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Old 10-23-2003, 12:45 AM
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Blower carbs..what size and whats the difference

I have a few questions for any blower experts out there......

1st. I have a BBC 468 with an 8-71 blower. What size carbs are recommended??

2nd. What are the differences between standard naturally aspirated holleys and blower prepped holleys?

Thanks,
johnp

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Old 10-23-2003, 08:36 AM
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I'll bump you up. How about it blower guys?
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Old 10-23-2003, 08:44 AM
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There is a lot of info in the Knowledge Base.
http://hotrodders.com/kb/search.plTe...+carbs&match=1

If you can't understand the difference, when I get the time I will find the site, instead of trying to type it.
There is a different base plate for the carb for a blow thru and a few other things.
IM use to a blown injected alcohol motor, now injected Nitro.
LOL
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Old 10-23-2003, 11:37 AM
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Blower carbs with mechanical secondaries work best and typically don't have a choke. Specialty built blower carbs are set up to run 40 to 50% richer, the blower motor can easily require this much more air/fuel. Additionally the power valve in a normal carburetor is designed to provide fuel when no vacum is present at the carb base. With a blower there is always vacuum present, therefore blower carbs are designed with a boost referenced power valve system to compensate and make the carb 'act right'.

I'm ruing two BG 750 blower carbs on a SBC with an 8-71. Barry Grant tech guys are very helpful, give them a shout.
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Old 10-23-2003, 02:35 PM
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Okay 68Nova, got a question. I was always under the impression that in a drawthrough configuration the carbs acted in the normal fashion. It seems to me if the carbs are sized to feed the engine at full power, vacuum would be very close to what it would be in the NA setup. Also, PV is usually designed to open as vacuum drops below a certain point not at 0 vacuum. I have never setup a blower engine, but this just does not makes sense to me if we are talking draw through. Which is where we would be with an 8-71. Now Blow through is a whole other ball game.

Chris
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Old 10-23-2003, 03:07 PM
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You see a lot of 750s on the BBs i say the 750 HPs with no power valves and modify the secondary cams a bit to delay the opening? I run a set of 660s this way on a sbc 671 and they work very good.
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Old 10-23-2003, 08:57 PM
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Yes blower carbs need to be boost referenced because under
throttle they pull vary little vacuum. By being boost referenced
the boost opens the power valves. Also running to large a carb. is
worse than running one to small. By running one to large you get
to much air and not enough fuel. I will share this dyno story with you. I started out with 850's and after 7000 rpm pull and killing the engine it had a explosion in the headers, to much raw fuel.
Bought two new 1150's and installed them, made a couple more
pulls and to lean. Changed jets to 99 square and still to lean,
bought new metering blocks to accept power valves and boost
referenced the carbs, now the fuel curve is perfect. Hope this helps and was not to boreing. By the way this dyno was on my a
604 c i.
Loy
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Old 10-27-2003, 08:02 AM
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Blower carburetors should be mechanical secondary with 1:1 linkage to get the proper distrabution in the engine. We always run boost ref. PV's on a roots style blower. This lets the PV see what the vacuum is below the blower. You can run into situations at part throttle where you have no vacuum (or boost) below the blower, and still have vacuum between the top of the blower and your carburetor adapter. This will give you a lean situation.

Novawagon if you contact our technical department directly at www.barrygrant.com with a complete list of your engine, and drivetrain specifications we can let you know which carburetor(s) will work best for your application.
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Old 10-27-2003, 08:57 AM
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Quote:
Originally posted by Tech @ BG
Blower carburetors should be mechanical secondary with 1:1 linkage to get the proper distrabution in the engine. We always run boost ref. PV's on a roots style blower. This lets the PV see what the vacuum is below the blower. You can run into situations at part throttle where you have no vacuum (or boost) below the blower, and still have vacuum between the top of the blower and your carburetor adapter. This will give you a lean situation.

Novawagon if you contact our technical department directly at www.barrygrant.com with a complete list of your engine, and drivetrain specifications we can let you know which carburetor(s) will work best for your application.
Now that makes sense. Thanks for clearing it up.

Chris
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Old 10-27-2003, 12:45 PM
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Thank's Tech @ BG
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