Not much hope for the Q Jet on my SP3

Discussion in 'Small Block Tech' started by Mark Demko, May 1, 2024.

  1. Mark Demko

    Mark Demko Well-Known Member

    :p:pDrove ‘er to work today with the Q Jet on, idle vacuum is better than the AED, drivability is great, but that’s about it.
    Even on the highway engine cruising at 3300 rpm, floor it, WUH WAAAAAA, noses over for a split second then goes, NOPE NOT GONNA WORK!
    I COULD tighten the spring on the doors, but all that will do is eliminate the bog, and then open the secondaries too slow, and Guy will beat me:p:p
    I tested a theory I had but it didn’t hold water.
    The engine needs the fuel NOW to make power when I slam it to WOT, NOT over a period of seconds.
    I “think” the issue with the Q Jet other than no accelerator pump on the secondary side is while the small primary’s give good fuel economy and drivability, there’s too much of a difference in size between the primary’s and secondary’s.
    Also I noticed while on the highway the sensitivity to the throttle is much softer with the Q Jet, it’s super crispy with the AED, same on city streets, with the AED, I go full throttle at 30 mph or less I get sideways, the Q Jet just delivers TOO SMOOTH power, no tire smoke.
    While it worked fine on my dual plane, it just doesn’t perform well on my single plane.
    Back on goes my AED DP:D
     
    patwhac likes this.
  2. Stage 2 iron

    Stage 2 iron Platinum Level Contributor

    Mark see if you can find one of these problems solved 850 competition series problem solved. Great Street Carburetor, and you won’t lose all your gas mileage. IMG_2480.jpeg
     
    Mark Demko likes this.
  3. rkammer

    rkammer Gold Level Contributor

    Have you tried launching a little harder to get your 60 ft. down into the 1.75 range? You might just be able to tickle the 12s with just a little more tuning?

    Re: The Carter Thermoquad, I had one on my Son's GS350 many moons ago and it was truly a great carb. That car went low 14s with 9.8 compression, a KB 118 cam and stock converter.
     
    Mark Demko and Stage 2 iron like this.
  4. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    You'll need to adjust the power piston spring to a softer size for it to work properly. That's your issue
     
  5. Stevem

    Stevem Well-Known Member

    Does your Q-jets air valve flap have square holes to the left and right of the air cleaner stud?
    These square holes allow the secondary transfer circuit to kick in as soon as the secondary throttle blades crack open which act like a short duration accelerator pump until the main jet discharges kick in.
     
    Dano, DaWildcat and Mark Demko like this.
  6. Mark Demko

    Mark Demko Well-Known Member

    My converter (JW 9.5”) flashes to 3500 on launch, doubt I could launch harder unless I had more stall.

    I’ll have to check.
    But from an overall strictly “performance” standpoint the AED wins;)
    I COULD go backwards and try my original iron intake and Q Jeto_Oo_O
    Heck, now I’m thinking again:p
     
    Mart likes this.
  7. Mark Demko

    Mark Demko Well-Known Member

    Is it possible to get more flash stall from the converter by bringing the rpm up against the brakes to 2000 or more???
    It might push thru the beams.
     
  8. rkammer

    rkammer Gold Level Contributor

    If you can hold more than 2000 rpm you should get a better short time. Also, how much air are you running in the MTs? Some have improved their short times with as low as 16 psi. Gotta experiment with that but, you should be able to get better than 1.95 60 ft. for sure.
     
    Mark Demko likes this.
  9. Mark Demko

    Mark Demko Well-Known Member

    I run 18 psi. I tried 20 and spun.
    My best 60’ last year was a 1.85
     
    rkammer likes this.
  10. rkammer

    rkammer Gold Level Contributor

    Did your ET and/or MPH improve from what's in your signature? What rpm did you launch at? I can usually hold about 2500 RPM with my JW 9.5 2800 converter and I don't have disc brakes.
     
