Another Carb Size Question

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bobscuda67

bobscuda67

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I have a 340 based 373 ci motor that is mainly to be used for the street driving. I used several online calculators and based on a ve of .86% they all say I need a 556 cfm carb. Even at 100% it only at a 647 cfm.

I'm leaning toward a 650 Edelbrock and was wondering if its big enough. I hear a lot of people using 750's on street driven 360's and according to the calculators, they are way over carb. So what size are you using, and with what kind of results?
 
First, you should probably post some info on your engine. 373 ci is good info, but what intake, cam, compression and exhaust manifolds/headers? That's info that's really needed to pick a carb.

Just based on the displacement though I would say that a 750 cfm carb is going to be closer to the right ballpark than a 650. Mopar Muscle magazine did a dyno article on a 340 they rebuilt to stock specs, stock cam, pistons, the whole works, including an original Carter AVS carb (~600 cfm). They ended up with 281 hp at 5200 rpm and 328 ft/lbs at 3900 with all the stock gear. They also found that they were running lean at the top end.

For their second set of pulls they bolted on a bone stock 800 cfm Edelbrock AFB carb, straight out of the box. They ended up with 316.9 hp at 5200 and 351.3 ft/lbs at 4000 rpm. Thats a 35 hp increase!

Now, thats a bone stock 340. I'm guessing that your 373 is a far cry from bone stock, so while I'm not sure what calculators you're using, I'd go with at least a 750cfm carb...
 
I think what you`ll find is two different things in theory and practice. Fishman and me both know a fellow running a hot 340 in a Daytona. The car runs in Super Gas and is capable of 7 second times yet he runs a 650cfm carb.????? (Fishman,correct me if I`m wrong).Chrysler engineered the 340 with a 625 cfm carb in 68 so you can at least start from there. From what I`ve read the Avenger 670 is a good carb but comes from the factory a bit lean. That may be one avenue to pursue.
 
600 cfm is plenty enough carb for a small block anything...everybody thinks that bigger is better......600 edelbrock is awesome carb....buy it you will love it.....i will send you mine try it....read the plugs they don;t lie
 
Oops ! It's a 340/373ci
zero decked k/b dish pistons
Hughes cam-219I/ 228E duration at .050 522I/558E lift 111 lsa
magnum replacement heads, 57cc, stock valves, gasket matched
9.68 comp. ratio
Mopar M1 dual plane
340 exhaust manifolds and full stock 340 system
904 with hemi shift governer 5800 rpm shifts /low gear set
2800 stall converter
355 rear gearset

Thanks guys, you can see why I'm a little confused.

As 72bluNblu pointed out the Mopar Muscle article,which I read, used a 750 with great results.
And John brought up the fact that a 7 second small block, with a ve of close to 100%, only uses a 650.
The online calculator gave me the 600 as the right carb, just what chasduster said.
Maybe with the added info we can narrow it down some.
 
Bob, the thing about carbs is that if you take the time to tune them, you'll find that any carb on top can be dialed in and run. A properly sized carb will not lack in low end response or give up top end HP. And this is where you can confused with how people do things and what magazine dyno's report. In general, on line calc's are slightly small in there cfm rating.

The on line calc you got for 647 cfm is closer to what you could use and have built dispite the fact it isn't a race engine.

Considering your build, I would not think twice or second guess myself on a 650 cfm carb.
 
I run a 670 Street avenger like John mentioned. It was lean out of the box, but it works very very well on my 340, even at 6500 rpm.
 
If its a street "only" car a 750 with vacuum secondaries will be just fine,street/strip i'd go 750 mech. secondaries...those on-line calculators are old and outdated..
 
I'm with ya stroked, there a bit light on cfm. While I think the 650 cfm would be good for his pure street ride. Considering the cam and gears.

I ran a 750 on my .030 over 360, but that's a 4spd/4.10 geared E body.
(292/.509 & RPM head/intake w/ super comp headers.)
The package was good.
 
Longgone said:
I think what you`ll find is two different things in theory and practice. Fishman and me both know a fellow running a hot 340 in a Daytona. The car runs in Super Gas and is capable of 7 second times yet he runs a 650cfm carb.????? (Fishman,correct me if I`m wrong).Chrysler engineered the 340 with a 625 cfm carb in 68 so you can at least start from there. From what I`ve read the Avenger 670 is a good carb but comes from the factory a bit lean. That may be one avenue to pursue.
Click to expand...

I remember an old guy told me that back in 68-70 they would get a 340 car, go into the dealership to the parts counter and order a carter for a 440, which I believe is 725.
 
Common cfm given for the 440 is 750. reguardless, that is an old school hop up trick that works well then and now. Also realize the OE 340 cam is larger than what bob is running now.
 
If you are planning on driving your car more than 4 times a year, don't want to pull over after a few miles of driving and retune your carb, not drag racing it, care about quality control and customer service that actually knows what they are talking about and gives a damn STAY THE HELL AWAY FROM ANYTHING MADE BY BARRY GRANT!!!!
 
rumblefish360 said:
Common cfm given for the 440 is 750. reguardless, that is an old school hop up trick that works well then and now. Also realize the OE 340 cam is larger than what bob is running now.
Click to expand...

Rumble, I totally agree. I think a 600-650 eddy would be perfect. Maybe just a rod change....

388dart, The 650 mighty demon IMO is too big. I have never had good luck with any demons. I swapped out an 850 demon for an 850 QFT carb and the car ran so much better. Once again this is MY OPINION from MY experience.
 
Keep in mind not all carb flow specs use the same test, some are dry flow ratings and some are wet flow.

Street Avengers and BG Demons are both rated for wet flow, so thats with fuel and air going through the carb. The result is that a wet flow rating is about 12% less than its equivalent dry flow rating. Edelbrock's are dry flow rated, so if you want to compare the Street Avenger cfm rating to an Edelbrock rating, you need to add 12%.

So a 670 cfm Street Avenger will actually flow 750 cfm dry, ie, a 670 Street Avenger flows the same as a 750 Edelbrock...
 
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