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  • Power Loss with an auto...

    What is the percentage of power loss from the motor to the rear wheels with an automatic trans on these cars?

    Thanks

    '95 TA A4, 118000 on the clock!
    Borla, Strange 3.73's, SLP CAI, Vortech elbow,AFS Z06 Wheels,White gauges/blue backlighting,blue custom interior,MBA Shift knob,MadZ28 Tune, Intrax springs, Bilstein shocks, ES Trans Mount, Honeycomb taillights.

    13.685@102.11

  • #2
    i believe 17%, not sure though maybe someone else can chime in
    -Lou -

    1997 30th Anniversary Firebird Formula

    Comment


    • #3
      16-18% is probably a good guess. I actually measured the losses on my car when it was running the T56.... a little under 13%, with the actual percentage dropping as HP levels went up - closer to 12% at the 800HP level. Adding 3-5% for the 4L60E is reasonable.

      Also was able to measure it with the TH400, and it ranged from a shade under 20% at 500HP to almost 22% at 800HP. Buts that's with a very loose, high stall (5,000rpm flash-stall), non-locking convertor, and a tranny with very beefy internals.
      Fred

      381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

      Comment


      • #4
        Thanks guys I was trying to use a HP calculator and it does not account for drivetrain loss apparently.

        It seems that the number is way high though. If I add 17% to the number I'm given ( 298 based on trap speed ) it comes to 348.6

        I really do not think my car with just a Borla cat back and an SLP intake is making that kind of power.

        If I use the et calculator it says 254, which when adding the percentage equals 297 and that seems low?! I was thinking about 305-310. Am I off on that assumtion? I know that my ET estimate is problably low because I can never get traction or launch the car properly. ( my best 60' time is 2.2 ) I am really not driving the car to it's capabilities as I think it can run 13.90's.

        Just being curious. What do you guys think?

        '95 TA A4, 118000 on the clock!
        Borla, Strange 3.73's, SLP CAI, Vortech elbow,AFS Z06 Wheels,White gauges/blue backlighting,blue custom interior,MBA Shift knob,MadZ28 Tune, Intrax springs, Bilstein shocks, ES Trans Mount, Honeycomb taillights.

        13.685@102.11

        Comment


        • #5
          It's even worse than that. To convert rwHP to flywheel HP, you do not add the 17% loss. You divide by (1 - loss) or (1.00 - 0.17) = 0.83

          298rwHP / 0.83 = 359 flywheelHP

          I don't think you're making that. I think its reasonable to assume that you are close to 300 flywheelHP with your mod's.

          What is your trap speed? I have a slightly tweeked model of the classical "HP from trap speed" equation that I find fairly accurate at estimating flywheel HP.
          Fred

          381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

          Comment


          • #6
            Originally posted by jerrysta
            Thanks guys I was trying to use a HP calculator and it does not account for drivetrain loss apparently.

            It seems that the number is way high though. If I add 17% to the number I'm given ( 298 based on trap speed ) it comes to 348.6

            I really do not think my car with just a Borla cat back and an SLP intake is making that kind of power.

            If I use the et calculator it says 254, which when adding the percentage equals 297 and that seems low?! I was thinking about 305-310. Am I off on that assumtion? I know that my ET estimate is problably low because I can never get traction or launch the car properly. ( my best 60' time is 2.2 ) I am really not driving the car to it's capabilities as I think it can run 13.90's.

            Just being curious. What do you guys think?
            If I understand you correctly, you are saying the calculator that you are using is saying 254 RWHP. If you divide that by 0.83 (17%), you get 306 at the crank. That seems about right.

            Comment


            • #7
              The calculator has an ET estimator and a trap speed estimate. The trap speed estimate says 298 the ET estimate says 254.

              My car is capable of a much better run than what it has done so far, that is why I have kind of discounted that estimate. With a 14.22 ET it comes up 254. However I have never cut a 60' time better than 2.2 The 14.22 run was with a 2.3 60' time.

              Fred, my traps are consistently 101-101.5

              '95 TA A4, 118000 on the clock!
              Borla, Strange 3.73's, SLP CAI, Vortech elbow,AFS Z06 Wheels,White gauges/blue backlighting,blue custom interior,MBA Shift knob,MadZ28 Tune, Intrax springs, Bilstein shocks, ES Trans Mount, Honeycomb taillights.

              13.685@102.11

              Comment


              • #8
                We're both using the same model... I just tweeked a couple of constants on mine. Everyone uses the calculators, and assumes it must be "rear wheel HP" because A) some calculators erroneously state that, or 2) they figure that the calculator has no way of knowing whether you are running through a low loss manual or a high loss automatic. They assume that you can't correlate flywheel HP to MPH, only rwHP. But that's not the case. While many automatic cars show way less rwHP than manuals, they use the "area under the curve" much more effectively. Put a high stall convertor in, with a good torque multiplication, and the loss of peak rwHP is offset by the gain in low end torque. You end up with "roughly" the same area under the curve.

                The formulas were developed by the Chrysler factory drag racing team back in the 1970's. At that time, no one ever thought about "rear wheel HP"... and there was no chassis dyno sitting in a spped shop or two in every town. They built the model using emperical data comparing drag strip performance to the values they got on the engine dyno... = flywheel HP.

