Here’s what I got, here’s what I want to do.

Discussion in 'Engine Performance + Maintenance' started by Txlock, Apr 13, 2021.

  1. badco

    badco I'm Awesome

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    Off a superflow flow bench. With the injector tower on and in stock location they dont flow much at all. Move the injector and opens up alot but never tried just open.
     
  2. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Factory 454 or marine TBI unit is 660 cfm @ 3 in/hg. Run one on a single plane victor jr 2bbl and you can make a ton of power.
     
  3. badco

    badco I'm Awesome

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    I had one on 28" flow bench like everyone flows heads with and didn't make 660, flowed a little over 500. With tower double gasket it almost got to 590 and that was as far up as fuel line fittings would allow.
     
  4. badco

    badco I'm Awesome

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    Single plane intake would hurt a tbi engine. Out of its rpm range.

    My old tbi liked a performer rpm with the 1/4" adapter plate but I had a 400 with the rpm cam and a factory th400 (technically a 375b) in a 90 swb sport truck. Made good torque down low low and not horrible on mpg but was alot faster with my Holley carb.
     
  5. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Single plane runs great with a TBI. The low-rise single plane like a torquer 2 works great with the stock heads. The high rise victor jr works great with good flowing heads like a vortec head. Even a 232/240 on a 108 LSA had great off-idle torque with the victor jr on modified vortecs on a 10.5:1 355.

    Friend of mine had an old Weiand 7525 on a TBI 305. Great runner with a smallish roller cam.

    Sounds like you really needed to tune your TBI. I went from a Q-Jet to a 2" bore marine TBI on a ~400 hp 355 and made the same hp but had better driveability.
     
  6. L31MaxExpress

    L31MaxExpress I'm Awesome

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    My factory TBI had a 1/4" spacer in stock form. Also the ridges that usually rise up and shroud the bore were not there from the factory. TBI was off a 350 hp mercruiser 6.2. That 6.2 is basically the same longblock as a HT383.
     
  7. badco

    badco I'm Awesome

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    Qjet is a 750 and in stock eliminator form makes 470+hp on dish 350 and 440+ on 305. The last stock mercruiser tbi we did made 237 with the stock boat tbi set up and 276 with a 750 holley and locked out distributor with 34* timing. Only change was intake/carb/distributor on a fresh built 350 tbi mercruiser.
     
  8. badco

    badco I'm Awesome

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    A cam of any kind that was bigger duration @.050 lift would help tremendously. The stock roller cams out of tpi engines pick them up a lot as does the vortec cam
     
  9. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Something sounds off on that TBI mercruiser. They are factory net rated at 300-340 hp depending on the unit. I have personally watched a stock 260 hp rated 305 L30 vortec engine with TBI crank out 310 hp on an engine dyno with no accessories on it and 1-5/8" primary long tube headers. 30° total timing and 12.6 air/fuel ratio.

    I tuned a MEFI 4 ECU on a 305 Vortec with the 395' cam that put 270 hp to the ground through a SM465 and 12 bolt in a C10. 305 had a dual plane 4bbl intake, factory marine tbi adapter and factory 2" bore marine tbi. Headers and dual 2.5" exhaust. Same engine that was on the engine dyno.

    The Q-Jets I build are 850 cfm rating. Everyone mistakingly calls them 800 cfm but properly adjusted they are 850 cfm. Made no difference though. At 350 hp the CFM of a stock 2" bore marine TBI was more than adequate for the 350. I have made 370 hp at the wheels with a 2" bore TBI and spun it 6,600 rpm. Was still not restricting the 350.
     
    Last edited: Apr 22, 2021
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  10. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Factory vortec cam has less duration than the TBi cam. Factory Vortec cam is 191/196 @ 0.05, factory TBI cam is 194/203 @ 0.050. If I have one apart that is roller compatible I have been known to throw one I have laying around in, but never noticed much of a performance difference. Aluminum head LT1 or stock 96 LT4 cam is a different story though.
     

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