CFM'S Required?

[michaelmopar]

How many cfm's are required for a 318 small block with about 275 to 300 h.p.?
And which carb is going to have the best throttle responce. [I have a edel ld340 i am going to be trading with demon for a performer intake. That should fix the dead spot from idle. Hoping get rid of the falling on its face as it does when i stomp on it.] Next i have a edel 600 cfm is there a better carb. Do i need more cfm's. Demon tells me i do and i tend to believe him, that a tuned thermoquad would do the trick. Any feedback would be great.

[340demon]

to find cfm required by an eng. divide cu of eng by 2 multply by rpm you will run and divide by 1728 this will give you the max cfm that an non super charged eng will need

[rumblefish360]

Mike, I'm a little confused. (Might just be tired some) but IF i was in your socks, I'd keep the LD-340 and T-Q for it. I'd just port match the head to the intake. You would want a smaller 800 cfm T-Q over the larger 850 cfm unit. The primarys are smaller. Better for a 318.

The Edel. Performer will work very well on the 318 without mods and the carb would still be the above 800 cfm T-Q.

[michaelmopar]

460 cfm sounds a little low based on 340d's figures. 318/2 = 159 x max rpm is 5000 = 795000 / 1728 = 460.0469. I dont know about you but that sounds a little small for any mild small block. if i were to reverse those numbers i would need a 552.96 cu.in. big block to be able to use the 800 cfm thermoquad i have. i am confused. i think those are numbers from a perfect world and not a real world. i couldnt get a 460 cfm carb to move the car any faster than 40 mph if i were lucky.

[rumblefish360]

If Demon sizzler does a 800 cfm T-Q for you to go ontop of a performer intake, you'll be set.
The stock 318 4bbl. used a 800 cfm carb. It should easily be the most responsive carb for what you have. I know 800 sounds like a ton of cfm for a 318, but it works. And well. Once tuned in, it's not like it's dumping in gas and wasting it. In just the reverse, you'll get the best mileage and power out of this carb.

[pishta]

The TQ will never see 800 CFM's on that motor. Its an air valve secondary so it opens enough to meet demand. A 390 will get out of its own way, ever see a restrictor plate on a Stock car? Might as well be using a 390 as they are rated at a certain Hg level, put 8000 RPMs under them and they will pull more than 390 CFM, a little off topic but something to chew on.

[DEMON SIZZLER]

Originally Posted by pishta

The TQ will never see 800 CFM's on that motor. Its an air valve secondary so it opens enough to meet demand. A 390 will get out of its own way, ever see a restrictor plate on a Stock car? Might as well be using a 390 as they are rated at a certain Hg level, put 8000 RPMs under them and they will pull more than 390 CFM, a little off topic but something to chew on.

That is exactly right! But that 390 cfm Holley will never make any power on a mild street V-8 like his engine while even an 850 cfm T.Q. will make lost of power. Try an 800 or 850 cfm Holley and it will be hard-pressed to ever run

[LA360Dart]

Hi All;

I had a very mild 360 in an A body. Small cam, 340 resto type. Compression 9 to one maybe, iron TQ intake and a 625cfm Street Demon or TQ. It would get about 11mpg in town and would run 13.90 to 14.20 in the quarter. Ran the stock TQ or the Demon only difference was that the TQ had about 2 mph more than the Demon. I tried a 750 holley and milage, performance were not as good as TQ or Demon... A freind had a 331 sb in a 65 chevelle and with the Street Demon it ran quicker and got better milage than his 700DP Holley. Alas he would rather fight than switch ( mopar guy could not be right ).

[dwc43]

Originally Posted by michaelmopar

460 cfm sounds a little low based on 340d's figures. 318/2 = 159 x max rpm is 5000 = 795000 / 1728 = 460.0469. I dont know about you but that sounds a little small for any mild small block. if i were to reverse those numbers i would need a 552.96 cu.in. big block to be able to use the 800 cfm thermoquad i have. i am confused. i think those are numbers from a perfect world and not a real world. i couldnt get a 460 cfm carb to move the car any faster than 40 mph if i were lucky.

You can't use that equation for the very reason you have already discovered. It leaves out too many variables and most of the time leaves the engine in question under carbed. USe the stock 800 cfm TQ with teh LD340 or Weiand 8007 and you'll get the most out of it.

