brand choice for carburetors? - Impala Tech
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post #1 of 8 (permalink) Old 05-28-2012, 11:31 AM Thread Starter
 
 
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brand choice for carburetors?

I've been loking around at carburetors to find a cheaper 670-700 cfm 4-barrel unit for my '67 327 impala. its not going to be a strip car, more for just driving around town and maybe a few highway trips to some local car shows. most of the carbs i've seen are either holley's or edelbrock's, but i ran into a "Quickfuel" brand carb advertised for about $100ish cheaper than either of the others, and i was wondering if anyone has ever used one.
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post #2 of 8 (permalink) Old 05-28-2012, 12:16 PM
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It's a personal preference thing and you will get different answers from everyone.

I'm a Holley guy myself and tend to run them on everything, even my daily drivers. Some folks say they are better suited for racing and won't hold an adjustment but I have never found that to be true. Quadrajets are hard to beat IF you know how to tinker with them. They are very complicated and in my opinion, have more to go wrong. I just don't get along with Edelbrock carbs and have always been unhappy with them. Seems like they always like to idle rich and often have a pretty good bog somewhere in the RPM range. I do still have one though and it's been better than others... but I still don't like it.

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post #3 of 8 (permalink) Old 05-28-2012, 01:08 PM
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Quote:
Originally Posted by Dan's67 View Post
I've been loking around at carburetors to find a cheaper 670-700 cfm 4-barrel unit for my '67 327 impala. its not going to be a strip car, more for just driving around town and maybe a few highway trips to some local car shows. most of the carbs i've seen are either holley's or edelbrock's, but i ran into a "Quickfuel" brand carb advertised for about $100ish cheaper than either of the others, and i was wondering if anyone has ever used one.
Quickfuel is essentially a copy of a Holley. I've never used one, but know guys that have had good luck with them. Because they use much of the holley design, they are cheaper. I recommend the Holley Street Avenger You would be surprised at how great your 327 will run with a 570. You really don't need a 670-700 CFM carb for that little small block, unless you're expecting 500-600 HP from it.
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post #4 of 8 (permalink) Old 06-06-2012, 03:09 PM
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I have a 600cfm edelbrock on my 327 and it runs perfectly. I wouldn't recommend anything much bigger.
-Nick

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post #5 of 8 (permalink) Old 06-06-2012, 03:41 PM
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The Rochester QuadraJet was introduced in 1965 with the design engineering team at GM (which back then had about 1,500 degreed engineers working on research and design) having two totally divergent criteria to meet in one carburetor. First demand was for lots of power to justify the higher priced big block. The other was to reduce emissions (which has the side effect of improving fuel economy) as the federal government had already passed laws limiting idle output of pollutants.

So to meet these criteria the QuadraJet has two tiny primary bores that contains the accelerator pump circuit and the idle circuit which limits the amount of gas at idle. The rear bores are a variable venturi design; which will with enough vacuum beneath the car flow 780 cfm on top of a big block, or 640 cfm on a smaller 327 at wide open throttle. The limiting factor isn't the carb (it is basically the same one), but in the fact that the smaller motor can not draw enough vacuum depression to draw more air through the carburetor. As such it is the ideal carburetor, not too big and not too small.

I agree with Adam that the exterior of the Rochester QuadraJet is very complex appearing with all of the actuating rods and can be intimidating. The good news is that once the carb is set up; it stays that way for 100,000 miles. Problem is few are specialists in this carb. There are two national carb shops that do a good job in rebuilding them and configuring them for your size motor (these carbs were put on everything made by GM from a 262 V-8 to a 455 cubic inch displacement V-8).

For this carb to be tuned correctly it often requires custom made brass fuel supply rods, hand bored tapered brass main jets, and a pipe plug (with some epoxy) sealing the main fuel well. Once tuned it performs very well.

Big Dave
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post #6 of 8 (permalink) Old 06-16-2012, 02:22 AM
 
 
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Quote:
Originally Posted by nicke View Post
I have a 600cfm edelbrock on my 327 and it runs perfectly. I wouldn't recommend anything much bigger.
-Nick
Same here.. had the quadrajet with stock manifold switch to edelbrock eps manifold a wooden spacer to keep the carb cooler and am alot happier with the perfermance. But whichever carb you go with I wouldnt go bigger than 600cfm edelbrock, 550cfm holly
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post #7 of 8 (permalink) Old 06-17-2012, 01:18 PM
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You might be interested in this thread over on the Corvette Forum.
http://forums.corvetteforum.com/c3-t...-holley-2.html
This is page #2 where Lars presents some back to back dyno runs - Rochester QJet versus Holley. Lots of good history throughout the entire thread.

Jim
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post #8 of 8 (permalink) Old 06-17-2012, 03:01 PM
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That is kind of cheating. The QuadraJet has a variable venturi secondary. It has a fairly large cfm rating (850 cfm on a 454) if you can pull enough vacuum. The Holley has fixed venturis and as such the flow rate is determined by the size of the carb's throat. So you are really not comparing apples to apples.

Generally any carb will mix the "correct" ratio of gas to air regardless of the cfm rating of the carb (they all mix it the same or the engine couldn't burn it). Going to a bigger carb gives you the opportunity to pull in more fuel and air if your motor can use it. Otherwise a bigger carb is just a hindrance. Where the QuadraJet shines is in that the rear barrels can flow as little or much as your motor needs. It is the "Goldilocks" of carburetors in terms of cfm rating (it does have an upper limit which is why Holley Dominators are used exclusively in racing and not QuadraJets). I have not found an engine where the QuadraJet can feed 1,050 cfm to 1,500 cfm and still meter the fuel to the air flow.

Big Dave
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