    Mark Demko likes this.
  11. Mark Demko

    Mark Demko Well-Known Member

    I tried to update my signature but couldn’t figure out how:rolleyes:
    I just bring it up to about 1500 rpm, then it will flash to 3500 when I floor it.
    I gotta stop being a pussy and giver more:p
     
    rkammer and 72gs4spd like this.
  12. Fox's Den

    Fox's Den 355Xrs

    Soon as you start seeing my taillights you'll push on it lol
     
    Mark Demko likes this.
  13. Mark Demko

    Mark Demko Well-Known Member

    Drum brakes have more holding AND stopping power than discs, the only drawback to drums is they don’t shed heat well, and it’s tougher to modulate them.
     
  14. Storm1

    Storm1 Silver Level contributor

    Glad you gave it a shot Mark!

    I finally fired mine up yesterday. Met my buddy with a 2010 Lingenfelter vette and we drove up to a show. On the way we staged on open road at about 25-30mph. I kept up with him and even and hit 6k before I let off. I was pretty happy and surprised at the same time.

    6k has been difficult to hit with the qjet and SP3 just like Mark, but different also. A typical WOT for me see's 4k ish before it noses over. Happens from a dead stop or roll "most" of the time. Intermittently I can hit 6k.

    Last year I ran a fuel gauge through the hood and taped it to the windshield. It drives and accelerates (up to around 4k) at 7psi, then drops down to 2ish.
    Within the next couple weekends I'm replacing the tank, redoing all the rubber hoses, and adding a RobbMc sender, filter, and pump. All the hoses are brittle and dry rotted anyways so while I'm there I figured I should just do it all.

    I want to see if that changes anything before I go asking for Mart's Holley :D
     
    Mart, patwhac, rkammer and 1 other person like this.
  15. BQUICK

    BQUICK Gold Level Contributor

    I've always found square bore carbs work best on square bore manifolds.
     
    Mark Demko and rmstg2 like this.
  16. Mart

    Mart Gold level member

    Makes sense...
     
    Mark Demko likes this.
  17. Mark Demko

    Mark Demko Well-Known Member

    Thanks!
    I figured I’d try the Q Jet one more time with a few theories, guess it will get boxed up and the AED goes back on!
    At least I won’t wonder “hmmm, I should try that”
    On a dual plane the Q Jet ROCKS!
     
    patwhac likes this.
  18. Storm1

    Storm1 Silver Level contributor

    I'm sorry to be the bearer of bad news :D, but the qjet is alive and roaring on the SP3! Took 11 hours but I "finally" got this car getting the fuel it needed to hit the high rpm's and not nose down intermittently at 4k.

    First...The old fuel sending unit and sock were toast. To say it was sucking shut would be an understatement. I honestly don't know how it even ran.
    New RobbMc sending uint.

    Second....All the rubber lines were toast. Like rotted brittle don't even touch them toast.
    All new rubber lines replaced.

    Third....Old tired ACDelco pump. I just don't think it could keep the bowl full. Maybe with a new sock??? Ill never know!
    New RobbMc Pump.

    Fourth...got rid of the filter at the carb. It honestly didn't look bad, but
    New RobbMc filter before and after the pump.

    So, time to take it out for a road test! Hit a vacant road and nailed it. NO BOG!!! Straight smooth shifts 1st thru 3rd in drive. I gotta say I was pretty happy!
    Next some manual shifting to see if I can hold the rpm's. NO PROBLEM!!! 1st to 6k - 2nd to 6k - 3rd time to slow down idiot you're on a public street!

    Then finally to see how the tires hook. They don't. Staged like I would at the track, ran the rpm up holding the brake and burned the tires through 1st, 2nd, and chirped 3rd.

    It's a whole new car!

    Now the only real issue. The gas gauge is not working properly. I tested it up to 90ohm before install and it showed fine on the meter all through the float range. I put 5 gallons in and it didn't register anything. I keyed up again and it showed between 1/8 and 1/4 tank. This was before I stated it up for the first time.

    Started it up and it went to E and it wouldn't move. Checked ground and sending wire and got it to bounce between F and E but nothing in between. Drove it around and did all the stuff above and it never moved off E.
    Took it to the gas station and put 5gal more in and its holding steady just under 1/4 tank. Its a 20 gal tank and I know there's at least 8-9 gallons in there now so I'm a bit baffled at why its not working right.

    But its alive!
     

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