your law does not apply so neatly here...

1. IF we had a easy way to measure imput(motor hp) then this would have been settled along time ago... but so far no one with a engine dyno room has stepped up...
2. your formula is correct for what it was ment to measure... however that is not what is being argued here. yes everyone knows if you CAN measure the input and output, then the ratio of one to the other will be a percentage. What has not been proven however, is IF the initial percentage holds constant regardless of change in the input number... It is my belief that this CANT be true(nor can the flat rate theory)
the reason it CANT be true....
Math, like the formula you have provided is cold and lifeless, it does not take reality into account... this is not algebra 1 my friend... it is not a2+b2=c2....
we take a stock a4... at the begining of its life its ME is 80% give or take ....
now we remove that factory fresh motor and replace it with a high compression iron 408 with a 250 shot... what will the ME be for this run? well about 0... give or take... why? because it will break. did the ME remain constant? for ANY change in input? no...
but thats not fair we all know a stock a4 cant take that... but what caused it to fail? stress? heat? friction? yes... all of these played a part. to varying degrees, and at the time of breakage the tranny had reached its maximum of one or all of these things... but are these things light a light switch? you add power you add power you add power then some magic point is reached and all of a suddon the switch is flipped and heat,stress,and friction get turned on and break the tranny?
no of course not... each one of these things increases as power goes up, and whats more because of the measures we take to combat them, none of then increase at the same rate, each one increases independant of each other in its own relation to the increase in power input... and because each one of these things DIRECTLY effect the drivetrains ME, the ME absolutly CANNOT remain perfectly the same... at 300 input hp it might be 20% at 500 it might be 25% but then it might be 22% or 27%... who knows? as a matter of fact it might not even be exactly the same on 2 dyno runs back to back... it might be 20% the first run and 20.08% the second run just because the parts are now hotter...

Math used to be my favorite subject(as you can see i hated english) but as i grew older i learned to rezent it... because you can not apply formulas to life... life has its own logarythem and it is like pi, ever growing and ever changing...

you gave us a Physics law.... good for measureing something IF you have 2 KNOWN parts of a 3 part equation.... nothing wronge with that, but your trying to use it to prove that the ME will remain CONSTANT even when you change the input portion of the equation...
So in return i will give a LIFE law back to you...

In life, there is only 1 CONSTANT.......change...

 

That sounds a lot like what I always thought about this. People who think it is a constant number and not a percentage, answer me this: If the drivetrain only takes so many horsepower (say 26) whether it is behind a 350 or 500 horse motor why is it that you need stronger parts behind the more powerfull motor? Where does the force/power that breaks the drivetrain components come from? If every single horsepower you add at the flywheel makes it to the ground there should be no additional stresses on the drivetrain. The only thing that would change is the rate of acceleration of the drivetrain, but that alone shouldn't cause it to break. Otherwise spinning your tires wildly in a low traction environment or hitting the gas with the rear wheels suspended would be just as hard on the drivetrain as accelerating HARD down the track behind a very powerfull motor.

I agree it may not be an exact number or an exact percentage, but a percentage of input power lost seems more reasonable to me.

And about the nitrous: Who is to say how much a "100 hp" shot actually makes?


Thoughts?

 

First, let me say that you guys are all trying to THINK, not just blab! Props.

Jab, what I said was a "given" drivetrain. Some cars are factory "freaks". IMO that's not only the engine being a little better, but the drivetrain as well. If we could measure EACH engine and EACH drivetrain that came from the factory, we would see some differences from one to another (so you and blkZ28 are both right there). But I know from over 35 years of engineering and testing, that the variations would not be very large - they would average out. But though EACH INDIVIDUAL drivetrain has its own INDIVIDUAL efficiency, THAT INDIVIDUAL EFFICIENCY WON'T CHANGE unless something else happens. That is up to its mechanical limits of course. Jab, you're absolutely right, when it breaks, then its ME goes suddenly to 0! So I'm trying to say that the relationship of power input to power lost is LINEAR, that is, it's a percentage. Can we predict what each INDIVIDUAL percentage will be to 3 decimals? Hell no! Can we predict the efficiency based on a close average? I say, hell yeah, and that IS the real world!

