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Boring 2 BBL Intake for TBI

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  • Boring 2 BBL Intake for TBI

    When looking at the old iron manifold and sizing it up for boring, one would think there isn't enough material to remove. From my measurements this morning, I need to remove about .287 from the outside of the intake holes.

    Question: does one remove all of the material all of the way to the bottom of the intake? Or does one just go far enough to where it opens up? The left one concerns me more

    Question: how critical is the fuel flow path from the TBI unit to the adapter to the intake?

    I have touched up the drawing that Mike Deschamp has on his site, the bores in my gm tbi are about 1 11/16" diameter instead of his 2". Will be buying aluminum today for the adapter plate, how thick should I go? Considering 6" x 4 5/8" x 1", around $19. I have a 79 345 (summer time should be 392) and 2" body lift.

    Thanks,

    Jeff

  • #2
    Hmmm.... been pondering that myself. I was going to center a TBI gasket over the intake bores and mark the area to be removed. First thought was to chuck a 1.75" hole saw in the drill press and drill them out. Then I got wondering about just flaring the bores from my new marks down to the stock hole kind of like you would when you gasket match the ports on a cylinder head. I don't know what effect either one would have on flow.

    You only need 1/4" for the adapter, but again, I've seen spacers for stock GM apps about 1" thick claiming to make more power. I also thought about an adapter about 1" think and flaring the holes to match the TB down the stock holes in the intake. Again I don't have any idea what effect that would have... good or bad. :confused: :confused:

    Comment


    • #3
      adapter

      The pic on the main FI page is my 1/4" plate on a 2 barrel man. There are a lot of ways to do the same thing. I also used JB weld on the studs to lock them in place.
      Some things to keep in mind.

      1. Clearance to hood---My stock scout does not have much room from the top of the air cleaner to the hood. So a 1" spacer may hit. On that scout I did nothing more than bolt the plate right to the manifold. No boring or cutting or grinding. It's my street scout so it is working fine the way it is.

      2. Small holes means low end Big holes means top end. Creating a venturie effect can actually help. So if you just taper the intake holes it should work fine. That's what I did on my trail scout.
      If you are looking for max HP and not torque than I would say to go crazy and hog the intake and the runners out as much as possible. But I almost ruined a good 460 ford that way once. Lost some of the bottom end that big blocks are known for. Kind of like our 3600 rpm IH motors.

      Your main concern should be to eliminate obstructions(mismatch) and turbulance like TORC mentioned with the gasket matching of the ports. Just try to give the air and fuel a smooth path to the cylinder. But not to polish the intake runners, that causes puddling.
      HTH
      Last edited by Bill usn-1; 01-17-2003, 05:36 PM.
      Bill USN-1

      COMMITED TO TEACHING PEOPLE THE "PROPER" WAY TO EFI
      HAMILTON FUEL INJECTION
      May be the answer to all your fuel injection needs!
      Learn to do it right.

      Comment


      • #4
        I get the gist of what you're saying, but I wasn't talking about port the intake runners or the port to the heads. I was talking about gasket matching the plenumn bores instead of hogging them out to full TB bore size. Just create a taper from the top of manifold down into the plenumn.

        Comment


        • #5
          I concur....

          After looking at the intake some more this afternoon, I do believe I'll be doing the boring on it. Enlarging the holes at the top and tapering them in towards the bottom.

          Probably going to do the spacer at 1/2" thick. A little bit easier to work with in the vise.

          Bill, did you leave the AC computer path in your ECM? I was rethinking it with the idea of using it to control my OBA with the ac switch setup. Whatcha think?

          Thanks guys,

          Jeff

          Comment


          • #6
            Re: I concur....

            Originally posted by Jeff Eggemeyer
            After looking at the intake some more this afternoon, I do believe I'll be doing the boring on it. Enlarging the holes at the top and tapering them in towards the bottom.

            Probably going to do the spacer at 1/2" thick. A little bit easier to work with in the vise.

            Bill, did you leave the AC computer path in your ECM? I was rethinking it with the idea of using it to control my OBA with the ac switch setup. Whatcha think?

            Thanks guys,

            Jeff
            Absolutely!!!! All the ECM does when it detects the A/C clutch is engaged is to bump the idle up a bit. The ECM has no way of telling if the compressor is compressing freon or air. I plan on doing this myself.

            Comment


            • #7
              AC

              Since there seems to be 2 of us....

              It works fine on my street scout tied to the ac.
              I'm also thinking about using it with the on board welder when I get it done.
              Just have to pick the right RPM. I plan on putting a toggle switch in line so I can manually enable it. Ya don't want the rpm to raise at the wrong time when the pressure in the tank(bumpers) drops.

              Make sure you check the throttle plate clearance when it's on the adapter. You don't want the throttle sticking!!
              Last edited by Bill usn-1; 01-17-2003, 05:38 PM.
              Bill USN-1

              COMMITED TO TEACHING PEOPLE THE "PROPER" WAY TO EFI
              HAMILTON FUEL INJECTION
              May be the answer to all your fuel injection needs!
              Learn to do it right.

