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4bbl TBI high idle

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  • #16

    Re: 4bbl TBI high idle

    Blade sealing secrets

    Kevin,
    Why Thanks!
    Xjs12... The Jensen's arch nemesis...
    If youve got a lathe, whip up a 5 deg turning fixture (couple of precision rods inserted into a round (smaller than the blades but bigger than the two-bolt pattern...) that has the 5deg angle at the correct orientation. Drill and Rough cut the blades (or have them punched if you're making a lot) and spin em down on the lathe to the exact needed dia. (at the 5 deg angle) Sure shot... Our non-round blades are cut on the mill and are much more problematic sealing wise.
    Attached Files
    www.FBthrottlebodies.com
    Bruce K Bridges

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    • #17

      Re: 4bbl TBI high idle

      I got the idle issue sorted out. I don't have a lathe yet, but that's next on my list of equipment. I used a little more care on the BP and just kept creeping up on the diameter, testing one port at a time.
      BKBridges, If you don't mind sharing, How do you recommend finishing throttle shaft bores? I just peck drilled these but assume a reamer would be best. What kind of clearance should I use with and without bearings?
      DG, Do you think the HP limit is caused by atomization, injector timing, or something else? Is it RPM dependent? Could you make more power on a 632 Vs a small block? I see the "self tuning" systems are advertising similar limits.

      Thanks,
      Kevin

      Comment


      • #18

        Re: 4bbl TBI high idle

        I got the idle issue sorted out. I don't have a lathe yet, but that's next on my list of equipment. I used a little more care on the BP and just kept creeping up on the diameter, testing one port at a time.
        BKBridges, If you don't mind sharing, How do you recommend finishing throttle shaft bores? I just peck drilled these but assume a reamer would be best. What kind of clearance should I use with and without bearings?
        DG, Do you think the HP limit is caused by atomization, injector timing, or something else? Is it RPM dependent? Could you make more power on a 632 Vs a small block? I see the "self tuning" systems are advertising similar limits.

        Thanks,
        Kevin
        I am pretty sure the limitation is fuel distribution. The symptoms for us were popping/banging/misfiring under load/WOT, and the plugs showing random rich/lean conditions that don't make sense. You'll know if it's a problem, I truly hope it's not an issue for you though!
        www.realtuners.com - catch the RealTuners Radio Podcast on Youtube, Facebook, iTunes, and anywhere else podcasts are distributed!

        Comment


        • #19

          Re: 4bbl TBI high idle

          , How do you recommend finishing throttle shaft bores? I just peck drilled these but assume a reamer would be best. What kind of clearance should I use with and without bearings?
          DG, Do you think the HP limit is caused by atomization, injector timing, or something else? Is it RPM dependent? Could you make more power on a 632 Vs a small block? I see the "self tuning" systems are advertising similar limits.

          Thanks,
          Kevin
          Kevin,
          We ream the throttleshaft bores to size for a nice smooth accurate finish. The sizing depends on the application, throttleshaft material and length of the bore. We standardized on 17-4PH SS for the shafts, and we anodize the bodies so no contact is allowed bore to shaft. We used to size to +.002 (ball bearing suspended), but with all the Nitrous out there we had to increase the clearance to avoid shaft bind due to thermal contraction of the aluminum body. For a brass to aluminum journal bearing Id size it to +.0005 to reduce leakage and add some lube to it. The shafts gotta be pretty straight though.
          I have some knowledge of TBI as our Flathead system is essentially a TBI unit. We had a lot of distribution problems until we improved the atomization at the injection site. Lots of ways to do that, but basically, and it depends on the actual injector's spray pattern, the injected stream needs to impinge on something... even another injected stream, to atomize well enough to work in the wet manifold. Carbs atomize really well, injectors not so well. To aid atomization, a small platten placed in the path of the injector about 3/8-1/2" away from the nozzle breaks up the spray of most injectors pretty well. A 200 micron screen in the same spot does a good job too! Our flat head system uses a bit of both since the flathead has such a stellar intake tract. TBI gives you all of the distribution problems of the original manifold combined with the challenge of atomization. The FAST guys seem to have this stuff down pretty well on their EZ TBI. Two of them will support 1000hp, Ive seen other TBI systems that cant support more than 400hp due to reversion and poor fuel control due to injector location and sizing...The bigger motor will require more injector/fuel, which may be worse if its not the desired atomized droplet size.
          www.FBthrottlebodies.com
          Bruce K Bridges

