What is the difference in a 350 Q-jet and 454 Q-jet? Other than jet size and needles?
Kelly
Kelly
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Re: Q-jet
The Q-jet was manufactured in two air flow ratings - 750 and 800 CFM at 1.5" Hg depression. The 800 CFM version has slightly larger primary throttle bores - 1 3/16" versus 1 1/4" IIRC.
The break point for going to the larger version was about 400 CID, so 454s have the 800 and 350s have the 750.
The relatively small primaries offer a good metering signal for precise fuel flow control at low load, and the large secondaries yield very little restriction at WOT. It's a very good carb design - and like the AFB, it has no "wet" gaskets that can leak. Small WOT mixture adjustments can usually be made by swapping the secondary metering rods, which is very easy.
It never ceases to amaze me how many fools swap Q-jets for 650 CFM Holley "double pumpers".
Can you say duhhhhhhhhhhhhhhhhhhhhhhhhhhhh!!!
Duke -
Re: Q-jet
The Q-jet was manufactured in two air flow ratings - 750 and 800 CFM at 1.5" Hg depression. The 800 CFM version has slightly larger primary throttle bores - 1 3/16" versus 1 1/4" IIRC.
The break point for going to the larger version was about 400 CID, so 454s have the 800 and 350s have the 750.
The relatively small primaries offer a good metering signal for precise fuel flow control at low load, and the large secondaries yield very little restriction at WOT. It's a very good carb design - and like the AFB, it has no "wet" gaskets that can leak. Small WOT mixture adjustments can usually be made by swapping the secondary metering rods, which is very easy.
It never ceases to amaze me how many fools swap Q-jets for 650 CFM Holley "double pumpers".
Can you say duhhhhhhhhhhhhhhhhhhhhhhhhhhhh!!!
DukeComment
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Re: Q-jet
the size is 1-3/32" vs 1-7/32" the 800 is found on 71-73 buicks and 73 pontiacs big inch enginesComment
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Re: Q-jet
the size is 1-3/32" vs 1-7/32" the 800 is found on 71-73 buicks and 73 pontiacs big inch enginesComment
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Re: Q-jet
Duke-----
As I've said many times before, the Q-Jet is the absolute best street carburetor EVER designed. Anyone that would rather use a Holley for primarily street operation is absolutely nuts. The Q-Jet does have a few "weak points" but nothing like the "weak points" for Holley carburetors----just no comparison, at all. For racing applications, the Holley may be preferable, but I still think that one could do real well with a properly set-up Q-Jet, too.
As a matter of fact, my greatest "point of concern" with my "ZL-1" is the use of the Holley carburetor. I've been very worried for a long time that my decision to go the Holley route is one that I'm going to come to regret (maybe that's why I've been so slow in getting the thing running----I don't want to face the consequences of my decision to go Holley).
To change the carburetor decision is going to be a MAJOR problem for me. That's because to change the carburetor, I need to change the intake manifold (that part's no problem since I have plenty of the 69 Corvette Q-Jet manifolds "in waiting"). However, to change the manifold, I also need to change the heads from rectangular port to oval port design. That's where things get more difficult and , certainly, expensive.
Fortunately, I won't be driving this car day-to-day. So, MAYBE I'll be able to live with the Holley under those circumstances. The last Holley carburetor-equipped car I drove on a day-to-day basis ended on September 30, 1969 when I sold it. But, I've NEVER forgotten it. I didn't shed a tear when I saw that car drive off after what I'd been through with it.In Appreciation of John HinckleyComment
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Re: Q-jet
Duke-----
As I've said many times before, the Q-Jet is the absolute best street carburetor EVER designed. Anyone that would rather use a Holley for primarily street operation is absolutely nuts. The Q-Jet does have a few "weak points" but nothing like the "weak points" for Holley carburetors----just no comparison, at all. For racing applications, the Holley may be preferable, but I still think that one could do real well with a properly set-up Q-Jet, too.
As a matter of fact, my greatest "point of concern" with my "ZL-1" is the use of the Holley carburetor. I've been very worried for a long time that my decision to go the Holley route is one that I'm going to come to regret (maybe that's why I've been so slow in getting the thing running----I don't want to face the consequences of my decision to go Holley).
To change the carburetor decision is going to be a MAJOR problem for me. That's because to change the carburetor, I need to change the intake manifold (that part's no problem since I have plenty of the 69 Corvette Q-Jet manifolds "in waiting"). However, to change the manifold, I also need to change the heads from rectangular port to oval port design. That's where things get more difficult and , certainly, expensive.
Fortunately, I won't be driving this car day-to-day. So, MAYBE I'll be able to live with the Holley under those circumstances. The last Holley carburetor-equipped car I drove on a day-to-day basis ended on September 30, 1969 when I sold it. But, I've NEVER forgotten it. I didn't shed a tear when I saw that car drive off after what I'd been through with it.In Appreciation of John HinckleyComment
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Re: Q-jet
joe,the popular q jet to holley adapter can be flipped over to provide the reverse with ease if i recall---but surely your big motor would be happier on a 850 holley double pumper---or 950 cfm hp holley if you want some serious get go---philComment
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Re: Q-jet
joe,the popular q jet to holley adapter can be flipped over to provide the reverse with ease if i recall---but surely your big motor would be happier on a 850 holley double pumper---or 950 cfm hp holley if you want some serious get go---philComment
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Re: Q-jet
PHIL-----
I would never use an adapter. Besides, the extra height usually won't fit under a stock 68-72 hood, anyway.
I don't really need any of the extra power that a bigger Holley would THEORETICALLY provide. I will have WAY more power than one could ever use on the street as it is. More power is just an aid to breaking things you don't want to break.In Appreciation of John HinckleyComment
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Re: Q-jet
PHIL-----
I would never use an adapter. Besides, the extra height usually won't fit under a stock 68-72 hood, anyway.
I don't really need any of the extra power that a bigger Holley would THEORETICALLY provide. I will have WAY more power than one could ever use on the street as it is. More power is just an aid to breaking things you don't want to break.In Appreciation of John HinckleyComment
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If one were interested in acquiring...
...a restored 750 Q-Jet, any sourcing suggestions? This would be for use on a 383 crate SBC, so numbers & date are of no concern - only quality of the product. Thanks, DennisComment
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If one were interested in acquiring...
...a restored 750 Q-Jet, any sourcing suggestions? This would be for use on a 383 crate SBC, so numbers & date are of no concern - only quality of the product. Thanks, DennisComment
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i buy parts from these guys and they sell carbs
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i buy parts from these guys and they sell carbs
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