              Comment


              • #8
                Forgive me for sharing some useful information.... I'll STFU now

                Comment


                • #9
                  TBI adapter is almost ready....


                  Almost finished with the TBI adapter for my 2 bbl intake manifold. Need to counterbore the 4 mounting holes. May round the edges off a bit when I have more time. I ended up using a 1 3/4" hole saw and the throttle plate clears no problem and they are not too big. I ended up going with 1/2" thick aluminum, now I'll have to use an extra washer under the bolt head or grind them off about 1/16" or both.


                  Looks pretty good sitting there on top of the manifold.

                  I put some tape on the intake to see where I would have to grind on it to match the TBI unit. Looks to be fairly easy enough to do. I don't think its quite a $50 job. Will be doing that shortly after lunch.


                  Jeff

                  Comment


                  • #10
                    Why not just taper the aluminum adapter?
                    It would be a lot easier than working with IH steel?
                    The plate I have is 15/16 thick and looks like it will work well.
                    It's also the same height as the performance adapters that are being sold.

                    Now if you were boring the manifold to match the TBI so everything is the same I could see that. Then you could look into the Ultimate TBI Upgrades that the guys at ThirdGen.org do.

                    http://www.thirdgen.org/newdesign/te...matetbi2.shtml



                    http://www.thirdgen.org/newdesign/te...imatetbi.shtml
                    [CENTER]1994 Buick RoadMaSSter Estate Wagon LT1/4L60E. White and Woodgrain Sleeper...PCM 16188051 With SS/V4P/Custom Tune! WOT 12.9 AFR!

                    1990 Chevy Suburban Silverado 5.7L 2wd ECM 1227747 HiWay Lean Cruise 18.5 MPG and 12.5 to 1 AFR at WOT!

                    1972 IH 1210 Isky Cammed Balenced 345 4 speed PCM 16197427 Project!

                    [SIZE=3][B][URL="http://www.gearhead-efi.com/"]GearHead-EFI.com[/URL] EFI Conversions and Chip Tuners![/B][/SIZE]
                    [B]May be all you need to know about EFI![/B]

                    and I still help local JustIH members (for fun) free! :cool: [/CENTER]

                    Comment


                    • #11
                      Very interesting reading.....

                      Mark,

                      They make some good points to think about and try as ya go. Nice thing is they can be done pretty easily.

                      I thought about tapering the aluminum adapter, but decided the carbide grinding bit would make a more gradual taper versus one as abrupt as I would have to have in 1/2" area.

                      Any pics or info on the insides of your gm disty conversion? I have my "new" holley disty sitting in the parts cleaner soaking all the old grime and nasty stuff off. Supposed to be 40 here on Monday. I feel a shopping trip coming up

                      Thanks,

                      Jeff

                      BTW if all my rust and leaks disappeared, I wouldn't have an IH
                      Last edited by Jeff Eggemeyer; 01-18-2003, 11:49 AM.

                      Comment


                      • #12
                        But if your adapter plate was 15/16 thick it would be a slighter taper and a performance add-on!
                        What exactly do those risers that they sell do anyway?

                        Distributor is running in Bill's Scout.
                        Pictures will be developed pay day.
                        Machinist will have measurements next week.
                        Write up to be finished after that.
                        [CENTER]1994 Buick RoadMaSSter Estate Wagon LT1/4L60E. White and Woodgrain Sleeper...PCM 16188051 With SS/V4P/Custom Tune! WOT 12.9 AFR!

                        1990 Chevy Suburban Silverado 5.7L 2wd ECM 1227747 HiWay Lean Cruise 18.5 MPG and 12.5 to 1 AFR at WOT!

                        1972 IH 1210 Isky Cammed Balenced 345 4 speed PCM 16197427 Project!

                        [SIZE=3][B][URL="http://www.gearhead-efi.com/"]GearHead-EFI.com[/URL] EFI Conversions and Chip Tuners![/B][/SIZE]
                        [B]May be all you need to know about EFI![/B]

                        and I still help local JustIH members (for fun) free! :cool: [/CENTER]

                        Comment


                        • #13
                          holley adapter

                          holley made one too.
                          2300 to TBI, tapered
                          holley

                          Bill USN-1

                          COMMITED TO TEACHING PEOPLE THE "PROPER" WAY TO EFI
                          HAMILTON FUEL INJECTION
                          May be the answer to all your fuel injection needs!
                          Learn to do it right.

                          Comment


                          • #14
                            for the spreadbore crowd

                            Bill USN-1

                            COMMITED TO TEACHING PEOPLE THE "PROPER" WAY TO EFI
                            HAMILTON FUEL INJECTION
                            May be the answer to all your fuel injection needs!
                            Learn to do it right.

                            Comment

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