Carbureted LSX forum - I'm Running a Q-jet on my 5.3 and Love it

I've seen people asking about running a Q-jet, I've gotten mixed answers but I've never seen anyone actually do it..

I did... I'm running a 1968 Q-jet from a stock Vette 350 and it absolutely runs like a champ.. WAYY better than the Holley 750.. No matter what I did to that carb it ran ok...but PIG rich...

The only downfall is I had to run a shitty adapter.. but i don't even notice it..

I used an Olds 307 throttle bracket (for the correct geometry for the Th2004r TV cable) and fuel pressure is set at 6PSI

Ultimately this setup is as close as im going to get vs EFI but its a hoot.. Im currently doing my research and I plan on going back to EFI but I still have some learning to do.. so in the mean time Ill play with carbs..

Heres a pic and some video

http://sphotos.xx.fbcdn.net/hphotos-ash4/486584_10150899249752190_876678005_n.jpg

http://www.youtube.com/watch?v=4T7iQgxHRs8

Awesome, Q-Jets are great carbs.

I had a 750 holley on my 5.3 because that's all I had and it was fat like I knew it should be. Went to a 650 and runs like it should. At least you won't get gas everywhere.

nice.. I'm currently doing a carb Lq9, I've already have a Qjet. I wonder how good it will perform vs the $500+ aftermarket carbs, for sure mpg will be up there with efi.

It will perform GREAT.
the only issues I have had with the Q-Jet, are when you put a big cam in, with low idle vacuum. Tuning parts for the "power enrichment" circuit, are hard to come by, and that means everything to the driveability of the combo.

Thank you for your praises guys! I have great vacuum but I believe its just the perfect carb for my setup...

I mean I know the hardcore guys go with Holleys and thats just how it is.. I too ran the 750 because thats all I had to play with and while it ran ok.. It would load up on the freeway cruising... Id cruise then step into it a bit to pass a car and it would load then clear out and go... The Q is just happy all over.. I have sloppy throttle shafts which I plan to correct but other than that I never thought it would run as well as it does

I wonder how it would do with the howards #190245-12 222/225 @50 .561/578 cam

If it work it works. Having complaints of a 750 on a 5.3 are common as they are usually set up for large engines. But a 650 Holley is usually great. I want to try a edelbrock on my 4.8 but then the TPS bracket and sensor will need to be some how made to work..again.

Well ya I figured it would be bad in regards to mileage but I tried it anyways... the q jet is a superior street Carb however the square bore manifold was my only issue

Superior? No idea. I know a vac sec Holley and a q jet are both street oriented, and I'm sure they boil down to the tune. If one or the other is off, it is the better tuned that would surely win. We are talking controlled fuel leak either way. Never seen a comparrison on the same engine.

Qjet,s are great carbs! Great post!!!

The quadrajet is superior street Carb for the simple fact GM spent countless time and money on the Carb which served on many vehicles from grandmas grocery getter to many hot rods of yesterday...and its street oriented life span lasted for almost 30yrs from the factory.
Holley doesn't have the same cred in that respect. For racing there is no doubt Holley is.the top.dog
But on the street the quad wins

That's just from my point of view and experience.. I have plenty of experience with both and only partial to each per application...

Have never had luck with used quads, but a used Holley, always pay off. New is new though.

That's because they're designed for specific applications...I too have run into issues with used carbs but a stock 350 Carb on a mild 5.3 just happened to work for me.

Lots of people seem to think that the VS Holleys can't be tuned to run comparable to OEM, even on a mild/street combo.....I disagree. It just takes time and proper size selection. Everyone thinks they need a 750cfm for the street, even with small cubes and relatively low redlines. I assume this is because all the factory issued Q-jets (other than the rare 800s) are 750s, even on small engines, so people feel that a 750 square bore will also be fine with vacuum control over the secondaries. I disagree. Q-jet is a spread bore, so the primaries are small and will respond well at part throttle even with small displacement. A 750 square bore obviously uses bigger primaries than a 750 Q-jet, so throttle response will be less crisp with a small(er) engine. If some of the guys that have poor street manners with a 750 Holley on their small displacement street engines would just try a 650 or even 600, I think they would be surprised at how good it could run with some tuning. Granted this may not be the best course if you rev to 7000rpm though.

There is no arguing the fact that a Q-jet will offer superior MPG over most aftermarket carbs, but too many people just give up on their Holley thinking that it just can't be tuned well for the street even on a rather mild combo. Often I think this is because they are overshooting their cfm requirements, and jump right to a 750 for street applications, even with small cubes and relatively low redlines. Another part of the issue is bad tuning habits people have delevoped for Holleys, some of which were perpetuated by Holley themselves (such as their poor recommendation for power valve selection).

