Quadrajet questions

Discussion in 'Street/strip 400/430/455' started by 1969RIVI, Mar 16, 2018.

  1. 1969RIVI

    1969RIVI Well-Known Member

    Hi guys I'm looking at buying this Qjet carb for my 72 455GS engine and getting rid of the Holley 750 double pumper that's on it now. I'm pretty sure this I the correct carb being #7042240 with the manufacturing date of 11th day of 72. Can you guys tell me if I'm correct and also what does the "MB" mean??
     

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  2. rkammer

    rkammer Gold Level Contributor

    Last edited: Mar 16, 2018
  3. carmantx

    carmantx Never Surrender

    Correct. 72 455 Quadrajet.
     
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  4. 1969RIVI

    1969RIVI Well-Known Member

    Another question is where/who would I get a good performance rebuild kit from? Any suggestions on a good setup and jetting?
     
  5. LARRY70GS

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

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  6. 1969RIVI

    1969RIVI Well-Known Member

    Ok thank you. I figured they'd need specs on my engine in order to give jetting recommendations. How precise do I have to be on mods? I have a rough idea what cam was used and am waiting to hear back if the guy can remember what pistons were put in. Does brand of parts matter to them?
     
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  7. LARRY70GS

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

    Whatever you can give them is better than nothing. A rough idea of the cam, compression, and if the engine uses headers or not are the important things.
     
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  8. carmantx

    carmantx Never Surrender

  9. 1969RIVI

    1969RIVI Well-Known Member

    Well with the info given to me I'm 99% positive it has a comp cam xtreme energy 274/286 duration with .506/.506 lift and stock 72 pistons, rings, lifters pushrods, rockers,connecting rods all bearings gaskets, new valve covers. Crank was polished valves heads and block all cleaned up. New timing cover, timing chain and gears,water pump, oil pump with pressure regulator,booster plate. It has TA shorty headers with 2.5"dual exhaust b&m2400 converter b&m shift kit & shifter edlebrock intake DUI distrib. Holley blue fuel system 3.08 posi rear gears, 2 row aluminum rad dual 14" fans, seperate tranny and P/S coolers. There's other odds and ends I'm forgetting. What's your opinion on it all??
     
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  10. StagedCat

    StagedCat Platinum Level Contributor

    I'd recommend letting Mark or Ken do it, bushed throttle plates, and other worn parts that need replacing are sometime more than we can do or have. A couple bucks more and you know its done right, these guys do it all the time IMHO......
     
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  11. KenneBelle455

    KenneBelle455 Well-Known Member

    Just my .02, when it comes to Quadrajets I would definitely let a professional build it for you, at least when starting out with a new combo that requires some tweaking. If I have a known good carb that is already set up for a particular engine and it just needs a little minor refreshment, I would do that myself, but when it comes to rebuilding an unknown and dialing in that carb to a new engine, I'd definitely leave it to a quadrajet specialist.
     
  12. 1969RIVI

    1969RIVI Well-Known Member

    Thanks guys for the help! I think I might just look into having carmantx do one for me rather than me find a core (who knows what I'll get) and play the guessing game with setting it up. Just out of curiosity with the build that I have mentioned above and adding a properly setup performance Qjet where would my HP level be at?? Rough guess obviously.
     
  13. Bigpig455

    Bigpig455 Fastest of the slow....

    My 72 455 with just a Q-Jet, cam, intake and headers puts down 360 hp at the wheels (105 MPH), which translates to roughly 445 hp at the crank. I'd say our builds are similar, but I'd have to know more about your heads. My point is, 450 hp is not an unrealistic guess. Definitely have Ken or Mark do your carb, it's money well spent and the 7042240 is a great carb to begin with.
     
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  14. LARRY70GS

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


    8:1 compression and no head work? You are lucky to see 400 HP at the crank. IMO, there is no point at all in asking for a HP estimate. Get it to the track and get a trap speed. Then you'll be able to estimate HP. The Riviera is a heavy car.
     
  15. Bigpig455

    Bigpig455 Fastest of the slow....

    x2 - it's cheaper and a lot more fun than dyno time!
     
  16. 1969RIVI

    1969RIVI Well-Known Member

    Thanks guys! There's still a lot of unknown about my car and the build. The nearest track to me is 2hrs away but I'll definitely take it out there this coming season to see what it can do. I've been trying to get to know this car mechanically before I beat on it and cost myself unnesscary money that could go towards better parts. As for the heads I think other than a clean up they're stock 72's I'm looking at finding some 67-69 430 heads to put on it to bring up the compression a bit until I can save up the cash for some TA aluminums. Any other quick tip easy mods to help out that I can do myself or that isn't big money?? I know buick parts aren't cheap so there's no "cheap mods" ha ha
     
  17. LARRY70GS

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

    Don't waste your time looking for earlier heads, it won't raise the compression appreciably. The best way to do that is to change the pistons and get them to 0 deck.
     
  18. 1969RIVI

    1969RIVI Well-Known Member

    I was hoping to avoid pulling the engine and tearing down since the build is only 3 yrs old with not many miles on it. When it comes time to do another rebuild you guys have given me a full arsnel to use on this thing! Larry do you think for now just to "help" out the current build 430 heads with a bit of valve work would give me a bit more? That way the moror stays in the car and I can do it over a rainy weekend and not be down my ride all season. I know TA heads is the real answer I just don't have the $3G to get them right now. And if I do use 430 heads what kind of compression would I be looking at 9:1? With or without valve work?Thank you
     
  19. LARRY70GS

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

    The money you invest in earlier heads, and porting? work will be wasted money you could put towards the aluminum heads. Save your money. You are looking at a 3cc difference in chamber volume. That won't do anything. The problem is your stock 72 pistons are low compression and sit as much as .050 in the hole. You are lucky if you have 8:1 compression. The aluminum heads will give you a bigger power increase than you could get doing anything else, even with the low compression. If you have low compression, you need to stay small on the cam. Read up on Dynamic Compression.

    http://cochise.uia.net/pkelley2/DynamicCR.html

    DOWNLOAD THE CALCULATOR AT THE END OF THE ARTICLE!
     
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  20. 1969RIVI

    1969RIVI Well-Known Member

    Ok thanks Larry! I do want to change the cam it seems to be to "big" for the car if that makes sense? Even the guy who built it for the previous owner said it was little big for it and a smaller cam would go better with the rear gears (3.08) but that's what the guy wanted so he put it in. What street/strip cam would you suggest would be a good fit given that eventually I will be putting the better 10:1 pistons in it from TA.
     

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