Ok, the experience that I have with dyno's are only dynodynamics AWD dynos so maybe this is different for other dynos but I hear everyone comment on how much HP they are making at the wheels and then you can add 15% - 25% to get the round about fly wheel HP. The only issue I have with this that doesn't make sense to me becuase when you baseline a car you see about a 60 HP loss at the wheels which figures out to be about 22.14% loss on the stock EVO but where the question comes in is after you add mods I didn't think that you continued to loose 22.14% you only still loose the 60HP only, you can't loose anymore unless you have drivetrain issues or do you? If so please explain so I can completely understand.

Thanks in advance.
GTVEVO

 

More friction in the drivetrain with the higher load of the Dyno due to more power output results increased losses.

if drive train losses are 10% and flywheel hp is 100 then 10 hp are lost in the drivetrain.

If hp is increased to 200 and losses remain at 10% then 20 hp are lost in the drivetrain.

A bit of a simplistic example. Realworld isn't so linear. But you get the idea.

 

well, the idea is that the loss of hp is related to all the mechanical loss used to drive each part and as such can be measured. the usual number for standard transmission is about 15% now realize that that number is an approximation. each car my be different slightly but really should vary by much. some cars with shorter driveshafts lighter smaller parts may net only 12% and other like trucks with heavy parts , longer shafts and increased frictional contact maybe more 18%. but 15% should get you close and as we all know close is good enough for back yard bragging rights. now automatic transmissions have more loss due to torque converters and slipping clutches and more internal parts. usually calculate 20% for autos. this fractional loss from the motor back is constant. so if your moving parts take 20% of your power to move. ie motor turns the flywheel, which turns the transmission, which turns the shaft which turns the axle and tires +- frictional loss. this is a fixed number it doesnt matter how big your motor is or how many of them you have . from a starting point to another point in time.
what you are thinking about is the idea of how much power does it take to keep a car at a certain point. like it may take 100hp to keep your car going 50mph so if you have 300hp you will have 200hp left to go faster with and if you add more power and go to 400hp then at 50mph you should have 300hp. the difference is the dyno calculates the power based on the cars ability to move a large object a certain distance in a certain amount of time . thus calculating hp that was generated to do this. thats the bug in you soup. other wise you are correct once moving if you lost somemuch power to get to your wheels if you add 10hp more you will have 10hp more than before at that same speed.
hope this helped some. other may be able to explain it better.

 

Sometimes power going down isn't uncomon. Some mods give you more low and mid range HP, while decreseing peak HP. It's all about tuning...

 

Nope. You are not taking into account that when you put more power through a gear system of ANY kind you get more frictional losses. In the engine itself your main variable loss is piston friction. At higher HP levels you have more side loading on the pistons in the bore form the increased combustion pressure. In the transmission you have meshed gears, and as stated above, more power through a gear set gives you more friction losses. Transfer case? Another gear set. Rear diff? Yup, another gear set!

Now, the rotational inertial losses DO remain constant no matter what HP you have, I think this is what you were refering too. If you have a heavy set of wheels, it doesn't matter how much HP you have or how little.... the losses will be the same in the real world, and they will be the same on a dyno dynamics dynometer or a dynapack dynometer no matter what you HP level. Now on a dynojet, the less rotating mass in your drive line the more HP you will have on the graph. Do you actually gain HP from putting on a lighter set of wheels? Nope. Do you gain performance in the real world in proportion to the gained HP on the dynojet? Yup!

Personally I like both systems I would love to do testing on both... but there isn't an AWD dynojet in my area.

Keith

 

It's all a rough approximation anyway. Drivetrain loss and dyno numbers are rarely accurate.

It's really meant as a tuning tool.

 

Well said. There sure have been enough "mines bigger than yours" discussions
(if you can call them that) on this board.

As far as losses go, we have seen the results of stock evo pulls and they come in at, let's say,
235whp (on a particular dyno).
What we all assume is that the car was actually getting the purported 271 at the flywheel.
But who knows if that is the case.
We still use that number to calculate the % loss. What else is there...

What's useful is before and after pulls on the same car on the same dyno in similar conditions.
Then the numbers are relational unto themselves for tuning purposes.