Drive train power loss

[mrr23]

And one more thing to bake your noodle. There was one 2001 z06 that dynoed 335. Which is pretty low compared to the average out there. So.eone asked a gm engineer wjy the vatiances. His statement was the engine rating we give is the minimum it will produce. The monday/friday theory.

[85vette]

Would it make sense to say that a certain car, say Rich's C5, will have a certain amount of drive line loss regardless of horsepower that the engine makes? That would be a constant variable in percentage of loss, but the amount of horsepower lost should remain the same. In other words if he lost 65 horsepower with that car on the dyno(assuming you know your crankshaft hp)with 800 horsepower then it would be accurate to say you have a 65 hp loss with, say 650 hp? Or would it be a higher actual hp loss because the engine is not as powerful? (Talk about opening a can of worms)

[mrr23]

Actually that is what this whole conversation is about. What is the constant? Percentage or initial horsepower at stock?

[Rich Z]

The reason why I qualified my question with a constant RPM stipulation is because I would imagine that the actual loss would be directly related to the rpm of the engine and drivetrain. It would make sense that the higher the rpm, the higher the friction levels of the rotating parts that involve bearing surfaces. So more friction at higher rpms would indicate a consequently higher loss of hp. So at a steady rpm, my guess is that any particular drivetrain will have the same amount of friction, and consequently the same amount of loss indicated by a constant hp or torque value, regardless of the amount of power the engine can produce. That is as long as the engine has the minimum amount of power necessary to rotate the drivetrain at all.

Now a lot of this conversation might actually revolve around how a dyno actually determines horsepower and torque. I confess that I have never really looked into that, so it is a blank spot in my understanding. But some hints I've gotten from readings of other materials seems to indicate that the dyno determines those values by calculating off of the rotating drum to determine how quickly it can be accelerated within given timeframes. Obviously this is all programmed into the program code for the dyno. But I have heard of some dynos having something called a "dynamic brake" for steady state tuning, but honestly, I am not clear on what exactly that does.

In any event, if a typical dyno determines from raw acceleration what the horsepower and torque ratings are of a test vehicle then it would be logical to assume that a more powerful engine that is capable of spinning that drum of the dyno faster within a given time period would incur increased friction because of that speedier spin up. But even thinking about this, I still can't see any way logically that the percentage of drivetrain loss could possibly remain constant. That would imply a linear amount of increased friction caused by the increased speed of rotation of the drivetrain, and that would manifest itself by an exactly 45 degree slope of the trace shown in a dyno run for each and every run made on it. The only change would be the start and end points of the run itself. As a matter of fact, one contributing cause for why we see noticeable dropoffs in the slopes of dyno traces at high rpm might just be because of the friction loads beginning to take a toll on what the engine is able to overcome.

Anyway, just thinking out loud here. Might be completely all wet in my thoughts.....

[mrr23]

there are two main types of chassis dynos in use. inertia and eddy current, or load dyno. dynos measure torque, then calculate horsepower.

http://www.hotrod.com/how-to/additio...is-dyno-guide/

inertia basically just measures how fast you accelerate the drums over time with a lead on a plug wire to get an rpm reading.

eddy current dynos give you the ability to add resistance to slow the acceleration of the dyno based on vehicle weight. they can also hold the engine at a given rpm to fine tune the pcm. basically if you want to hold the engine at 3000 rpms at WOT you can do that.

i have been on both the dynojet inertia and load and mustang load dyno.

here is my dyno page from my 2000 pontiac formula. you can review them and see if the percentage or loss remains consistent assuming the aftermarket parts claims for increased power are accurate. even with nitrous added. can also see how gears affect dyno results. spoiler alert, the higher numerical the gears, the lower your number will be.

http://tredalign.com/formula00/2000formuladynos.html

[mrr23]

here's an article i just read with an interesting statement.

http://www.superstreetonline.com/how...in-power-loss/

It's also worth noting that the more powerful you make your engine, the greater the thrust force and angular acceleration it's able to exert on the drivetrain, generating even more friction and heat in the process. But because both steady-state and dynamic friction vary depending on engine speed, engine load and the efficiency of the engine and drivetrain's design (how well they limit friction and the associated thermal conversion of torque to heat), there's no way to apply a universal percent loss to it. Nor is it possible to apply a fixed drivetrain loss figure to your car (say 60 whp from my RevUp G35 example), because as you modify the engine and increase its output its ability to generate thrust force and angular acceleration also increases (though not in a linear fashion).

basically we cannot necessarily apply any constant. it does, however, give credibility to the more horsepower loss as you increase engine horsepower. so shoots down the drivetrain only absorbs x amount of horsepower no matter how much power is applied. gives credibility to percentage because there is an increased loss of drivetrain power as engine horsepower increases. the percentage value won't be constant.

in the end, percentage value would be more prudent to use.

[mrr23]

just referenced my stock versus adding 150 engine rated horsepower nitrous dynos

stock engine 305 chassis 276 resulting in 29hp loss or 10%

nitrous engine 455 chassis 405 resulting in 50hp loss or 12%

for giggles i applied 10% loss to the nitrous and came up with 46hp loss.

my own testing confirms what the article states. increased loss as more engine horsepower is added. so again, applying x amount of horsepower regardless of engine horsepower is an inaccurate assumption.

[Rich Z]

Quite frankly, after this discussion, I believe that this is basically unanswerable. You can't even start off with a yardstick of any known length, because unless you dyno your engine out of the car, you don't even know what the true power it is putting out. The figure from the manufacturer is just an estimate. So when you put the car on the dyno to get the RWHP, how do you KNOW what the actual loss is? So you increase the horsepower of the engine and make another run. Was the drivetrain loss less, more, or the same? How would you know? You really don't know what the base line loss was.

So anything quoted as a probable drivetrain loss is going to be nothing more than a rough guess. And even then, it most likely won't apply precisely the same for any other vehicle, even the same make and model, since obviously if there are going to be variances in the output of the engine because of manufacturing tolerances, the same will apply to the components of the drivetrain as well.

Heck, I read that post you made about the changes in dyno results from different ratio differentials. Obviously a variance in gear ratios makes a difference. Why does someone use shims when putting together a differential? Because DIFFERENCES in clearances. How much will this affect the power output because of a variance in resistance? What about the gearing itself, not only in the differential but in the transmission. All mechanical drawings will provide the specs of machined parts along with an acceptable tolerance of variation. It is NEVER zero. The closer you want to get to that value, the more money it's going to cost to machine this stuff. And certainly a automobile manufacturer is going to be counting the bottom line as a pretty high priority.

So yeah, it looks like the answer to my question about whether drive train losses are a constant percentage or a constant hp value is "none of the above". It's not a multiple choice answer, it requires an essay to explain why this cannot be nailed down to an accurate estimate.

[mrr23]

Pretty much just guesswork. No accurate starting point at stock. Dynos are good for measuring gains/losses when modifying from a starting point. Even xhanging dynos will give a different result. So, when using a dyno, pick one and stick with it. I did a local orla do dyno comparison in one day. A dynojet 248 vs a dynojet 224. They were within 5 hp of each other.

They are only useful as a comparison tool.