyo Torquer wrote:A 4-71 GMC blower is 280ci.. you would have to overdrive by 40% to reach 16 lbs of overheated boost on a 327ci engine. That is far too much for pump gas and 8.5:1 compression. More reasonable is 12.5% overdrive which would give you ~10lbs boost on the 327.

Mike , my doubt is exactly about that: 4-71 blower aren't very efficient, I think 12.5 % overdrive will not do ~10lbs boost...maybe 5 lbs at that ratio...have you some own experience with they?
I'm choose a SV intake mainly because the air gap it have...it can lower the intake charge temp a few degrees...


That cam is awefully big for that little engine.. are you looking to winde that blower motor past 7000rpm?

Yes the cam is big, but they say that a blown motor "tame" about 10 cam degrees ...shift point would be at 6800

You dont mention whether this is mostly street or track.

40%street 60% track

Dual 750 holleys is far too big for that engine. Dual 600s will do just fine even at that high boost, and never bigger than dual 650's on that 327.

Ok I apreciate your opinion, and now I remember Bill Jenkins had two 1100 dominators on his pro stock 327ci 9000 rpm N/A Vega... :shock:

Big Al's Toy Box can sell you an adapter plate to convert a real (6-71) blower intake for a 4-71. You will get better fuel distribution than with the converted 4-barrel intake.

A 355 with a 6-71 would be much better to work with.

I agree 1000%... but both are hard to find and expensive here... :x
Thanks for reply

mike
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Postby Tokyo Torquer » Sun Oct 04, 2009 9:32 pm

"Mike , my doubt is exactly about that: 4-71 blower aren't very efficient, I think 12.5 % overdrive will not do ~10lbs boost...maybe 5 lbs at that ratio...have you some own experience with they? "


.. I have lots of resources here to calculate boost for any size roots blower on any engine as well as the BDS and Dyers reference charts.. they all say that you can achieve 10lbs boost with the suggested % overdrive. My first blower was a 4-71 but that was a long, long time ago.

mike
1973 RS Z28: 401ci Dart Little M, Littlefield 8-71 supercharger @14lbs boost, Callies Magnum crank, Lunati rods, JE pistons, 7.8:1, AFR 227 Comp heads, T&D 1.6 shaft rockers. Reed solid FT cam (240/250@.050-.523/.542 lift-112 LSA), QFT 750 carbs
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Postby BrazilianZ28Camaro » Sun Oct 04, 2009 9:39 pm

Tokyo Torquer wrote:
.. I have lots of resources here to calculate boost for any size roots blower on any engine as well as the BDS and Dyers reference charts.. they all say that you can achieve 10lbs boost with the suggested % overdrive. My first blower was a 4-71 but that was a long, long time ago.

mike


Mike I was thinking hard anodize the rotors and case to tight up the blower clearances a little...

You think that would help??
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Postby Tokyo Torquer » Sun Oct 04, 2009 9:47 pm

stripping the rotors will help, but it wears out eventually. the tighter the clearance the more boost you make. teflon strips get you very tight bit wear the fastest. Nylatron doesnt wear as fast, but still wears out. cant say if the hard anodizing is the way to tighten up clearances.
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Postby BrazilianZ28Camaro » Sun Oct 04, 2009 10:14 pm

Tokyo Torquer wrote:stripping the rotors will help, but it wears out eventually. the tighter the clearance the more boost you make. teflon strips get you very tight bit wear the fastest. Nylatron doesnt wear as fast, but still wears out. cant say if the hard anodizing is the way to tighten up clearances.


What rotor/rotor and rotor to case clearance is aceptable to that little blower to work fine?

Hard anodizing can add about .004" to the rotor diameter, thus reducing the clearances...

Thanks for replies
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Postby Baprace » Tue Oct 06, 2009 3:01 am

BrazilianZ28Camaro, you need disimilar materials to run clearances that may touch, aluminum rotors and magnesium case work well together, a rotor that has teflon strips in it will take up the clearance problems.
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Postby stealth » Tue Oct 06, 2009 1:39 pm

Are you sure your 100 octane is the same as the US 100 octane? Different counties measure it differently. Some do and average, some do other things...

just so you know what your actually dealing with.
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Postby ap72 » Tue Oct 06, 2009 2:00 pm

If you only want 500hp you can get there with 10psi or less, it becomes VERY dependant o the rest of your engine combo. A box stock 327 will need a lot more than one that has been thuroughly warmed up. You mentioned that imported parts cost a lot- which sucks- but you are not restricted in that manner to local machine work. Find a competent machinist and get your 327 in top notch condition then boost it. A great porting job can do a lot for you, and the exhaust you run can affect boosted power in a BIG way. If you can build a 9:1 327 that puts out 400hp NA then getting 500hp with 10psi should be pretty simple. And a 400hp 327 is not that hard to do- even with mostly stock parts.

It sounds like you listed a lot of good parts but you don't need to be spending all of that money, you don't need half of the parts you listed to hit 500hp, I would instead maybe look at buying a 6-71 in place of your 4-71.
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Postby BrazilianZ28Camaro » Tue Oct 06, 2009 11:56 pm

Baprace wrote:BrazilianZ28Camaro, you need disimilar materials to run clearances that may touch, aluminum rotors and magnesium case work well together, a rotor that has teflon strips in it will take up the clearance problems.


Yes, sure, the idea was reduce the clearances to a good level with out the rotors touching the case...

I heard that 471 blowers have as much as .012" rotor to case clearances..seem a little on the high side... :roll:

Teflow strips would be perfect, but is difficult to install..

Thanks for reply.
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