Chassis dyno vs Engine dyno

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On 2007-04-04 05:38, cmf60 wrote:
I don't get what you mean allenman85?
Are you saying that it takes 5 ft/lb to rotate your 9" on axle stands?
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Yes. Actually less.
[addsig]

Seems where i'm from, a motor with 580 HP on and engine dyno, usually does around 460 rwhp on the chassis dyno through auto/9 inch.

Mine made 280 rwhp and estimate at 400hp.
Runs just under 113mph in 3550 pound car.
[addsig]

So what does it take at 6500rpm on the ground??

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On 2007-04-05 02:34, cmf60 wrote:
So what does it take at 6500rpm on the ground??
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The same -- but now the ground introduces other losses but doesn't add to the 9" loss. Sorry if this is too complex for you.
[addsig]

Oh, on the contary, this one will be easier than the last.


With what you are saying, if you hook a torque wrench on the input shaft of your trans you will be able to measure what drive-train losses your setup has??

Ok, at what rpm were you doing when you took your 5ft/lb reading?

Allenman, I see you have been on and by the lack of response...it sounds like you may have put abit of thought into it now.
I am not here to "pick" on you, so lets keep the snide remarks to ourselves shall we? There is nothing wrong with abit of "friendly" debate ....

The reason that your theory is flawed is you are not applying any load to the measurement. Think of it this way... the reason why drivetrain losses are computed as a percentage is because it is a near linear figure rather than a fixed figure.
Example..... say you have a 400hp engine, that in a vehicle produces 300 rwhp. You have a 25% drivetrain loss that equates to a 100hp. You remove that engine and put an 800hp one in there. Rwhp will not be 700 (800 - 100hp) but will still be a similar 25% loss.
Why??
The reason is gear(sets) do not have a fixed power "loss". Meaning... the more power that is applied .... the greater the loss will be.
This applies to transmissions as well as rear ends.
The 9" has a higher power "loss" than most other rear ends because of its pinion placement.

"..... say you have a 400hp engine, that in a vehicle produces 300 rwhp. You have a 25% drivetrain loss that equates to a 100hp. You remove that engine and put an 800hp one in there. Rwhp will not be 700 (800 - 100hp) but will still be a similar 25% loss."

An engine making twice as much power will not lose twice as much through the drive train. The loss will fall somewhere in between. The reason is because the mass of the internal components are required to accelerate faster. The engine creates more power but more power is lost along the way.

More heat is generated and more heat has to be dissipated. More flex is created in the motor/trans mounts, springs, suspension, chassis, etc. Energy has to be absorbed in countless other ways but if no larger/heavier parts are used, the percentage will definitely go down.

I possibly didn't word that correctly Brian....it should have read just "similar loss". Whilst the final figure may not be exactly the same percentage, it will be relatively close to that percentage.
It is an example, so we will assume that no components need upgraded.

True, the mass of the components will be accelerated faster, which is part of the hp loss BUT if you use a chassis dyno (not enertia) that applies load and do fixed rpm testing....you will find still find that the higher hp engine will create a similar loss percentage compared with testing the original engine using the same method.
It is also true that the percentage may be slightly less.... but the point I am trying to make is that gearsets do not have a fixed hp loss.... the loss is directly related to the amount of power being applied.

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On 2007-04-12 15:52, cmf60 wrote:
the point I am trying to make is that gearsets do not have a fixed hp loss.... the loss is directly related to the amount of power being applied.</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

Given a fixed rotational speed, what makes you say that an increased torque input will cause the gears to absorb more energy?

Please explain and quote at least one engineering text.

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

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

Given a fixed rotational speed, what makes you say that an increased torque input will cause the gears to absorb more energy?

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Yes, that is what I'm saying, but under load ofcourse. I do not have any related engineering texts here...but I see what I can find.

In the meantime, here is a question you might like to ponder on.

It is a fact that increased power thru a drivetrain results in increased temperatures in those components at similar rpm.
What creates that heat?

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I was reading the discusion you are involved in on the Ford Transmission Forum. There isn't too much fact getting produced there either with comments like "it doesn't feel like its absorbing that hp" etc.
Planetary losses are barely mentioned and the pump is working constantly regardless of how fast you are driving....it jjust dumps the excess back into the pan.
We mess with C4's which are relatively small componentary wise. Are you familiar with the artermarket 6 pinion planetaries for them? The additional force required to rotate them compared with a 3 pinion is very noticeable.
There is always much debate on auto power loss but rarely do you see much information on it apart for the TCI figures that are posted on a regular basis. There was however a recent article in MM&FF that directly compared a TS prepared C4 with a Tremec prepared by Hanlon MS's. They were put in the same vehicle (bracket car)...all other running gear was the same.
There were no real surprises ET wise with the Tremec being marginally faster with better 60' times. Given the deeper ratios of the manual (and more of them) that stands to reason doesn't it? What was the surprise was the fact that on the rollers, the C4 actually produced more peak rwhp than the Tremec (12hp more) which surprised everybody. This was ofcourse after converter stall speed (lock-up) so converter multiplication is not a factor. Why?

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One thing that is for sure is that drivetrain loss is not a fixed number, given that rotational mass has not changed....what has.... and we are talking load testing here. Sure if you are cruising the actual loss figures will be similar as the hp required to maintain the speed is similar.... This is what you are simulating with your torque wrench are you not?