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

[stroked340]

Quickfuel 850 been running one on my 360 and 416 has performed flawlessly..too big not if you know how to tune properly..

 

[lilcuda]

The 427 stroker in my Valiant made 519 hp @ 5800 with a BLP 650 cfm carb.

 

[AJ/FormS]

I ran a little TQ on a mostly stock teener, a few years ago. I heard those were over-rated. It didn't take much to dial it in.
I have read that MRL formula before. Posted in HP books of the 60's to 90's. But I thought they used the rpm of peak hp x the VE x cid devided by 3456.

If that were true; then;.................guessing at the VEs;
(408 x 6000 x 1.05VE)/3456 = 744
(408 x 6000 x 1.00VE)/3456 = 708
(408 x 6000 x .95VE)/3456 = 673 or
(408 x 6500 x .90VE)/3456 = 690 or
(408 x 7000 x .85VE)/3456 = 702
and your stock teener might look like
(318 x 4800 x .80)/3456 =353cfm
So if you put a 800TQ which might be a 650(rated the Holley way) then 650 /353 is about 84% too big.IDK. It ran gangbusters.heehee

And a hot 360 might look like
(367 x 5800 x 1.05)/3456 = 647
(367 x 7000 x .88)/3456 = 654
I can tell you without hesitation, that the DP750 that has been on it for 12 years, is staying on it. So Ima gonna agree with cracked ; that the formula probably spits out a minimum cfm size.

 

[crackedback]

Formula says our old car should use a 650.

Every time a 100 cfm larger carb was put on the engine to a 1050, car picked up ET/MPH.

IMO, the formula is the way to pick the smallest carb size to run on an engine.

 

[496 polara]

My 496 (albeit mild) has run anywhere from a 750 vac sec,750 hp mech sec,850 mech sec,to a 950hp vac sec.With the exception of the 750 vac sec they all feel pretty close on the butt-o-meter.I prefer the 950hp vac sec as the car is heavy(4500lbs) and an automatic with a mild (2800) converter.The part throttle response seems cleaner.

 

[MRL Performance]

2 cfm per HP........I would run a 850 on that minimum if you are truly 450HP

I was going by this as you stated, 2cfm per HP. carb size is by CI vs RPM not how much power you think its going to make.

 

[rumblefish360]

Quickfuel 850 been running one on my 360 and 416 has performed flawlessly..too big not if you know how to tune properly..

Truly the key to it all no matter the cfm rating.

Formula says our old car should use a 650.

Every time a 100 cfm larger carb was put on the engine to a 1050, car picked up ET/MPH.

IMO, the formula is the way to pick the smallest carb size to run on an engine.

Track only car?

 

[bballfan1]

I have a 750 and 850 for sale. Pm if interested.

 

[crackedback]

Track only car?

Doesn't matter, track car, street car, the formula is not the definitive answer.
Every car I've had has done the same compared to that formula. The carb sizing was never the best for the numbers it spit out.

If you can't tune a carb, then go with the smallest one you can find. If you can competently tune a carb, going larger is not an issue. Along with the vacuum secondaries for auto cars, DP's for manual... total bs.

 

[273]

Like i said there just guide lines
Look at a 650 carb people will run it on a 200-400 hp engine. At the 2hp per hp that should be carbs from 400-800 cfm and look at the formula most sb would have to turn 6000 plus rpm to run a 650. Then there things like dual plane vs single duals need more carb cause all cylinders don't share the whole carb. Every time you see them do carb shoot outs the biggest almost always wins and just not peak but average but as size goes up gains gets smaller and smaller and says nothing about driveablity . On a full race car I'm sure a 1050 might add a few ET's.

 

[MRL Performance]

The formula gives you good starting point. Bigger is NOT always better. And yes you have to factor in the setup of the engine and car.

 

[273]

I was going by this as you stated, 2cfm per HP. carb size is by CI vs RPM not how much power you think its going to make.

Wouldn't going by hp be more accurate since say 400 hp is the same amount of fuel and air within a relatively small variable no matter if it's turbo 4 vs big block vs small vs supercharged /6 etc... ?

