Thread: lowrise dual quad 350 sbc horsepower???

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I have a 78 350 sbc and am putting a dual lowrise intake on it and 2 edelbrock 600cfm electric choke carbs and a crane energizer cam with duration of 246 intake and exhaust and .500 lift intake and exhaust and a jackson noisy gear drive .
Does anyone know how much horsepower i can expect or how much gas milage will be?

Too much carb, too little velocity going to be a real chore to drive on the street. It might work with more cubic inches.

Way over carbed, gas mileage will probably be around 6. Along with wasting a lot of gas, plan on buying a lot of spark plugs when they frequently get fouled out. Dual fours and tunnel rams work good in high rpm (6000 and up) race motors, most of them on the street are just for looks and have a huge bog when trying to go fast.

I'm guessing about 2/3 the horsepower it would have with the right sized carb.

Those quads would feed a 600 CID engine at 6000 RPM.

Do a bit more research to find smaller carbs if you really want dual quads . Multiple carbs that are properly sized and setup are a dream to drive . The idea that it is difficult to properly tune a multiple setup always seems to come from folks that are not running them , or have had bad experiences in the past . Try going to some rod cruise in nite and talk to rodders that are running them . Going too big is a really bad direction to take ,,

Geo

I tend to go with four webers on this one except for the carb size. Several years ago I was running a 350 with a mild cam, headers and four speed in a 65 Chevy Biscayne. I started off with a single 625 AFB and eventually went to a pair of 625s on an Offy dual quad intake. It ran great, and I only dropped about 1 MPG.

The 600 CFM carbs should do fine once their dialed in and here's why.

PROPERLY set up the linkage should be progressive. This means that during the majority of driving situations he'll only be running on the front 2 barrels of the rear carb. When He kicks it the front 2 barrels of the front carb will open. The rear barrels on both carb open "on demand". There is a butterfly valve over the rear throttle plates on the AFB style carbs that is counter-weighted to remain closed until enough vacume is under it to pull them open (and then only as much as the engine will take. Chances are that the secondary air valves will open very little if at all.

Chances are that going to 500 CFM carbs will not run as well as 600's as the 2 barrels that he will be running on the majority of the time will be too small.

The one suggestion I would make would be to only run the choke on the rear carb. Even though it does idle on both carbs the only one that is critical to have a on choke is the primary one.

Mike I totally agree with you , it seems that multicarb systems are getting a bad rap from people that do not run them . Exotic carb setups are the very essence of hot rods .


Geo

They're not getting a bad rap from me, I just ordered a six carb manifold for my nailhead. What I give a bad rap to is the people who think a dual quad intake is instant horsepower. As with all the components in and on a performance engine, it is a matter of using the components that compliment each other and work together well. I ran a tri-power J-2 Olds in the late 60's and many unique setups since then, including a set of Webers on a 347 stroker motor. I would disagree that multicarbs are the essence of hotrodding, I would say that individualism, self expression, and creativity are the essence.

that dual setup is fine...those will work on a stock 350 if you set the carbs right...just jet them down....I have used this same app before and know it will work....It will idle high though...I would also use a 4 hole phenolic spacer under the carbs. A one inch will do....

I would suggest using the Edelbrock 500cfm carbs though because of port velocity and just convert them to electric choke....

These intakes are good for 425hp without mods. These intakes are a very good flow design and do better than most think while still maintaining slow speed torque!

I do run these on a 1to1 ratio (running on both carbs equally) and chokes on both carbs for my customers....

I ran 2 600 CFM Edelbrock competion series on an Offenhouser dual quad low riser for all of 2 months. That's how long it took me to get fed up with the setup. Stand on it and the cars shadow would be a block away before the engine could catch up. Miserable gas milage,very poor low rpm performance. Looked nice but driveablity sucked. I went the whole gamot, jets , accellerator pump mods, velocity stacks, etc, etc, etc. Just bolting on a good dual or single plane made all the difference in the world.

Dave S , I saw your post with the 6 carb manifold and was really impressed to see someone out there taking time to build a setup like that . I myself [drooling here] just can't wait to see it . With all due respect that comment was not aimed at you . Hmmmmmm, a J2 you must be a bit of a senior rodder toooo,,,,,

Geo

OOps. Geez, I guess I kind of dated myself with the J2 reference !!!! I am still at a loss as to which carbs to run on the Buford. I'm kind of leaning towards the large Rochester in the center of each bank, and 4 small ones on the ends. I wanted to run a rack of 97's until I started checking price and availability. Fortunately, it's not something I have to decide today. Any input??? How about adapters and some sidedraft Webers????

Dave , I have no idea what 97's would cost , but carb prices in general are out of sight .Are those carbs generally found at swap meets etc , or perhaps hemmings. When I built my setup, I purchased the moon manifold and then went shopping for carbs , linkage , fuel lines etc . It can take a while to get everything scattered together , to say nothing of the cash outlay .I have no experience with weber adapter plates and the such , but I would bet it would be costly . I saw a nailhead in my youth [ long ago ] with the six carb setup ,,,,,,,,,, it was looking hot . Looks like you are going to bite the bullet and keep hunting ,,,,,,, what the heck you will be pleased with the results .


Geo ,,,,,,,,,,,,, geezer circa 1939

happy huntin

Yup, sounds like a good excuse to hit all the swap meets again this summer!!!