Given parasitic loss

[Octanewide]

Anyone know the HP % drivetrain loss for an A8 or M6? 15% for the A8 sound correct?

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[Old Mopar Guy]

Hey Jeff, I’ve always heard 15% for the A8 and about 12% for the M6. Hopefully someone who has more knowledge comes along with more concrete info.

 

[Speedy!]

This has long since been a debate. Rule of thumb I always heard is 15-20% but that can't be linear I don't think. 15% on a R/T, Scat Pack, and Hellcat wouldn't all be the same drive train loss through the same drive train. My Hellcat made 670rwhp bone stock and that would mean a lot less than 15% based on 707hp.

What are you trying to calculate?

 

[Old Mopar Guy]

Or the engine is making more that the published 707hp. Using the 12% figure for an M6, with your 670rwhp the engine would be making upwards of 750 at the crank. Did Dodge take the 707 number lower in the power curve, saving some gimme hp for a later claim without having to make substantial upgrades?

 

[Speedy!]

Or the dyno read high, who knows.

The bigger thing to consider is that the HP loss across models would have to be a pretty static number I'd think. So like drive train loss is 80HP through an A8, diff, axles etc. Couldn't really be a percentage.

 

[Octanewide]

Or the engine is making more that the published 707hp. Using the 12% figure for an M6, with your 670rwhp the engine would be making upwards of 750 at the crank. Did Dodge take the 707 number lower in the power curve, saving some gimme hp for a later claim without having to make substantial upgrades?

Hey Tony, I think your correct as the engines especially in Hellcats are under rated from the factory.

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[Octanewide]

This has long since been a debate. Rule of thumb I always heard is 15-20% but that can't be linear I don't think. 15% on a R/T, Scat Pack, and Hellcat wouldn't all be the same drive train loss through the same drive train. My Hellcat made 670rwhp bone stock and that would mean a lot less than 15% based on 707hp.

What are you trying to calculate?

Trying to calculate crank HP after someone has their Cat dyno'd and gets a horsepower number.

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[Speedy!]

Trying to calculate crank HP after someone has their Cat dyno'd and gets a horsepower number.

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I think we'd probably need to see a dyno from a stock R/T, Scat Pack, and Hellcat and then extrapolate an average drive train loss static HP amount.

 

[BULL]

@rayzazoo a very long time ago, on the other forum, posted a very lengthy dive into this. The long and short of it was that (according to the referenced articles) that you can't use a single number, and that it changes very dynamically.

When I tried to counter and say that there must be an average, even just for our cars, and further even for one of our two transmission options, it didn't go well.

Needless to say, if you go look at dyno numbers, and enough of them, you can start to extrapolate a number.

And if your next question is "What's that number?", I haven't kept track... Sorry. I myself still use 15% when I have a casual curiosity.

I do have anecdotal evidence that the M6 has lower loss than the A8 based on Standing Mile trap speeds between M6s and A8s.

 

[Speedy!]

A 2000HP car with 15% drive train loss loses 300HP. A 1000HP car with 15% drive train loss loses 150HP both through the same drive train?

 

[BULL]

A 2000HP car with 15% drive train loss loses 300HP. A 1000HP car with 15% drive train loss loses 150HP both through the same drive train?

Exactly the issue as I remember it, not only that, but rpm/load plays in, among a bunch of other variable variables.

 

[jroyk]

A 2000HP car with 15% drive train loss loses 300HP. A 1000HP car with 15% drive train loss loses 150HP both through the same drive train?

 

[drag racer]

@rayzazoo a very long time ago, on the other forum, posted a very lengthy dive into this. The long and short of it was that (according to the referenced articles) that you can't use a single number, and that it changes very dynamically.

When I tried to counter and say that there must be an average, even just for our cars, and further even for one of our two transmission options, it didn't go well.

Needless to say, if you go look at dyno numbers, and enough of them, you can start to extrapolate a number.

And if your next question is "What's that number?", I haven't kept track... Sorry. I myself still use 15% when I have a casual curiosity.

I do have anecdotal evidence that the M6 has lower loss than the A8 based on Standing Mile trap speeds between M6s and A8s.

It is a complicated scenario with a lot of variables and no single magic formula, BUT that is precisely when real engineers begin to develop empirical models based on observed data to describe complex systems, especially us enthusiasts who don't have access to the multi-million dollar laboratory and test equipment that the OEMs have. So whoever the internet forum keyboard engineering experts were back then - most haven't a clue what they are talking about.

I too was doing the same thing for a while back then, collected some chassis dyno data for a while that appeared to be trustworthy, and then kind of moved on. I will say, I have the SAE certification test report for the original 2015 model year 6.2L engine, and with very limited rear wheel dyno data points, the magic drivetrain loss % I was seeing is significantly better than 15% for the A8. I will not disclose the number, but I was very impressed, and the engineering excellence and optimization of the ZF converter/trans and differential is obvious.

 

[Octanewide]

It is a complicated scenario with a lot of variables and no single magic formula, BUT that is precisely when real engineers begin to develop empirical models based on observed data to describe complex systems, especially us enthusiasts who don't have access to the multi-million dollar laboratory and test equipment that the OEMs have. So whoever the internet forum keyboard engineering experts were back then - most haven't a clue what they are talking about.

I too was doing the same thing for a while back then, collected some chassis dyno data for a while that appeared to be trustworthy, and then kind of moved on. I will say, I have the SAE certification test report for the original 2015 model year 6.2L engine, and with very limited rear wheel dyno data points, the magic drivetrain loss % I was seeing is significantly better than 15% for the A8. I will not disclose the number, but I was very impressed, and the engineering excellence and optimization of the ZF converter/trans and differential is obvious.

Why the secrecy for the A8 parasitic loss?

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[drag racer]

Because I know my data is limited, and not totally scientific, and I don't have time or desire to argue the topic with internet "engineers" because I really don't care that much. I know what I know, but it might not be totally accurate.

 

[Speedy!]

Well, my math suggests the same @drag racer and somewhere in the 5-7% range but folks would balk at that low of a parasitic loss and it could be a combination of under rated and an efficient system. If only a performance shop or similar would engine dyno a couple Hellcat and Redeye motors and publish the results. We'd have a pretty good idea then.

 

[Octanewide]

Remember the rear end also requires some HP to turn as the trans is not the only thing that diminishes crank HP.

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[Unholy707]

My bone stock 2015 m6 put down 686 to the wheels on dyno jet.

 

[drag racer]

Remember the rear end also requires some HP to turn as the trans is not the only thing that diminishes crank HP.

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The toque (power) available at the wheels on the ground includes differential and CV joint efficiency, no?

 

[Octanewide]

The toque (power) available at the wheels on the ground includes differential efficiency, no?

Yes but I was talking about A8 efficiency when things got secret.

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