Either way, Q-jet is certainly a good carb, offering OEM engineering, best potential MPG, and will run well on a wide range of engine sizes and applications...no arguements there. But Holleys can be excellent street carbs as well, when properly sized and tuned.

Lots of people seem to think that the VS Holleys can't be tuned to run comparable to OEM, even on a mild/street combo.....I disagree. It just takes time and proper size selection. Everyone thinks they need a 750cfm for the street, even with small cubes and relatively low redlines. I assume this is because all the factory issued Q-jets (other than the rare 800s) are 750s, even on small engines, so people feel that a 750 square bore will also be fine with vacuum control over the secondaries. I disagree. Q-jet is a spread bore, so the primaries are small and will respond well at part throttle even with small displacement. A 750 square bore obviously uses bigger primaries than a 750 Q-jet, so throttle response will be less crisp with a small(er) engine. If some of the guys that have poor street manners with a 750 Holley on their small displacement street engines would just try a 650 or even 600, I think they would be surprised at how good it could run with some tuning. Granted this may not be the best course if you rev to 7000rpm though.

There is no arguing the fact that a Q-jet will offer superior MPG over most aftermarket carbs, but too many people just give up on their Holley thinking that it just can't be tuned well for the street even on a rather mild combo. Often I think this is because they are overshooting their cfm requirements, and jump right to a 750 for street applications, even with small cubes and relatively low redlines. Another part of the issue is bad tuning habits people have delevoped for Holleys, some of which were perpetuated by Holley themselves (such as their poor recommendation for power valve selection).

Either way, Q-jet is certainly a good carb, offering OEM engineering, best potential MPG, and will run well on a wide range of engine sizes and applications...no arguements there. But Holleys can be excellent street carbs as well, when properly sized and tuned.

It all boils down to ones tastes and patience I suppose..

Hi guys... I'm running a Q-jet of an 86 chevy 1 ton dually 4x4 on my LS3. Its an 800,,I've recalibrated it. My Ls has Lingenfelter stage III heads,10.5 compression,,A comp cams xer278 cam,,I think. Idle vacuum is only 12" @ 850rpm. Light power piston spring to keep rods down at idle,,adjust power piston half to 1 turn up from bottom etc. Did alot of tuning to mine,running a built non electronic 700r4,with a lock up convertor on a switch that I control.Carb is on a GMPP LSX intake and I run an adapter like yours. I get 16-17 mpg,,Runs stupid fast,,Oh yea,Its in my 82 jeep CJ7 street toy. Will destroy 35's if I let it,will pull the front wheels outa the hole if launched hard. Mosier 35 spline dana 60 in back and waggoneer dana 44 in front with 4:10's. Tried 2 holleys,,,POS. I did end up putting a divider in the carb adapter to increase my vacuum signal to the carb and to help bottom end torque. I've suprised More than a couple of mustangs and camaros,,and alot of trucks... End result ,,,Q-JETS??? Hell yes!!!

It is all the same as far as not liking a carb, a poorly tunes holley or quadrajunk will always be a POS.

:corn:

I've seen people asking about running a Q-jet, I've gotten mixed answers but I've never seen anyone actually do it..

I did... I'm running a 1968 Q-jet from a stock Vette 350 and it absolutely runs like a champ.. WAYY better than the Holley 750.. No matter what I did to that carb it ran ok...but PIG rich...

The only downfall is I had to run a shitty adapter.. but i don't even notice it..

I used an Olds 307 throttle bracket (for the correct geometry for the Th2004r TV cable) and fuel pressure is set at 6PSI

Ultimately this setup is as close as im going to get vs EFI but its a hoot.. Im currently doing my research and I plan on going back to EFI but I still have some learning to do.. so in the mean time Ill play with carbs..

Heres a pic and some video

http://sphotos.xx.fbcdn.net/hphotos-ash4/486584_10150899249752190_876678005_n.jpg

http://www.youtube.com/watch?v=4T7iQgxHRs8

I like it I'm about to drop a LS1 out of a 2003 Suburban into my 79 Firebird, I had a 400 in it I also have a Q-jet off the 400 & 600 CFM carb I might have to try the Q-jet. If there anything that you can help me with hit me up.
Thanks

Its all about knowing how to tune them they are a totally different beast from a holley. I used to work for a guy that could tune a q to runn with any holley!

Basically you can't expect a Q-Jet off a big engine with a lower power band to perform the same on a smaller engine with a higher power band..

In my case I got lucky.. A took basically a stock Q-jet off a 350 Vette motor and tossed it on a motor thats only 25 cubes smaller but has a better combustion chamber and different power band.. It seems to work perfect.. I need to get a wide band 02 to really dial it in but as it sits right now it runs badass.. 2nd gear pull from 40 on up is amazing the carb doesnt miss a beat.

