2 different dynos,2 very different numbers.why?

Discussion in 'Small Block Mopar Engine' started by jdsduster, May 15, 2018.

  1. jdsduster

    jdsduster Well-Known Member

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    same 408 stroker.built by a very rep.builder.his dyno shows 498 hp.518 tq.the rings did not seal and he did not want to stand behind his work.engine biulder #2,torn engine apart and corrected the problem.his dyno shows 433 hp and 467 tq.wow,why the huge difference?thats 60 hp and 50 tq.both are engine dynos.can dynos be fudged to put out bigger #s
     
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    • pittsburghracer

      pittsburghracer Well-Known Member

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      Can dyno's be fudged to put out bigger numbers. YES, And often are. And that's the number one reason some guys high horsepower builds never show those numbers at the track. Not many calibrate their flowbenches either. I would LOVE to test some of these heads on my bench.
       
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      • RustyRatRod

        RustyRatRod Just another dumbass. Technical Editor

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        Dynos can be manipulated to show whatever their operator wants. Drag strips cannot. Guess which one I recommend? Oh and if your answer is "I don't plan on racing" then there's no need to worry about it.
         
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        • Charrlie_S

          Charrlie_S Well-Known Member

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          These numbers, with rings not sealing, would give me pause
           
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          • Hellrats

            Hellrats Still wrenching after all these years FABO Gold Member

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            Garbage in garbage out
             
          • doogievlg

            doogievlg Well-Known Member

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            My engine is going on the dyno today. The guy running the dyno told me that f I wanted high numbers then I can take my engine somewhere else, if I want someone to take an entire day to break my engine in and tune it then he will take care of that.

            Chasing a number gets expensive fast.
             
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            • IQ52

              IQ52 Well-Known Member

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              It's not all that easy to jerk the dyno around and make it lie. I've got a balance knob under the console and can move things around 7-8 lb-ft. But why?

              However, you can load the engine differently and make big power changes.

              As an extreme example. Put an engine on the dyno and load it manually. First no load and 6,000 rpm. If you don't load it, it makes no torque. 0 lb-ft / 5252 X 6000 = 0 HP. Now load it so it makes 200 lb-ft / 5252 X 6000 = 288 HP. If the engine will do it, 500 lb-ft / 5252 X 6000 = 571 HP. All three are accurate readings but vary greatly.

              You can even load an engine so hard it cannot pull the load at rpm. It will stall and not accelerate.

              There is a difference in power readings by running the dyno at 600 rpm/sec acceleration rate and 300 rpm/sec acceleration rate. 300 rpm holds the engine back and makes it work harder. You get different HP and TQ readings, but neither is a lie.

              I took my Demon to a chassis dyno contest at a car show where they were running diesel trucks on the dyno. Talked them into letting me run 'Tetanus' on the dyno. 596 RWHP. That sure wasn't right.

              So I asked the operator if he changed the load before my run. And he said he put the load for a car. I said this isn't a regular car, increase the load like you would for a diesel. (Make it push against more resistance and make the engine work harder). The result? 650 RWHP.

              You cannot race two different dynos or flow benches. But you can use one to see how changes in design effect the power.
               
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              • roccodart440

                roccodart440 Well-Known Member

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                Dyno's are controlled methods of break in and tuning tools.

                My low hp combo runs as fast as the high hp braggarts do. More fun to tell them what I make.

                How the hell did the OP's combo make those numbers without ring seal and what tests were done to prove it didn't seal?
                 
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                • j par

                  j par Well-hung Member

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                  Bahahahaha!
                   
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                  • Fisher

                    Fisher Old Guy with a Cool car.

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                    I have seen guys here who have bought an engine with a dyno sheet from a few of the big US engine shops, only to see 150 HP less on the dyno here. I guess that 150 hp got left at customs. lol

                    My local engine builder/ dyno shop is pretty accurate. His engines run what the dyno said it should at the track. MPH+Weight = REAL HP.
                     
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                    • j par

                      j par Well-hung Member

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                      Personally I think dyno's are for people who either don't know a damn thing or people know way too much. I've got hundreds of Dyno sheets on my motor all of them are about a foot long and 3 in wide and not one of them tells a lie.
                      My "Dyno" is a 73 Duster! I would be more than glad to LOL put anybody's motor on my Dino, Run it in for 20 minutes and then give it a time slip that will be 100% guaranteed accurate horsepower reading.
                      Edit: I'll be having a half-price sale for the rest of the year! LOL
                       
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                      • 67Dart273

                        67Dart273 Well-Known Member

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                        You have to get things down to basics. ALL THAT a dyno "is" when you take off the hood, the stickers, the fancy software, and all the rest, is a TORQUE MEASURING DEVICE. ....PERIOD..... HP is computed from that torque reading + RPM, and I'm sure you realize, that getting "halfway accurate" RPM readings are not difficult.

