Hey fellas, been awhile since posting but I've been busy. A year or so ago I was asking ?'s RE: headers,exhaust,etc... Well I got that done with A set of Flowtech long tubes and Magnaflow muffs. I also swapped the 2bll for a 4bll setup, Performer intake and a 750 Qjet given to me by a friend.

Here lies the problem. I seem to have lost my low-end torque(tire squealing) and mileage that I had with the 2bll. The shop that hung my headers suggested that the Q was too much carb for my setup. My 350 is literally stock except the parts mentioned above and a water pump. The guy at the machine shop thought that a Holley Street Avenger 570cfm would be the one to go with, but my buddy at Oreilly's says that's too small and rec's a Edelbrock Thunder Series 650. If I remember correctly most posters think Edles are crap, but what about the size? I know Barry Grant has a 650. Any and all comments appreciated.

 

I'd make sure the advance is correct and that your air/fuels are correct as well. Sometimes a $100 chassis dyno session is worth the money. It'll tell you alot.

 

i can't tell you what size to go with, but i know a lot of people over carb an engine. for just a stock 350 a 650 or 670 cfm is probably plenty, a bigger cube engine needs a bigger carb that flows more cfm, but putting a big carb on a small motor can hurt your performance, you might lose the low end responsiveness. at least that is what i have always been taught, especially if you just want a goot street carb. also you are probably going to want vacuum secodaries and as far as what brand to get i think its just personal preference holley, edlebrock, qjet etc.

 

Don't forget that Q-jets were originally available on SBO engines. I suggest you look at your timing and carburetor settings before ditching the Q-jet.

 

Based on that statement, they're idiots. As noted, the Qjet was factory offered on the 350. The primary side is SMALLER than on the 2GC and should give you BETTER low-end torque. The secondary air valves don't open until the engine needs the air flow.

Where did your carb come from? Was it calibrated for your engine? If the air valve spring wrap is too loose, you'll loose bottom end.

 

Thanks to everyone for their response. As I'm just learning the wrenching hobby, I have to go with what I learn from sites like this and the guys at the auto stores.

What I know is that the timing was set for the 2bll that was original and it still hits the mark, it starts cold with 2 pats and hold to the floor, and I can reach in the window and crank it after it warms up(0 pats). I know that the Q came on 350's stock, but didn't know if the internals(cam, lifters, crank, etc...) might have been different.

As I'd stated above, this carb was given to me by a friend when I ran short on cash for a new one. He had it on his '79 Firebird which has the GM SB(403?). He said that it was the same block as my 350 just bored out more.
To my limited knowledge there are only 2 dynos here in Oklahoma and both are over 100 miles away(googles my friend), so not sure if that makes fiscal sense. I also read somewhere about curving the distributor but am clueless. Is it possible that the Q just needs to be rebuilt for a smaller engine? Or is a rebuild a rebuild?
ANY further feedback is welcomed.
Thanks
Walt

 

http://www.corvettefever.com/techart...wer/index.html

The beauty of a Q-jet is that the small primaries are great for throttle response and fuel economy but the large secondaries are there when you need the extra air and fuel. A carb in good working order off of a stock 403 should be fine for your application, sounds like there is an issue elsewhere else, carb, tuning, etc.

 

Might want to check posts again...Edelbrock carb is unbelievable. Had mine for 8 years and worked better than my Q-Jet right out of the box. Also, the Q-jet works off of vacuum, so your 350 won't get the full 750 CFM unless the motor mandates it, so this notion that the Q-jet is too much is simply incorrect.

 

I've had this argument with folks on other forums. The Q-jet is NOT a vacuum secondary carb. The air valves are opened by mass airflow. The secondary throttle blades open mechanically. The air valves won't open unless there is airflow through them. This is different from a vacuum secondary Holley, for example. If you were somehow to cover only the secondary barrels of the Holley, the secondary throttle blades would still open because they are controlled by a vacuum diaphragm that is tied to venturi vacuum in the primaries. If you did the same thing to a Qjet, the secondary air valves would NOT open, because there would be no airflow through them.

