Carb size suggestion
10-11-2012, 07:31 PM
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Carb size suggestion
I am in looking to install 2 carb on the top of my B&M 250 blower on my 454ci .030 oversize. What can be the best size between 2 x 750 or 2x 850 cfm carb for my engine for best max power. How to know if carb choice is not too big?
IMO i think 2 x 750 cfm carb is plenty enought but i need to know what is the effect between the right carb size and a too small or a too big carb?
Any help would be great.
IMO i think 2 x 750 cfm carb is plenty enought but i need to know what is the effect between the right carb size and a too small or a too big carb?
Any help would be great.
10-11-2012, 09:05 PM
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10-12-2012, 03:12 PM
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11/2/2011 – A/F with Jets of 78 & 85 6.5 PV . Wieand 250 super charger with dual Holley 750 carbs each motor. # 28 Bravo 1’s prop
382 Formula ( Non FASTEC) 62 degree day 48% RH calm water
Bravo XR 1.5 drive. Timing 29 degrees total, Idle rpm 1,000
RPM MPH Boost Vac #1 Vac #2 Stb Eng Port Eng EGT
3000 36 0 6
4000
5000
382 Formula ( Non FASTEC) 62 degree day 48% RH calm water
Bravo XR 1.5 drive. Timing 29 degrees total, Idle rpm 1,000
RPM MPH Boost Vac #1 Vac #2 Stb Eng Port Eng EGT
3000 36 0 6
4000
5000
10-12-2012, 03:19 PM
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Whoops not done
540 cid AFR aluminum heads – Jets of 78 & 85 6.5 PV . Wieand 250 super charger with dual Holley 750 carbs each motor. # 28 Bravo 1’s prop
382 Formula ( Non FASTEC) 62 degree day 48% RH calm water
Bravo XR 1.5 drive. Timing 29 degrees total, Idle rpm 1,000
RPM MPH Boost Vac #1 Vac #2 A/F Stb A/F Port EGT
1000 0 0 14 13 11.4 11.8 550
3000 36 6 6 11.8 12.0 1,200
4000 58 0 0 0 11.9 12.3 1,390
5000 72 4 0 0 12.3 12.4 1,410
540 cid AFR aluminum heads – Jets of 78 & 85 6.5 PV . Wieand 250 super charger with dual Holley 750 carbs each motor. # 28 Bravo 1’s prop
382 Formula ( Non FASTEC) 62 degree day 48% RH calm water
Bravo XR 1.5 drive. Timing 29 degrees total, Idle rpm 1,000
RPM MPH Boost Vac #1 Vac #2 A/F Stb A/F Port EGT
1000 0 0 14 13 11.4 11.8 550
3000 36 6 6 11.8 12.0 1,200
4000 58 0 0 0 11.9 12.3 1,390
5000 72 4 0 0 12.3 12.4 1,410
10-12-2012, 04:38 PM
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The size of carb(s) or CFM required for a given application can be calculated by the following formula A: {(CID x RPM) ÷ 3456} x {Boost ÷ 14.7) + 1} = CFM required. The amount of CFM required will determine carburetor size and quantity. If you try to use a carb with less CFM than required, performance and economy may be greatly reduced. Bigger is not always better when selecting carbs that are 30% over what is required, you may encounter problems in fuel distribution
That is a quote from BDS website. Using that calculation, if you wanted enough carb to feed a 460 Inch motor, at 6000RPM, lets say running 7lbs of boost. You will need 1,174 CFM. If you wanted to go 25% larger, which is fine on a roots setup, thats 1467CFM. A pair of 750's would work great(1400CFM).
BTW, in my master holley catalog, they have carbs recommended for certain setups. For example, 871 blower on a small block chevy, recommended carbs are twin 750's. 871 on a big block chevy, recommended carbs are twin 850.
On top of the blower, the carbs are a source of gas and air. the blower works better with no air restriction to draw thru. Kind of why a 1000HP roots blown setup you'll see twin 1050 Dominators feeding the engine, and a 1000HP blow thru procharger it will have a single 800 carb. You wouldnt want to take the big air inlet on the procharger, and say ''Its to big, I wanna close this opening up and restrict some airflow''. Same idea somewhat.
That is a quote from BDS website. Using that calculation, if you wanted enough carb to feed a 460 Inch motor, at 6000RPM, lets say running 7lbs of boost. You will need 1,174 CFM. If you wanted to go 25% larger, which is fine on a roots setup, thats 1467CFM. A pair of 750's would work great(1400CFM).
BTW, in my master holley catalog, they have carbs recommended for certain setups. For example, 871 blower on a small block chevy, recommended carbs are twin 750's. 871 on a big block chevy, recommended carbs are twin 850.
On top of the blower, the carbs are a source of gas and air. the blower works better with no air restriction to draw thru. Kind of why a 1000HP roots blown setup you'll see twin 1050 Dominators feeding the engine, and a 1000HP blow thru procharger it will have a single 800 carb. You wouldnt want to take the big air inlet on the procharger, and say ''Its to big, I wanna close this opening up and restrict some airflow''. Same idea somewhat.
10-12-2012, 09:35 PM
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The size of carb(s) or CFM required for a given application can be calculated by the following formula A: {(CID x RPM) ÷ 3456} x {Boost ÷ 14.7) + 1} = CFM required. The amount of CFM required will determine carburetor size and quantity. If you try to use a carb with less CFM than required, performance and economy may be greatly reduced. Bigger is not always better when selecting carbs that are 30% over what is required, you may encounter problems in fuel distribution
That is a quote from BDS website. Using that calculation, if you wanted enough carb to feed a 460 Inch motor, at 6000RPM, lets say running 7lbs of boost. You will need 1,174 CFM. If you wanted to go 25% larger, which is fine on a roots setup, thats 1467CFM. A pair of 750's would work great(1400CFM).
BTW, in my master holley catalog, they have carbs recommended for certain setups. For example, 871 blower on a small block chevy, recommended carbs are twin 750's. 871 on a big block chevy, recommended carbs are twin 850.
On top of the blower, the carbs are a source of gas and air. the blower works better with no air restriction to draw thru. Kind of why a 1000HP roots blown setup you'll see twin 1050 Dominators feeding the engine, and a 1000HP blow thru procharger it will have a single 800 carb. You wouldnt want to take the big air inlet on the procharger, and say ''Its to big, I wanna close this opening up and restrict some airflow''. Same idea somewhat.
That is a quote from BDS website. Using that calculation, if you wanted enough carb to feed a 460 Inch motor, at 6000RPM, lets say running 7lbs of boost. You will need 1,174 CFM. If you wanted to go 25% larger, which is fine on a roots setup, thats 1467CFM. A pair of 750's would work great(1400CFM).
BTW, in my master holley catalog, they have carbs recommended for certain setups. For example, 871 blower on a small block chevy, recommended carbs are twin 750's. 871 on a big block chevy, recommended carbs are twin 850.
On top of the blower, the carbs are a source of gas and air. the blower works better with no air restriction to draw thru. Kind of why a 1000HP roots blown setup you'll see twin 1050 Dominators feeding the engine, and a 1000HP blow thru procharger it will have a single 800 carb. You wouldnt want to take the big air inlet on the procharger, and say ''Its to big, I wanna close this opening up and restrict some airflow''. Same idea somewhat.
Is that the calculation is good for all blower size?