I get the feeling that our thinking is muddled by trying to factor in (in our minds) things like a gear change or a TC change. That DOES change the ME - no doubt!

To be reasonably accurate, you have to have some basic ground rules to base things on. I'm just telling you guys what mine are for my remarks. Maybe that clears up my point some. HTH

 

i see what your saying, and dont get me wronge, its not that i dont think that the percentage wont be close all the way up to breakage...

that being said , what i wanted to point out was that although graphing that "given" drivetrain will prove to be LINEAR, it will not and can not prove to be an EXACT percentage. as stress on the moving parts increases, so will that parts resistance to the imputed power. it does not mean that i think the same th400 will lose 20% for a 300 hp motor and 35% for a 600 hp motor...
more like if the th400 remained the same but you swapped motors from 300 to 600 the loss at 300hp might be 20% but at 600hp 21% maybe 22%... not a HUGE change... but a change no the less

More over i think the flat rate hp is by far the more grossly off of the 2....

 

you know i couldn't put my finger on it right away, as to why this one part
sat wronge with me... so i had to go back and look at it again....
and then it hit me...


if his motor is 550ish hp
then
75 hp as his estimated drivetrain loss is......

14% (rounded up for simplicity)

 

You may be right about a small/slight increase in loss, even though my testing over the years has shown not so. There are variations in testing and measuring that are related to repeatablilty. For instance, two back-to-back dyno runs can be (and usually are) slightly different. All I can say is that if you are right, then graphing the relationship wouldn't produce a straight line on the graph (linear). It would have some curve to it and get steeper as more power is put in (as your example suggests).

I believe you and I are essentially saying the same thing with only minor differences. So I guess we are now just splitting hairs, huh? As I said, and I think you agree, the percentage is an ESTIMATE of loss. A pretty good one, but still an estimate based on averages. And averages are always just that, somewhat inaccurate when applied to a single unit. Nice talkin' to ya'.

 

I've seen this argument on a number of car boards before, on most of them the guys with the fixed driveline number (ex. 26rwhp) ended up not only on the short end of the stick but ridiculed. So Im glad this hasnt turned into that.

Drivetrain loss is parasitic in nature (meaning it leaches off of what is available, more available, more leaching) and it comes largely from friction, from what I understand. I am not convinced that ME can be universally applied to extrapolate other data points though -- just because ME is 15% at one level, doesnt mean it will be 15% at all levels when not everything else is constant -- example gear oil viscosity will change as more heat is generated which introduces something that may not be linear. Overall I think it is fairly accurate though once you know what your % is for measuring increases at the engine.

We may speak rwhp, but the rest of the world likes the hear about engine (bhp) output, thats why this discussion comes up in the first place.

 

EZ, you are on the money, this has been a spirited, civil discussion among good folks looking for real info.

I think you're making the same point that Jab is, that the ME doesn't hold true throughout the usable power band.

You guys may have something, but I've never seen it to be so. The major parasitic (good word ez, right on!) loss is friction - that is linear. OK, for you guys to be onto something, we have to find some parasitic loss in the drive train that ISN'T linear, right? You mentioned oil viscosity as a function of temperature. OK, that could be so, but I dont know how much of the loss is due to viscosity. I do know that most dyno runs and track blasts seek to get the whole vehicle at the right heat (oil and water temps in the low green, etc). Yes? So, of the observable data we have, that probably doesn't play very much of a part. As in 1% of 20% is 0.2%. Ya' know? I am open to any other loss element that might be non-linear, but I confess, I can't think of one at this moment.

My point is that the numbers we use to calculate (estimate!) engine hp comes from a set of fairly closely controlled conditions. I still say that under most dyno and track conditions, the estimates are accurate within a very small probability of error. That estimate is the observed average of a series of "identical" drivetrains, and is a set percentage of input power.

