Parasitic Loss

Discussion in 'High Tech for Old Iron' started by Briz, Aug 11, 2017.

  1. Briz

    Briz Platinum Level Contributor

    Not sure where to put this so mods feel free to move.

    Took the regal to the dyno today for a tune. They did 3 pulls to establish a baseline. so 402 HP and 410 Tq was the starting point Over 6 - 8 pulls and tweaks along the way, jetting / timing it came up to just shy of 470Hp and 472Tq. Not corrected for temp or humidity ect
    On the engine dyno after the build the final numbers were 620Hp and 700Tq.at the crank. My quandary is this. The Hp suffered a loss of about 24% while the Tq was around 35% My thinking is that it should be the same loss across the board or is it an average. The engine is driving nothing except an Alt up front. All the loss is from driveline.
     
  2. flynbuick

    flynbuick Super Moderator Staff Member

    For a frame of reference a 2014 GT 500 has a driveline loss of 10-12%. These are all 6 speed manuals.
     
  3. JR Wills

    JR Wills Well-Known Member

    Porsche had 1 of the Lowest losses back in the 60s with 12% in their 4 speed Transaxle. (A TH400 was about 30%) You have a Loss in the Converter/ Transmission, drive shaft & the rear as well.
    You can also vary the numbers on a Chassis Dyno, by changing the diameter of the rear wheels & tires, which is why many people don't go by those figures.
    The figures You have mentioned are actually quite good & considering that primarily you are working with engine design & so forth that is roughly 50 years old technology, That's Not Shabby!
    JR
     
  4. 300sbb_overkill

    300sbb_overkill Well-Known Member

    With your QM times and your miles per hour what does the calculator tell you your HP is? I would go by that and not a just for reference chassis dyno.

    If you don't like the chassis dyno numbers you can go down the street to a different chassis dyno shop and your numbers will be different.

    I'm sure the numbers are repeatable with the chassis dynos so when they tune your car from the baseline to the improved numbers that it has a bit more power now. But even though the chassis dyno made HP improvements that doesn't guaranty better QM times.

    Derek
     
  5. Briz

    Briz Platinum Level Contributor

    I hadnt done the figures on the calc as of yet but Im willing to bet they are close. Also not at all bothered by the numbers. I was hoping for 500 is at the wheels but as long as the car runs consistent numbers it does not really matter to me. Havent run it out the back door as of yet in the 1/4 miles. gearing is set up for the 1/8 and it does what its supposed to there.

    My main question was why such a difference between the percentage of loss between HP and Tq.
     
  6. sean Buick 76

    sean Buick 76 Buick Nut Staff Member

    From my experiences the torque on the chassis dyno is really effected by converter slip. I ended up measuring 30% converter slip on the dyno but under full throttle driving at 120 MPH I was only seeing 12% slip. So the converter was slipping a heck of a lot more on the chassis dyno VS real world use. My rear wheel HP was 450 and TQ was 400 foot pounds. My other car with a lockup torque converter and the same engine setup did the same HP and 50 more TQ using lockup torque converter so the converter makes a huge difference. My theory is that the way the chassis dyno loads up against the engine it makes the converter slip a lot more than when driving. Like you already know the chassis dyno is great for tuning but relying on it for an exact HP or TQ number is not very accurate.... Just too many variables.
     
  7. Briz

    Briz Platinum Level Contributor

    I was thinking along the same lines. The operator said that my converter was flashing right at 5000 rpm and thats where his computer said the peak Tq came in at. It was built to be a 4500 and I launch at 4300 off the trans brake and 2 step. With a 140 60' in a 2900 lb car id say its doing its job. The car has to act differently pulling its own weight than it does sitting on some rollers. I'll get a vid posted shortly of one of the pulls
     
    300sbb_overkill likes this.
  8. Briz

    Briz Platinum Level Contributor

  9. hugger

    hugger Well-Known Member

    620 HP in 2900lb should go low 1.30's with ease

    Should trap 108+ to the 1/8
    Should et in the 6.teens to 6.30s

    1. The engine simply doesn't make the HP
    2. The converter is off
    3. A combination of both

    From my experience an auto is going to lose 100hp give or take thru the driveline
     
  10. Briz

    Briz Platinum Level Contributor

    When they informed me the converter flashed right at 5000 I started thinking it needed to be tightened up a bit. It was supposed to be 4500. Going to run at Gainesville this weekend. we'll see if the new found power get me down into the 6.50 range. I was fairly happy with the car running 6.70's. Big / huge improvement over the 7.80's the old engine was running. Maybe towards the end of the winter i'll pull and ship out the converter .
     
