On drivetrain losses, again [AW article on the front page]
05-30-2006, 11:00 AM
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On drivetrain losses, again [AW article on the front page]
I don't think this is a repost. The AW front page has a new <a href="https://www.audiworld.com/news/06/shootout/" target="_blank">S4 shootout article</a>; it's an AWE vs. APR Stage 3 shootout on KTR's Dyno Dynamics. FATS runs included. They also used a stock S4 (Bahn Burner) to get a baseline number.
In it, there are some interesting comments made from KTR's GM about the drivetrain loss factors we often use in estimating crank power:
<i>"Franz was able to give us an estimated crankshaft power figure for our runs, but we're sticking with the power at the wheels because that way there is no interpretation required. Franz also went on to explain the problem with using a static percentage (which is common practice) for factoring drivetrain loss. His example: if a given car made 150 hp and had an 18% drivetrain loss, the same car could not have an 18% loss at 400 hp since things such as bearings, axle joints, transmissions, etc, would be molten from the heat generated by such resistance."</i>
If I understand this correctly, drivetrain loss *decreases* as power increases on the dyno. Correct?
On a less interesting note, KTR's Dyno Dynamics returned nearly identical results to <a href="http://maxhawk.bravepages.com/car/Dyno-010805/" target="_blank">my own run here in Georgia</a>.
My wheel hp vs. Bahn Burner:
<img src="http://pictureposter.audiworld.com/57452/dynoday_010805_wheel_hp.jpg">
<img src="https://www.audiworld.com/news/06/shootout/images/stock_small.jpg">
In it, there are some interesting comments made from KTR's GM about the drivetrain loss factors we often use in estimating crank power:
<i>"Franz was able to give us an estimated crankshaft power figure for our runs, but we're sticking with the power at the wheels because that way there is no interpretation required. Franz also went on to explain the problem with using a static percentage (which is common practice) for factoring drivetrain loss. His example: if a given car made 150 hp and had an 18% drivetrain loss, the same car could not have an 18% loss at 400 hp since things such as bearings, axle joints, transmissions, etc, would be molten from the heat generated by such resistance."</i>
If I understand this correctly, drivetrain loss *decreases* as power increases on the dyno. Correct?
On a less interesting note, KTR's Dyno Dynamics returned nearly identical results to <a href="http://maxhawk.bravepages.com/car/Dyno-010805/" target="_blank">my own run here in Georgia</a>.
My wheel hp vs. Bahn Burner:
<img src="http://pictureposter.audiworld.com/57452/dynoday_010805_wheel_hp.jpg">
<img src="https://www.audiworld.com/news/06/shootout/images/stock_small.jpg">
05-30-2006, 11:05 AM
#2
That's correct. The overal drivetrain loss percentage DECREASES as power increases..
but again, it's not a static number, it can not be applied car to car. The only way to really truly know what the engine puts out at the crank is to measure it at the crank. That's why I didn't resort to any sort of crank estimates.
05-30-2006, 11:05 AM
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Cross-link to original thread....
<ul><li><a href="https://forums.audiworld.com/s4/msgs/2374098.phtml">https://forums.audiworld.com/s4/msgs/2374098.phtml</a></li></ul>
05-30-2006, 11:22 AM
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"power @ the wheels" .. look at the diff wheels the 2 cars have .. that is a substantial diff
in WHP right there .. enkei 18" vs one of the lightest wheel ssr comp 17" .. i know the enkei-s are not bad either , but still .. not the same. they should have used stock wheels.
i'd also use the 93 oct file.. the AWE race file is just the best* from what i've seen.
i'd also use the 93 oct file.. the AWE race file is just the best* from what i've seen.
05-30-2006, 11:23 AM
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Depends how you measure
If you use a stepped or very slow test like some dynos [used to?] do, then your drivetrain losses are going to [essentially] be a fixed number over a given rev range, regardless of output, because you're only measuring losses from friction.
If you test at a rate like that used on the DD, then you're also expending energy accelerating the drivetrain components, so the amount of drivetrain loss will scale up with engine output.
If you test at a rate like that used on the DD, then you're also expending energy accelerating the drivetrain components, so the amount of drivetrain loss will scale up with engine output.
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05-30-2006, 12:34 PM
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I don't really agree with the dyno guy's explanation.
The drivetrain components will be measurably hotter (as well as the engine components) as power levels increase.
This is why high powered cars DO have such things as differential and transmission coolers. This extra heat is also driveline loss.
He's right in saying it isn't an exact percentage...but in many cases, a percentage is the best way to estimate it.
This is why high powered cars DO have such things as differential and transmission coolers. This extra heat is also driveline loss.
He's right in saying it isn't an exact percentage...but in many cases, a percentage is the best way to estimate it.