Carb questions
Thread Starter
Pro
Joined: Jun 2000
Posts: 663
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From: Denham Springs Louisiana
Carb questions
Why do magazines suggest a holley 750 double pumper on every 350 build up? I have a Speed Demon 750 right now that I can't seem to lean out. The next set of jets I try this weekend will be the smallest I have (64's). I have tuned on this thing quite a bit and it still runs rich. The cfm calculaters I have found throughout the internet suggest I need a 650cfm carb. 700cfm max. (383ci,6000rpm,100%VE) My setup is hotter than most small block buildups in magazines yet they always seem to need a bigger carb? Am I missing something?
I am looking at Holley's 650 HP pro series carb right now. $581.99
Jegs part #:510-O-80541-1 650 cfm, Progressive Mechanical Secondaries, Double 30cc accelerator pumps, Gasoline
Is this the best street/strip carb for me. The car sees the strip once a week and street driven everyday.
The weather here is usually hot and humid. I live in near sea level altitude. I want 11s!
Comments appreciated.
:seeya
I am looking at Holley's 650 HP pro series carb right now. $581.99
Jegs part #:510-O-80541-1 650 cfm, Progressive Mechanical Secondaries, Double 30cc accelerator pumps, Gasoline
Is this the best street/strip carb for me. The car sees the strip once a week and street driven everyday.
The weather here is usually hot and humid. I live in near sea level altitude. I want 11s!
Comments appreciated.
:seeya
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Carb questions (KNEVER)
The reason is you get more HP at WOT with more CFM on a dyno. They never mention how it will drive.
I also have a 750 Demon and was able to really dial it in for my application. Demons have a very rich idle system. So to get it where the four corner adjusters are all out @ 1 1/2 turns I drilled a 1/8th inch hole through each pri. throttle blade @ 1/4 inch from engine front edge. This is a very comon mod for all Holley type carbs.
Your primary jetting has nothing to do with the idle cuircut. Stock jetting was 76 and 83 I think. mine really ran good with 72 and 82 with 6.5 power valves that it came with. The stock squirter hole dia. .035 and I went to .044 because of a when you foor it idling down the road it had a hessitation.
So drill some holes and install 72/82. I have talked to people with oxy sensors and they would end up with 71/82's but my plugs would turn pure white on a freeway run.
I believe that any carb can be mastered. I have since moved to a 825 cfm race Demon and it runs nice with 74/83 on my 383. More dyno HP :lol:
It has some off idle issues yet but it really seems to come alive over 6000. I might revert back to 750 since I only street drive.
I also have a 750 Demon and was able to really dial it in for my application. Demons have a very rich idle system. So to get it where the four corner adjusters are all out @ 1 1/2 turns I drilled a 1/8th inch hole through each pri. throttle blade @ 1/4 inch from engine front edge. This is a very comon mod for all Holley type carbs.
Your primary jetting has nothing to do with the idle cuircut. Stock jetting was 76 and 83 I think. mine really ran good with 72 and 82 with 6.5 power valves that it came with. The stock squirter hole dia. .035 and I went to .044 because of a when you foor it idling down the road it had a hessitation.
So drill some holes and install 72/82. I have talked to people with oxy sensors and they would end up with 71/82's but my plugs would turn pure white on a freeway run.
I believe that any carb can be mastered. I have since moved to a 825 cfm race Demon and it runs nice with 74/83 on my 383. More dyno HP :lol:
It has some off idle issues yet but it really seems to come alive over 6000. I might revert back to 750 since I only street drive.
Thread Starter
Pro
Joined: Jun 2000
Posts: 663
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From: Denham Springs Louisiana
Re: Carb questions (gkull)
Thanx gkull, I'm gonna take your advice and put the 72/82's in and drill those holes. I am new to tuning carbs as you can probably tell. I will probably be back on here with some more questions later. :chevy
Melting Slicks
Joined: Sep 2000
Posts: 3,099
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From: PITTSBURGH PA
Cruise-In IV Veteran
Cruise-In V Veteran
Re: Carb questions (KNEVER)
honest you cant go wrong with a 750 cfm vac i went from 1 to a trcked out carb shop 850 dp flowing something like 950 cfm and picked up just 1 tenth save your money ps the car was no slouch it was a 10:80 car in the quater :cool:
Thread Starter
Pro
Joined: Jun 2000
Posts: 663
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From: Denham Springs Louisiana
Re: Carb questions (gkull)
gkull: I drilled the 1/8" holes like you suggested. Then I swapped out the 69/83 jets for some 72/82 jets. Man, what a difference. Thanks a lot! I still have a slight hesitation off idle to WOT, but at least it isn't missing like it was. Do you think I should upgrade my squirters too? Or do I just need to play with the jets some more? Your engine combo is a little more extreme than mine if I remember correctly? Weren't you running some big dart heads and a solid lifter roller cam? If so wouldn't I need smaller jets than you? Thanks again, I'm new to tuning and this is starting to be fun.