  11. 8ad-f85

    8ad-f85 Well-Known Member

    You aren't losing 24% from the driveline, the number is bogus.
    I know you said not corrected for temp and humidity, but bear with me.
    Which SAE correction factors on each?
    There are different rules of how things apply, not just a different correction #.
    Which metrics actually used on each dyno?
    Actual weather conditions on each?
    Each dyno could be using an actual baro or airport baro nearby, maybe even an altitude adjusted baro. (Google that one, lol)
    Each dyno could be taking air inlet temp reading from different place, which might alter the formula 6-10%.
    (Dirty chassis dyno trick, although probably not done in your case. I've used this one to bust suspicious dyno numbers before. You can find the actual recorded data for many places by the hour on the net.)
    Temp correction number from anywhere but under the hood would seriously affect the number.
    Correction from metrics NOT applied would show huge number loss.

    ***One thing to note is the rate of rpm on the chassis dyno and how it's internal inertia correction formula (before the correction factor is even applied) , is applied.
    Unless steady state rpm, as in a step test, is done...there HAS to be an inertial correction.
    There's no possible way for the chassis dyno operator to know how to factor inertia for the engine combo, let alone the driveline combo.
    Chassis dyno engineers know this and assume a pre-programmed fudge number percentage before the raw number. Dynojet went through huge scrutiny over the 15% added, prior to any SAE corrections applied.
    There wasn't any ill intent from them, the owner just wanted the number from his sport bike to reflect the factory rating, and this is what they came up with.
    The occasional unscrupulous dyno operator wanting their clients to see huge numbers is at fault with the misapplication of this glitch.
    *It's worse at high altitude, where the dyno's programmed SAE correction must break SAE rules on the altitude range and how they are allowed to apply.
    This doesn't apply to every dyno, just some correction factors. lol.

    No ill intent is implied towards either of your dyno facilities, they cannot compare.
    The chassis dyno would need to steady state the torque reading and go around it's own programming to a raw torque number to factor out inertial correction.

    Modern vs archaic designs and the concept of comparing percentages and efficiencies are entirely out of place in this particular thread (sorry, Porsche Dude!)
     
    Ken Warner likes this.
  12. Briz

    Briz Platinum Level Contributor

    Ok thats all well and good but the improvement in HP and Tq is what it is and thats what I paid for. Didnt really care what the numbers were as long as I got the best numbers I can out of this combo the way it sits in the car. Going to the track Saturday and well see if there is any real world gains.
     
    8ad-f85 likes this.
  13. 8ad-f85

    8ad-f85 Well-Known Member

    I should have put that with my previous answer and cut some of the text down.
    There isn't that much % loss.

    Your project is quite impressive, so don't take this negatively...
    Now that I re-read your original post,
    I'm not believing it would increase 62 lbs tq from timing and jetting that the engine dyno would miss from basic tuning.
    Would you have expected to see 762 tq from the original dyno if more time was spent?
    (ignore the % change because would that mean +83tq? with the 35%)
    I'd believe getting the hp near the same tq number or beyond from what I recall on your build, but then the torque number wouldn't have increased so much.
    I guess you'll find out what happened at the strip and we can analyze that if need be, lol
    I'd suspect that the hp increase was more modest, maybe 30hp.

    I haven't thought about the percentage difference between tq and hp yet, that has me curious.
     
  14. 8ad-f85

    8ad-f85 Well-Known Member

    Another thing I'll interject is that a half days testing without weather correction could easily show a 10% change in any direction.
    Even after I moved the vacuum motors out of an early version of my flowbench to a different room, the friction through the bench throws the corrections off quickly on a humid day.

    There was some discussion on a different forum about the dyno unit itself picking up efficiency or mysteriously showing improvement that was lost the next morning when everything cooled down again.
     
  15. Briz

    Briz Platinum Level Contributor

    They didnt do any tuning or very little on the engine dyno. Hooked it up made a few pulls. set the timing and that was about it. He looked at the numbers on the screen and said the A/F was good. Was a much cooler day than the chassis dyno. However, the chassis operator did say that he had worked with many builds that came from the engine dyno guy and his numbers were usually pretty close.
     
    8ad-f85 likes this.
  16. 8ad-f85

    8ad-f85 Well-Known Member

    If the timing and A/F was close, is 62 lbs. reasonable?
    Hopefully the car improves at the strip.
    Awesome car, BTW.
     

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