What size carb?
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What size carb?
I have a 77 ford f150 that is strictly a mud bog (race) truck. It has a 466 with 12.5 to 1 compression, C9VE-E heads fully ported and polished with 2.25int/1.76 Ferrea Stainless Steel valves. The cam is a lunati solid cam with .557/.572 lift & 305/310 ADV duration 237/247 duration at 50. Weiand stealth intake, msd 6a , mallory unilite dizzy.
The question is I have an 850 holley dbl pumper on the engine right now. I was wandering if I might need to go to a bigger carb like a 950 or a 1050?
The question is I have an 850 holley dbl pumper on the engine right now. I was wandering if I might need to go to a bigger carb like a 950 or a 1050?
Post Fiend
Joined: Mar 2004
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From: Union, Washington
Carb size is dependent on many things, but primarily CID and RPM. Holley says this about it.
"You take the engine cubic inch and multiply by the maximum RPM and divide by 3456."
For a true race motor you can go 10% to 20% over this recommendation.
"You take the engine cubic inch and multiply by the maximum RPM and divide by 3456."
For a true race motor you can go 10% to 20% over this recommendation.
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Does the compression ratio have any factor in the carb size. I also had a race this past weekend. I was having trouble half way down (100') the track (250') , my truck was maxed out at 6000 rpm and it seemed like I was starving the motor for fuel.
Post Fiend
Joined: Mar 2004
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From: Union, Washington
Compression has nothing to do wih it. You need to look up the specs on the cam and see what the manufacturer say the RPM range is. The cam can do what yoiu are describing.
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The operating range on my cam is between 3000 and 6500. I used the formula in your post CID (466) x RPM (6500) divided by 3456 = 876 cfm that is about what I have now. Add 10% it shows 950, add 20% it shows 1050. So by using the formula my motor could use a bigger carb like the 950 or the 1050.
Somebody correct me if I am wrong.
Somebody correct me if I am wrong.
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I have a 77 ford f150 that is strictly a mud bog (race) truck. It has a 466 with 12.5 to 1 compression, C9VE-E heads fully ported and polished with 2.25int/1.76 Ferrea Stainless Steel valves. The cam is a lunati solid cam with .557/.572 lift & 305/310 ADV duration 237/247 duration at 50. Weiand stealth intake, msd 6a , mallory unilite dizzy.
The question is I have an 850 holley dbl pumper on the engine right now. I was wandering if I might need to go to a bigger carb like a 950 or a 1050?
The question is I have an 850 holley dbl pumper on the engine right now. I was wandering if I might need to go to a bigger carb like a 950 or a 1050?
Last edited by tenforty_2; Apr 20, 2009 at 01:19 PM. Reason: added more
Post Fiend
Joined: Mar 2004
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From: Union, Washington
The question would be, How many RPM is the motor turning when it rolls over and goes flat? If it is above 6500, then it is the cam. If it is doing this below 6500 I would suspect fuel starvation rather than not enough carb. FYI, for street motors you drop whatever CFM number you come up with by 20%. With a race motor and especially your's, that you need some mid range power I would go no bigger than a 950 and would lean more towards a 900. Overcarburation kills a motor's low end and can make a motor sluggish in the mid-range.
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the motor falls on its face right about 6000 maybe a little less. It has a 1.5 open spacer. Would the jets or the power valve have anything to do with it?
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Post Fiend
Joined: Mar 2004
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From: Union, Washington
It very well could. You need to do a test run and when it falls on it's face, just turn the key off without releasing the throttle. Then pull the plugs and look at them. If they are not a nice chocolate brown on the insulator tip, you need more jet. That is unless they are black, which is to rich. Very unlikely, BTW. What is the number on your power valve? What kind of fuel are you running?
Post Fiend
Joined: Mar 2004
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From: Union, Washington
I would chang the power valve to one of the High-flow ones and change to an 8.5 or even a 9.5. Like this one.
Holley Performance Products Single-Stage " High Flow" Power Valve 125-185
Holley Performance Products Single-Stage " High Flow" Power Valve 125-185
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