[gthomas]

Check out this site: http://www.corvetteactioncenter.com/...ools/carb.html

[teddy1500]

I have a 318 package much like yours. a 600 holley or eddy would work well
You have decent compresion, a mild cam. there is nothing wrong with keeping a mild carb

[Robertson_Tech]

I agree a mild carb.. But the point that is lost I think is the TQ is mild small pri and only the air you can use for 2nd'arys. Best 318 I built used a AVS carter. glad too see eb bringing them back for smaller apps

[Tarrbabe]

on my 78 318 with a set of Hookers. The thing pulled hard to 5500 with the stock 2 bbl manifold. Mileage wasn't it's strong suit. I pulled the 318 and put in the 72 340 with Crane 284 cam, hookers and a Holley spreadbore 650 dp. Ran strong to 6000 and got 16.5 mpg on the road with 3.23's.
My next carb? Demon Sizzler is doing it now. 800 cfm tq.

[michaelmopar]

Originally Posted by Tarrbabe

on my 78 318 with a set of Hookers. The thing pulled hard to 5500 with the stock 2 bbl manifold. Mileage wasn't it's strong suit. I pulled the 318 and put in the 72 340 with Crane 284 cam, hookers and a Holley spreadbore 650 dp. Ran strong to 6000 and got 16.5 mpg on the road with 3.23's.
My next carb? Demon Sizzler is doing it now. 800 cfm tq.

hard to believe you got 16.5 with a mild 340 w/cam and the holley gas drinking DP. Were you going down hill lol.

[turbododge]

The Holley spreadbore DP 650 is a very good carb with metering at both ends. We ran one on the TT340 Chally for 4 years, and it would consistently get 19 to 19.5 mpg if you kept your foot out of it. The primaries are small enough, and tuneable enough, that you can tweak it in to run very efficiently.

[Tarrbabe]

the 650 dp get's short sold a lot. In town isn't that great but cruising can be great. The best I ever got with it was 19.5 but I figured you would not believe me. It's all in how you drive it. It does have the small primaries.

But you know how hard it is not to mash the pedal.

[pishta]

Ill second that. My spreadbore vacuum Holley had the best idle and response, no mileage report though. Probably the small primaries. Looked kinda weird though with its strange bowls and leaning vacuum pot. I just got a 4010 Vacuum spreadbore 650, all shiny and new looking. It has the solid gasket base, not the spiderweb base of the squarebore 4010 600 so it doesnt leak but I have nothing to put it on. Any interest?

[Robertson_Tech]

Originally Posted by pishta

Ill second that. My spreadbore vacuum Holley had the best idle and response, no mileage report though. Probably the small primaries. Looked kinda weird though with its strange bowls and leaning vacuum pot. I just got a 4010 Vacuum spreadbore 650, all shiny and new looking. It has the solid gasket base, not the spiderweb base of the squarebore 4010 600 so it doesnt leak but I have nothing to put it on. Any interest?

Speaking of weird looking carbs I picked up a holley 7456 450 cfm as a replacement for the rochester that came with the 360 intake I picked up for my 318. I got 2 carbs for 15 or so both need rebuilt but have little wair.

[rumblefish360]

Originally Posted by pishta

I just got a 4010 Vacuum spreadbore 650, all shiny and new looking. It has the solid gasket base, not the spiderweb base of the squarebore 4010 600 so it doesnt leak but I have nothing to put it on. Any interest?

I need the secondary cluster to that carb. Feel like parting it out? LOL I used that carb for a check it out and drive for a few days. It worked well. No problems.

On what Tarrbabe was sayin on mileage with his 650 DP, I had a 600 DP on my Cuda when it had a 318 TorkerII and a small crane (272/284) headers and 3.23's. I grabed good mileage with that carb. But like he said, we all suffer from Led foot fever oncein a while, or more often that not.

[triggerbear]

Hey Rumble I have a carb like the one you need parts for #R84014 speadbore vac sec. The only thing wrong with it is it blew a pwr valve and the screws holding the pv cover broke off. The choke has been removed but the tower is still there. I need a set of centerhung bowls for a #R6210 spreadbore DP. Got any we can trade out?

[rumblefish360]

No spare Holley parts in my garage really. I have a box of jets and a 4150 bowl w/ the screws on the end for quick jet changes. I've had it so long now, I *Think* it's for the primarys.

[pishta]

OOH, I need that bowl! whach ya need/ want for it? Wonder if that 7456 would make a decent dual quad carb as it has puny primarys/CFM's and annular discharge boosters? Speaking of weird looking, any more info on the toilet bowl Demon 3 barrel?