 

So the consensus seems to be that the Q-jet is fine, it just needs to be calibrated for my 350 right? I know I'm not gonna get the same mileage I just want my torque back.

 

Somehow I mistated what I meant. Joe we are saying the same thing, I never meant that the Q-jet works like a Holley. You wrote, "The air valves won't open unless there is airflow through them." I said the same thing in different words by stating, "Your 350 won't get the full 750 CFM unless the motor mandates it." As the saying goes, "things get lost in the translation." I should have worded my previous post in clearer terminology, especially using the word "vacuum" to mean "airflow".

 

did you rebuild the Quadrajet you got from your buddy? I would put a good bet on the Quadrajet just needs to be rebuilt and tuned on the car. This is the reason many people foolishly toss them in the trash.

you dont "need" dyno time, but it does help. You need to find a local shop who can rebuild it and tune it on the car.

 

Or, send your Q-jet to a rebuilding guru like Danny S. He is a member on our site (70Wcars) that rebuilds Q-jets. If you send him a carburetor core he will rebuild it specifically for your engine. I had him tune my Q-jet for my newly rebuilt 455. It works great!

 

money well spent instead of buying a Holley type replacement.

 

That should be a 800 cfm Qjet, even better. Rebuild it and record what jets and primary rods are in it. Also see what secondary rods and hanger are in it. The secondary door should be set to around 1.3" measuring full open, back of the door to the back of the opening. Mine was much less, around 1.6". Cliff Ruggles book is a good resource for understanding these carbs.

 

I got a Qjet Carb that is freashly rebuilt...And Iam totally lost on where all the vacuum hose's go..It has a electric choke on it....Can any of you show pictures or what not of where the hose's are surpose to got....Cause iam having a time trying to even get the car started....I cant even get the distributor on how it surpose to be....HHHHHHHEEEELLLPPPP!!!!!!!!!!!!!

 

As was stated the Q-jet properly tuned is going to get you the best MPG.
It's smaller primaries being the reason from what I was told.

The Edelbrock is idiot proof though IMO.
I'm no carb expert but the Edelbrocks seem to be the best for newbs.
I put an Edelbrock 1407 on mine.

I'd actually like to learn more about the Q-jets though because properly tuned we have a guy on Nastyz28
with a 1980 Z28 and a T-56 6-speed getting over 23mpg with his on the highway. His motor isn't over 300hp tho.

 

Aceshigh is correct on the Edelbrock. It's superior and more effecient design makes it the best carb I've ever had...whether a "Neebie" or experienced hotrodder. No Q-jet bogging problems, etc, just great performance. No gaskets below fuel levels, etc. make it the only way to go IMO.

 

I ran an Edelbrock on my 1964 Olds 98 for a time. It worked well.

FWIW, if you decided to buy an aftermarket carburetor you might consider the Summit carburetor. Here is their 600 cfm version:

http://www.summitracing.com/parts/SUM-M08600VS/

 

Bogging problems? Can't use an allen wrench and small standard screwdriver? I haven't used any AFB carbs but have ran the Thermoquad and BBD. The Thermoquad's choke was junk, just couldn't get it to work. The BBD also sucked, would just flood itself. Rebuilding it made it worse, not the only one with that problem. I know others have said they are NOT efficient carbs. I pull around 20 mpg with my mild 403, 2004r and 3.42 gears with 25.5" tire. The Qjet's drive-ability and economy just kills most other carbs, was one of the reasons GM was #1. Ford and Dodge's carburetor's sucked, pigs on fuel and less driver friendly.

 

"Quadrabog"... nickname didn't come out of thin air..but from the experience of too many people, thus its circulation.

 

it came from inexperienced people who then assumed the new holley they put on was better since the car ran better.

