So I've been searching for carb sizing charts, but they want max RPM. I don't know that. I do know that my engine is mild built, 351w, ported and polished aluminum comp heads, pro comp cam, roller rockers...Not building a race car. Don't care about gas mileage...Don't know what else is important. My neighbor says a 750cfm with manual choke... Any advice would be greatly appreciated!! thanks guys
ps-i don't like my valve covers

 

I will look for carb sizing info for my engine, not a 351w but a 5.0 L HO. There was some info on multiple engines and carbs, that I got from a Holley carb tech after searching on line but it was a few years back.

Went with the Holley Street Avenger 570 CFM on mine as per the specifications for my build. Block bored .040 over, hypereutectic pistons, Moly rings, Comp Cam, roller rockers, Weiand manifold, and all balanced, blueprinted with MSD distributor and coil.

Runs fantastic so far, and lots of go when I want it.

Kevin

 

Err slightly on the smallish side for a street ride. Too much carb is misery on the street. I've overcarbed street cars many times. 750-780cfm is plenty for a 351 with your mods. You could get by with a carb as small as 600cfm and notice no big difference anywhere but WOT. Whatever you decide, take the time to jet it correctly and get it dialed in.

Like to hear the reasoning for a manual choke. Electric chokes have been perfected for 35 years.

 

thx.
Don't know if it helps but i have a c6 tranny and 8.8 lincoln rear end. don't know gears yet.... Workin' out the kinks from PO

 

gears ratio would be helpful to know. As would cam specs and intake.

 

For mild build like you have I would suggest a 625 Street Demon built by Barry Grant at Demon Carburetors you can check out the website.
The polished look will tie in with the way your engine is dressed.

 

Hey Jason,
Nice looking engine. We also have a 351W with a mild cam, roller rockers, etc. & an 8.8 Explorer rear end with 3.73 gears. We are currently using a
750 cfm carb we got from Summit (part #EDL-9913 - around $260).

To me it's a lot of carb for street driving not sure we'll leave it
as is. Just an opinion - I'm sure experts can help you arrive at
what may work best for your truck.

Ben in Austin
1950 F1 (351W/AOD)

 

Here's how to figure it out:

On a perfect day, your non-supercharged 351 cubic inch engine will want to draw in 351 cubic inches of fuel/air mixture every time it makes two full revolutions (it's a 4 stroke engine).

So...figure out what the max RPM is that you'd ever run. Let's say that is 6000 RPM (I've never spun my 351w at 6000, but let's just say that you do).

At 6000, you are taking in 3000 x 351 every minute, so 1,053,000 cubic inches per minute. Since there are 1728 cubic inches in a cubic foot, divide 1,052,000 cubic inches per minute by 1728 cubic inches per cubic foot. That comes out to 609 cubic feet per minute.

Now...let's address a couple of notions. First, I firmly believe that overcarbureting is a lousy idea because the air flow through the body of the carb is too slow...the fuel won't mix with the air as well. When you consider it, if you have a 600 cfm carb for your 351 and run it at any RPM 6000 or below, you'll have plenty of capacity. In fact, if you run closer to 3000 RPM you'll be in the middle of the capacity.

Let's address the perfect day as well. There are no perfect days, so the volumetric efficiency of your engine will never be 100%. That means that each time the piston goes down in the cylinder, it will want all of the fuel/air mixture that will fit in, but because of valve timing, friction, and the viscosity of the air, 100% of that volume will never be filled up unless you supercharge. On a nearly perfect day, expect around 70% Volumetric efficiency. That means that what flows through the carb will most likely not be 609 cubic feet per minute at 6000 RPM....it will be closer to 426 cubic feet per minute.

I put an Edlebrock 550 cfm carb on my 351 and it runs really well.


Dan

 

Wow. Thx guys. Sounds like edelbrock is the way to go on brand. I don't hear too much about Holley. As far as size goes maybe ill meet Dan and Ben in the middle with a 650cfm... I like that intake mani Ben!!

 

Holley has a handy online selector at http://www.holley.com/applications/CarburetorSelector/CarbSelection.asp. Be honest (not wishful) with the answers that you give particularly max RPM. Dan and fatfenders are correct as the larger the carb the more bottom end torque ( can you say fun ) you lose and of course fuel economy.

As an example I'm always amused at people that put 650 CFM double pumper carbs on 304 V-8 Jeeps and then wonder why the engine keeps stalling in heavy off road situations. So they have to over rev the engine to get over obstacles. Usually the clutch or an axle shaft breaks first. So they fix the broken parts but never go back and fix the source of the problem. Then they put on big tires which only makes the torque situation worse. $$$

So if you are not running your truck in the NASCAR Truck Series but want a true street performer go small on the carb. A 600 ccm spread bore with an electric choke would give you the best of both worlds.

 

I'd go with a 600 cfm edelbrock with an electric choke. 600 cfm is plenty for a street driven truck that spends most of its time at low rpm. Face facts, most of your time will be under 3000 rpm where the 600 will be fine, and it's not a hinderance at higher rpm. The electric choke will be easier to set up, no fuss no muss. You'll never forget to turn it off. Ebrocks are simple to tune and don't leak.