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Technical Tri Power

Discussion in 'The Hokey Ass Message Board' started by Peter Nowak, Oct 10, 2019.

  1. The majority of chevy tri power setups that i am seeing seem to fit up to 86. I have an early 90s chevy 350 with a 600 holley. I would like something more visually impressive.
    How difficult would it be modify these earlier manifolds to fit ? The manifold center bolts are vertical on my motor. Is it just the bolts that are the issue ? Or does it include the port size as well ? Or anything else?
    Thanks in advance.
    Obviously changing heads would allow the use of the earlier manifold. Want to work with what i have right now.
  2. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 1,036

    427 sleeper

    From what I remember, the center holes needed to be ovaled out and wedges were available to put under the bolt heads to compensate for the difference in the angles. 90° vs 74° if I remember correctly. Hope this helps.
    Port size should be the same.
    Peter Nowak likes this.
  3. Hot Rod Nut
    Joined: Jul 1, 2006
    Posts: 538

    Hot Rod Nut

    Something different....I used a 3 deuce adaptor plate from Speedway that bolted to a 4 barrel manifold once and it gave the engine a cool look ??
  4. The current manifold has reversible inserts that apparently compensate for the angle.

  5. That would be too high for my hood. Nice idea though.
  6. See if you can find an Edelbrock 5417 manifold. Made for Vortec heads, using three 2GC carbs
    Tickety Boo likes this.
  7. EA09D0A5-78AB-4523-A55F-5D90E0A2FFB6.jpeg C3BD5B05-6FE1-4E78-9049-909499084761.jpeg This is where i am now
    Im thinking of just using rtv for the center bolts, no bolts.
  8. Moriarity
    Joined: Apr 11, 2001
    Posts: 18,890

    Staff Member

    skipping the middle bolts is not a good idea ... a very good chance it will leak vacuum and run like crap. get the correct manifold or do the modification necessary to use all the bolts on the one you have
  9. brigrat
    Joined: Nov 9, 2007
    Posts: 5,205

    from Wa.St.

    Like said don't do it, there's an exhaust passage on both heads that those 2 bolts encompass, the heat would distort and weaken any sealer put there even if blocked off......................................
    Moriarity likes this.
  10. Do they make wedges for this modification ?
  11. Tri-power37
    Joined: Feb 10, 2019
    Posts: 510


    Edelbrock 5417 tri power manifold that fits the vortec heads seems to be hard to find? Always comes up as discontinued and sold out.
  12. Vortec heads have a different bolt pattern than earlier heads. Then there are the early and later versions of the earlier heads. The earlier heads changed the middle bolts angle to be more upright then the previous 90 degree. I think that is the 74 degree mentioned, someone can verify exactly. The Vortec heads have a completely different pattern, it is not just the two center bolt angles.
    So OP Peter, it sounds like you have the earlier style pattern on your heads, but with the later version center bolts. You should be able to find the wedge pieces to allow the early style manifold to work. It may require some work to egg out the center bolt holes a little. Intake ports should cover OK and not leak. Vortec heads have raised ports and you need an intake with raised ports and the Vortec pattern.
  13. Lloyd's paint & glass
    Joined: Nov 16, 2019
    Posts: 2,479

    Lloyd's paint & glass

    Peter I'm not being disrespectful, but those heads aren't anything special. The good fast burn heads didn't start until 96. The heads you have should be the swirl port throttle body heads. But whatever they might be, I'd swap them. Voila! Problem solved, plus none of them centerbolt valve covers
  14. Budget36
    Joined: Nov 29, 2014
    Posts: 3,894


    Peter, looks like you have an intake for Vortec heads, so you need to use Vortec heads...or the others with the same bolt pattern. I/e you're in a world of shit if you try to mount it on a set of '91 GM heads.
  15. Budget36
    Joined: Nov 29, 2014
    Posts: 3,894


    The swirl port heads I think you're referring to were the TBI truck heads.

    Pretty much doorstops as far as performance goes, good for those heavy 'Burds and such to get it moving. Even knocking the vanes out of them and such, never saw a fun head.

    Yes, I wasted a few hours on them.

    Think they might be a tea pot in China now;)
    Lloyd's paint & glass likes this.
  16. Yea
    The heads are nothing special. They have the vertical center bolts.
    Have been considering a set of the aluminum ones from Speedway.
    The intake is the earlier style with tall ports. so hogging out the center bolt holes would be required using the current heads.
    The Speedway heads are the doublehump version. About 1200
  17. Lloyd's paint & glass
    Joined: Nov 16, 2019
    Posts: 2,479

    Lloyd's paint & glass

    Heck I'd put a set of 882's on it! Or throw a set of 305 heads on it. But I'm cheap lol.
    Peter Nowak likes this.
  18. gimpyshotrods
    Joined: May 20, 2009
    Posts: 17,483


    He does not have Vortec heads, though.
  19. I motion this be stricken from the record.

    There is nothing in this post having anything to do with vortec heads.
    alanp561 likes this.
  20. The modification is very simple.
    Out of the 12 bolts intake bolts only the center 4 need a bit of work, everything else lines up.
    The work is easiest done to the manifold. Elongate the center holes to accept the head’s bolt angle and a wedged washer to take up the difference between the bolt head and manifold.
    Also even though the intake has been modified it will still work on early style heads it was designed for.

    427 sleeper did remember correctly.
    Peter Nowak likes this.
  21. If a person had all 3 manifolds infront of them an early style up to 86, the TBI style from 87-95, and vortec from 96-2000, it’s easy to see exactly why the heads are different. It’s also easy to see the necessary modifications.
    It’s 100% completely impossible to put the vortec manifold on anything but vortec heads. It’s extremely difficult and you’d wish you didn’t even try to put a TBI manifold onto early heads but it is doable. And it is Very simple to put an early intake onto the TBI heads.

    The completely different 96 up vortec heads and or manifold can be spotted from 100 yards. There’s only 8 intake bolts and they are completely vertical.
    JNKYARDDOG_1 and egads like this.
  22. Is it possible you have a TBI motor? (throttle body injection) 1987-1995 These had a unique manifold specific to those model years only. Nothing else fits without modification due to the change in the manifold bolt angle. TBI heads.jpg
  23. As can be seen in the diagram above just the center 2 bolts on each side of the head that attach the intake have a different angle.
    I currently have an intake capable of going either way, early or tbi, with the use of wedge inserts. Cept it is a 4 bbl intake.
  24. Budget36
    Joined: Nov 29, 2014
    Posts: 3,894


    You're 100% correct, I scanned the pic and saw the two holes in the middle of the intake, just realized they are tapped holes.

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