TBI 305 Build:

Discussion in 'Engine Topic' started by 455 Formula, Feb 1, 2011.

  1. 455 Formula

    455 Formula Veteran Member

    1,421
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    Dec 8, 2009
    Fresno, California
    Out here in Kalifornia, we are mandated to use TBI (if the car came with it) so we are planning a buildup on my buddy's 305 once the 331 goes in. He wants to keep the original engine and we have to keep the TBI, so that is what we have to work with.

    His 1991 305 is a factory roller motor, so I wanted to ask, how much lift can we get away with on the 305 TBI heads????

    I found quite a few spring sets that give a higher installed height, but I wanted to ask you guru's before we order ANYTHING.

    The cam I am looking at is a Comp XFI Roller that is designed for the '87 up factory roller applications, buut its .560"/.555" lift seems like more than the stock retainer to guide clearance will allow.

    We will likely do some tuning when this 305 is donw, so we have a little freedom on the cam.

    Any advice from Chevy Guru's would be welcome!!!!!
     
  2. 80 camaro CJ

    80 camaro CJ Veteran Member

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    Nov 1, 2010
    Gilbert, AZ
    ive heard vortec heads and LT1 cam but 99% of the time ppl say dont waste the time on the TBI its useless after 4500 unless you do some major moding to the TB itself
     
  3. BondoSpecial

    BondoSpecial Veteran Member Lifetime Gold Member

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    Sep 20, 2004
    Southern Maryland
    That 305 has the swirl ramp heads (the 350 swirlies were '193, IIRC the 305 version is '191 casting #) that most people won't touch with a ten foot pole from what I've read over on third gen.org...the swirl ramp heads having better than average exhaust ports but very very poor intake flow, like 175 cfms...that build is another great candidate for 081 heads!! lol. I think you'd be the first person to run that much lift with TBI swirl ramp heads ever, I dont think those heads will benefit from that kind of lift
     
    Last edited: Feb 1, 2011
  4. 455 Formula

    455 Formula Veteran Member

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    Dec 8, 2009
    Fresno, California
    I agree...I have read that too.

    My buddy wants to keep the stock heads. Wouldn't '081' chambers be too large???? Do they have an exhaust crossover????

    We are facing many restrictions from the smog man, so we have to use less than ideal stuff....:mad:
     
  5. Kamikaze

    Kamikaze Veteran Member Lifetime Gold Member

    Steven beat me to the punch regarding the swirl ramp chamber heads.
    Get rid of those and replace them with at least a set of S/R Torqers or Edelbrock Performer Centerbolts and the valve lift is no longer an issue!
    Also adding the Edelbrock Performer TBI intake with the torque tubes will increase the mid to upper rpm torque range and allow the engine to pull as well as rev.

    Get the TBI modded by Tom Miller's Turbo City and up the pressure regulator, install an injector spacer and also get a small throttle body spacer. Modify the stock air filter base with a short velocity stack and remove the silencer assembly on the inside. I can't remember who we got the device from but there is a TPS interface and a MAP sensor adjustment that gives you much more responsive throttle throughout the rpm range.

    There are many reasonable hydraulic roller cams that will allow you to pass smog while increasing the performance of the little 305. Match them to your heads and gearing!

    Exhaust is the single best thing you can do but you can also go too far! Believe it or not, most mildly modified TBI engines run well with small smog legal tube headers into a single 3" high flow cat with a good flowing muffler. You could run Flowtech's Terminator Muffler with a single 3" inlet and dual 2-1/2" outs and have a nice aggressive sound without to harsh resonance.
     
  6. BondoSpecial

    BondoSpecial Veteran Member Lifetime Gold Member

    8,699
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    Sep 20, 2004
    Southern Maryland
    No, 081s are 58cc chambers. All of these heads have exhaust cross overs
     
  7. retorq

    retorq Veteran Member

    4,920
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    May 13, 2003
    Kingman, AZ
    Simple solution: move.
     
  8. Damon

    Damon Veteran Member

    12,811
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    Nov 16, 2000
    Philly area
    Plenty of guys have put a little extra umph in a TBI engine. The cam is the biggest restriction inside the engine. Outside the engine the biggest restriction is the entire factory exhaust system from the manifolds back.

    You know how to fix the exhaust problem (shorties, good flowing exhaust behind them).

    The cam is really in need of upgrading. It's called the "peanut cam" over on Thirdgen.org becuase of it's itsy-bitsy specs. 179/191* @ .050 with lift well below .400" on both valves. A stock factory TPI or later model LT1 cam is a popular upgrade and can get you quite a bit of power, even with the stock heads, while remaining computer-friendly. (Max lift on TBI heads is in the .450-.460" range before the retainers hit the guide seals.) This does not mean that tuning isn't required- it is, even on a dead-stock TBI engine to extract the most power.

    If you want to get fancy you can replace the factory intake with an Edelbrock TBI intake. Or use an entry-level dual plane carburetor intake with a home-built adapter plate on top. Either is worth some ponies.

    Cam, exhaust and tuning is probably a good 40HP over stock. Just about anything you do to a TBI engine will make more power IF you tune to match it. The factory system is NOT forgiving of even modest changes in the engine's basic breathing characteristics, hence the need to stay on top of the tune.
     
    Last edited: Feb 1, 2011
  9. 455 Formula

    455 Formula Veteran Member

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    Dec 8, 2009
    Fresno, California
    I appreciate the advice. We are looking at this from several different angles and the prospect replacement heads doesn't seem to bother my buddy like I thought it would. The Edelbrock TBI intake sounds like a good investment too.

    I just penciled him out an exhaust system that features a 3.00" pipe right off the cat into a Magnaflow straight-through, curving outward and exiting right in front of the RR wheel with a flat section of 3.00" pipe with a stainless tip.

    I have used the S/R Torquers on other people's 305's and felt they were really great heads.....
     
  10. 455 Formula

    455 Formula Veteran Member

    1,421
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    Dec 8, 2009
    Fresno, California
    On the bottom end we are planning on a set of KB Hupereutectic Flat Tops, Zero-Decked with Total Seal gapless Rings.
     

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