Can we change the ME of a given drivetrain? A hearty, "You bet!" and we should! Lightening the flywheel/rotating components, using slicker lubricants to fight friction are some of the ways and they absolutely do put more power to the wheels from given engine. What that does is change the ME from, say 80% to 85% (OK, now I'm throwing numbers - lol). Once any changes have been made however, my position is that the ME doesn't change anymore unless we intervene with more physical changes to the machine. I hope I'm clear. Everyone has the unalienable right to disagree!

 

Ok Guys....

I have done some more research and gathered a couple of more opinions of people I felt might be "in the know" regarding this hotly debated topic...."fixed" driveline losses versus the concept of "percentage" driveline losses. My opinion, as stated a few times earlier in this thread, is that a fixed loss is a much more accurate statement and the bulk of any gains seen on a flywheel dyno will ultimately make it to your rear wheels if the speed and driveline temperature tested remains constant (from 40 MPH to 140 MPH just as an example).

I have one last example which I feel might shed some additional light on why I feel the way I do. Take a given driveline in question....at a given speed (say 40 MPH) it will take "X" amount of power to maintain that velocity. Now lets spin it faster to 45 MPH....once again, "X" amount of power to maintain that given speed (and obviosly more than 40 MPH required). Keep taking all of these data points up to 140 MPH where you will see the highest given HP required to maintain that speed. Now lets put that driveline on an engine dyno with a 300 HP engine in front of it....It will accelerate that mass from 40 MPH to 140 MPH in a given period of time. Place an engine that is 500 HP in front of the same driveline....guess what....the driveline spins to 140 MPH in a much shorter period of time. The forces required to turn that driveline at EVERY RPM point hasn't changed at all assuming the same temperature in both tests....You might lose a small amount to additional tire distortion (causing higher friction) from the added power, but it would be a very insignificant amount of losses....single digits....Not 30-40 HP a 15-20% equation would lead you to believe.

I asked the opinions of two people in this industry who's opinions I greatly respect. One of them is Steve Brule who has been into this hobby/proffesion for over 30 years. Steve is an extremely sharp guy and primarily runs the engine dyno over at Westech Performance Group in Mira Loma, CA. but also spends a fair amount of time on the chassis dyno in the very same facility. If you haven't seen his picture or read his name in one of the magazines you haven't been in this hobby very long. When asked the question he immediatly responded that chassis losses are just that....losses, and it is not some given percentage that seems to be more of the common opinion. He also stated that they have had the opportunity to see similar gains on both (engine and chassis dyno) when they have tested a known combination in the vehicle, pulled the engine and baselined it before some changes (heads, cams, etc), put it back in the SAME vehicle and noted the power gains there to be the same as the engine dyno power gains for all intensive purposes (both the engine and chassis dyno will record slight differences from one run to the next).

Still not convinced I had enough ammunition to re-visit the LS1 Tech board I decided to make another call to someone instrumental in my career (long but good story) whom I felt his opinion would either clearly refute my opinion (as well as Steve's) or hopefully solidify it further. I spoke with Harold Bettes over at SuperFlow....going to this guy is as close to the "source" as you could possibly get (IMHO) and I had a lengthy conversation with him regarding this topic. Too make a long story short he stated without a doubt that chassis/driveline losses if tested over the same road speed (again say 40-140 as an example), are better represented as a fixed loss, not a percentage. While they of course represent some given percentage, adding more power to the engine would reduce the percentage because the fixed losses remain the same (at the same given range of speed in the test). He mentioned that the largest variable would be the tires used in the test and that if a very "sloppy" tire was used (such as a slick), it would add slightly to the driveline losses due to the deformation of the tire from the increased power appied to it. He also mentioned that the temperature of all the bearings, U-joints, trans and rear gear fluids would all have to be held constant to show close to a one to one relationship in gains (or losses) from the engine to the rearwheels.

Essentially, bolt on your favorite Heads/Cam combination and whatever you gain on an engine (flywheel) dyno, you will see the same (or extremely close to the same) type of gains at the rear wheel as well. A driveline doesn't rob more power to spin it faster....A driveline spins faster because an engine more powerful is able to produce the force necessary to accomplish that.

