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850 Q-jet vs Holley 850 mechanical secondary

Discussion in 'The Garage' started by midget, May 20, 2003.

  1. midget

    midget Registered Member

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    I am about to drop in a 481 (454 with 4.25 stroke and .030 over bore) into the 74'. Have been running a bone stock smog 454 with a Q-jet which performed outstanding off and on road.
    The 481 has a Scat rotating assembly, H-beam rods, JE pistons, and 781 early chevy heads with 256 cc intake runners. Cam is .516/.516 with 220 duration @ 50. 9.0:1 compression.

    I was initially planning on going with one of the Edelbrock 850 CFM performer Q-jets getting it calibrated to this particular configuration.

    I have been warned that even this Q-jet will significantly limit HP. Because of the outstanding off-road capability the other Q-jet provided I am OK with small decreases in top end HP,, less than 20. However, the guy at the dyno shop here said they ran healthy 383 first with the Edelbrock 850 and then a mechanical secondary 750 holley and went from 390hp to 470hp..... Pretty significant!

    If I ran a holley, I would have it massaged by a local performance carb shop. They have mentioned running it with spring loaded needles and I would run a fuel regulator set at low (1-2) psi for the rocks with a bypass valve for everything else.
    Also, I have been advised that with a holley I would be able to get away with more cam and still have the carb like me,, like .540 intake which would obviously free up more power.

    I just dont want to have a DOG at angles, which is what I was dealing with the previous Carter style (Edelbrock) carb. Big rocks and elevation were just way to much for it...

    If anyone can help solve this delima I would appreciate it.

    The truck is used as a DD, in the desert, rocks and towing.....it is the only ride.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd try the q-jet you have now first. Some minor tweaking (jets, rods, hangars) would be nice, and if you wanted to get fancy, you can massage a Q-jet for quite a bit more flow, although I don't know how much you can get with smoothing the throttle shafts, butterflies, and so on.

    I've seen some testing on SBC's that showed an 850CFM carb was limiting the engine at higher RPM's, so in some cases, yes, 850 won't be enough.

    You'll never know what you are gaining though if you don't start out with a baseline, and for that, I'd go with a known good carb, especially since its your only rig.
     
  3. gravdigr

    gravdigr 1/2 ton status

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    doesn't edelbrock make a 850 carb with mechanical secondaries? I know my 750 has em. If you are starving for hp maybe dual 600s
     
  4. Confedneck

    Confedneck 3/4 ton status

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    ok well.... since i work on newfangled crap, err fords everyday... how about them truck avengers? ?
     
  5. SUBFAN

    SUBFAN 1/2 ton status

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    I would start with your Q-Jet, and optimize it first. It looks like your motor was built for all around perf., so why not start there.

    That is a huge difference in numbers on their 'comparison', was it box stock vs. box stock? Or was it box stock (Ede) vs. spare dyno carb lying around?

    While it is true that a Holley makes more top end power, they don't call a Q-Jet a 'poor mans FI' for nothing.

    This doesn't really answer your question, but maybe gives you a different outlook. Just my .02 worth
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    There are no q-jets (that haven't been modified) that are mechanical secondaries, that I am aware of.

    A Q-jet can be tweaked to make lots of power, but the key is working at it. Getting a book like Doug Roe's on the Quadrajets, is a good idea. It's plain fun reading if you like to know how things work.
     
  7. midget

    midget Registered Member

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    The comparison i mentioned was an out of the box Edelbrock 850 they claim can handle 500+hp and i am not sure of the details on the holley. I agree about the q-jet being the poor mans efi,, they definately are solid off road. I never had the thing even sputter on the stock 454.

    The guy doing the machine work is an engine builder and he said he would limit the cam to the 230 degrees @50 and about the .515 lift because he said the qjets dont like much more cam than that.

    So based on that the holley would let me run a little more cam which i fee confident would get the power up pretty good. there is a big difference b/w .515 and .540 inches of lift.

    I just want to get the most out of what I think will be a pretty solid engine.... not limiting the power to much by running the q-jet.
     
  8. m j

    m j 1/2 ton status

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    interesting,
    so how does a 'bog know your lift specs?
    .500 lift on a big inch block sounds REAL mild
     

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