                        SO THE TORQUE MEASURING DEVICE has to be accurate, and if it ain't,...........well..............

                         
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                        • replicaracer43

                          replicaracer43 Old school member

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                          And in some cases, a builder will use inflated numbers as a "sales tool" ....There WAS a well known builder right on this site who I think used that technique, he always made huge power numbers, and all of fabo would oooooooo, and ahhhhhhhh, about his magic, but EVERY one of those builds if ran at the track, would MPH light years off the claimed HP.. Same thing happens with head porters and flow benches. Big numbers SELL
                           
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                          • doogievlg

                            doogievlg Well-Known Member

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                            Mph+weight= real hp??

                            I’m not the best with math but I don’t think that’s accurate.
                             
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                            • brian6pac

                              brian6pac Well-Known Member

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                              I have to agree with IQ52 it's all math anyway. I had a RZV500R Yamaha, for you that don't know what it is It is a Japanese 500cc 4cyl 2 stroke Moto GP replica that Yamaha made in 85 and 86 only and never got them in the states, but It made 90 HP on the Dyno at 10.000 rpm, another dyno it made 100 HP at 10.000 RPM. long story short the guy that had the 90 HP dyno bad mouthed the other guys shop for having a riged dyno.
                              It was a very fun bike to ride 320 lbs 90+HP, One of the baddest bikes of It's era.
                               
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                              • Fisher

                                Fisher Old Guy with a Cool car.

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                                MPH + weight of the car are the 2 factors you need to determine Hp. Pretty simple math.
                                HP = Weight * (MPH/234) ^ 3
                                 
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                                • replicaracer43

                                  replicaracer43 Old school member

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                                  It's EXTREMELY accurate
                                   
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                                  • doogievlg

                                    doogievlg Well-Known Member

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                                    That formula right there is not accurate. Yes those factors are used to determine power but if you add mph to weight it will not give you hp.
                                     
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                                    • MOPAROFFICIAL

                                      MOPAROFFICIAL Well-Known Member

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                                      I noticed long ago that most other flow benches give better numbers +3-5cfm than my bench does.... and I'm actually fine with that.
                                       
                                    • replicaracer43

                                      replicaracer43 Old school member

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                                      I wasn't talking about the formula, just in general terms
                                       
                                    • j par

                                      j par Well-hung Member

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                                      This is already gone way too far. The only true answer is in Post #9 and to give an answer of what a Dyno actually is, it's just a baseline machine.
                                       
                                    • pittsburghracer

                                      pittsburghracer Well-Known Member

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                                      For the last 44 years I’ve been racing cars that have run in the 8’s, 9’s, and 10’s and the first question people ask is “how must horsepower does it have.” I tell them I honestly don’t know as I’ve never had one on a dyno. The 572 I’m building now won’t see one either. I’m not a show car type of guy so all I care about is the ET numbers.
                                       
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                                      • jos51700

                                        jos51700 Well-Known Member

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                                        Peak power numbers make me want to puke.

                                        Area under the curve is the only useful number any dyno ever put out but most folks have no clue why that matters.

                                        Comparing one dyno against another is blondes vs. Brunettes.
                                         
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                                        • moper

                                          moper FABO Gold Member FABO Gold Member

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                                          Different dynos, and different operators, on different days. It's easy to fudge dyno figures. Flow bench too. That's why the real deals are the track results. Because it will always take "x" horsepower to accelerate a given weight to a MPH figure over a given distance. No way to fudge it. Reality sucks when the engine with 330cfm RPMs on a dyno'd 600hp 408 in a 3300lbs car runs mid 11s.
                                           
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                                          • 604B1duster

                                            604B1duster Well-Known Member

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                                            I bought a car with a 421 Eddie head motor that was done by a shop that was pretty popular on here but closed up not that long ago. It came with 2 Dyno sheets that were duplicates of each other except for the “numbers”.
                                            One for 600 and one for 700hp.
                                            MPH says maybe 575.
                                             
                                            Last edited: May 15, 2018
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