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Old 11-07-2009, 09:00 AM   #1
DTPerformance
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Default Blower Carb question

Im putting a BDS 671 blower on my BBC. I have had several Roots style blowers and always just put regular holly carbs on them and never really had an issue. My question is what is the differance with buying carbs "blower carbs" from like BDS ect from a reg holly on a roots blower?

Also what size carbs should I use. Its a 468, AFR 325 heads, jessel rockers, 8.5 to 1 stock block, blower cam motor and im going to put about 10-12 pounds on it (shooting for 700-800) and turn it no more than 65-6700

I have one brand new 950 HP and was wondering if I just got one more if that would be to much.

Thanks for any help
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Old 01-14-2010, 01:48 AM   #2
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Default Re: Blower Carb question

My BG 750 blower carbs are boost referenced. I pick up boost off the boost gauge line, ran to each carbs base plate on the primary side. There are no PV's on the secondary side, and I run 75 pri jets/85 secondaries.

I made three passes in a blown SBC, hotlapping, without the boost line plumbed, third run I ruined the engine, detonation, lean, aggressive timing.

I've heard people say boost referencing is a myth. BG tech says different.
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Old 01-14-2010, 10:57 AM   #3
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Default Re: Blower Carb question

I never boost reference mine, just plug the power valves, and up the jetting approx 10% over stock jetting, maybe some more squirter, never had any problems. Probably done 10 or 14 motors.I dont like adding additional lines with the boost reference.
Hard to over carb a roots, I'd run the 950's
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Old 01-14-2010, 12:30 PM   #4
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Default Re: Blower Carb question

After over a hundred pulls the stock 3310 vacuum opening carbs are very good with .035 shooters and converted to secondary #78 jets,Holley supercharge carbs are REAL rich and are very low on power. I have tried 950 hp's and they were good on a all out SBC-421...I have tried Boost ref. power valves and have found they open to early and at 10% overdrive they don't ever close...Oldhead
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Old 01-14-2010, 03:15 PM   #5
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Default Re: Blower Carb question

I did like Shawn said , just plugged the power valves and stepped the carbs up 10 jet sizes. Fired the motor up and glowed the headers bright orange inside of 30 seconds. Stepped the carbs up 10 more jet sizes and found a good starting point. I didnt even know about boost referencing and since I learned about it I have not run the motor.
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Old 01-15-2010, 07:16 PM   #6
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Default Re: Blower Carb question

I found out years ago when I was running a roots a carb is like a governor to the blower. The bigger the carb the better the blower breaths and the more efficient the blower is. Block off the PVs and jet up.
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Old 01-16-2010, 09:45 AM   #7
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Default Re: Blower Carb question

Ok, after reading this, I have questions.
I'm about to build a 496, 8.75:1, aluminium square ports with a 6-71 Weiand.
While looking for a pair of carbs, I came across a freshly rebuilt set of blower calibrated Holley 850 double pumpers for a really good price, so I scooped them up.
This is for a street driven car, but of course, I want all the power it can make.

Is there a downfall to the blower calibrated carbs, or is there something that I need to do, to use them effectively?

Thanks in advance.
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Old 01-16-2010, 11:37 AM   #8
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Default Re: Blower Carb question

Quote:
Originally Posted by 2 Windows View Post
Ok, after reading this, I have questions.
I'm about to build a 496, 8.75:1, aluminium square ports with a 6-71 Weiand.
While looking for a pair of carbs, I came across a freshly rebuilt set of blower calibrated Holley 850 double pumpers for a really good price, so I scooped them up.
This is for a street driven car, but of course, I want all the power it can make.

Is there a downfall to the blower calibrated carbs, or is there something that I need to do, to use them effectively?

Thanks in advance.
In your case, the carbs won't be the limiting power maker, the blower will.
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Old 01-17-2010, 08:23 PM   #9
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Default Re: Blower Carb question

Thanks for all the advice and replies.
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