My Thoughts On Dynos...

Discussion in 'SRT Hellcat Performance' started by VanishingPoint, Jan 31, 2015.

  1. VanishingPoint

    VanishingPoint Silver Member

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    Caveat: I am not a professional racer, engine builder, dyno operator, etc. but 25+ years of owning and dynoing performance cars/motorcycles, I have determined the following:

    Dynos can "lie."

    If one town has two dyno shops, one will always claim the other dyno numbers are juiced up to make the vehicle owners feel better, and the other guy will say the other guy's dyno is junk or he doesn't know how to operate it, hence his lower numbers.

    Guess who will get more business? The guy who gets the bigger numbers.

    I took a BMW M5 V-10 (one of the original "twin" setting engines of 400 vs 500hp) and ran it both ways. Driveline loss through the SMG (semi auto manual) 7 spd equaled roughly 15% in what I would describe as a fairly efficient semi automatic manual trans which was NOT capable of handling much torque. This 15% was determined after multiple runs on a dyno using the same settings vs factory stated power.

    It helps to think of "driveline loss" as a percentage of drag, that rises and falls but is a rough equivalent-which is why the more you make, the more you lose. (just like it is claimed the 6.2 2.4 supercharger uses 80 HP to make HP; it doesn't suck -80 hp at idle. Maybe 5-10 hp. But at say 6,000 rpms the drag imposed costs 80 hp on the engine to make, 707 hp).

    In my mind, a big, heavy duty 8 speed auto designed to handle this cars power and abuse for over 100,000+ miles-in my mind-would have a driveline loss of at least 15% (remember, driveline includes the trans, driveshaft, rear end, axles, brakes, and rim/tire weight (these are 20's). According to that, the dyno *should* read roughly 600 Rear Wheel HP (RWHP is HP appllied from the wheel to the road directly, always less than engine output).

    Companies build X-amount of engines, and dyno them. Some engines make more, some less. What a company DOES not want is numbers that are too low so I think they set a very low median (if not the lowest average) amount as a "minimum" to protect them from false advertising (Those old enough to remember, think the Ford Cobra engine fiasco where a new intake slipped into the model line cost -20 hp; owners sought action and Ford ate crow).

    As a speculative guess, I think the most poorly made production Hellcat engine will be 715 hp at the crank, with the best one probably 735 hp. Don't think the press vehicles numbers, think the guys who own production Hellcats and their dyno runs, and then take that with a grain of salt because the dynos they run on may be "juiced."

    Anyway, this is my feeling. If your cat runs anything consistently above 600 RWHP in back-to back runs, you are making every HP Dodge said it would.

    If their are some dyno operators here, feel free to chime in, as this thread is not about "how wicked smat" I am, but meant to be educational as we all all receive our dyno sheets nationwide and either jump for joy because we have a 670 RWHP Dodge ringer "monster," or cry in our beer because we have a 605 RWHP dud.

    As always, your mileage may vary (YMMV) ;)
     
    Last edited: Jan 31, 2015
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  2. Next Phase

    Next Phase Silver Member

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    Cliff notes please...

    ;-p

    Agreed on most of your points...

    However, the A8 (from what I have heard from a few videos) has less drivetrain loss versus some of the older 4 and 5 speed automatics. Having 670 rwhp and 10% drivetrain loss is my guess. Still underrated hp from the factory.
     
  3. B5 Blue

    B5 Blue Platinum Member

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    Never went on a dyno cuz $50 gets me runs on the dragstrip where you get to smell GTandO and race for clams:) then calculate HP
     
    Last edited: Jan 31, 2015
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  4. VanishingPoint

    VanishingPoint Silver Member

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    Automatics tend to have more driveline loss than manuals. The old 7 speed BMW SMG is a low torque manual trans with an auto clutch, hence pretty efficient.

    Next Phase below is a video with low dyno readings. On an estimated 10% driveline loss that equates to 686 hp at the engine, well under what Dodge reports?

    At my "estimated" 15% we have 717 at the fly.

     

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