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Quadrajet to Holley

25K views 55 replies 26 participants last post by  handy7rick 
#1 ·
I have a mild Chevy 350 in a 28 Nash street rod. The carb on it is an OEM Carter built quadrajet. Performance is lacking. It runs ok, but I know it should run better. A trusted friend reccomended I scrap the quadrajet and put on a Holley 650 with mechanical secondaries. The car has sat for a while so I had planned to rebuild the carb anyhow, but if I'm better off with the Holley, then I'll go that direction. My question is, is it a straight swap? Will the Holley fit on the same manifold (it's and Edlebrock manifold)? Is it as simple as going to the auto parts store buying a carb and bring it home and slapping it on? (Then fine tuning I'm sure) if so, which Holley to I want they seem to offer a million.

It may seem like a silly question to a lot of you more knowledgeable folks. I've been a motorcycle mechanic my whole life and have some boat engine experience, I have the mechanical abilities and the tools, I just have very little experience with carbureted small block Chevy engines.
 
#2 ·
I like Holleys but if I were you I would send that Q-jet to a performance Q-jet rebuilder with your specs and let him do it. Just switching to a Holley won't cure you problem plus it won't fit on your spreadbore intake w/o an adapter.....and the adapter is a no-no. Do a search on this forum for "Q-jet rebuilders" or "Q-jet help"
 
#3 ·
You think getting the Q-jet rebuilt would be a better solution than swapping for a Holley? I'm not trying to save money here, I'm not wealthy, but I want it right. If a new manifold and and carb are the right solution, I'll go that way. But if paying a proto rebuild the Q-jet is the way to go, I can do that as well, however, I do prefer to do everything myself.
 
#5 ·
The Q-jet, when properly rebuilt and tuned for the application, is one of the best carbs ever designed and built. Problem is, most have no idea how to properly rebuild them or adjust them. Just replacing gaskets, float, seals, etc. , wont return your q-jet to its proper form.(I also suggest sending it out to a Q-Jet Pro) The q-jet will offer better idle quality, off idle response, full throttle power, and the best possible economy of any factory carb.

There are cars out there knockin down 25mpg, others running 9 sec ET's, others pulling huge loads with big block trucks, all with a Q-Jet. There are only 2 sizes of Q-jet, 750 or 800cfm, yet they can be tuned to work on anything from Chevy and Olds 307's to big torque Buicks and Pontiac. From grocery getters to Super stockers.

My first suggestion would be to pick up Cliff Ruggles Q-Jet book, its current considered the best Q-jet book available. Check Amazon or here:
Cliffs High Performance Quadrajets :: Qjet Carburetor Rebuild Kits, Parts, Quadrajet Rebuilding, Quadrajet Parts, Bushing Kits, Carb Tuning

Read it a couple of times, then decide if you want to tackle the rebuild/mods yourself, or send it to a Q-jet pro.

Good luck with your decision
 
#8 ·
I realize I could have other issues, but I'm playing a hunch. The car has sat for a while. That usually means the fuel varnished to some extent, and I'm sure we've all seen what that can do a million times. I had planned to rebuild the carb just for piece of mind when my friend reccomended I toss the Q-jet and put on a Holey 650 spread bore. So I just figured I'd run it by you gurus.

I did find one problem. I had guessed my secondaries might not be opening. So after some research here and other places, I found that there is a little latch on the Q-jet that prevents the secondaries from opening while the choke is on. On my carb, that little latch appears to have been installed improperly. It just hangs there and never moves out of the way when the choke turns off, so it was preventing my secondaries from opening. I wired it out of the way, and the car runs better. But I still feel like the upper flaps aren't opening. When I first started poking around, they were stuck slightly, like they hadn't moved in a while. So now I'm going to check for vacuum issues.

I'm learning as I go here.
 
#7 ·
Q jet is one of the best fuel mixers commonly on GM, another would be the carter AVS found on many mopars. Cliffs book is the good way, and will identify what you have. my library can get these type books, and there are tons of women there. After camming up, my q jets had drilled idle ports, and quicker vacuum break pod timing to open the secondaries, the G hanger , rods. They call them quadrabogs when the secondaries just flop open from too much secondary pod.
 
#11 ·
The secondary top stuck when you tipped it in? That will do it.

Yes, the throttle shaft is gunked up. You can clean that. This so common, yo show remove the carb top and soak it. The screws holding the butterfly flaps on the shaft can be so tight thats it bends the shaft slightly causing this. Possible, not likely. Once the choke switch position or bend is fixed that will not be a problem.
 
#12 ·
Yes. Not bad, I didn't need a crow bar to free it or anything. But when I moved it by hand, it had a little stick to it. Like it hadn't moved for a while. Once I moved it, it freed right up for the entire range of its travel. I assume if it moves freely, then the upper flaps are functioning correctly, right? There isn't a vacuum line to open the upper flaps that I can see, they appear to open once the secondary butterflies open and air begins to move past them. They are hooked to a little vacuum puller, but that looks like its made to close them, not open them, another choke bypass maybe?
 
