whats the most you can overdrive a 671? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-15-2010, 08:07 AM
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whats the most you can overdrive a 671?

got a weiand 671 here on a built engine that would like to see ~25lbs of boost on, while running E85. Wondering how much I can overdrive the blower and have the boost still be effective and not too hot.

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Old 09-15-2010, 09:05 AM
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10-15 PSI is really the most you would ever need on a 6/71 blower... remember, that it was designed and sized to feed a 426 CID 6cyl diesel equally in volume ( diesels don't use superchargers to boost )... so that's a lot of air volume.
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Old 09-15-2010, 09:11 AM
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well the engine is built for 25psi, so I need to either see if I can overdrive this 671 enough to accomplish that or start looking for alternatives
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Old 09-15-2010, 09:51 AM
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buy a turbo then... the principals of forced induction are the same, except the turbo relies more on preassure and less on volume...

not sure why you would want to crank more preassure than you need to just because the engine is " built for 25 PSI ". which is what, a forged rotationg assembly/ O ringed block with copper gaskets?.. you will need at least that if you try to put a lot of boost thru a 6/71
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Old 09-15-2010, 09:58 AM
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Quote:
Originally Posted by matt167
buy a turbo then... the principals of forced induction are the same, except the turbo relies more on preassure and less on volume...

not sure why you would want to crank more preassure than you need to just because the engine is " built for 25 PSI ". which is what, a forged rotationg assembly/ O ringed block with copper gaskets?.. you will need at least that if you try to put a lot of boost thru a 6/71
The purpose of this thread was to see how much I could overdrive a 671. Not that I should only need 15psi, or I should get a turbo kit instead.
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Old 09-15-2010, 10:14 AM
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well, the efficiency range for a 6/71 is 8-12 PSI.
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Old 09-15-2010, 10:25 AM
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Quote:
Originally Posted by matt167
well, the efficiency range for a 6/71 is 8-12 PSI.
so after 8-12 psi the boost charge just gets too hot then?
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Old 09-15-2010, 10:51 AM
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weiand should be able to supply you with a blower curve if you ask for one- its pretty standard stuff.
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Old 09-15-2010, 10:58 AM
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Quote:
Originally Posted by turbolover
weiand should be able to supply you with a blower curve if you ask for one- its pretty standard stuff.
they told me to just keep the rpms of the blower under 13k...they seemed to not really be that helpful to be honest.

With the old stock 350 at a 12% overdrive i got 14lbs of boost. I can overdrive this blower up to like 70% from what the techs said, but that doesnt sound right to me.
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Old 09-15-2010, 11:06 AM
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That's about right, HOWEVER your heat will rise DRAMATICALLY, The heat will kill your engine and your blower, not the speed. The pressure/flow is outside its efficiency zone. Its not about the blower speed at all, if you overdrove it 70% on a 502 BBC it could survive (though it'd still produce a hell of a lot of heat, on a sbc the amount of heat generated from the boost is tremendous though. If you want that much boost you need to have some serious intercooling capabilities.
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Old 09-15-2010, 11:16 AM
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Quote:
Originally Posted by turbolover
That's about right, HOWEVER your heat will rise DRAMATICALLY, The heat will kill your engine and your blower, not the speed. The pressure/flow is outside its efficiency zone. Its not about the blower speed at all, if you overdrove it 70% on a 502 BBC it could survive (though it'd still produce a hell of a lot of heat, on a sbc the amount of heat generated from the boost is tremendous though. If you want that much boost you need to have some serious intercooling capabilities.
thats what I was getting at. I was trying to figure out the point on the 671 where its efficiency tapers off with how much its overdriven.
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Old 09-15-2010, 11:57 AM
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I could not imagine pushing 25lbs out of a 671. I would definately be concerned about the heat build up. This old style huffer is not inter-cooled, I would think things would start melting at that range. Pushing 25lbs will not be too efficient for this blower, (heat soak). To answer your question, it would not be wise, even on a forged bottom end....
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Old 09-15-2010, 12:26 PM
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Quote:
Originally Posted by Madmax305
I could not imagine pushing 25lbs out of a 671. I would definately be concerned about the heat build up. This old style huffer is not inter-cooled, I would think things would start melting at that range. Pushing 25lbs will not be too efficient for this blower, (heat soak). To answer your question, it would not be wise, even on a forged bottom end....
well thats where i would eventually like to end up at as far as boost goes...but that was the purpose of this post...to figure out how much the 671 can be overdriven without building up an excessive amount of heat. Boost is a restriction in the engine so its not an accurate number to go off since every engine is different, thats why I wanted to know what maxiumum rpm a 671 should be driven at before the boost charge gets too hot.
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Old 09-15-2010, 12:39 PM
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Quote:
Originally Posted by darkostoj
well thats where i would eventually like to end up at as far as boost goes...but that was the purpose of this post...to figure out how much the 671 can be overdriven without building up an excessive amount of heat. Boost is a restriction in the engine so its not an accurate number to go off since every engine is different, thats why I wanted to know what maxiumum rpm a 671 should be driven at before the boost charge gets too hot.

A large part of my job is specing pumps- for both gasses and liquids, and I can tell you boost is a HUGE part of it, ignore it and expect a failure, no matter what RPM the blower may be turning.

You can't run a stock 6-71 up to 25psi.
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Old 09-15-2010, 12:42 PM
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Quote:
Originally Posted by turbolover
A large part of my job is specing pumps- for both gasses and liquids, and I can tell you boost is a HUGE part of it, ignore it and expect a failure, no matter what RPM the blower may be turning.

You can't run a stock 6-71 up to 25psi.
everybody seems to be getting super confused here. I just wanted to know how much you can overdrive a 671 until the boost charge gets too hot...thats all. You guys are going to make me drill and tap the intake for an IAT here!
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