I'm having horrible luck with my 750 mechanical secondary on my stock 5.3 in my s10. I have a q-jet laying around and after reading this I think I will buy the adapter and throw it on and see what happens.

I don't want to be a a hole, but it is a duh factor, a 750 mechanical, wide open on a 5.3 in a car with not large converter that has some weight is not going to perform as you wish. A 650 DP maybe, but not a 750. A 750 vacuum secondary would be fantastic. If you have a spare a jet, try it, or sell the 750/trade for a VS.

Yea had I known that in the beginning that's what I would have bought. My plans are a big cam and 243s eventually so I bought the carb with the intentions of doing all that. But for right now with stock internals, its definitely not a good choice.

Edit: actually zone, at wide open throttle it runs hard. It's the part throttle cruising and acceleration that really sucks. It misses and bogs at about 1/4 throttle. So you either have to barely give it any throttle or give it over half. It's a pain for daily driving.

It is out of tune as well, the mid range throttle is where i had issues as well on a 5.3 with a cam and my mechanical 750 off my 89 RS with the 6.0, the 3000 converter was not enough to help either.

Yea that's why I think I'm just gonna throw the q jet on it for now while its still stock. Seems a better option at this point.

I say you invest in a wideband O2, then you will have some VALUABLE feedback in order to tune it to run as good as it possibly can, no matter what parts you throw at it.
Barrett

Yea that's why I think I'm just gonna throw the q jet on it for now while its still stock. Seems a better option at this point.

As Ive said I had great luck using a Q-jet off a motor with similar displacement and compression.. A stock 5.3 using a Q found on a stock 9.0 350 would get you close to where you need to be... My point is dialing one of these carbs in from scratch is a bitch no matter what..

A Q found on a 305 might suit a 4.8 better as well as a carb found off a 400 or 403 Olds might be close in the ball park for a 6.0.. Just a thought.. My opinion is not law just from what I've experienced..

Also mentioned before if your running a wild cam a Q-jet probably wouldnt be a good carb for that application because they so depend on the all important vacuum signal from the motor..

Well I threw the q jet I had on my truck tonight. I think it needs rebuilt. It's squeeling super loud and running like crap. I'm thinking its a loud vacuum leak but have yet to trace it. Ran out of time tonight. I did drive around the block and it ran better except for the inconsistent idle and loud noise.

Well I threw the q jet I had on my truck tonight. I think it needs rebuilt. It's squeeling super loud and running like crap. I'm thinking its a loud vacuum leak but have yet to trace it. Ran out of time tonight. I did drive around the block and it ran better except for the inconsistent idle and loud noise.

I wonder where the squealing is coming from... Thats odd.. My Q-jet hisses like a sumbitch but from what ive gathered thats how most sound with an open air cleaner..

Yea I have no idea where it came from either. I took it off and replaced it with an identical one and now it runs perfect! I couldn't an happier. Now my biggest problem is traction. Haha

Yea I have no idea where it came from either. I took it off and replaced it with an identical one and now it runs perfect! I couldn't an happier. Now my biggest problem is traction. Haha

Hell ya.. It would be nice if someone made an intake with a spreadbore mounting boss.. but that almost seems unreasonable..

It is all the same as far as not liking a carb, a poorly tunes holley or quadrajunk will always be a POS.

:nod: Agreed.

I think the small primaries of the spreadbore Q-jet makes it easier for people to toss one on and get decent part throttle performance, and also good driveability on a street engine with little effort. Holleys need to be sized properly (even in VS format, IMO) to give crisp part throttle manners, and they rarely just drop on and perform their best. You really need to work with a Holley out of the box to get best results; usually they will run if you just toss them on, but you'll never get ideal performance without some adjustments. There is a lot of mis-information on Holley tuning that leads people down a path of frustration and poor results, and then this leads to people posting about how "holleys are junk, POS, etc.". If Holleys really were all hopeless junk, then how can you explain all the cars that run well with them? It's all in the tuning.....same as with any fuel delivery setup. ;)

Yea, I have been lucky and dropped them on and also had to spend a day getting them in the ball park. But I do run a VS on my 4.8 with zero issue. I am going to try a edelbrock on my 4.8 going in my 91 RS to see if I can get over 25 MPG out of it and piss off the efi guys that simply refuse to believe a carb can get decent economy.

Yea, I have been lucky and dropped them on and also had to spend a day getting them in the ball park. But I do run a VS on my 4.8 with zero issue. I am going to try a edelbrock on my 4.8 going in my 91 RS to see if I can get over 25 MPG out of it and piss off the efi guys that simply refuse to believe a carb can get decent economy.

