Question .... Why wouldn't losses (Engine HP - RWHP) stop at a certain point. Say you figure in 12% loss from engine to wheels ... that makes a big difference if you are making 800hp vs 300hp ...

Do you really see that much loss?

Crowley

 

its a 16-17% drive train loss. its just something we all have to deal with. trust me its alot better than the mustang guys, they are losing about 20% on their manuals and even more on their trashy c4 automatics those things are stupid they have to be losing liek 22-23% in those things.

 

My question is ... at a certain point, wouldn't you stop losing (at least at a higher % )?

 

no, if anything, [most stock] drivetrain components would experience more drag as a result of higher engine speeds and increased load.

 

Can you explain this?

thanks,
Crowley

 

I assume you're asking why are drive train losses a certain percentage rather than a fixed number like 30 hp. If that's not what your asking, ignore the following.

The main two drive train losses are friction resulting from gear mesh and inertia loss to rotating components. When two gears are rotating, there is friction due to the contact and sliding motion between tooth faces. As more force (torque) is applied to one gear, the contact force between the teeth increases causing an increase in friction. Inertia is an objects resistance to acceleration. The harder you try to accelerate something, the harder that object fights back. So again, as more torque is applied to the gears, driveshaft, etc., the higher the inertia loss is.

I made a "C" in machine design, and that was nine years ago, so all of the above may be entirely wrong.

 

The T56 loses a pretty much fixed amount of HP. Generally considered to be in the 55RWHP range.

Auto trannies are slightly different. (Whether they have lockup converters, stall, STR etc)

This doesnt take into account, clutch/flywheel types or other drivetrain changes (12 bolt, 9 inch, heaviers rims/DS etc.

 

And a TH400 is about 50rwhp+ lower than a T56

 

Here'e one for ya...

"Percentage" driveline losses are a fallacy.

Every driveline of course has a certain amount of "loss", or essentially power required to turn and rotate all of it's mass, frictional losses included, BUT once you knew the "delta" between flywheel HP and RWHP, IT DOES NOT CHANGE.

For example, if you had the oppurtunity to test your engine on a flywheel conventional dyno and it made 400 HP, then installed it in your car and saw 335 HP at the wheels, your driveline losses are obviously 65 HP. Now take that same engine out and bolt it back on the same engine dyno where you now add a set of your favorite heads and a performance camshaft. Presto, you pick up 75 HP on the engine dyno....install in vehicle....back to the chassis dyno....low and behold a 75 HP gain at the wheel!!!

% driveline losses are rough estimates and are only close in a very limited power band. You are correct in your thinking....the same driveline with a 300 HP engine in front of it doesn't mysteriously eat up another 100 HP at the wheels because you just installed an 800 HP powerplant in front of it.

What I like to call the "DELTA" always remains the same. A particular driveline takes "X" amount of power to spin at a certain RPM. It has no idea of how powerfull an engine is bolted in front of it....once the "delta" has been accounted for, any additional power made will simply make it to the rear wheels.

And the best thing about my theory is that it's been proven on the dyno....both of them.

I'm sure this post will stir some controversy....

Regards to all,
Tony Mamo

 

Controversy indeed!!! Tony I had always though like you and then I read on thread on this very forum about the %losses. It was explained in such a way that imagine a 400 hp engine turning the drivetrain it gets a certain hp loss. Now say a 500 hp engine turns the same drivetrain but because of the extra power it turns the drivetrain quicker thus taking more power to actually get the drivetrain to turn quicker. Common sense up until that point had always told me that you only lose a certain amount of hp regardless of the engine. I even thought that a bigger engine might lose less hp becuase it can turn the drivetrain easier.


I actually did get my engine dyno and I should have my chassis dyno hopefully withen the next couple of weeks. Then I'll no for sure what % drivetrain loss I have. if its nowhere near 15% then I will throw that theory out the window. If it is close to that then I guess I'll have to believe it.

 

Mike...

Depending on your power output CURRENTLY, it might still turn out to be 15%, or close to that. My point is that as you make MORE power, the percentage loss becomes less and the "Delta" remains the same. There are some other issues involved that will play into this (engine/driveline speeds where max power occurs could influence the "delta"), but overall driveline loss is more of a constant, not a varying "percentage" situation.

Go baseline your car and get your numbers....If you have a good idea of what your engine is making at the flywheel you will have a good indication of what your particular driveline "delta" is....In the future, any added power found in ENGINE performance modifications (not gears, convertors, etc.) should find its way direct to the rollers and your favorite stretch of road.

Regards,
Tony

 

Tony I am so glad you posted this, as this has been my train of thought for a while now.

 

I'm not an engineer but I would think there are both fixed and variable losses. So the more horse power a car makes the lower the total loss percentage would be.

If it was fixed, I don't know why there would be any controversy at all. A lot of companies have/or have access to both so why wouldn't somebody just do some testing and provide the information?

 

"And the best thing about my theory is that it's been proven on the dyno....both of them."

Your theory would be much closer to truth on a steady state dyno rather than an acceleration dyno. Of course, in the real world we are accelerting too.

Drivetrain losses are neither a fixed percentage or a fixed number. As power goes up, the loss number goes up (again, especially when accelerating) and the percentage goes down.

 

so what we are saying is the loss is not linear or constant but at an increasing rate but just a slower decreasing rate (some call that the 3rd derivative).

i personally have never believed that a 700 hp motor would loose the same 15-17% on an MN6 tranny as compared to a 350 hp motor in the same driveline. but i have always been quiet about it.