428 Cobra Jet Carb

Discussion in 'Classic Mustang Specific Tech' started by bluegt500kr, Aug 2, 2013.

  1. Any suggestions on a Holley carb to replace the stock Holley on my 428 Cobra Jet engine. I was thinking about going to 650 cfm with mechanical secondary. Something strictly for the street.
  2. Hold on, I am gathering pitchforks and torches.

    Seriously tho dont let anyone talk you outa that carb if the air horn numbers are for a CJ!

    Other than that all I could recommend would be a edelbrock carb, good drivability with a simple design (no metering blocks). Summit has them at a decent price and everyone will be able to answer tuning questions should they arise.
  3. Auto trans? Manual? What gears? I would rather have a Holley than an Edelbrock, even though I have cars with both.
    I would use the 670 Holley. I have one on my 69 Cougar with a 351W, and am happy with its performance..
  4. Why would you want to replace the stock carb????
  5. It came with 735 cfm so I would at least put 750 Holley back on it. Double Pumper??
  6. If its the OEM carb, it is already optimally jetted, tuned, set up, etc. for your engine. Unless the casting or other parts are worn or damaged beyond repair, you will likely find no better carburetor for you car. Even a full on restoration (you likely only need a good rebuild) would be cheaper and less hassle than going to an after market unit. Once you get the after market carb, you will likely need to re-jet and otherwise modify to be right for your application AND it will no longer be original.
  7. Holley has a carb selector program. I think you should use that. Let me tell you in advance that Holley doesn't generally recommend mechanical secondaries for street cars unless they are super light (under 3100 lbs) with gearing over 3.73. I think vacuum secondary is a better way to go - the carb uses the engine's vacuum signal to determine how much the secondaries should open. It's a better setup - more likely to give you the correct amount of carb your engine needs. Here's the link:


    I'm thinking you're going to be 850 or larger. 750 is pretty small for a 428 unless it's a very mild build. I somewhat agree with Gene - if you have done zero mods to the engine. If you've put a cam, intake and headers on it, ported the heads, etc to improve performance that original 750 could be holding you back. What I've heard of people doing is monitoring the vacuum at the intake under full load and throttle. There should be very little vacuum if the carb is sized appropriately. If the carb is a restriction it will be at near the maximum engine RPM. If you avoid winding out the engine a 750 could be plenty.
    #7 Hack, Aug 4, 2013
    Last edited: Aug 4, 2013
  8. "Something strictly for the street".....Holley also makes a 770 Avenger, but I think you would be happy with the 670 too. Smaller carb, crisper street performance.
  9. Thank you for all the info! I've been away from my computer for a few days. The reason I'm looking for a 2nd carb is that I haven't found anyone that can rebuild the stock carb so that it will run properly. I'm planning to sell the car in the next few months and figured that at least it would be dependable to drive but I would include the original carb. Any rebuilder suggestions? Has anybody used Quick fuel technology for refurbishing?