Perhaps all three of us are out to lunch and completely off base on this situation....I always try to keep my mind open so I might consider the fact that another theory might make more sense, but based on my thoughts, my personal experiences (like my "100 shot" adding 126 to the tire), and others whom opinions I highly respect, I'm sitting tight on this one till I see proof I should be thinking otherwise.

Regards,
Tony M.

 

No, you and friends are not out to lunch Tony.

Too bad we don't have an engineer with enough time to explain it or maybe dig up an SAE paper that covers this.

I still maintain that a large part of what the percentage loss proponents count as drive train loss is due to the use of an inertial dyno, and would go away if they used an absorption dyno.

 

I edited your quote some to show the points a little clearer.

Tony, here's the objections that I have to your conclusions: 1) steady state mph uses a given amount of hp to drag the car through the air no matter what the engine hp is. 2) Acceleration is entirely different because you're using the full available power of the engine, and it does increase the load as the power climbs.

Look at a gear tooth engagement point at a 40 (or 140) mph cruise. The pressure on the tooth is what it takes to keep the car at a constant speed. That hp is largely determined by the power to overcome air and rolling resistance and depends on the car shape and rolling stock, not the total hp available at WOT. BTW that steady-state hp requirement goes up as the square of the speed. IOW, it takes ~12 times the hp to maintain 140 as it does to maintain 40 mph.

Now look at the same gear tooth engagement point at WOT to ACCELERATE the car, you have much more force acting on the engagement point because you have all of the available engine power loading it. It takes a much larger force to accelerate a mass, than to keep it at any given velocity. (FYI, the equation for a steady speed is Force = Drag due to Velocity, and the equations for acceleration are Force = Mass times Acceleration; Velocity = acceleration times time; Distance = 1/2 acceleration times time squared.) For example, see what happens to the force when you add 33% to the acceleration at the same mass (that's the difference between 300 and 400 hp).

As I stated before, when you apply a much larger force to the drivetrain, as in WOT, full engine power acceleration, the friction increases in direct proportion to load. Therefore so does the drivetrain loss in hp and it is a set percentage. Good luck.

 

OH, BTW, just noticed this this morning: 04 GTO (350 chp advertised) ~300 whp dyno, that's ~85% to the wheels. 05 GTO (400 chp advertised) ~340 whp dyno, that about, guess what, ~85% to the wheels. Engine gain: 50 hp, wheel gain: 40 hp. A data point to consider. HTH

 

The reason you see nearly the same gains is because the added horsepower is not nearly as much as the total output, IE if you add 80 hp 15% of that is only 12 hp.

Like I said earlier I have dynoed 590 on an engine dyno and then 500 to the wheels same combo, I can turn my driveline by hand which is not even 1 horsepower. The answer is easy to understand and you do not need a formula, it is because the faster you turn it the harder it is to turn simply because it takes more energy to turn it faster.

Sure 15% is not an exact but its a general guideline that is pretty damn close.

I did not believe it myself but I saw it firsthand with my own engine.

 

Mike,

The 90 HP delta is about average....it just happens to be close to 15%. My point is now that is established (the delta between flywheel and rearwheel HP), if you added a blower and picked up 200 HP at the crank, I'm betting you will have damn close to 200 additional HP at the tire....not 170 (85% of 200).

I would like real world proof and hard data that shows the "percent theory" might be valid (from TeeKay or anyone else who hangs their hat on that theory)...and/or "expert" opinions that would contradict the few I obtained. I would think Harold Bettes, an engineer and THE lead guy over at Superflow, a company that manufactures both types of dyno's in question might have a pretty good idea about the mechanics and the forces in play here. It seems that there is no hard data backing the percentage theory you guys are touting....just heresay and "opinions". I've given you guys testimony from a veteran dyno operator, my own test with a small hit of NOS (an .051 oriface will NOT produce close to 150 extra HP) which backs the fixed loss theory, and opinion from a veteran engineer at a company that builds and manufactures the very machines we are debating.

