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  • chassis dyno question.

    Last night our car club had its meeting at a dyno shop. We made pulls on 4 different cars. All the results were about what we expected but one.
    They did a pull on a nitrous Viper(200 shot) spray comes on at 3000 rpm. it made 625 rwhp, but the torque makes me wonder. 974 ft lbs. The graph for Tourque has a spike to 974 @3000 rpm,but 500 rpms later it drops by 350 lbs. and maintains for a while.
    I figured tire spin, but I know nothing about chassis dynos. i know Hp is factored from torque. Not trying to put hammer the owner, but it looked a bit odd .
    what do you guys think?
    Doug
    Reading , Pa
    Good Guys rodders rep.
    "putting the seat down is women's work" Archie Bunker.
    Ban low performance drivers not high performance cars .

  • #2

    Re: chassis dyno question.

    Re: chassis dyno question.

    Yep. Looks a bit odd. What kind of dyno? There are dynos and there are dynos (this is my field). If you were on an inertial dyno with no power absorption unit (PAU), tire slip and other inertial factors can strongly bias the results. On an inertial dyno, all you can REALLY do is measure how quickly the car can accelerate a known, fixed weight, so anything that effects the acceleration of the mass effects the reading.

    The dyno is a tool, and like any tool is useful only for the results you can produce with it. If your car is faster than mine, it doesn't really matter that yours was built with dime store tools and I used Snap-Ons. Frankly, I think comparing dyno numbers from car to car is silly, even though human curiosity almost dictates that we WILL do that.

    If I was the Viper owner, I wouldn't put too much stock in that data anomaly.

    Dan

    Comment


    • #3

      Re: chassis dyno question.

      Re: chassis dyno question.

      Dan,
      How about writing a little primer on Dynos for us? Maybe a few do's and dont's or what to look for when choosing a dyno shop operator? ETc.....

      I know you are retired and have plenty of time on your hands. ;D

      Joel
      (little VW pickup)

      Comment


      • #4

        Re: chassis dyno question.

        Re: chassis dyno question.

        I know that it is a dynojet 248x . I think just as a engimne dyno , it is a great tumimg tool. like the saying goes....you cant race a Dyno
        I was asking you because it didnt makes sense to me. thanks Dan
        Reading , Pa
        Good Guys rodders rep.
        "putting the seat down is women's work" Archie Bunker.
        Ban low performance drivers not high performance cars .

        Comment


        • #5

          Re: chassis dyno question.

          Re: chassis dyno question.

          I know that it is a dynojet 248x . I think just as a engimne dyno , it is a great tumimg tool. like the saying goes....you cant race a Dyno
          I was asking you because it didnt makes sense to me. thanks Dan
          What you saw was definitley tire spin on a Dynojet.

          This is exactly what happens when the tires spin, but the dyno still has an accurate RPM input... We've had them read as high as 2000 ft-lbs. Usually on nitrous, it happens when the nitrous hits. They should strap the car down a little tighter, or put about 100 lbs over the rear axle, and that'll likely go away!

          www.realtuners.com - catch the RealTuners Radio Podcast on Youtube, Facebook, iTunes, and anywhere else podcasts are distributed!

          Comment


          • #6

            Re: chassis dyno question.

            Re: chassis dyno question.

            Thanks Geek and Dan, that is what I thought. A primer on Dynos would be nice , it would help those of us that may only go to a dyno once in a while get the most out of it. It could be for both engine and chassis types.
            I noticed that there is a lot of difference in numbers with varying oil temp on a engine dyno, what temp should they be pulled at? or as long as they stay constant with each pulldont really matter?
            thanks again Doug
            Reading , Pa
            Good Guys rodders rep.
            "putting the seat down is women's work" Archie Bunker.
            Ban low performance drivers not high performance cars .

            Comment


            • #7

              Re: chassis dyno question.

              Re: chassis dyno question.

