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Discussion in 'The Garage' started by adamforsythe, Jun 27, 2005.
Hey what size carbs do you guys run on your 350 engine?
A stock motor is better off with a Q-jet--or a 600 CFM Holley or Edelbrock,or 625 CFM Carter AFB...some motors with higher lift cams and hi-rise intakes run better with a 750 CFM carb,but they usually need to be re-jetted a bit leaner than they come out of the box...
You dont really need a huge carb--you dont gain as much as you'd think!---there are plenty of 2 barrel carbs on 350's as well--I had a 455 olds motor that had one factory!--and it would bake the tires posi for 300 ft!..I've had a few motors with 2 barrel carbs that would run better than the 4 barrel carbs did I swapped on with aluminum intakes...they actually LOST some performance,and were much worse on fuel....
My 305 has a 600 CFM edelbrock,and I wish it were a smaller carb,like a 450 CFM--I think the 600 is a bit too big for it--you can feel it "flatten out at 3/4 to full throttle,like the carb is letting too much air in...if it had a cam and headers and an aluminum intake it would probably run much better..but in stock form,I wish I'd just used a Q-jet--but I dont have a non EST version one handy,so I used the Edelbrock...it still gets 13-15 mpg..not too shabby..
Running the Holley Truck Avenger 770 on my 383... for a stock to mild 350, I'd recommend the Avenger 670...
I am running an Edelbrock 600 cfm with a mild cam in the 350. Put in the off road needles but have not really had it too off camber yet to see if they made a difference. From what I have seen of the Truck Avengers vs. the Edelbrock go with the Truck Avenger. My buddy has a 670 on a 302- after jetting down a bit that thing runs awesome at any angle.
I run a Quadrajet on my 305 .
I am going to run one on my 355 when its freshened to replace 305 .
I may run one on my Chevelles 360 , and sell the Holley on that
Quadrabog. I just took off my 600cfm Edelbrock in favor of old faithful. Wanna buy a 600. I wont be using it anymore not while I have a half dozen quadrabogs.
I have the same problem with mine. I calculated it with edelbrock fomulas that are in their book and a stock 305 needs something less than 300 I beliave.
Even on stock 350 a 600 is pushing it for cfm.
Don't fall for the "Bigger is better' trap alot of guys do. The carb runs on the vaccuum signal that the motor generates, and a bigger carb doesn't translate that into good carb booster signal very well. A smaller carb will give you better throttle response, and work more efficiently. It's kind of like the difference between sucking through a straw and a paper towel roll, which do you think is going to have a better airflow signal flowing through the carb venturi's? You're off idle acceleration will be much better with a smaller carb. There's no sense putting a 750 carb on a motor that will never see the high side of 3500 rpm, and never even use half of the carb's rated cfm. There's an old racer's saying, "Don't give the engine what you think it needs, give it what it wants". Larger carbs are for radical cams on motors that are going to see alot of time at wide open throttle, which is pretty much the opposite of what 4X4 truck motors do. Keep in mind that all the ads you see and dyno tests you read are on motors that are run at WOT. The car magazines and advertisers all assume that everyone is a drag racer. The demands of a typical 4X4 motor are quite the opposite of what you read in the magazines.
holley 670cfm truck avenger... LOVE IT
Barry Grant Mighty Demon 750, Love it!
You've got to build the engine with what will work with it, not what some formula says will work.
Here's an article that goes into the carb size formula myth.
GM obviously didn't believe smaller was better either. Both the Chev 305 (in trucks) and the Olds 307 in the 80's used 800CFM carbs, which meant a 300CFM primary, while the 750's had 250CFM primaries, and were used on engines larger than 400 cubic inches. That had nothing to do with the "lockout" of the secondaries to restrict maximum CFM potential, the primaries are the majority of usage.
I don't know what happened with David Vizard's website, but he also tested carb size, and as I recall, found that a larger carb helped torque production. Obviously, as with anything, variables are many and will affect the outcome, but his testing was extensive and documented.
I have a Holley 670 truck avenger on my zz4.
Proform 750cfm double pumper racing carb.
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