I have a Quadrajet on my car and there is no bog or driveability issues.

 

The nicknames came from Experienced hotrodders who knew when it was time to move on. "Quadrabog" and "Quadrajunk" are well circulated nicknames for the Q-Jet across the internet. If you want to use it, then use it.

 

Sorry, but the E-brock is a Carter AFB with a different nameplate. The design predates that of the Qjet by almost a decade - the AFB (which stands for Aluminum Four Barrel) was first marketed in 1957!!! You can see how I'm struggling to understand how this older and less sophisticated design is "superior and more efficient" than a newer one. The reality is that the derogatory names for Qjets come from people who were too lazy to find out the proper way to rebuild and adjust them. The Qjet is a far more sophisticated design, with triple venturies on the primary side for amplified and thus very sensitive signal. This allows very fine control of the low speed mixture, improving part throttle response and mileage. At the same time, the large secondaries provide good flow and power for WOT operation. By the way, the Qjet also has no gaskets below the fuel level, and the alleged leaking well plugs only applies to the first couple of years where Rochester used the small press-in sheet metal plugs. All Qjets built since 1968 use spun-in aluminum well plugs and I've NEVER seen one of those leak in 35 years of working on them.

Yes, a brand new FIFTY year old design carb will work better out of the box than a newer one that's worn and incorrectly rebuilt or adjusted. Naturally, a used Qjet needs to be inspected for things like worn throttle shaft bushings, warped castings, and leaking vacuum break diaphragms. When built correctly, you can't touch a Qjet for responsiveness. The AFB is a solid second place and a good carb as half a century of history shows, but it is not nearly as sophisticated as a Qjet.

 

I think the big deal with Q-jets is that they are difficult to fine tune. I've rebuit numerous Q-jets and had decent success but it wasn't until I had Danny S. rebuild one for me that I was able to get the full potential. I also ran a new Edelbrock and Oldsguy had a Holley on his 69 Delta 88. These both worked well; however, the Holley never worked quite right even after numerous rebuilds (I think the carb was heat damaged). You just have to decide if you want to spend the money on a new carb, or spend money on a Q-jet to have it rebuilt properly. FWIW, I think most folks that are decent with tools can setup a Q-jet well enough to run on the street. You just have to be willing to spend time getting it there.

 

Joe,
You are correct regarding AFB, but Edelbrock has done some redesigning on that carb so it is not the same "old thing" as 1957. As for the argument, "Well, people just can't work on Q-Jets which are always screwing up" I don't think there is any sense to it. Top engine builders tire of them and chuck them out. Even Q-Jet users complain about Q-Jets,(read the post above as only one example), not to mention the fact that Q-Jets always seem to be the carbs screwing up...you know, the ones no one knows how to fix. Who wants to own the brand of carb with the "Always screwing up reputation?" Again, the nicknames are there for a reason, and no one has explained that away. If someone wants to use a Q-Jet and claim its great for them, so be it. For me, I'm in the Edelbrock crowd...going faster and more trouble free than w/ the Q-Jet I had.

 

agree to disagree.

can we discuss ford vs Chevy?

 

Sure. Did you know that Ford used a factory-installed Qjet on the 429 Cobra Jet motors? I am not making this up.

 

That is interesting Joe. Didn't B bodies in the mid 60s with manual transmissions use a Ford Toploader?

 

Can we throw Hemis into the mix? I thought they used the AFB carb

 

Not just the B-bodies. The base trans on both the 442 and the GTO for a lot of years was the "Dearborn" HD three speed manual.

 

Yes...the Hemis used TWO AFB's...My Olds just ONE Q-jet...LOL...

Seriously, thanks for the kind words and I have spoken with Walter about his carb and we are well on the way to getting his issue resolved.

And Q-jets are required in legal Stock Elim. racing per NHRA...with 10 sec. ET's using essentially the same Q-jet that Granma had on the Caddy!!! Versatility PLUS!!

