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Old 03-15-2011, 07:02 AM
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B&M 250 blower on a 396 ?

I have a B & M 250 blower, which I thought to use on a chevy 396 engine. I have some questions about carb choices and cams.the heads on the engine are merlin, 1-043c casting number. match two Edelbrock 1407 carbs good? or is it best to run with one big carburetor?, camshaft fit best on this engine to get the most power?

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Old 03-15-2011, 10:48 AM
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The engine must have a low compression ratio to run with a blower on available pump gas. Th edelbrock carbs are fine. They will need some modification to run on the blower. Two carbs is way better than 1 on a blower. Find a cam with 242-250 @.050" wider 112-114LSA .500 to .600" lift Solid cams work the best on BBC's.
The good old factory 396-375 L-78 ls6 454-450hp cam 242 242 .520 .520 114 is sweet with a blower on the street.

If your 396 has big domed pistons its not going to work on pump gas.
You want 8.5;1 or less. less is better. 7.5:1 is ideal.

396 blower cams
www.cranecams.com
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Old 03-15-2011, 12:34 PM
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edelbrock carburators

thanks! what modifications must Edelbrock 1407 carburetors have to work on the blower?
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Old 03-15-2011, 02:09 PM
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Quote:
Originally Posted by rumo
thanks! what modifications must Edelbrock 1407 carburetors have to work on the blower?
In the owners manual to the carb , they explain what needs to be done. You'll need to change out the jets, needles and possibly the springs. Edelbrock recommends 1405's for blowers up to 6-71

Edelbrock Carb Owners Manual
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Old 03-15-2011, 04:57 PM
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Besides that stuff, you need to modify the path internal vacuum passage for the power enrichment piston so it is external so the power piston (that works the primary metering rods ( rich power when up .. lean cruise when down in the jet) works off intake manifold vacuum below the blower.

If you don;t do this mod the metering rods won;t work right according to engine throttle load, the motor will go lean under power at WOT.
It will burn up the motor. A little drilling and epoxy rework gets it done.

If you were to flip the carb over and look at the base and find the vacuum passage that goes up the two power pistons, you will see what has to be done. you need to create another vacuum nipple on the carb base and connect it to that power piston vacuum signal passage.
You can also fabricate a carb spacer with a external boost reference vacuum port on it to connect the carbs power pistons to the intake manifold vacuum below the blower. Starting with a 4 hole carb spacer.

Its refered to as boost referencing the power piston (power valve for holley carbs) Look at the base of the carb, you`ll figure it out.

The 1405 500cfm carbs are too small. The edelbrock recomendations are non specific-generalized for dual quad applications. Blowers need big carbs. use the 750`s
The 500-600cfm carbs are too small for roots blower applications that actually have to make any horsepower.
most all of the dual quad carb applications like the tunnel ram and the new RPM dual quad manifolds work much better with the 750cfm carbs, unless its a very low horsepower near stock motor and you just want the looks of a dual quad setup.

Last edited by F-BIRD'88; 03-15-2011 at 05:16 PM.
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Old 03-15-2011, 11:57 PM
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Definitely run two fours, not a single, on the 250 blower. While my engine is a 350 SBC, and not a BBC, I tried repeatedly to run a single 850 cfm Edelbrock atop a 250 with poor results. I did that because i successfully had run on both the street and drag strip a single 850 atop a smaller Holley/Weiand 144/142 blower. While the 250 is roughly equivalent to a GMC 4:71 in swept volume, the blower case of the 250 is much lower and much longer. The result is that, whether using the Weiand/Holley center mount for a single four, or the forward single carb mount for marine use, the longer, lower blower case starves the front cylinders for fuel, risking detonation and substantial engine damage. We know this from a dozen engine dyno runs as I tried repeatedly to run a single large four barrel on a 250, and found nothing but problems. Cylinders 1/2/3 always ran 200 degrees hotter than all other cylinders with a single carb. Going to two fours, two boost referenced 600 cfm Holleys in my case, evened out the cylinder temperatures and with that, reduced the potential for detonation.
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Old 03-16-2011, 10:56 AM
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thanks for all the details, is it some pictures of the modification of the Edelbrock carburetor when it is used on the blower?
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Old 03-16-2011, 11:54 AM
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No I don;t have any pictures for you.
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Old 03-18-2011, 02:27 PM
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carburator plate

hey, does anyone know where I can buy a Super Charger Adapter Plate, 2-4V 250, part number Weiand 93151 - Weiand Carburetor Sealing Plates?
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Old 03-18-2011, 07:10 PM
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Summit Racing carries Weiand part 93151 listed at $ 239.95 US.
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