Carb suggestions

[mmag36]

I was looking for some advice for my carb selection. I have a 67 gto with the original 400. The motor has been rebuilt, bored .030 over, zero decked and has a mild insky cam installed. Edelbrock performer intake, Doug's headers and 2.5" pypes exhaust purchased. The tech that worked on the engine suggested a Holley 770cfm/elec choke/vac secondaries. Any comment and or suggestions regarding The 770? It seems a bit much for 400hp or less.

[mburrow]

I'm running a 355 Performer RPM aluminum heads, rpm airgap intake making 334 rear wheel hp and I'm running Edelbrock AVS 650 and it is perfect. Performance is 12.80 at 121 and I get 21 + mpg with my 3:73s and Tremec 5 speed.
I had a 600 cfm and it bogged a little at about 3,500. The 650 took that away and is very responsive right out of the box.
Good luck.

[kryptik]

Honestly, if you have the money and want to spend it, look into a Quickfuel 680CFM SS carb w/ vac secondaries and elec choke.

Definitely one of the better carbs I've owned, picked up one or two inches of idle vacuum over my old 750 Demon. The carb has amazing throttle response, torque, drivability, and power on my ZZ383 (440hp), should do great on your motor.

[wmhjr]

If you have the money, my very strong recommendation would be to talk to Shaker455. So long as you have the detail of what's in your motor, you get a hand built carb, tuned specifically to your build, and tested prior to getting shipped to you.

Not to say any other brand or solution isn't good - but - when you have somebody who really knows their stuff building something specifically for what YOU have....... Nothing beats a custom built carb. And Jeff really knows Pontiacs. He's real real well known over on the Poncho Forums.

[Tom Welch]

check out Cliff Ruggles, he's the man when it comes to Quadrajet carbs, dont laugh until you talk to him. You will be pleasantly surprised.

[wmhjr]

Cliff does some great work with Q-Jets. However, I've never seen any proof that even his Q-Jets can compete head to head with a well built Holley. My feelings are that if you've got to retain stock appearance with a Q-Jet equipped car, Cliff is exactly where you go. However, if you don't have a carb and don't need to stick with stock appearance, there is no good reason to go that route.

[mike renick]

i would put a 750 dbble pumper on it

[H2Ogbodies]

There's a lot more to consider when it comes to a carb than just the engine specs. I tune my customers carbs for maximum all around performance. If your car is a stick, stay away from vacuum secondaries if you have a 5 or 6 speed and very low gears (4.10's or steeper) because often, the first two gears combined with steep gears create a situation where the slight hesitation where the secondary circuit is trying to dump more fuel can start to bog too much and you get unstable fuel delivery as you are grabbing for gears...and wiht a fairly heavy car, you may need to swap out the secondary spring for a lighter one so the secondaries come on quicker. Generally speaking, a heavier car requires lighter springs and vice versa. Then, if you have a very broad torque curve, you need to pick out an accelerator pump cam that more closely supports your power curve. So now, if you plan to be able to deliver more fuel, you need to swap out to a 50cc pump kit, increase your squirter nozzle size and go up in jet sizes. Stick with the 90 degree dog leg boosters because they offer much better throttle response on the street. To illustrate a real world scenario, I will explain how I went through a Holley 3310 vac. secondaries to be able to wake the motor up when the RPM climbed past 6000. I had a 78 Monte that pulled great up to around 5500 and then just kinda flattened out-still pulled strong but no real grunt behind it. I suspected it was due to lack of fuel, not spark or valvetrain flutter. Again, this is just to show you the ways in which you can really knock a problem completely out of the park and even surprise yourself. My Monte had a 355 with 461 iron heads which I ported (about 10.4:1 comp.), 3310 vac. sec. Holley, 282 cam with .466 lift, Performer manifold, TH400 with 3.73 limited slip rear with 275/60/15's. I raced against my friends 406 70 Camaro which had 4.10 rears and I launched hard and got the jump on him-he had to run me down but blew totally past me when he caught me. I knew he'd get me but I figured it would take him longer-my car just seemed to run out of steam upstairs and I decided to get into the carb a bit. To start with, it was an out-of-the-box bolt on carb with nothing done to it. I'm willing to bet most people do little as to swapping most or all of the internals in the search of the perfect combination but hey, I was willing to experiment. So here's what I did-I first swapped to a secondary metering block just so I could now change rear jets. Then, I decided to swap out the stock 30cc pump for a 50cc one. Then, I swapped from the stock front jets from 66 to 74. Rear jets I went with 82's. I experimented with various secondary springs but found the stock one (plain, no color banding) was the most responsive in this situation. I changed out the main accelaerator pump cam to the second from the largest progressive ramp style (dark red one I believe)-I visualized the longer, larger pump ramp as extending the RPM fuel delivery as well as allowing for a larger volume of fuel, so with larger jets, bigger pump cam and more fuel volume, I obviously need to increase the squirter size-I went from the stock .031 to an .041. The power valve I left it at 6.5, and knowing I now have the ability to empty the fuel bowls faster, a higher volume mech. pump was next so I installed an Edelbrock 6-valve pump regulated at 6.5 psi. So the next time out on a flog run, not only was the car much quicker off the line, it pulled like crazy well past 6500! Now the car had to off-idle bog which it did have before, mid range was very strong, and top end was very strong too. No doubt that my friends Camaro did still catch me, but it would now take him the entire length of the 1/4 to do it-and just barely by then. His 406 was a beast, but my 355 was much better tuned for my car than his was for his. This is just an example of basic Holley carb tuning which can vary from one car to another. There is no one carb for any engine combo. You have to experiment to get the most out of it. Even if you think it runs great now, making a few well reasoned changes can really wake it up!