          Comment


          • #20

            Re: 4bbl TBI high idle

            Thanks for the info. I'm going to start shopping for reamers. A platen or screens shouldn't be too hard to add. When I got home from my job that actually pays the bills today, I made a couple easy pulls on the dyno. On the last pull I took it to 3 grand in third(5spd). The wideband stayed in the high 12's. Throttle response seems way faster than the carb. The truck sounds completely different though. It's very raspy, pissed off sounding when you crack the throttle and under load. It sounds great but I'm sure it's indicative of something wrong. It seems like it's drivable, but we'll have to see what it does wide open. I have some electrical noise issues to sort out before I do anything else and I should take the dyno over to a buddy's shop so I don't disturb the neighbors. I guess I should ease into it, keep an eye on the plugs and not trust the wideband too much.

            Thanks,
            Kevin

            Comment


            • #21

              Re: 4bbl TBI high idle

              Kevin,
              Paying job? What a luxury! If its not Super lean or Super fat, the WB O2 should be a good guide. Check your plugs as well! Electric throttle response? EFI is fun that way.
              Good luck
              BKB
              www.FBthrottlebodies.com
              Bruce K Bridges

              Comment


              • #22

                Re: 4bbl TBI high idle

                I've got the noise issues sorted out and it's just acting all kinds of crazy under load. It doesn't know what it wants. I'm thinking of setting up a multiport intake with the tbi on top. Eight injectors in the manifold and eight in the tbi. I'll plumb the fuel in series through both sets of rails to the same regulator and be able to switch which injectors are firing. I'll set the tune with the multiport and then start sorting out the tbi. Am I correct is assuming I can use very similar VE and timing tables with both if the TBI is working? What intake would you recommend buying or converting?

                Thanks,
                Kevin

                Comment


                • #23

                  Re: 4bbl TBI high idle

                  With MPI it doesnt really matter what manifold you use, if it worked well wet it works better dry! Id stay away from manifolds with known issues wet (Cross Rams, certain tunnel rams) but dual plane vs single plane doesnt seem to be an issue at the lower n/a hp ranges (under 650hp) With identical programming we saw a 12 hp and 22ft lb increase switching from a simgle plane MPI Mopar perf manifold to a dual plane Mopar Perf MPI six pack mfld on a 360 mag. Not sure if that would be the same with TBI though...
                  Bruce
                  Attached Files
                  www.FBthrottlebodies.com
                  Bruce K Bridges

                  Comment


                  • #24

                    Re: 4bbl TBI high idle

                    I finally got back to this today. I promised the family I'd fix the boat and have been working on some other stuff. Any way I decided to weld in a couple plates for the injectors to spray on. It seems to have solved the problems. Thanks Bruce! It also looks more racy as it's condensing water on the outside at idle.
                    I had the electric pump in series after the mechanical pump. Now that it's running I need to move the pump to the tank and run a separate line up to the motor. I want to leave the mechanical pump on to make switching back to the carb easy. Other than running another bypass back to the tank for the mechanical, is there a good way to bypass it without removing it? If I valve off the inlet will just sitting there pulling a vacuum damage it? How much pressure can I have in my EFI return line and also Tee in the mechanical pump?

                    Thanks,
                    Kevin

                    Comment


                    • #25

                      Re: 4bbl TBI high idle

                      Cool..
                      Most mechanical pumps will do something bad if you cap the inlet and/or outlet and leave it in place... (bend the disks, blow the diaphragm, etc.) If the pressure were equal on the inlet and outlet of the mech pump it might survive, but the diaphragm isnt designed for a high Delta P (12 psi max?) Id just leave the inlet and outlet open (atmospheric) and hope for the best...Alternatively you could run a dual regulator system and just swap to the low pressure reg for the carb and put the mech pump on the shelf...Since Ive never really "gone back" to a carb, I usually pull the mech pump off and put it in the trunk (customers cars) or the shelf (my cars) so this post is mostly hypothetical.
                      Bruce
                      www.FBthrottlebodies.com
                      Bruce K Bridges

                      Comment

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