                I have the advantage of having the engine dyno curves from a decent number of LT1 engines, and the time slips from the same cars. I can use the formulas to estimate flywheel HP, and they come up with the correct answers.

                For example, if I put my time slip in as 127.6MPH with a race weight of 3,760# the calculator gives me 635HP. That is EXACTLY what my engine put out on the ENGINE dyno with the first stage (125HP) of nitrous. The rwHP with the M6 was about 555rwHP, and with the TH400 was about 505rwHP. But the car performs pretty much the same in terms of MPH with both trannies.

                A buddy of mine ran 155MPH with his 3,800# 30th SS convert. The calculator shows 1,200HP... and that's actually a little more than the engine dyno of 1,125HP. But the simple fact is, his car was not in any way shape or form making 1,234rwHP nor is my car capable of 635rwHP on a 125-shot.


                If I use 3,650# for your race weight, I get the 298rwHP. The model also says that if you could get the perfect, 100% use of the available power, you could be running low 13's. With your 14.2 ET you're only using 80% of the available power. Get that number up to 90%, and you're at 13.75-sec ET. Just getting your 60-ft down to 2.00-sec would put you at 13.9.... not sure why you don't think you can get the 60-ft time down to 2.0. Think positive
                Fred

                381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

                Comment


                • #9
                  So, by using your formula mid 13's should not be out of the question? That's funny because my friends dad, who is a very experienced drag racer, guessed that mid 13's should be my goal with current mods.

                  Thanks as always Fred.

                  '95 TA A4, 118000 on the clock!
                  Borla, Strange 3.73's, SLP CAI, Vortech elbow,AFS Z06 Wheels,White gauges/blue backlighting,blue custom interior,MBA Shift knob,MadZ28 Tune, Intrax springs, Bilstein shocks, ES Trans Mount, Honeycomb taillights.

                  13.685@102.11

                  Comment


                  • #10
                    With my best run (listed in sig) it says

                    Based on trap---312

                    Based on ET---290

                    '95 TA A4, 118000 on the clock!
                    Borla, Strange 3.73's, SLP CAI, Vortech elbow,AFS Z06 Wheels,White gauges/blue backlighting,blue custom interior,MBA Shift knob,MadZ28 Tune, Intrax springs, Bilstein shocks, ES Trans Mount, Honeycomb taillights.

                    13.685@102.11

                    Comment


                    • #11
                      Originally posted by jerrysta
                      Thanks guys I was trying to use a HP calculator and it does not account for drivetrain loss apparently.

                      It seems that the number is way high though. If I add 17% to the number I'm given ( 298 based on trap speed ) it comes to 348.6

                      I really do not think my car with just a Borla cat back and an SLP intake is making that kind of power.

                      If I use the et calculator it says 254, which when adding the percentage equals 297 and that seems low?! I was thinking about 305-310. Am I off on that assumtion? I know that my ET estimate is problably low because I can never get traction or launch the car properly. ( my best 60' time is 2.2 ) I am really not driving the car to it's capabilities as I think it can run 13.90's.

                      Just being curious. What do you guys think?
                      how are you thinking it is capable of running 13.9 when it says your best time is 13.6??

                      Comment


                      • #12
                        The date he posted this thread was previous to the one where he broke under 13.9. The thread was started on 06-18-2005 03:19 PM.
                        94 Black T/A GT, Advanced Induction 355, 3200 stall, built 4L60E, Moser 9", Baer Brakes, Shooting for 11s...

                        Comment


                        • #13
                          Yeah, sorry I did not clarify that.

                          '95 TA A4, 118000 on the clock!
                          Borla, Strange 3.73's, SLP CAI, Vortech elbow,AFS Z06 Wheels,White gauges/blue backlighting,blue custom interior,MBA Shift knob,MadZ28 Tune, Intrax springs, Bilstein shocks, ES Trans Mount, Honeycomb taillights.

                          13.685@102.11

                          Comment


                          • #14
                            jerrysta how did you run a 13.6 with your mods? that is incredible. what do you guys think i should run on street tires?

                            The mods thus far are as follows.I just had the tranny beefed with a shift kit and 2800 10" coan converter. It has a 3 inch catback with a flowmaster muffler. I had pcmforless tune it. It has a cold air intake, descreened maf,tb bypassed, better flowing intake elbow, air foil, motive 373 gears, poly trans mount.
                            1995 LT1 bird
                            10" 2800 stall coan converter,beefed tranny, supreme shift,motive 373 gears,3 inch catback with a flowmaster muffler, pcmforless tuned,slp cold air intake,tb bypassed, better flowing intake elbow, air foil,poly trans mount.
                            275/40/17 Nitto NT555R extreme drags in rear

                            2005 Dode SRT-4
                            agp billet adjustable wastegate,Maxxfab 3 inch catless downpipe, borla catback ,K&N drop in filter,mapclamped,tuned,mopar blow off valve, Prothane motor mount inserts,21 pounds of boost!
                            6 dics cd changer, 10 inch MTX fully loaded with moonroof and viper style seats

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