I'm aiming for 20 MPG on mine, but then my carb might be a bit big. I put a 800 CFM Edelbrock Thunder AVS on. Still needs tuning (which seems pretty straight-forward), but it sure is fun :nod:

The wide band O2 sensor helps big time.

recomendations on a wideband? Only thing i don't like about my setup is it stinks when i start it in the garage etc. Ive tried getting the smell cleaned up by adjusting using a vacum gauge, but I probly need to check jetting too.

recomendations on a wideband? Only thing i don't like about my setup is it stinks when i start it in the garage etc. Ive tried getting the smell cleaned up by adjusting using a vacum gauge, but I probly need to check jetting too.

Main jets won't have any effect on how it smells (or runs) at idle. If you don't have cats, it's always going to smell some. If you have a cam with a lot of overlap, it's going to smell even more. This is still the case even with a perfectly tuned EFI setup. Verifying your jetting with a wideband is a good thing, but this isn't going to clean up the idle any further.

Main jets won't have any effect on how it smells (or runs) at idle. If you don't have cats, it's always going to smell some. If you have a cam with a lot of overlap, it's going to smell even more. This is still the case even with a perfectly tuned EFI setup. Verifying your jetting with a wideband is a good thing, but this isn't going to clean up the idle any further.

what cats are recomended. Im running 2.5 inch ex w/magnaflows and a dr. gas x pipe

I went with a pair of hi-flow 2.5" cats from Pypes. You can prolly get something similar at jegs or Summit for around 70 bucks a pop.

what cats are recomended. Im running 2.5 inch ex w/magnaflows and a dr. gas x pipe

If your car is the first gen in your avatar then no cats are recommended; no state in the nation would require cats on that old beast. :) They don't help power in any way. Only reason you would ever need them is to pass emissions, assuming the car was a model year 1975 or later and you have a sniffer to deal with.

If your car is the first gen in your avatar then no cats are recommended; no state in the nation would require cats on that old beast. :) They don't help power in any way. Only reason you would ever need them is to pass emissions, assuming the car was a model year 1975 or later and you have a sniffer to deal with.

Want to get rid of gas smell

With the right tune and exhaust exiting correct you will not smell fuel.

beeterolds....do you think there is enough material in the 7118 intake to machine out the spreadore pattern?

looks like it has the dual bolt patern....and some extra material on the sides....i may just have to try this.

i too am a q-jet supporter. they are more tuneable than a holley, you just have to get over being afraid of them. lots of parts, but very simple once you break one down and know what does what. i just canned the 1406 edelbrock that was on my dd when i bought it, went back to a M4ME.

With the right tune and exhaust exiting correct you will not smell fuel.

Got me a fast wideband on the way, so maybe i can get this dialed in just right.

You may also consider putting a charcoal canister off of a later model on the gas tank vent. My car will really stink up the garage on a hot day even if it is not running.

For BEETEROLDS, does your Qjet have an electric choke or a conventional thermal one? Cause Im about to install a Qjet on my LQ9 79trans am but my Qjet has the thermal choke..

Q-Jets are great carbs. I'm not pushing any one type as I agree with everyone here that any carb is only as good as the person tuning it. Rochester carbs typically give the best fuel mileage vs performance but a few companies like JET and SMIcarburetors can really wake them up, but they are expensive. I like BIGS carburetors for Holleys. Anyone try the new Demon with the google valve? Can anyone say Holley 3-barrel! I think pretty rare to come by but Holley tried this a long time ago.

I have not yet proven this to be factual but i've been told by a few older engineers that the q-jet was initially developed by GE. Not the version everyone is using here but the first Rochester carbs to be used by GM.

I just picked up a beautiful 4bbl Q-jet for a friends '81 GMC for a little over a $100. It looks like it was removed from a new car back in '81. It is for a small block. When searching for a Q-jet be aware they come in differnat sizes just like Holleys so size accordingly to your needs. I agree with the comments of oversizing the cfm's and expecting to get max performance and mileage. A general rule of thumb is multiple your cubes by 2 then multiply by .8 to come up with the required cfm carb for your engine. You still have to factor from that point how it will be used. Drag race at high rpm's -- you can go a little bigger. Daily use and best mileage -- better to be conservative.

Sorry Fellas Ive been away these past few days! To answer your questions, I do not believe the carb pad has enough material to machine it for a Spreadbore carb, However I believe you could perhaps "weld" the aluminum spacer (assuming both aluminum components are of the same quality) and start grinding from there..

I have no issue to speak of with the spacer, punching it at WOT gives me no bog whatsoever..

Also I am not running a choke at all.. I had the car out today and just got home with it (Its about 45 here in Akron) and the car started with little trouble.. I thank the high output of the DIS ignition system for that..

Speedtigger- Dude.. you could not be any more correct!!! Thank god for an exhaust fan otherwise my house would REEK right now!!! I think im going to get a canister myself I cant stand the damn fumes anymore

Buy the book by Cliff Ruggles on Qjet performance.

It's full of knowledge and gives info about setting them up for specific applications.