how much cfm in a carb should I be looking for?

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Jonathan

Jonathan

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Hi. I have a 74 plymouth duster. I'm getting ready to put a rebuilt stroker 360 . 450 hp in. I have 3/8 Fuel line , new holley diaphram pump and an edelbrock 600 cfm carb on it from my old 318 that was in car.would that b enough cfm for my build? Or will it b looking for more fuel? (Cfms)? Any experience or advice would b apriciated. :glasses7:
 
2 cfm per HP........I would run a 850 on that minimum if you are truly 450HP
 
Street or strip, that is the question!
Street, 750
Strip, 850/950.
 
wade said:
so if im making 550+ with my wilson 750dp i should upgrade?
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2x hp is a rule of thumb better than that old formula that makes everyone afraid of running more than a 500 cfm carb :)

If you really want to know. See how much vacuum your pulling at full throttle at load, 4bbl carbs are rated at 1.5 vacuum
And if your after every ounce of hp you want to be .5-1 vacuum don't know how much that would affect daily driving. Make sure it's the carb not the breather thats the restriction.
 
bbrroowwnn said:
2 cfm per HP........I would run a 850 on that minimum if you are truly 450HP
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RPMagoo said:
2 X Cubic Inches, is a good general rule.
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rumblefish360 said:
Street or strip, that is the question!
Street, 750
Strip, 850/950.
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Agreed x3.
one caveat---
Jonathan, as already mentioned, where did the 450 hp number originate?
 
That rule of vacuum, the .5 is for wide open throttle. Having a higher reading isn't the worlds end. It is a siignal that the engine would like a larger carb. it is not needed for the street.
 
engine size x desired RPM then divide by 3456

pick carb that is close to that size. add 25% for race setup
 
I used a 750 hp double pumper built by Patrick James at pro systems
Engine builder had it built for my 340
Engine has not been on Dyno but makes easy 400 hp
 
double pumpers are available from 600 to 850 at 50 cfm spacing..
 
MRL Performance said:
850 carb for 450hp is to big. with that way of picking a carb, a 525hp engine would need a 1050 dominator! that's nuts.
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Ok , lets use your own formula.....he said 360 stroker so probably 4 inch arm so say 408 cu in.....say max RPM he wants is 7000 / 3456 = 826.39 Seems to me 850 is right on the money...not too big even using your own formula...and you say add 25% for race application is another 206 cfm is 1026CFM for a 408 stroker whats up with that? So a 1050 Dominator you are saying should be OK for his 408 twisting 7000 RPM in a race application and wait, he only has 450 horsepower? You said it was too much for a 525 HP engine
 
bbrroowwnn said:
Ok , lets use your own formula.....he said 360 stroker so probably 4 inch arm so say 408 cu in.....say max RPM he wants is 7000 / 3456 = 826.39 Seems to me 850 is right on the money...not too big even using your own formula...and you say add 25% for race application is another 206 cfm is 1026CFM for a 408 stroker whats up with that? So a 1050 Dominator you are saying should be OK for his 408 twisting 7000 RPM in a race application and wait, he only has 450 horsepower?
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It's because of the HP amount doesn't warrant so much carb.
 
bbrroowwnn said:
Ok , lets use your own formula.....he said 360 stroker so probably 4 inch arm so say 408 cu in.....say max RPM he wants is 7000 / 3456 = 826.39 Seems to me 850 is right on the money...not too big even using your own formula...and you say add 25% for race application is another 206 cfm is 1026CFM for a 408 stroker whats up with that? So a 1050 Dominator you are saying should be OK for his 408 twisting 7000 RPM in a race application and wait, he only has 450 horsepower? You said it was too much for a 525 HP engine
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Problem with formulas and rules of thumb is there just guide lines and usually fall apart at the extremes and most trickle down from racing which don't care about driveablity and durability.
 
950 holley...work great on our 360s...probably dont have more then 450 hp either
 
Jonathan said:
edelbrock 600 cfm carb on it from my old 318 that was in car.would that b enough cfm for my build? Or will it b looking for more fuel? (Cfms)? Any experience or advice would b apriciated. :glasses7:
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Hell no is the short answer. More CFM is more AIR, not more fuel, and yes it
will need way more than 600. Street car I'd use a 770 street avenger, if you're set-up
for a max 1/4 mile effort maybe a 800DP carb, but as mentioned where did the 450 hp #
originate? Was this a package stroker that was rebuilt, 408, etc.????What heads???
I've made 440hp on a VS750 holley for the street, but You haven't given enuf
details to gauge the engines potential,and poss. appetite for atmosphere.
 
Whoa, 7000 in a stroker? Whoo hoo! 63-70mm throttle body and buy injectors for estimated HP...36lb-ers. Some on this forum have run huge carbs on hot small blocks and say they work better than the generic 750 3310.
 
For your average street car it is hard to beat a 750 vacuum secondary.If it is a stick car(or higher stall) and has lower rear gears then a double pumper is usually more consistent and can be quicker at the track.The newer HP carbs with the contoured air entry flow more than advertised in most cases.

A 408 stroker would be a minimum of a 750 if it were mine.
 
MRL Performance said:
850 carb for 450hp is to big. with that way of picking a carb, a 525hp engine would need a 1050 dominator! that's nuts.
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That's what I was thinking. I have the Mopar Small Block Stroker book and it provided the engine you showed above. When IMM built my 408, their intentions were to throw on a 750 onto it. It didn't make enough power so Brian threw on an 850. It makes 523 hp so idk how people are saying it needs double the horsepower rating. 7000 RPM for a stroker maybe? Mine stopped making power at 6000 rpm so why deal with the extra wear? At 6500 rpm, using the equation provided by MRL, I got 767 CFM's.
 
I'm using a mechanical 6 pack with a true 1050 or so CFM, on a 360 with a 4,400 stall 3.55 gear. Runs stronger than my old 750dp on a single plane. I have right around 400hp. I think a 950hp would be perfect street or strip.
 
70aarcuda said:
950 holley...work great on our 360s...probably dont have more then 450 hp either
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I have a 410 smallblock, it runs the best on the street with a old school 850 DP. I have tried and tuned a wide varity of carbs on this engine. It makes a REAL 460 HP, not some "dyno corrected" BS horsepower. That's my experience on the subject.
 
MuuMuu101 said:
That's what I was thinking. I have the Mopar Small Block Stroker book and it provided the engine you showed above. When IMM built my 408, their intentions were to throw on a 750 onto it. It didn't make enough power so Brian threw on an 850. It makes 523 hp so idk how people are saying it needs double the horsepower rating. 7000 RPM for a stroker maybe? Mine stopped making power at 6000 rpm so why deal with the extra wear? At 6500 rpm, using the equation provided by MRL, I got 767 CFM's.
Click to expand...

If you put a bigger carb on it and the HP numbers went up it obviously needed more CFM....If you ran the 750 you would have left HP on the table and never knew it
 
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