              I agree, engines make different power levels with differeing oil and water temps, and especially air temps. it gets even crazier when you start to factor the barometric conditions...

              one reason why Bonneville can be such a challenge! (6500' DA)

              So I always try to dyno the car in the state it's going to be run at the track. Some guys like to hot lap, some race with the powertrain completely cooled down. I think this is all a part of the plan one should have; the engine plan (how it's built) should consider the same question.
              www.realtuners.com - catch the RealTuners Radio Podcast on Youtube, Facebook, iTunes, and anywhere else podcasts are distributed!

              Comment


              • #8

                Re: chassis dyno question.

                Re: chassis dyno question.

                I wrote an article that was published in HR in September 2000. It goes into all the different types of chassis and engine dynos, with pics and the whole deal - even got cover mention. Maybe David and/or Jerry Pitt can weigh in as to whether I can scan it in and post it on CarJunkies, or maybe I signed my rights away. If I can't post here, I'm sure I could send copies to individuals if you give me snail mail addresses. Let's see what the publishing gurus say......

                Dan

                Comment


                • #9

                  Re: chassis dyno question.

                  Re: chassis dyno question.

                  If it was a dyno jet, depending on what software you have, under high hp conditions with rapid acceleration, The program has been known to "cough" if you will. probably has something to do with windows(Bill Gates likes men). Having seen around 2,000,000 dyno pulls, I can tell you that the latest software is the worst, and tends to give a lower power reading than the old software. Anyways the cough is usually just a giant spike and it goes back to normal, as diesel geek described, it could be tire spin if its a more gradual curve, or worse yet and more likely on a 200shot, clutch slippage, especially in a viper. stock c5 corvette cutches are also well known for this. The 248x is also the big dyno which like to put the mad hurt on drivetrains, and seemingly shift keys on t-56s in f-body's, not sure why

                  Comment


                  • #10

                    Re: chassis dyno question.

                    Re: chassis dyno question.

                    ...Having seen around 2,000,000 dyno pulls...
                    That's 5 a day for over 1000 years. A few too many 0s perhaps? :P

                    Comment


                    • #11

                      Re: chassis dyno question.

                      Re: chassis dyno question.

                      thanks everybody, i never thought of clutch slippage.
                      you know ive been trying to get my dealership to buy one way before they got popular. hell they had one in the 60s. maybe ill buy one for at home....mmmm parts breakage. Doug
                      Reading , Pa
                      Good Guys rodders rep.
                      "putting the seat down is women's work" Archie Bunker.
                      Ban low performance drivers not high performance cars .

                      Comment


                      • #12

                        Re: chassis dyno question.

                        Re: chassis dyno question.

                        i didn't think of clutch slippage either, but it would do the exact same thing as tire spin on the dynojet.


                        2 million pulls? :o And I thought 1200 miles on the dyno odometer in 14 months was impressive. :-\

                        www.realtuners.com - catch the RealTuners Radio Podcast on Youtube, Facebook, iTunes, and anywhere else podcasts are distributed!

                        Comment


                        • #13

                          Re: chassis dyno question.

                          Re: chassis dyno question.

                          If I've told him once, I've told him a million times - DON'T EXAGGERATE!

                          Comment


                          • #14

                            Re: chassis dyno question.

                            Re: chassis dyno question.

                            Shoot Daves camaro probably has half those pulls. NO LIE!!!! lol

                            Comment


                            • #15

                              Re: chassis dyno question.

                              Re: chassis dyno question.

                              For two years it was 4-5 cars a day 7-8 pulls a piece. 5-6Days a week, I can usually look at a graph and tell you what an engine or drivetrain is doing. So at a minimum thats 14,000 plus pulls and a max which is prolly closer to the truth of 20,800. So it would seem like 2 million, believe me it does. Plus my car has over 200+ on it by itself on open headers.
                              Dynojet didn't know what to say when we asked them if they had a process to refinish the rollers because any car that made over 500 hp needed the drums vht'd becuase the etching was so worn down

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