Lets do more homework and try and to find something more substantial to back our respective theories....We can all just keep typing our own opinions but that won't lead any of us to possibly consider the other side. This is good stuff and certainly warrants a little more effort and some digging to learn which theory actually holds water. My dyno testing in the next month (and subsequent testing in the vehicle) should be very interesting but not perfectly conclusive....the headers and exhaust will be different but besides that it will be a pretty good test starting with a baseline of my current combination on the engine dyno.

Will keep you guys posted....

Tony

 

What I don't like about what you said before was that it wasn't under acceleration. It was amountof horsepower required to maintain a given velocity. The force to spin the drivetrain at a given velocity hasn't changed but the force required to accelerate that drivetrain from one velocity to another in a shorter amount of time may have.

I'd still like an explanation for this:
If the drivetrain only takes so many horsepower (say 26) whether it is behind a 350 or 500 horse motor why is it that you need stronger parts behind the more powerfull motor? Where does the force/power that breaks the drivetrain components come from? If every single horsepower you add at the flywheel makes it to the ground there should be no additional stresses on the drivetrain. The only thing that would change is the rate of acceleration of the drivetrain, but that alone shouldn't cause it to break. If it did then spinning your tires wildly in a low traction environment or hitting the gas with the rear wheels suspended would be just as hard on the drivetrain as accelerating HARD down the track behind a very powerfull motor. We know this is not the case...so what gives??

 

It's, like, Newton, dude! More HP equals more acceleration. F=MA, so more acceleration implies greater force pushing the car forward. But every action has an equal and opposite reaction, so there must now be more stress on the driveline and internals.

If this still isn't clear, ask yourself why a worn clutch first slips in higher gears.

 

Interesting. And almost too obvious. I'll ponder that more tomorrow after work when I'm (hopefully) less tired, but you might have answered my question.

 

Both "theories" assume a driveline stout enough to withstand the forces the engine applies and the fact that mass doesn't want to accelerate on its own. An overpowered driveline (say a 10 bolt rear in a 3500 lb. car putting 900 to the tire) will register BIG power at the wheels right until it spits a tooth or three off the ring and pinion. My guess is that very close to the point of falling a given driveline will become slightly less efficient due to the deflection in all the parts involved (trans, driveshaft, ring and pinion, possibly even the rear case and trans case themselves) as some of the energy being produced at the flywheel is being absorbed in a manner that obviously the parts in question were never designed to withstand. However, its the "sledehammer" effect that really ends up doing most of the damage to driveline components....like taking a 90 lb. rotating assembly at 6000 RPM (HUGE stored energy) and side stepping the clutch with sticky tires....that will break parts long before an engine three times as powerful if that power is applied more gradually to a car already in motion.

 

Nice subject. That being said, correct me if I'm wrong here, but shouldn't this thread topic ask how much torque loss there is in the driveline? After all, horsepower is a derived mathematical formula based on torque. HP = torque times rpm divided by 5252 as I understand it. Torque is the measure of the expended energy of the working fluid of an engine, while horsepower is the the measure of the working fluid expended over a given period of time. Some engines might make their peak hp at say 5500rpm, and some might make it at 7000rpm. If they both made the same measured torque peak but at different rpms, wouldn't the higher rpm engine show a greater measured hp loss thorough the theoritical "same drive line" scenario?


I enjoy reading everyones input. Great discussion all.


Richard

 

a very valid point.. however because of the very formula you just quoted, the hp loss will be more evident. because if you lose 10 ft lbs of tq at 7000 rpms its a 14 hp loss so it stands out more...


i stand on my points before...


tony, something sits wronge with me even more now.. the fact that you contacted these 2 "sorces" is great, however .....

1. they provided you with no NEW information, or proof...
2. there opinions , until backed by proof, are just that.... opinions.
3. they are as you said respected names in the biz... however there are other names just as big who disagree...(you might find one or 2 in the links i provided.

so the input they gave holds the same weight as anyone elses here... until backed by proof it is nothing more then an educated guess... educated... but still a guess...

has no one found any PROOF yet???