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  • 383 SBC combo slower

    OK. This should be an easy one for all you car junkies. My '69 Camaro used to run 12.50s @ 108 MPH with stock 350 / 350 turbo with 2,000 stall converter. Engine had TFS-31400001 Trick Flow Twisted Wedge heads, 1 5/8" dia. Hedman Hedders blowing thru a 2 /14" dia. full exhaust.Top end I installed a 3310 Holley on Edelbrock Performer RPM. Out back, 275 X 50 BFG Drag radials, posi 3.73 gear, CE slapper bars with J bolts.
    Installed new engine with 383 Ohio Crankshaft Street Rodder kit #138093, 3.75 stroke, 6.0" rod with Comp. XE268H-10 cam. Bolted on the same TFS heads & intake but now with 650 vacuum sec. Speed Demon. Underneath it's got a 3 dia. full exhaust with Cal-Tracs running Hoosier Quick Time Pro 26 x 11.5 slicks.
    Car now only runs 13.6 @ 100 MPH. I've got a set of 1.6 rockers on the shelf along with a 3,000 stall converter & 750 mech. sec. Speed Demon.
    I want this car to run low 12's without spray. I like the TFS heads but they can only handle cams up to .520" lift unless I get them machined for larger dia. springs. Is a cam change in order?
    It's snowing like a SOB here in Ohio and I need to get wrenching. This combo doesn't seem right. Help!

  • #2

    Re: 383 SBC combo slower

    Re: 383 SBC combo slower

    The vacuum secondary carb is not opening all the way. Zip-tie the linkage to see if I'm right, then throw a 750 double-pumper on there.

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    • #3

      Re: 383 SBC combo slower

      Re: 383 SBC combo slower

      I agree with DF. I'd put on the parts you have. It's hard NOT to run 12s these days.
      Cognizant Dissident

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      • #4

        Re: 383 SBC combo slower

        Re: 383 SBC combo slower

        The vacuum secondary carb is not opening all the way. Zip-tie the linkage to see if I'm right, then throw a 750 double-pumper on there.
        Or even an 850 with annular boosters. That setup is definitely off. Did you degree the cam? A 383 is going to like a 110 LSA and a 106 intake centerline.

        I'm with Dave I think the vacuum is rising too high to keep the secondaries open all the way, a 650 on that engine is a small carb and if you measured the vacuum at the top of your gears I bet its 1.5-2.0" plus which will mean it is practically a 2bbl.

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        • #5

          Re: 383 SBC combo slower

          Re: 383 SBC combo slower

          I'll zip-tie the secondaries. I never have tried that method on the carb.
          I put the 750 Speed Demon on the car last summer and had a heck of a time getting the car to run right around town. Had to decrease the pri. & sec. jet sizes. Placed 0.062" dia. wire in the IFRs just to get the car run correct off idle and part throttle.
          I reinstalled the 2000 stall converter when I bolted in the 383 'cause I thought the XE268 cam was too small to handle it. Looks like the 3000 stall will be going back on.
          Don't know about degreeing the cam. A hot rod buddy of mine built the 383. He's a certified GM tech. I'll ask him.
          Not much I can do now anyway. We've got 4 inches of snow on the ground, so a test drive is out. When the roads clear, I'll let you know how it turned out. I really appreciate all the help.

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          • #6

            Re: 383 SBC combo slower

            Re: 383 SBC combo slower

            When you zip the secondaries, obviously make SURE they don't hang open at WOT.

            Even if the guy stabbed in the cam and lined up the dots, I bet it's not more than 4 degrees off (and probably not REALLY more than 1 or 2), and while that's bad, it shouldn't kill 50 hp.

            A 2,000-stall converter is like stock. It will kill your 60-foot but shouldn't hurt the mph. The 100 mph with the 383 says it's not making power.

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            • #7

              Re: 383 SBC combo slower

              Re: 383 SBC combo slower

              You sure your not runnig out of fuel, or maybe your tranny is going out since there is more torque(#1 new motor, #2 383 makes more torque than a 350) it could be slipping more and if high gear is going out you would actually be slowing down through the traps.

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              • #8

                Re: 383 SBC combo slower

                Re: 383 SBC combo slower

                If you still have the time slips, post your 60ft and your 660ft and compare them to the 1320.

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                • #9

                  Re: 383 SBC combo slower

                  Re: 383 SBC combo slower

                  How much does you car weigh? My brothers 383 I built for his firebird 11.3-1 Pro Action lightning heads .045 quench height on pistons, Speed Pro performance cam (was $90 with the lifters)cam specs 231/234 108 .520 lift with1.6 rocker, victor jr manifold , hooker super comp 1 3/4 headers w/full magna flow 2.5" exhaust with x pipe 3.42 gear (this is a street strip car), Blake built holley 830HP carb, stock HEI with MSD Modual. car weighs 3420 race weight with an allstar junk 3500 10 converter it would go 12.30's at 108 with a PTC Tight 8" 4300 it will run 11.80's at 112MPH runs on pump gas. I built the motor for a roller cam later on when he had the money for it.

                  Your motor will take a 750 carb all day long. Your car depending on the weight with some more converter should hit the bottom of the 12's top of the 11's with some tunning I would think.

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                  • #10

                    Re: 383 SBC combo slower

                    Re: 383 SBC combo slower

                    Carb is too small!!!

                    Comment


                    • #11

                      Re: 383 SBC combo slower

                      Re: 383 SBC combo slower

                      Make sure your timing is set at 34* advance. The TFS heads on a flat top or dish piston 383 will make best power at 34*. More timing will kill power, less timing will kill power.

                      The carb is a little small but should be OK with your combo. Every Demon I've played with wanted more jet than it came with out of the box. Try going up two jet sizes at a time and watch the MPH go up. When MPH quits going up drop back 2 sizes.

                      You could use a fairly aggressive spring in the secondaries on your 383 -- the yellow one would be my first choice.

                      Not sure what RPM you are shifting at but my guess is that your combo will like to be shifted about 5800 RPM. No higher than 6,000 for sure.

                      BTW, those TFS heads do NOT need to be machined for larger springs. They would just need the correct retainers and possibly +.050" locks to get enough installed height.

                      Hope that helps!

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                      • #12

                        Re: 383 SBC combo slower

                        Re: 383 SBC combo slower

                        Every Demon I've played with wanted more jet than it came with out of the box.
                        x2

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                        • #13

                          Re: 383 SBC combo slower

                          Re: 383 SBC combo slower

                          I'm going to go with the carb being to small thing...
                          The zip tie trick works really well, 9 out of 10 times when a car came in to get dyno tuned the secondaries weren't opening on a vac carb. You can also take the spring out as well, and the secondaries should just fall open.

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                          • #14

                            Re: 383 SBC combo slower

                            Re: 383 SBC combo slower

                            9 out of 10 times when a car came in to get dyno tuned the secondaries weren't opening on a vac carb.
                            Yep. Vacuum sucks. I run double-pumpers on everything.

                            Comment


                            • #15

                              Re: 383 SBC combo slower

                              Re: 383 SBC combo slower

                              You will need the 3000 converter, and it will pick up the MPH when you put it in, with no more gear than you have its taking to long to get up on the motor to make any MPH, so your killing 60 ft and mph.

                              You have raised the working range of RPM on the Motor, but you have not helped it get to it. I would have advanced the cam 4 degree's if I did not degree it in. Better to have to much bottom end with your converter and gear, it would getting it going up front which is better than trying to run it out the back.
                              2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
                              First to run in the .90s .80s and .70's in SBN/A
                              2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
                              2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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