600 HP with Q-Jet

Discussion in 'The Venerable Q-Jet' started by Daves 71 GS, Dec 28, 2019.

  1. Cliff R

    Cliff R Well-Known Member

    To add to the last post a few things need to be covered. Specifically "seat of the pants" testing. Before any track runs were made with these spacers I ran them on the street. The fully divided and semi-open "felt" really strong. Tires spinning, car getting sideways, engine revving very quickly to the shift point, hanging on for dear life, etc. I would have bet anyone reading this those spacers would have resulted in much quicker ET and MPH over nothing at all.

    At the track with perfect traction (my car does not spin) the shift in power resulted in some "lag" out of the gate and worse 60' times. By mid track the improved upper mid-range and top end charge was starting to get noticed, but even so a little more poew right up at the shift point doesn't improve much as the engine spends very little time there on a full pass. I did go thru faster on top end, but the loss of 60' was not to be overcome by a little more top end charge, no matter what spacer, spacers or combinations of gaskets and notching divider plates was done..........FWIW.......Cliff

    Pics of my factory iron intake (modified) showing the openings into the plenum areas and material added to run square flange carb w/o an adapter.
    View attachment 470348
    Intakes 005.jpg
     
    Last edited: Apr 16, 2020
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Well, I guess I am doing OK with my Q-jet then. The difference between it and the Holley has never been more than 1 to 2 tenths, and 1 to 2 MPH in trap speed. I am using the TA SP1 intake. I have never had any flat spots, on the street or at the track, ever, with either carburetor. The car runs consistent mid 11's at 115-116 MPH, with 1.6 60' times. I've gotten as good as 16 MPG on the open road with the Q-jet.
     
  3. Cliff R

    Cliff R Well-Known Member

    I'd say mid 11's and 16mpg's is getting it done pretty good Larry, especially at that weight.

    My car runs a bit quicker with less power simply because it's lighter. In full street trim on DOT's I typically see around 7.14-7.24 @ 95-97MPH in the 1/8th mile and bottom 11's up around 118-122MPH.

    I haven't done any MPG testing in a while, pretty difficult to do anyhow because I don't have enough self control to run clear thru a tank of fuel without a few full throttle blasts, or putting a few "box-cars" on a "fart-piped" Honda Civic or two.

    I also have a very well prepared Holley 4781-2 DP carb for my engine. It runs about the same as the Q-jet everyplace but hard pressed to get much past 160 miles on a tank of fuel, even with a lot of self-control. My Q-jet will go 200-230 miles on the same 14 or so gallons of fuel......so you know which carb sits on my engine most of the time........Cliff
     
  4. HotRodRivi

    HotRodRivi Tomahawks sighted overseas

    Wow thanks for the informative answer. So the qjet likes to be divided.ware is your notch on intake . secondary side?
    Are you runnig the factory air gap intake?
     
  5. 436'd Skylark

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

    I've been debating switching the SP1 and holley out for an edelbrock intake and putting the q-jet back on. This thread has been very interesting. With the 4 speed my engine gets lugged down lower than a loose auto car.
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Cliff,
    I have been running the SP1 for many years now, mostly with a Q-jet, on both my motors. I have never had any kind of flat spots or any kind of hesitation at all when transitioning from primary to secondary operation. That's on both my motors, street and track. Curiously enough, the TA Performance SP3 for the 350 exhibits what you describe as far as single plane intakes and the Q-jet. I know Mark Demko said he could not tune out the sag he experienced with his Q-jet and the SP3 when punching it at any speed. He ended up with an AED 850 I believe which solved the problem. Not sure if he ever tried a spacer or had the room for it.

    http://v8buick.com/index.php?thread...3-with-a-quadrajet.329027/page-4#post-2818942

    See post #68
     
    Last edited: Apr 17, 2020
  7. 87GN_70GS

    87GN_70GS Well-Known Member

    A 4 speed car will have different requirements than an auto. While racing, an auto spends time from off idle thru 1st gear shift point once (WOT) , so to get the car moving, it needs good low rpm torque. On the street, it spends quite a bit from idle to shift point (part throttle). So a dual plane favors here.

    With the 4 speed, your stall speed is whatever your clutch foot decides. It doesn't have to spend time in low rpm. A little loss in low rpm torque is not a key player. So a single plane is better suited.