[wmhjr]

I agree with the previous post. Which takes me back to my original post.

I had a carb built expressly for my application. The design took into consideration ALL of the aspects of the engine design, the car it was going in, the type of driving the vehicle would see, etc. Over on PY there are many examples of guys pulling off their Barry Grant, Pro or whatever and putting on a car built by the guy who built mine. They saw instant improvements. You get a carb with a build sheet that includes the specific mods and components - built item by item - for YOUR car.

No doubt that you can certainly build a combo yourself and get reasonable performance with some of the out of the box carbs. You'll just get better performance with something designed for your use. One that is actually tested on a real motor prior to you getting it. It was worth it to me.

[Jim Nilsen]

I had a Q jet built by a drag racer in my area named Walt Grey and what he did with it was amazing. The choke was locked out and it would still start and idle at -25 degrees below zero within 1 minute. It was truly amazing to everyone who ever encoutered the reality that it had a Q jet. I won a few bets that other claimed I had a Holley before I ever opened the hood.

Q jets can perform on the street if built specifically for you car while the car is there.

I was also told that I could pick up a few more hp if I went to a Holley from Walt but he said the overall driveablity for the car being a daily driver would not be the the same.

I was glad I went with the Q jet for my needs at the time.

[wmhjr]

Uh oh, Jim.... You've opened up that can of worms :)

It's interesting. There's Cliff Ruggles who builds some top notch QJets for lots of folks. I don't know Cliff but hear he's a great guy with great carbs. Then there are guys like Jeff (Shaker455) who are more partial to Holley. I'm no expert, but from doing a lot of checking before getting mine, I'm of the impression that a well built Holley type will outperform a well built QJet, and that you don't need to sacrifice streetability on the Holley. I know of guys running well designed (not stock) Holleys who have excellent street manners yet the motors are monsters. I'd agree that both can be great performers both on and off the track, and that if well done we're talking minor degrees of separation. It would be really interesting to have a real world way to do a comparison of both track and street performance, on the same car, on the same day.

[Jim Nilsen]

Uh oh, Jim.... You've opened up that can of worms :)

It's interesting. There's Cliff Ruggles who builds some top notch QJets for lots of folks. I don't know Cliff but hear he's a great guy with great carbs. Then there are guys like Jeff (Shaker455) who are more partial to Holley. I'm no expert, but from doing a lot of checking before getting mine, I'm of the impression that a well built Holley type will outperform a well built QJet, and that you don't need to sacrifice streetability on the Holley. I know of guys running well designed (not stock) Holleys who have excellent street manners yet the motors are monsters. I'd agree that both can be great performers both on and off the track, and that if well done we're talking minor degrees of separation. It would be really interesting to have a real world way to do a comparison of both track and street performance, on the same car, on the same day.

Yep it's a big can of worms but worms have great nutritional value!

The great thing about the Q jet was the mileage I got with it. he was able to make it so that when I was cruising the secondaries were not open yet and the car was what you might call fairly on the lean side but when you got past 80mph or put it to the floor it was as rich as needed to make full power. I had 2:73 gears so that helped too. 55mph was 2000 rpm and 80 was around 3000 rpm. I also had rhoads lifters that just started to come in at that rpm. I could consistanly pull 15 to17 mph in the city driving aggresively and on the hiway I could pull down 18 -19 mpg. The car would pull long and hard all the way to 125mph at the top of 3rd. it was like taking off in a jet. Not the quickest out of the hole and when you got to 3000 rpm in first it was like a turbo kicked in.

Tuning a Q jet is probably the hardest thing to learn. I have a book from HP books on how to tune them and it is about 3 times thicker than the one they have for Holley's. many Corvettes that road raced in the 70's used them with great success.

For the average guy the Holley is the way to go, but if you can find someone with experience the Q jet is a fantastic carb for the street and track.

[Jim Nilsen]

I can think of another option that I used for my pickup truck that worked so well right out of the box and that was an Edlelbrock carb. That thing didn't even need to have the idle screw moved even though I adjusted it a bit along with the air bleeds. By the time I got to the end of the next day I had moved them back to where they were to start with. It truly amazed me how well they had it adjusted. It came with a ticket with the guys initials on it that bench tuned it and he did a perfect job for the engine I had and it was damn near unable to run with the 2 bbl carb that was on it and the poor valves. It has gone over 40,000 miles and with just the carb and an intake change it has never failed to start no matter how cold or hot and and it picked up 5 mpg over the 2 bbl bringing it up to 17mpg and that is in a 77 C10 truck with a 3:08 rear and a 3 spd auto.

[H2Ogbodies]

Around here, the best dirt track guys are the best Q-Jet tuners...it's amazing how powerful these carbs can be. Common issues with finding suitable cores to rebuild (let's face it-they are getting hard to find) are warped baseplates and worn out throttle shafts-neither are fixable. I have a local guy who is the MAIN MAN to go to at a marina for Q-Jet rebuilds-his knowledge on them is pretty vast. I told him what kind of engine i was building once and based on that he gave me a list of possible donor cars/trucks to pull a Q-Jet from if that was what I was going to build. He has tricks for enlarging metering orifices, machining the metering rods for smaller secondary step diameters, etc., really cool stuff.