Discussion in 'The Venerable Q-Jet' started by sparki, Jun 23, 2018.

  1. sparki

    sparki Well-Known Member

    I was thinking about swapping my Q-Jet out for an EFI system on my 68 GS 400.
    Are any of you using EFI? If so, what brand is best, and any downsides?
    I rebuilt my motor last year, and I just don't feel that it has the balls that it should. My mechanic is pushing an EFI system, saying that it will give me what I am looking for, without the hassle of trying to get my carb dialed in just right.


  2. 436'd Skylark

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

    Efi will offer little if any performance gains over a properly tuned carb.

    Tuning your carb would be much less of a hassle than spending 2-3k and hours upon hours swapping to efi.

    Post more about your engine and we can help you with performance improvements.
  3. sriley531

    sriley531 Big green hunk of $#*^....

    There are varying opinions on this. Peruse through this section and formulate your own opinion and make an educated decision.


    That said, in my case, I had a Holley that was tuned on a dyno and then retuned and retuned. Car always started and ran great with it. I now have a fitech system, and I have no regrets with the time and money it took. The juice was worth the squeeze.
    OHC JOE likes this.
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    There could be a lot of reasons the engine doesn't perform as you expected. What is your static compression? What cam did you use? Was it degreed in? Is it the original Q-jet? What is your ignition timing, initial, total all in by what RPM. EFI won't correct any mistakes made in building or tuning the engine.
  5. BuickV8Mike

    BuickV8Mike SD Buick Fan

    How's your distributor and timing?
  6. 436'd Skylark

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

    I'll elaborate some on my first reply. Unless your car is running very poorly and the carb is to blame you won't see any gain. You aren't adding 50 horsepower or likely even 10 if the carb is tuned properly. If your carb is junk then sure it'll run better.

    These bolt on fitech systems and the like are tbi systems that have been outdated for 25 years. They are cheap to buy though. I question the reliability.
  7. sriley531

    sriley531 Big green hunk of $#*^....

    Yes, these fuel injection systems should be avoided due to being outdated technology, you know, unlike a carburetor....:rolleyes:o_O

    300sbb_overkill, 1973gs and sailbrd like this.
  8. 436'd Skylark

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

    I get your point but i think you are missing mine. Allow me to elaborate. Fitech and the like are in fact stone age in the land of efi and do not hold a candle to what the OEs are doing now and what they have been doing for the last 20 years. Some folks think all efi is created equal. Thats not the case. There are much better options out there. And call me crazy but i cant imagine your getting anywhere near OE level parts for that kind of money. Ie delphi sensors vs cardone.. and tell me how great it'll be when you can't walk into the local parts store to buy a TPS so you can drive your wife 200 miles back home.
  9. OHC JOE


    I have installed fitech efi also on my 67 impala and have drove it all week long it's great . No issues and easy installation.
    sriley531 likes this.
  10. Ken Warner

    Ken Warner Stand-up Philosopher

    Realize that most if not all of the aftermarket TBI systems use off the shelf sensors, generally from GM applications. A quick google search will allow you to quickly find cross referenced part numbers for just about all of them. BTW you have to be accustom to parts houses not having much if anything available for a 40-50 year old car let alone a Buick! :)

    I also get that your opinion of TBI is pretty low but what are these other options that are so much better? Popping holes into an intake that was never designed for F.I. with little to no consideration for injector placement other than "this is where they can go and the fuel rail will still fit"? A system with an injector per port might be slightly better but if you also consider any off the shelf intake available for a BBB/SBB was designed for wet flow then I bet if it's better its not by much. Until someone engineers and makes a proper port fuel injection manifold then you are stuck with what we have now.

    Next, who would do the engineering to figure out where to place and get accurate readings for a knock sensor to optimize timing? I get that technology has moved on but its a whole supporting network of technology that's moved on. In order for any of it to work ALL of it needs to work and the return on investment for someone to engineer all these supporting bits of technology would have a return on investment ratio that would require a price tag that few if any would pay for or volumes of sales that you will NEVER EVER get from the BBB/SBB community.

    At times I envy the LS guys and their ability to build HP/TQ levels to the moon by bolting on turbo chargers and blowers. Not to mention having to work around the Buick gimp of an oiling system or having to add a girdle to avoid pushing the crank out of the block, what a joy that would be! Could you go Tomahawk? Sure you could, at a price... You still would not have all the new tech available though.

    Like many things in life the TBI setup is a compromise. Fuel Injection especially TBI generally won't give you the WOT power a well tuned carb will. It will probably give you an extra mpg or two but it's not going to make your GS into a Prius either. It will give you great drivability at nearly any temperature, elevation or humidity level. It gives great cold starts and a pet peeve of mine hot starts as well. I don't think it's much more likely to leave you stranded on the side of the road than a carb either though. A lot of that depends on how much of a mechanic one is and how much inventory of spare parts you are willing to carry in your trunk.
    sriley531 likes this.
  11. sparki

    sparki Well-Known Member

    OK, here's the info on the motor:
    The motor was built to basic factory specs: Piston #L2273, Bore diameter 4.0400, Clearance .0020, Taper .0010. The original cam was reground to the following (performance mild street use).
    The carb is an aftermarket Rochester Quadrajet.
    Hi-rise Edelbrock aluminum intake manifold.
    I believe the timing is at 14 degrees, but not certain.
    Not sure what the compression is, I will have to ask.
    The distributor is an Accel HEI System.
    Plugs are NGK 6630 V-Power.
    Standard exhaust manifolds (no headers) through 3" exhaust system and Magnaflow mufflers.
    3-speed automatic transmission TH-400.
    Standard 68 GS 400 rear end.
    I had it tested on a Dyno and here are the results:
    4494 RPM: 282FT-LB Torque, 238.56HP at rear wheels. 3830RPM: 250FT-LB Torque, 209.25HP at rear wheels.
    They had told me that it was running lean at high end, so I replaced the secondary rods with new ones, 440 tip, as recommended by Mark at The Quadrajet Power Store.

