Understated Horsepower Ratings For The Hellcats

Discussion in 'SRT Hellcat General Discussions' started by Robo21, May 6, 2016.

  1. Robo21

    Robo21 Gold Member

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    In my online searches for Hellcat dyno results the average seems to be 670+ RWHP. We all know about the 15% rule for driveline loss. So adding the 15% back into the equation the flywheel horsepower should be no less than 790 HP.

    It would definitely not be unprecedented for an automobile manufacturer to understate horsepower ratings, particularly with insurance companies penalizing their customers for high output ratings. But I was surprised at the amount that Dodge has apparently understated the horsepower on the Hellcat - approximately 83 HP.
     
  2. CubeMan

    CubeMan Tri-State Overlord

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    The 15% drive-train rule may not apply to newer 8/9/10 speed transmissions. Modern engineering has given the capability of lowering the percentage of drive-train loss. There is no way it's 5% drive-train loss, but the 15% number doesn't seem to hold true to any car today thanks to modern engineering
     
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  3. saagz87

    saagz87 Senior Hellcat Member

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    I think we all know the 707 number is a bit understated based on some quarter mile times we have seen stock based on our vehicle weight. Still haven't seen a third party do a stock engine dyno on a bench. Would love to see that!

    I have also heard it makes 714 at 6200 rpm instead of the 707 at 6000rpm. But based on past experience, my bone stock ZL1 with TR6060 trans made 495whp before I modded it. Rated 580 at crank for 85hp loss.

    Hellcat with same trans has been said to make 670ish whp. Add 85 hp and your in the 750 crank hp range. I think that's somewhat accurate but it's hard to say. Some stick cars have dynod 650 range which would make more sense based on rating. But dynos are all different so.... Driveshaft angles and other things can change whp as well. It's not a direct or scientific comparison but I found in interesting to think about. As far as the 8 speeds go, I have no idea how much power they eat up to turn. But I love my 8 speed haha
     
  4. Rob Sold

    Rob Sold Silver Member

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    I had 674 on my back wheels on a dyno jet A8
     
  5. Robo21

    Robo21 Gold Member

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    Perhaps, the new auto transmissions are more efficient and perhaps the friction losses throughout the rest of the driveline have been reduced due to engineering improvements but a 33% improvement? Bringing it down to only a 10% drivetrain loss? I have a hard time believing that. But if that were true there should still be between 745 and 750 HP at the flywheel. The only way true numbers can be established is to either find exact driveline loss figures - hard to find - or bench test the engine. In any case, I think we can all agree 707 is underrated.
     
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  6. Lucky Campbell

    Lucky Campbell Rookie

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    SAE engineers measured 714hp @ 6200, 652 lbs @ 4800, rated it at 707 @ 6000, 650 lbs @ 4800. Limiting factor appears to be RPM limiter, I have observed on various Dyno sheets with the RPM limiter removed that HP peaks at about 720-725 @ 6400, then is flat up to 6600 then begins to drops off. Obviously a camshaft would change the power profile.
     
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  7. MABBRYFL30

    MABBRYFL30 NYS President Hellcat Car Club Gold Supporting Member

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    What is a typical dyno charge to run it? No experience doing this and I would love to know. M6 cat for my car.
    It is one of those things we always say we want to do but never do. Kind of like getting your home property lines surveyed.
     
  8. themarshall

    themarshall Silver Member Hellcat Car Club Gold Supporting Member HCC Charter Member

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    Everyone of you guys have good points. There is one other reason to think about N.H.R.A. Back in the day when Dodge & Plymouth uncorked the 426Hemi it was delibertly underated H.P. WHY? Insurance Comp. had not yet caught up with high H.P. engines. (1966-67) no problems there yet. Stock & Superstock class was decided by advertised factory H.P. vs. factory curb weight. Ford did this also with there 427 side oiler. Chev did this with there 427/ 435 vet. All NHRA tracks had what was called "weight brake" index books. The lower the factory H.P. the lower class you could race in, the lower class you raced in the more chance you had of going to the next round thus, " Win on Sunday sell on Monday " $$$$
     
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  9. CAR BUFF

    CAR BUFF Gold Member Hellcat Car Club Gold Supporting Member HCC Charter Member

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    Someone here posted a few months ago a a dyno sheet I don't remember the rear wheel numbers but it was 743hp at the crank.He stated it was a stock hellcat.
     
  10. Robo21

    Robo21 Gold Member

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    My '69 Z/28 was underrated as well at 290HP.

    743 HP is a helluva lot more believable than 707 based on the RWHP dyno reports and IMO still very conservative. I have a hard time believing the drivetrain loss below 12% but that's just based on gut feelings and educated guess work. Like I said above, we need to see a bench dyno or get some accurate drivetrain loss estimates.
     
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  11. usmc341

    usmc341 Gold Member

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    I'm thinking maybe 10-12% loss with the efficient drive train we have. Certainly not 15%
     
  12. sgoyal

    sgoyal Gold Member

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    May be they are waiting for Ford to announce their big hurrah before 2018 then with small modification, dodge go out with bang.. LOL
     
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  13. Robo21

    Robo21 Gold Member

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    Bingo, 12% I can buy - but I just don't see a magical 33% improvement in drivetrain losses - 20% is huge and that would bring it down to 12%.
     
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  14. phil hunter

    phil hunter Hellcat Member

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    NHRA quickly caught on to the low horsepower ratings as mentioned by themarshall. 426 Hemi was quickly factored from 425 hp to 525 hp. Ford 428 Cobra Jet was also quickly factored, but can't remember the number. Several other engines were factored as well.

    Phil
     
  15. 1949chopper

    1949chopper NC STATE PRESIDENT Hellcat Car Club HCC Charter Member

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    How can it possibly be a percentage ? If we use 15% as driveline loss, my wife's R/T challenger only takes 56 HP to move the rear wheels but my Hellcat takes 106 ? What if I add 100 shot of nitrous, does it now take 121 ?
     

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