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305 dual exhaust

Discussion in 'Chevy Trucks' started by 81c1500, Feb 9, 2005.

  1. 81c1500

    81c1500 Junior Member
    Messages: 29

    :yow!: Hello all,

    I have an '89 Chevy with a stock 305 and stock exhaust. My exhuast gaskets are leaking and the converter looks swollen. Can I put aftermarket headers and have dual exhaust or was there a reason that Chevy used the y pipe. Thanks
  2. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Headers and dual exhaust will only benefit... be sure you can legally do it in your area ie: emission testing etc.

    Keep the pipe sizes small to build torque and efficiency. Fresh dual cats will work well too.

    Check the JC Whitney catalog, they list pre-made packages for good prices.
  3. NJBuickRacer

    NJBuickRacer Member
    Messages: 59

    If you run headers, don't go larger than 1 5/8" on the primaries. Mount the cats as close to the collectors as possible, so they run hot enough to work properly. Random Tech has good cats for a swap such as what you're doing, you can find them through Summit Racing or Jeg's. Don't forget you need to weld an O2 sensor bung on one header too, or buy collectors that have the bung pre-welded. You're most likely going to run a little lean after the swap, so an adjustable fuel pressure regulator wouldn't be a bad idea.
  4. derekbroerse

    derekbroerse 2000 Club Member
    Messages: 2,377

    Ooops I misread and thought he was talking about the '81.

    If your truck has the A.I.R. injection system and it is still functional, purchase headers with the fittings for it, and likely the O2 bung will be there too. Agreed, 1 5/8" primary tubes are more than adequate (1 3/4" tend to be for racing) but if you intend to leave the engine stock and if they are available for your application, 1 1/2" primarys will give a little more torque as a 305 doesn't produce as much airflow as a 350. Now if you are planning modifications, or dropping in a 350 in the future, get the 1 5/8".

    Definately want the cats as close to the collectors as possible, helps with the light-off time and reduces emissions.

    The fuel pressure regulator in the TBI is adjustable, it is located near the rear of the airhorn under some security-torx screws. If you monkey with it be sure not to drop any parts down the intake!! I think turning the regulator screw in creates more pressure, but don't quote me on that because I have yet to do it on my own--just trying to get thru the winter plow season! Maybe someone who's done it can cast some further light on this operation, such as how big a turn to make=approx. how much change... you will definately need a fuel pressure guage for this job.

    But do the exhaust first, it will run ok afterwards but will likely keep tripping the SES light (code 44 lean condition) just like mine. Don't leave it like this unnecessarily long, you don't want to burn up the motor. I check my plugs regularly for indications of damage/misfire/etc. and while I have no indications of engine damage, I do have a few semi-related problems of my own(misfire).
    Last edited: Feb 12, 2005