When I was still in the game, we had installed over 10 Q carbs. What a difference in tuning. Ran like a Holly, tuned up like an Edlebrock...they ALL worked great out of the box and we were buying them from Advance Autoparts cheaper than anywhere else I priced them! Great carb. Its what will be going on every one of my project cars...If going with a Holley style carb, I would go with one by Quick Fuel. Out of the box one of the best carbs you can get. And for a 331 cid small block I would go with a 750 cfm carb. A 600 would leave HP on the table. It is all about getting the air/fuel right. I can make that 331 run good on a 250 cfm 1bbl. carb or make it run good on a 1100 cfm Dominator. The HP difference between the two carbs would be huge, but they would work, no bog or anything. If the air bleeds are right and it is jetted right the size does not matter. If this is a fuel economy build (and with those heads and intake it will not be) then a 600 cfm would work just as well.
That is what the recommendation used to be. Now the recommendation is typically only mechanical secondaries if the car is extremely light, the engine very powerful and very little street use. The problem with mechanical secondaries is your carb will be wrong for every situation except wide open throttle racing. Here's a link to Holley's carb selector program.from what everyone was saying, they all recommend mechanical secondaries for a manual trans. and vacuum for auto. i understand what you are saying, it just seems to be "a bit against the grain"
decisions decisions... lol
That is what the recommendation used to be. Now the recommendation is typically only mechanical secondaries if the car is extremely light, the engine very powerful and very little street use. The problem with mechanical secondaries is your carb will be wrong for every situation except wide open throttle racing. Here's a link to Holley's carb selector program.
http://www.holley.com/applications/CarburetorSelector/CarbSelection.asp
I'm building a 408 Cleveland manual trans Fox Mustang and Holley recommends vacuum secondaries for me.
.... except wide open throttle racing. ......
Is there any other way to drive? who cares about cruising and idle.
thats all some good info. i like those carbs. im researching those in 650-750ish CFM.Cast my vote for QFT!
http://www.summitracing.com/parts/QFT-HR-580-VS/
This is generally an updated/upgraded version of the Holley Street Avenger
http://www.summitracing.com/parts/HLY-0-80570/
Almost identical, except with 4-corner idle mixture adjustments, easily changeable idle and high speed air bleeds, easily changeable idle fuel restrictors AND externally adjustable secondaries and for only a few pennies more. A read of all the items on this page:
http://www.quickfueltechnology.com/technical-info
is extremely informative on carbs in general. I have the HR-580-VS and can't say enough good things about the carb and QFT customer support.
My $.02,
Gene
My internet knowledge tells me that a slightly smaller carb, (I.E., 600 or 650 VS 750) will give better overall throttle response. You mentioned stop lights and street fun, I would stay 700 or under. Actually, my recommendation is either a 600 or 650...Preferably a Holley product.
I think Holley recommends vacuum secondary carbs because they'll run better "out of the box" with less tuning. It helps to keep calls to their support line down. I have 3 different cars with mechanical secondary carbs that run flawlessly. I have a friend who is an ex-GM engineer who worked on designing carburetors and distributors. He is an expert at tuning Holleys and Demons, and dyno tested cars with both vacuum secondaries and mechanical secondaries. His test results showed that you do pickup horsepower with a properly tuned mechanical secondary carburetor.the only people ive ever heard say a mech secondary carb doesnt work on a street car, havent owned a quality mechanical secondary carb.
my buddy and i have been trying to tune this cleveland headed stock stroke 351w shortblock. since it is a budget deal we have been trying to keep it simple. we tried 3 holleys. an 830, a 750 hp and a 650 hp. they all had a stumble. finally we got tired of screwing around with junk and pulled an AED HO modified 750 out of the box from summit. with only tuning the idle mixture screws it picked up .3 of a second in the 1/8 mile (from the cars previous best of 7.28). the difference is amazing and we havent even pulled the bowls off it yet. dont worry so much about the cfm, especially on a street type carb. its BS. the only people ive ever heard say a mech secondary carb doesnt work on a street car, havent owned a quality mechanical secondary carb.
http://www.summitracing.com/parts/AED-750HOM/
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