#13 ·
The q-jet has a gazillion pieces in it. It really is a good carb if you have the time to learn it,,,,or,find a local super stock racer that uses a q jet,make a minor sponsorship to his car and I guarantee he will make your q-jet into a fabulous street carb with little tweeks you wont know about until you rebuild a few or he shows you.
 
#14 ·
It's funny that you guys like the Q-jet so much. Every time I take it anywhere the first thing other car guys notice is the carb. I took the car to lunch today and a guy looked the car over for maybe 15 seconds and said "Nice car, but you got to get rid of that Quadrajunk and put a Holley on there." that must be the 5th or 6th time I've heard that in less than a week!
 
#15 ·
those are all people who had one get out of tune and had no idea how to fix it. When I was young I was the same way, just bolt on a holley. I can tune a Holley with one eye tied behind my aching back.
For the Q-jet, I needed some help. On a car that see's a lot of cruising, the Q-jet is fantastic, great part throttle response, the best mpg this side of an EFI unit.

I used them on wagons, 4x4's, stockish muscle cars, anything thats built mainly for street use.

Even the Holley spreadbore carbs. need tuning, and wont get anywhere near the mpg that the Q-jet can pull down. They will make the car seem faster, but for the cost you can get your Q-jet professionally restored and calibrated for your motor.
 
#16 ·
Stick with the q-jet they have a lot less tuning issues , not knocking holley I like them also but if you have never tuned one it could be a horrible nightmare for you. The name of a good performance shop that deals with q-jets and holleys is the Carb shop they can take care of any problem with a q-jet and they are pretty reasonable on their prices.
 
#17 ·
I'm wondering about something. Earlier in this thread, someone mentioned that a carb adapter is a big no-no. So I got to looking at this set-up. The intake is a Victor Jr., which appears to be a square bore intake, and the Q-Jet appears to be mounted to an adpter plate. So assuming I was going to replace the carb with something else, if I wanted to not use the adapter plate, I'd need a square bore carb, not a spread bore, is that correct?
 
#19 ·
Check this out. Its not just a carb adapter, it is designed to move the q-jet further back to improve fuel distribution.
Edelbrock 2693 - Edelbrock Carburetor Adapters - Overview - SummitRacing.com

A lot of people say adapters are bad. I can see how necking down a spreadbore to a squarebore could cause problems when the secondaries open, but by the time you are opening the secondaries you are not worried about throttle response, etc. Primaries I think the impact would be minimal at best. I have been trying to find any dyno numbers on the subject and not been successful. Also since the adapters are open spacer plenums that would tend to mitigate any negative impacts on a dual plane intake.
 
#20 ·
Just replacig the Q-jet to a holley will not improve the performance. The motor can run very strong with a Q-jet carb. What you are lacking is compression, gears for the rear end, a good exhaust system, and a high stall converter, and if you do not have those four items. The motor will not pull any power. No matter what carb you are using or manifold. They all have to work together to get results.
 
#21 ·
I'm not trying to make more power. Gears, exhaust, compression and stall converters are a separate topic. (As they apply to me.)

My goal for the carb isn't more power, if and when we start trying to wring more power out of this engine, that will be a different discussion. For right now, I just want it to run good in it's current configuration. I have zero doubt that the Q-Jet can be made to run terrific. But it would appear that the intake on the car now is made for a square bore carb, not the spread bore. And since I read that adapters were bad, I thought I'd run it by you guys. I'm just trying to make it run well for the rest of our short season here. Come winter time, we can, and will be discussing all manner of power increases. ;)

So my question was, (I know it was answered) if I want to bolt a carb straight to my Edlebrock Victor Jr. intake with no adapter, do I want a spread bore carb or a square bore carb?
 
#27 ·
A vac. sec. carb is just much more gas mileage friendly, You can change the spring rate in the housing to either quicken or slow down the opening of the secondary's. A mechanical secondary carb uses non-adjustable secondary linkage and it's gas mileage is in direct correlation to your right foot.
 
#29 ·
It is only a street vehicle. And always will be. The only type of racing I'm interested in take place on 2 wheels, and it's not drag racing. ;-)

That said, it will always be a street vehicle. Right now, it's a matter of straightening out drivability issues more than peak power. Come winter time, I could see me making some serious mods in the pursuit of power, maybe even a whole new engine and tranny, but still street power. I don't see many 1928 Nash's on the race tracks!

Thanks for all the input gents!
 
#30 ·
Edelbrocks are the best street carb I have seen for a basic 350.

Quadrajets are the best carb if you have too much time on your hands and want to spend it trying to tune a carb. They can work well, but it just seems like a lot of needless effort to me.

They're are also a lot of great holley based carbs out there but they can get pricey.

I've heard good things about the summit carbs but never used one myself.
 
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