Danny S.

 

2 carbs and a lot more horsepower as well...can't forget that one small issue.

 

I ran all types of factory carbs, worn out is worn out. I have rebuilt a few Qjets that turned out goofy. Bad new parts, worn throttle shafts, crap floats and carbs set too lean come to mind. Edelbrock has improved the design over the original. Notice what year the AFB disappeared, was not efficient enough to pass emissions. Good design but the Qjet was the pinnacle in carb sophistication. Setting up for high performance takes expert hands. The Edelbrock RPM carb really one of the few Qjets set up for radical performance engines. I did see quite a few Mustangs with Edelbrock carbs at our track. Just shows some use them for racing over the Holley.

 

And I'm sure that was solely due to carb selection and had NOTHING to do with, oh, say cylinder head design...

 

Shhhhh, Joe..you're gonna make everyone switch to MOPAR! Talk about setting off a firestorm--everyone will be using AFB carbs, I mean the whole thing will be a mess!

 

The original AFB design was introduced in 1957
The AVS design was introduced in 1966
There is also the later model AFB made later on into the '60's that's used today.
Q-jets have been around for nearly a century as well as Carters.......and Carter also built Q-jets.
There's a BUNCH of drawbacks to the old Q-jets, but they were called the best for their time.
http://en.wikipedia.org/wiki/Quadrajet#Drawbacks

I've heard they were not for the novice, that's why I never gave it a shot.
Getting a used one I had too many risks of getting warped parts that would just promote aggravation.

I rebuilt a Holley 1850 which was the most common used back then and I threw it on the shelf
because it was too much of a PITA for me to tune right. The Eddy was plug and play. Ran great.
I just think Q-jets are more for the guys who have been around the block and know how to deal
with those aggravation points.

I'd give it a shot though if I had one built right and tuned right, just to compare performance.

 

A BUNCH? Did you actually read that link?

Which is pretty much what I said above.

The other "drawbacks" are a small float bowl (only a problem under extreme use conditions), stripped inlet threads (due to ham-fisted installers), casting warpage (due to overtightening - see "ham-fisted installers"), worn shaft bushings (see my post above), and deteriorating float due to modern gas. I'm sorry, but how many of these "drawbacks" are the fault of the basic design of the carb?

 

Chrysler ended up DROPPING the AFB's in the 70's, and went to...of all things...
a Quadrajet. Better emissions, better power, better than the Thermoquad, better than the AFB.
Had one on a 86 Ramcharger. Have another in the shop.
Even Chrysler figured it out.
The people who threw them out did not bother to take the time to learn it.
Those who called it a quadrabog, could not figure out how to adjust the secondary air valve. These work FANTASTIC when adjusted right.

If anyone here want's to get rid of a vintage Q-jet, or a 403 Q-jet... I will gladly Paypal $15 for the U.S.P.S. flat rate postage to you, to have you ship it out to me.

If you have an AFB, you can keep it.

Jim

 

Holley's have several advantages in performance applications. Huge fuel bowls, VERY easy to fine tune pump shot, east to change jets and set float level. They work very well at WOT and pretty good at part throttle. But a Q-jet is hard to beat on a daily driver. They are a nice nix of performance and economy. My one bone to pick is that they are not easy to tune. Yes, once set up they are great, but they are not easy to change jets on, or the big thing IMO is modifying the initial shot. There can also be fuel supply issues on a large CI/HP engine, the fuel bowl is pretty small.

So, the question is; are you willing to give up a few HP to gain the manners, economy, and reliability of a Q-jet? Your call. I have a 3310 Holley on my 10.25 to 1 355. It sat for several month in the FL heat, started right up after one pump, no choke. Car runs great. I had a 670 Street Avenger on my 9 to 1 355, ran great, terrific throttle response.

Bottom line, a carb is a device that meters and atomizes fuel. Functioning properly and calibrated correctly, any one will work, they all have pros and cons.