 

[273]

I think for street guys it's pretty simple mild 650 wild 750 crazy 850 plus. And for track guys measure and tests there's ton of carbs out there beg borrow or steel to find the best.

 

[rumblefish360]

Doesn't matter, track car, street car, the formula is not the definitive answer.

Well, I disagree. IMO, there is a big difference (or should be) between a street car and a strip car. It is not the formula I argue, just what would be best for the arena the car works or performs in.

If you can't tune a carb, then go with the smallest one you can find. If you can competently tune a carb, going larger is not an issue.

I believe that a carb to large for the given application will cause a few problems. The stock 318 engine probably won't like a 1050 on top while in rush hour traffic.

 

[crackedback]

I'm out, this is going the straw man route.

Go put a 1 barrel /6 carb on a pro stock engine, ridiculous.

 

[AJ/FormS]

I must say that I have always liked the response of a small primary carb,on any of my street SBMs. The TQ/Qjets boosters were fantastic.

OP, since you already have the 600, why not give it a try. It will be very nice up to 5000 or so;and that would be 46mph with 3.55s and 27inch tires, and a Torqueflite in Low. If/when it stops pulling hard just shift! and you will be back in action. At some point you might want to explore the top end, and that would be the time to upgrade.It's very easy to get into trouble,after 46mph, with a stroker and a fully functioning top end rush.Think of it as a sortof safety net, while you sort the car out.
IIRC many BBs came out with less than 600s

 

[leblanc]

Seems to me I saw a formula for figuring out CFM somewhere on the net.

 

[bbrroowwnn]

I'm out, this is going the straw man route.

Go put a 1 barrel /6 carb on a pro stock engine, ridiculous.

x2

 

[Hot Metal]

Well I can give you real track performance numbers, at least on my junk.......

10:1SCR 340, stock unported 2.02's, Strip Dominator, 850DP, + 2" open spacer, DC. 590" solid, 4200 verter, 4.30's, 10x28's, 1.75" chassis hdrs. I had a multitude of racers tell me the carb was too big, so 1 day I told them, ok, I'll show you lot, so I put on the 750DP that came with the car originally and jetted up some to make it fairer and it ran 2/10ths slower, same day/track/conditions. Its engine size/rpm to a point, I only revved it to 6300, more importantly its the use and everything else that it has, bigger was better for my set up.

In fact I have posted this before...........I made a further point by convincing a fellow racer with 215ci Buick (rover3500) cortina to try my 850 over his 600cfm, he went 2/10ths quicker....yes 3500cc, ok it was a stick car and he revved it but..................

 

[ir3333]

John (the poster) still hasn't told us what he's doing with the car.
If it's a street car.. a big,expensive carb to gain 2 tenths he'll never see is pointless.
i think the earliest 375 hp 440's may have had 600 or so cfm Carters
..and is it an estimated 450 hp?

 

[rumblefish360]

Exactly, though some will still argue how wrong you are by not putting an 850 or bigger carb on it.

 

[Hot Metal]

I posted actual real world information under race conditions with specific information on the car from which you either take something from or not. A Street car is a different animal and requires a different set up. Carb choice is down to USE, Heads/intake/cam/trans type/ gearing/converter/tyre height, the lot, forget formulas. I even ran a rare 1050cfm 3bbl VS carb on that car on the street for a while, it ran ok, but crap on the track.

 

[Jonathan]

Hey jonathan here again .car gona be a street car .occasionall race. 408 .edelbrock stroker intake 360 heads slightly ported with bigger valves for now. (Will b putting edelbrock rpm heads on maybe next winter). Msd distributer and ignition system . 3 spd automatic.

 

[mech1nxh]

engine size x desired RPM then divide by 3456
pick a carb that is close to that size. add 25% for race setup

For curious minds, "3456" is the product of 1728, the number of cubic inches in a cubic foot, and 2, the number of revolutions it takes for a 4-stroke engine to fill and empty all its cylinders.

Apologies Mr MRL, just kibitsing
Back to or regular schedule .

 

[Thumperdart]

2 cfm per HP........I would run a 850 on that minimum if you are truly 450HP

THIS..............I ran an 850 demon(flowed 930 dry)on my stock stroke high 11 second 360 years ago w/great results..........