ditching the q-jet, need advice

[dukcaln]

So I am ditching the stock manifold and q-jet and going a different route. street performer manifold and probably a summit carb or ??? I don't want to get into a this carb is better than that carb thread... all I want to know if for my modes listed in my signature, what cfm should I run for good all around performance.

[flashed]

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[soxplayer]

Get a vacuum secondary carb and even then stay around 600 CFM. People tend to spec an overly large carb and lose throttle response without gaining any power. A properly set up vacuum secondary carb is better at avoiding this trap. If your throttle plates and shaft seal well you should carefully consider keeping the q-jet. It is a true vacuum demand secondary and has great response on the primary side. If you get it set up and tuned properly, you will really like. If you are still set on another carb so you can run a square bore intake, I like the performer carb with the metering rods for tuneability. I have only run the vacuum secondary model. I have also heard the summit carb is good but I have never run one.

[OJ1988]

Well we need some more info than what is in your sig,

Compression, cam specs, etc....

If I were to guess, and assume, all parts are near stock specs, I would agree on 600cfm.

[MacGyver72]

I've only used Quads and Holley's. Hated the Holley and loved the quads. Lots of people I know recommend the Edelbrock and until I read on this forum about the Summit carbs, that's what I was going to use on my 350. I totally agree with the 600cfm. Unless you have a huge cam, roller rockers and the intake valve is slamming shut just before spark, that's all you'll need.

[RUSHNBOBO]

Originally Posted by MacGyver72

I've only used Quads and Holley's. Hated the Holley and loved the quads. Lots of people I know recommend the Edelbrock and until I read on this forum about the Summit carbs, that's what I was going to use on my 350. I totally agree with the 600cfm. Unless you have a huge cam, roller rockers and the intake valve is slamming shut just before spark, that's all you'll need.

yup , 600-650 gives better velocity at all streetable rpm ranges, the 700-750 will usually show a small advantage on a warmed over motor in the 5500+ rpm range.

I run BG speed demon vacuum sec, for just over 400 bucks you get cnc billet metering blocks unlike Holley at the same price range....not the best part throttle carb by any means, but at WOT they are hard to beat.

If you got a daily driver, go spreadbore either Holley vacuum (0-80555C) , or whats wrong with the Quadrajet? ....great cruising carburetors ...good fuel mileage.

For a square bore daily driver, go edelbrock which btw ...is just a modern version of the Carter AFB, virtually identical.

[MARKDTN]

Have an expert build your q-jet. I can build an engine, but for some reason I cannot sucessfully build a q-jet.

If it were me, I would take this chance to swap to TBI or TPI fuel injection.

[pumpkin]

There is only one step up from a properly tuned Q jet,,,,fuel injection. If your changeging for something different an old carter, also known as an edelbrock carb seems to be the route of a lot of people.

[dukcaln]

take a look at my post again.... none of the below apply to my post..

make it a great day!

Originally Posted by flashed

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[dukcaln]

9-1 comp and pretty much a rv cam

[leddzepp]

Originally Posted by dukcaln

take a look at my post again.... none of the below apply to my post..

make it a great day!

That canned reply/edit was directed at the poster (flashed) not towards you. Just for clarification.

[cleszkie]

Totally agree with 600 cfm. I would have your q-jet professionally rebuilt. I had mine set up by Jet Performance. I gave them all of my engine specs and they sent me a perfectly set up unit that I still run today. I've not had such good luck with Edelbrock or Holley units.

Jet Performance also asks for the range of altitudes that the truck will be run in to select the correct jetting.

[dukcaln]

Originally Posted by leddzepp

That canned reply/edit was directed at the poster (flashed) not towards you. Just for clarification.

Oops.... thanks

[dukcaln]

maybe a good builder will help, like I said it was rebuilt before I bought the truck but just to me don't run right.....

Originally Posted by cleszkie

Totally agree with 600 cfm. I would have your q-jet professionally rebuilt. I had mine set up by Jet Performance. I gave them all of my engine specs and they sent me a perfectly set up unit that I still run today. I've not had such good luck with Edelbrock or Holley units.

Jet Performance also asks for the range of altitudes that the truck will be run in to select the correct jetting.

[RUSHNBOBO]

Originally Posted by dukcaln

So I am ditching the stock manifold and q-jet and going a different route. street performer manifold and probably a summit carb or ??? I don't want to get into a this carb is better than that carb thread... all I want to know if for my modes listed in my signature, what cfm should I run for good all around performance.

Sorry about the "wondering thread"....they start as apples and turn to oranges. I even find myself doing it once in a while

Since your dead set on ditching the qjet...here's what I used to run all the time......decent mileage, good performance, tons of part and accessory options, and few moving parts

Holley list# 1850 600 cfm vac sec (also comes in a polished flavor) ....and a performer square pattern manifold. (Inexpensive entry level performance carb) This is a universal part# "non smog." There are emissions compliant versions if needed...depends on your states smog requirments

Great carb out of the box, but get the basic tuning parts, especially the secondary spring kit and even a quick change cover. It has been my experience with these carbs that the secondaries are setup for low gears and or lightweight vehicles. They will sometimes have a "bog" when the secondaries first open up with heavier vehicles...just start steppin up the secondary spring stiffness one size at a time till the bog goes away.

Another minor problem you might experience is "off idle" hesitation ...if this happens the accelerator pump nozzle needs to be replaced with one size larger at a time. it can then be "fine tuned" with the cam profile if needed.

Jetting is usually more forgiving....unless it surges or blows black smoke down the freeway your probably in the ballpark.

Once you understand how they work, the tuning is really easier than it sounds, you might get lucky and it will be dead on right out of the box.

[dukcaln]

hey thanks