871 Supercharger Street set-up when trans is in overdrive?!? - Team Camaro Tech
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post #1 of 5 (permalink) Old Jul 7th, 15, 05:02 AM Thread Starter
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871 Supercharger Street set-up when trans is in overdrive?!?

OK so I had a random thought yesterday. I want to build a BBC with an 871 BDS or Weiand Supercharger. The only manual trans that I can find to fit my application correctly would be the T-56 Magnum for my gearing and torque specs. I posed this question to BDS, Weiand, my machine shop and even Tremec and everyone has concerns but no one actually has a feasible answer to this question. Obviously a supercharger thrives on rpms to make boost.....well what happens when I hit 5th or at worst 6th gear and the rpms drop that significantly? Will the motor just load up in overdrive? Have any of you had a set-up like this for the street? Thanks
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post #2 of 5 (permalink) Old Jul 7th, 15, 07:20 AM
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Re: 871 Supercharger Street set-up when trans is in overdrive?!?

Will not be a problem.

The BBC will cruise along just fine at the lower rpms of 5th and 6th. You'll just need to determine what rpm the motor likes. As with any set up if you accelerate from the lower rpm in OD you will need to downshift.

I would chose a rear end gear that will enable you to use 6th. My last car built LS7 T56 with 3.50s and 26" tires only liked 6th above 90-100 mph. I usually cruised at around 80 mph in 5th. I'm going 3.70s in my new car with the T56 Magnum close ratio.
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post #3 of 5 (permalink) Old Jul 7th, 15, 08:56 AM
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Re: 871 Supercharger Street set-up when trans is in overdrive?!?

I have 3.9 gears with a 6th gear of .5. I can use 6th above 60 but that is a little above an idle 1700 rpm at 70 mph. Mine is a 496 with a Procharger. Tires are 275-60-15.
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post #4 of 5 (permalink) Old Jul 7th, 15, 10:07 AM
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Re: 871 Supercharger Street set-up when trans is in overdrive?!?

I am running a small 144 blower on a .060 over 400 small block in my '65 chevy van. Smaller blower, but same general concept. With a roots blower, it is only making boost when the throttle is open. During cruise on the freeway, the throttle blades are only open just a slight bit, so you are not cruising in boost. The blower is simply going along for the ride, not in boost, and the engine is pretty much acting normally until you put your foot down, then it will go into boost. As long as you are simply cruising with light throttle, the engine is actually pulling a vacuum like normal. This is why superchargers are so steerable, because the boost is there when you put your foot down, but during light throttle periods, your engine acts normally.

The important thing here is that you ask me what kind of car I've got. "I've got a BITCHIN' CAMARO"
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post #5 of 5 (permalink) Old Jul 8th, 15, 05:50 AM Thread Starter
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Re: 871 Supercharger Street set-up when trans is in overdrive?!?

Thanks for the input guys!
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