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Carb Recommendation

3K views 32 replies 19 participants last post by  200170 
#1 ·
I've tried the formula and the carb calculators but I get so many varying cfm numbers.

What do you guys recommend for a street car that I like to put my foot in? Here are the details:

Small block 350 bored 30 over and am going to run a flat tappet cam with an rpm range of 2500 to 6500. Compressions is 9.5:1 with headers, high rise, etc. I have an older 600 cfm edelbrock and a holley 870 cfm. I think one is too little and the other is too large. Something in the middle?
 
#5 ·
I don't disagree with the above selections but if you already have a 600 and a 870, either of those will work fine also. Unless you are looking for gas mileage or a race carb, there will not be a noticeable difference in a weekend cruiser. I would just use either one that you have and save your money for something else.
 
#12 ·
If you can get the 600 Eddy right it will be the best carb on that engine. Go with the 1405 specs as the jetting and rods are great. The key to making it work right is getting that sec. air valve to not open to fast then you get a bog off the line. The Holley 870 while it is big you can never over carburetor with a VS model, the stiffer the sec. spring the lees likely you will have trouble with it. As far as DP carbs go I have run them on the street all the time with no problems that happens when you go too big. Get a 4777 650 DP and it would work great also but the Eddy will be better on fuel mileage.
 
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#13 ·
Big Cam, small block, 9.5 to 1 compression ---- I recommend a carb. with "idle-eze". I use a Holley 750 Ultra XP body (has idle-eze) with standard double pumper 4150 Holley/Quickfuel throttle plates, bowls, metering blocks in my 402 (bored 30 over). The idle-eze is so important because with a big cam and a nice lean 850 rpm idle, it allows you to pass air to the motor without opening the throttle blades. You can keep the throttle blades closed, metering screws turned out, and as soon as you open the throttle - no lean stumble. It made a huge difference for me with my Comp Cam 292H. PS. You can accomplish the same thing by drilling your throttle blades, but, the idle-eze is much easier to fine tune.
 
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#15 ·
Of the carbs you have I would use the Edelbrock. The 870 will work but won't be as responsive with the huge primaries and you'll have trouble getting the idle/transition/mains balanced. Fuel mileage will suffer and it will feel lazy. You might be giving up a little power with the 600, might not, but the response will be better and it will be pretty easy to get set up. If I were in your shoes that's what I would do. I wouldn't buy another carb, I'd save that money for an EFI.
 
#16 ·
Unless you plan on using one of them in the future, sell the two carbs to replenish the cash outlay for the Holley VS 750.That way you have the correct carb.
 
#17 ·
Also consider your type of use. I have a 454 (461) with peanut port heads with max 4,800-5,000 rpm. The formula for my car comes in at 600-660 cfm, depending on what you input for volumetric efficiency (that's probably where your variations come from). I have 650 Edelbrock AVS on there. It's very crisp and responsive. I may have given up some power in the higher rpm range on the highway, but with 3.07's, I would have to be going more than 100 mph to take advantage of that. I rarely go above 90 mph. Also, the low-end torque on the engine compensates for the lower numeric gear and lower max rpm. I'm sure a bigger carb would also work on my car, but it may affect the daily-driving manners.

Using the formula (cid * max rpm/3456 * VE = cfm), your Edelbrock 600 seems to be plenty of carb. The bigger Holley would also probably work, although, as mentioned above, probably not as well. I'd give them both a try, each for a week at a time, and see how well they function. You may be blown away at the top end power of the Holley, but get really annoyed with it driving in rush hour traffic. You'll get a feel for what something in the middle would be like, and decide if a new carb is needed.
 
#18 ·
Great post 658. One thing I ought have added to my answer was, better smaller than bigger. So 600cfm trumps 800 cfm here, if you dont prefer to find something in the middle. The increased velocity thru the small carb will give you much better throttle response at anything other than WOT, and maybe even there to a peak rpm.

BTW, if you DO opt for a new carb, I'm really digging on the new line of Holley Street Demons. Reasonably priced, 625 and 750 cfm versions. As far as old carbs, the 3310 is ubiquitous, and I love the elegance and efficiency of Qjets.
 
#20 ·
Just bought a new 2 barrel for my 66 Malibu with a 283. Idles fine but have to choke it with my hand to gain rpm. It just falls on its face when you open the throttle by hand unless you are putting your other hand on top to choke it a lot. Is float level my issue? What is the measurement for float in both positions. Runs and drives with old factory carb but not as good as a new carb would. Any help out there would be appreciated. Thanks!
 
#21 ·
First my 70 LT1 had a vacuum secondary 780 from the factory and even though I changed secondary springs the delay was terrible. Here is a real world comparison with two LT1 Z28's with everything identical except my friend had angle 202's over my 70 factory 202's. First race I was running my 650 DP and he went with a 750DP and I pulled him buy 3 lengths. 2nd race he changed out to a 700DP and I pulled by one car length. He never went to a 650. I think the 650 double pumper is one of the best 350 carbs out there for power. With that said a tuned 750 CFM Quadrajet is a very nice overall carburetor where the Holley is much more touchie. Go with the 650DP however your compression is on the lower side compared to a LT1 but it should do great.
 
#26 ·
Wow, Reelysalty got all indignant because I asked to refain from listing parts for sale on the tech forums. Said he'll try to avoid us in the future. Or something like that. Too bad, I thought he was pretty good.
 
#27 ·
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