TBI heads on 5.7 Vortec short block

Discussion in 'Engine Performance + Maintenance' started by ht89, Feb 13, 2019.

  1. ht89

    ht89 Newbie

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  2. ht89

    ht89 Newbie

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    The only info I've been able to find is in regard to putting the Vortec heads on a TBI short block and then using the the Vortec / TBI manifold.
    Is there any advantage to using TBI heads on a Vortec short block?
     
  3. 88monteSS

    88monteSS OBS Enthusiast

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    About the only thing I can think of is the vortec short block would be a roller cam. For the bump in performance I'd think the price of the gm vortec TBI intake would be worth it.

    Sent from my XT1254 using Tapatalk
     
  4. Supercharged111

    Supercharged111 I'm Awesome

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    It's not the wrong way to go, you really just have a roller TBI motor at that point. Not sure if compression changes with this setup.
     
  5. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

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    Roller cam and slightly higher compression pistons

    Casting #193 "swirl port" TBI heads from 87 - 95 don't flow for s***. Vortec heads are better while Summit Racing (Trick Flow) 162108 Aluminum TBI heads flow even better (~$1,100/pair). #193 and Vortec heads have 1.94/1.50 valves 64cc chamber, the Summit heads have 2.02/1.60 valves 62cc chamber which means a little more compression.

    The Vortec TBI intake manifold is ~$100 more (see links below), better to go with a Vortec 4BBL intake and TBI adapter plate. Depending on where you live and what emissions regulations you have, you need to keep in mind EGR and A.I.R. "smog pump" requirements.

    https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=12496821

    https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=3704
     
  6. L31MaxExpress

    L31MaxExpress I'm Awesome

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    I can think of several reasons to do it. Non cracked TBI heads are probably easier to find then Vortec heads. The TBI manifold will bolt right on. The Vortec PM rods are stronger than TBI rods. Vortec block has factory roller provisions were many TBI blocks do not. Also when you swap a TBI to Vortecs you create the need to tune the PCM. Finally if it still has the tiny Vortec cam it won't see 10-15 hp difference TBI head vs Vortec head. LD TBI and Vortec use the same pistons.
     
  7. c1500deathtrap

    c1500deathtrap I try

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    So this is someone who needed a new shortblock and slapped the old TBI top end on it. Nothing more. You end up with a TBI motor that has a wimpy roller cam. Did the guy just use a junkyard shortblock? Was it rebuilt? Heads gone over, new springs valve job etc.? No performance gain here though.
     
  8. Supercharged111

    Supercharged111 I'm Awesome

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    Should get something from an extra 13 degrees on the intake and .032" intake lift.
     
  9. c1500deathtrap

    c1500deathtrap I try

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    Whoaaa shit better hold on tight!
     
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  10. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Factory TBI cam in my 8600+ GVW 350 was 194/203 @ .050, .390/.410 lift, 112 LSA, 108 ICL by my degree wheel, dial indicator and micrometer.

    My factory Vortec cam in my stock 97 Van engine I pulled apart after it destroyed itself at 57K was 191/196 @ 0.050, .414/.428" lift, 111 LSA, 106 ICL.

    Numbers calculated from lobe lift off a theoretical 1.5 rocker ratio. In actuality both cams are slightly smaller at the valve with factory rockers in the 1.42:1 range.

    The Vortec cam is smaller in duration, larger in lift, 1* tighter LSA and has an intake centerline 2* advanced from the TBI cam. It is also roller. GM claimed a modest 5hp increase in the 1987 LG4 305s with identical cam specs upgrading to a roller cam in place of the flat tappet used in 86. The most direct comparison of friction effects on the roller cam on a low rpm engine I can find. I would expect similar HP numbers due to more lift under the curve and roller lifters but more torque with the L31s cam due to the ICL and LSA change closing the intake valve sooner. I would expect the Vortec cam to give slightly better fuel mileage as well.
     
    Last edited: Feb 13, 2019

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