    I would keep the open intake, but experiment with the qjet
     
  8. Cliff R

    Cliff R Well-Known Member

    Larry, I've only ran into the stumble/hesitation/bog going quickly to full throttle issues using dual plane intakes with either the dividers cut down too much, or trying open spacers on them.

    Never had any issues with single plane intake, but have street, dyno and drag strip tested a pile of them. They pretty much REQUIRE at least a 1" spacer to be at their best, especially with a spread bore carb on them.

    This fact creates a couple of issues. Hood clearance on some set-ups is one problem. Second problem is that even if you stuff it all under the hood with a "drop base" or shorter air cleaner assembly that deal moves the lid too close to the carb and you loose more power than you ever hoped to gain.

    At the track back to back I have yet to have a single plane intake ET quicker than my dual plane, but have had a few run a solid 2MPH faster on top end (with 1" spacers on them). Any testing I've done dual plane to single plane w/o a spacer shows a strong advantage to the dual plane intake for 60', short times, and more often than not faster on top end as well.

    Of course this is just what I've seen, so not to be taken as gospel, just food for thought. Even with that said I'm testing these part on a 455 engine making over 550hp/600tq, TH400 with a 3500 flash stall converter, and 3.42 gears. Imagine what some of these parts are doing for killing power (torque) on smaller engines making considerably less power. My 455 is also 11.3 to 1 compression with CNC ported aluminum heads on it, and .639" lift roller cam with 289/308 @ .006" seat timing.

    Just some things to think about when you pull the stock intake off your 9 to 1 compression 350 with an RV size cam in it and bolt down a big single plane intake thinking you are going to make more power someplace......FWIW.......
     
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I agree Cliff. There is no room for a spacer due to hood clearance for me. I know JW tested a spacer on my engine when it was on the Dyno. It didn't like it, but I don't remember the details. I always remove my air cleaner at the track. I also have to remove that center section of hood insulation as well. Don't ask me how I found that out.:D. I'm pretty sure the SP1 was worth up to 50 HP vs. the Performer intake on Alan Wander's car when JW had his engine on the Dyno. I'm happy with the SP1 on the street and the track. This engine has such an abundance of low end torque that a Dual Plane intake might make it even harder to avoid spinning the wheels while rolling along.

    The SP3 intake for the 350 definitely requires a more stout build on the smaller engine. I was kind of surprised that Mark couldn't tune out the hesitation he experienced with the Quadrajet and SP3. His engine has the compression, and cam for it, and he shifts it pretty high.
     
  10. Cliff R

    Cliff R Well-Known Member

    I can vision the "insulation under the hood" deal.

    A few years ago we had an iron headed 11 to 1 compression 455 strapped to the dyno. The owner of it had us install an Edelbrock Torker intake and we ran my Q-jet right on it w/o a spacer. The thing was a complete TURD! We made half dozen pulls messing with timing and fuel and it' only got worse.

    I replaced the Torker intake with my "modified" cast iron intake shown above sitting beside the P4B, same carb, no spacer. The next pull netted an additional 49 HP......yes, nearly 50hp with nothing more than an intake swap!..........
     
    sean Buick 76 likes this.
  11. BennyK81

    BennyK81 Well-Known Member

    Old thread but you guys do not recommend to cut down the Performer divider to much?
     
  12. TORQUED455

    TORQUED455 Well-Known Member

    I think it would depend on your entire build. I actually switched to a QFT-950 this summer, and holy smokers there was a significant kick in the pants increase in power at 600 HP vs the Qjet.
     
  13. Brandon Cocola

    Brandon Cocola Well-Known Member

    I think he is referring to the wall in the manifold between left and right bank of the carb opening.
     
  14. TORQUED455

    TORQUED455 Well-Known Member

    Yes, I know that, and it would be dependent upon his build if it would be helpful or not. IMO, if you realize and gains with that mod you would realize even more gains with an SP1.

    If you read the entire thread, there was a lot of discussion on Holley vs Qjet @ the 600HP level. I just shared my experience in making such a change.
     
  15. BennyK81

    BennyK81 Well-Known Member

    I like to have a q-jet carb with small primaries. Square bores just guzzle so much gas
     

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