    The car starts great, runs well, sounds healthy. It just doesn't seem to have the power that I would expect. And I get a slight hesitation if I slam my foot into it from a dead stop.
    I have tried adding Boostane, which seems to make it run a little better, but I see no huge performance difference.

    My mechanic is saying that adding EFI will eliminate any inefficiencies that the carb has. And that it will self learn the motor and my driving habits.
  12. sriley531

    sriley531 Big green hunk of $#*^....

    Despite other posters input, I can tell you throttle response compared to my tuned Holley is greatly improved. My car never caught 4th gear rubber and it does now. I know multiple other guys that will attest to the improvement in throttle respons as well. I agree with others though, make sure your timing/ignition is lined out, FI is not meant to be a bandaid for other deficiencies. Study and follow Larry's power timing thread, it's free power and you'll be glad you did. But if all else is right, you will see a difference, I've lived it first hand, I know. Theoretisists be d*mned...
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    It's really important to match the cam to the static compression. Not knowing what the cam specs does not help. You also need to know what the timing is for sure, initial and total advance, and when (RPM) its all in. Aftermarket Q-jet means remanufactured, and they are the absolute worst.
  14. sparki

    sparki Well-Known Member

    I will see if I can get the cam specs from the machine shop tomorrow. I will also ask my mechanic what the timing is set at.
    And yes, even Mark commented that the aftermarket QJets are a crap shoot. I think this is why my mechanic is pushing the EFI.

    DEADMANSCURVE my first word : truck

    just thinkin' - quick question - is the mechanic that is pushing the EFI the same mechanic that rebuilt motor ?
  16. sparki

    sparki Well-Known Member

    No Deadman. Machine shop rebuilt the motor. My mechanic is not affiliated with them. He has been dialing it in since the build.
  17. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    Went EFI before it was cool =P No regrets, especially the mileage I drive out west over mountains, to sea level, from 5ºF to 120ºF, and on. The car can sit for months and fires up like it was running a minute before. As for the TBI's, the feedback I've heard from friends is the systems with the injectors above the throttle blades have better fuel distribution than the ones under the blades. Likely because the fuel goes through the same holes as the air improving mixing.

    MPI lets you run a taller single plane intake with the same overall height as a dual plane and carburetor/TBI. A true EFI designed intake with super long runners would be nice, but would not be economically manufactured.
    300sbb_overkill likes this.
  18. Cliff R

    Cliff R Well-Known Member

    In addition to building carburetors and custom tuning I'm very well versed at FI and not overly fond of any of the TBI systems, especially any that are fixed MAP. Difficult to make the power of a carburetor with them as well.

    We can outrun the TBI set-ups and get better fuel economy with correctly rebuilt/tuned carbs and distributors at much less cost.

    Completely different deal if you take a single plane intake and have 8 bungs welded into it and go to a modern MPFI system. Expensive move there, but a nice upgrade from an electric carb sitting on the intake.....IMHO.....Cliff
    TheSilverBuick likes this.
  19. sparki

    sparki Well-Known Member

    Sorry its been a couple of weeks, but I just received the cam specs.
    Compression test was done, and all cylinders were 145-150. This was what Larry was asking for.
    Cam specs as follows: Grind: 270-80H. Rocker ratio: 1.6. Lobe separation: 112. Degree intake lobe to 110. Intake valve lift: .472, duration 270. Exhaust valve lift: .496, duration 280. Intake cam lift: .295. Duration at .050 camilft: 214.
    Exhaust cam lift: .310. Duration at .050 camilft: 224.
    One question I have is on the Dyno test, the max HP to the rear wheels was 238.56. I know this is different than engine HP. Does anyone know what the factory HP to the rear wheels was supposed to be with the TH400 automatic?
    Everything I read on factory specs just says 340HP motor.
  20. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    OK, here we go. Based on what I can glean about the L2273 piston from this thread,


    Those pistons can sit as much as .060 in the hole. Not knowing what the dish volume is on that piston, I can only guess at maybe 20cc? Combining that with 69cc for 67-69 400/430 heads, I come up with about 8.4:1 Static compression, and that might be generous.

    Using your cam specs, advertised duration 270*/280*, Lobe separation 112*, Intake lobe center 110* (2* advanced), I come up with a Dynamic Compression of 6.75

    Target DCR is 7.5-8.0 for pump gas and best performance. That might be one reason for the lack luster performance. Other reasons may be the Q-jet is remanufactured, which makes it a paper weight, and total timing at WOT. (unknown)

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