Chassis dyno vs Engine dyno

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On 2007-04-14 09:03, allenman85 wrote:

Please explain and quote at least one engineering text.

I am waiting. Intuition (yours) is not an acceptable answer.

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Ok, I have wasted some of my own time and have found an engineering text to back up my "intuition", which I would prefer to call logical thinking.
It is from a NASA paper 1622 by Anderson & Loewenthal regarding gear efficiency under load.
The paper pertains to a large helical gear setup that is running at a constant speed of 1450rpm. As load increases from 25% thru 100% frictional gear losses increased from .3 thru 10.8kw.
To quote from the text - "it can clearly be seen that the sliding friction losses are heavily load dependent, increasing with load."
Whilst I could not find anything directly relating to automotive applications but would imagine that the results would be relative to smaller diameter gears with higher teeth to diameter ratio's. The bottom line is that gear friction rises with load.
Keep in mind that these tests were conducted with a single helical gear in parallel configeration (think manual main and lay-shaft layout) with a 25 deg helix. It is also travelling at a relatively slow speed.
A rear end has a hypoid configeration with a larger degree helix and much more tooth contact area, plus the pinion is placed low relative to the crown wheel.

i cant believe after all these years,drivetrain losses are still THEORETICAL. its crazy and frustrating at the same time,there are no real articles out there that PROVE one way or the other. We need to at least get two engines that make different power at THE SAME RPMS,dyno them on an engine dyno and install them in a car and dyno them on a dynojet with everything else being EXACTLY the same, and to make things interesting,find a way to see if higher RPM engines lose the same HP as Lower reving engines that make the same HP. (stroker vs destroked) to see if parasitic losses have more to do with RPM than the power itself.

i cant believe after all these years,drivetrain losses are still THEORETICAL. its crazy and frustrating at the same time,there are no real articles out there that PROVE one way or the other. We need to at least get two engines that make different power at THE SAME RPMS,dyno them on an engine dyno and install them in a car and dyno them on a dynojet with everything else being EXACTLY the same, and to make things interesting,find a way to see if higher RPM engines lose the same HP as Lower reving engines that make the same HP. (stroker vs destroked) to see if parasitic losses have more to do with RPM than the power itself.

I think the reason it is still estimated is because there are just too many variables involved to actually compute an accurate figure.
I think the helical gear tech paper shows that load does have a major effect even though rpm didn't change so it is most likely load (power) and rpm are both factors.

yeah but it might be helpful to know which one is more of a factor. why dont any of these tech articles and mags try to tackle this problem? Obviously there are variables and always will be, but to funnel it down at least a little more would contribute GREATLY to everybody interested in this great hobby/lifestyle we have.

_________________
2003 Mustang Cobra Vert.
2001 F4i - 600cc's
2000 Audi TT
1994 Impala SS Clone - 383 with goodies ~R.I.P.~
1993 Mustang GT - 13.02 @ 109.22 - stock sortblock/NA - SOLD!
1968 Mustang - Bringing out of ritirement!
1968 Galaxie 500 - 390

<font size=-1>[ This Message was edited by: bluelightning302 on 4/20/07 11:01am ]</font>

So I'll add some fuel to the fire. I have a stroker big block Ford that made 820 hp @ 6400 and 730 ft/lbs at 4800 at the crank on a Super Flow dyno.

With an identical tune on a Mustang chassis dyno we saw 503 RWHP, 465 ft/lbs. This is just shy of 62% or a 38% drive line loss. The car, a 4220# wet, 71 Mustang convertable, has run 10.80's at 127 in fair air and excellant track conditions, and yes there is more in the chassis set up, but it's street car right? The drive line is a Lentech AOD, Stange 9" and MT 325/50 28" Drag Radials.

As a way of validating the %'s, a 100 hp shot of N2O yielded a 61 hp gain at the tires.

Another car, a 10.60's 3600# GTO, made 423 HP at the tires on the same chassis dyno and with a 175 shot made 110 more at the tires. That car has a 200R4, 12 bolt and 295/65 MT Drag Radilals. The well sorted GTO semed to have a slightly better 37% driveline loss based on quarter mile calculators.

We found five hp with a change in tire pressure and spun the tires on the drums with larger N20 shots.

At the end of the day the chassis dyno or engine dyno are great tuning tools but trying make comparisions between different machines with different operators is futile. use them to make your ride better and let track be your standard of comparison, DA adjusted of course.

[addsig]

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On 2007-05-03 21:25, Silverliner wrote:

At the end of the day the chassis dyno or engine dyno are great tuning tools but trying make comparisions between different machines with different operators is futile. use them to make your ride better and let track be your standard of comparison, DA adjusted of course.

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I think that sums it up perfectly! It's a tuning tool! Nothing more![img]/forums/images/smiles/icon_smile.gif[/img]

<font size=-1>[ This Message was edited by: 289nate on 5/5/07 11:38pm ]</font>

ok but to just say "its just a tuning tool" and brush the issue aside wont resolve the REAL issue, how to properly calculate or understand how drivetrain lossed even occur. Dont sell yourselves short

So, I may have some additional data for this in a week or so as I'm taking out the AOD and putting the T56 back in the car. The motor will be untouched and I'll be back on the same chassis dyno. according to just about every theory out there we should see more RWHP through the clutch and stick vs. the converter and automatic.

This will precede a carb to efi swap using an identical manifold and a 4500 style throttle body vs. the dominator carb so that will be interesting as well.

This doesn't address MauriSSip's question but I'm not sure I can. Based on two cars I know well this particular Mustang chassis dyno seems to tkae 37-39% driveline loss.

For comparison the GTO saw 1000 rpm slippage on the dyno ves. 500-600 typically at the track again using stnadrad formulas. On the dyno we had crank speed measured optically compared to wheel speed on the rollers in 3rd gear so we know what difference is with the way the dyno loads the car. We'd need a wheel speed sensor and data logging to have actual track data which neither of us have currently. I will be able to add that soon with the Innovate LM-1. More quater mile lap= more data. Eventullay I may actually learn something.
[addsig]