Percentage Problem

[The Rezanka]

Originally Posted by CamaroQueen

I have no opinion on the subject but was wondering if that is what you think you are doing?????/

Ya that is pretty much what ended up happening. I could see why its a % loss in my head, but I'm not the best with explaining things so as it went from my head to the computer, things got lost and what not. After I posted it I ended up going wtf did I just post grade pretty much ended up saying what I was trying to say before I confused myself

[CamaroQueen]

Originally Posted by The Rezanka

Ya that is pretty much what ended up happening. I could see why its a % loss in my head, but I'm not the best with explaining things so as it went from my head to the computer, things got lost and what not. After I posted it I ended up going wtf did I just post grade pretty much ended up saying what I was trying to say before I confused myself

Yep I do that too. LOL

[Paulster2]

Originally Posted by thesoundandthefury

There are two elements at play here:

Inertia Loads

Frictional Loads

The inertia load is a function of how much the parts in the driveline weigh and how quickly the engine can accelerate them. That's going to be a fairly "static" number.

Friction on the other hand is directly proportional to load. Increase the torque being transmitted by a factor of two and you increase the friction load on the bearings and gear faces by a factor of two. So in other words, friction loads are directly proportional to the power being transmitted. So let's say we're putting power through a 700R4 transmission. The inertia loads will not change with power, but the friction loads will. Since the friction loads are the greater percentage of the loss, the power losses through the tranny will increase almost (but not quite) in proportion to the power being transmitted.

An 800HP engine is going to produce a subtantially higher amount of friction than a 400HP one. If you build up a 400HP engine to produce 600HP, you're also producing 200 more HP worth of friction along with it. There's no free lunch.

Top that off with the fact that automatic transmissions use a fluid coupler, (torque converter), which introduces a third issue of hydraulic losses which increase exponentially with load, and the picture becomes even prettier.

Okay, this helps me understand what is happening. I guess you need to take all of the factors into account

Originally Posted by thesoundandthefury

That's just it, there really isn't a whole lot you can do with trannies or rearends. Well, not cost effectively at least. I'm sure if somebody was ambitious enough, they could try developing lightweight transmission internals, which would help with the inertia load side of things, but in the racing world, lightweight means $$$ and not many people are willing to drop that kind've money on something that has no real guarantee of lasting.

About the only thing I've seen lately that's attempted to address frictional losses is a process called "Mikronite." It's basically a high tech shot peening procedure that smoothes out and hardens wear surfaces. (Like gears.) Smoother surfaces produce less friction, so one of the benefits they claim is that you'll gain RWHP from reducing frictional losses in your drivetrain. They claim they can do this process on any metal part but the one they're pushing the most is their rearend gear assemblies.

Something that I think you need to take into account is that as you reduce your inertial load, you will reduce your frictional load. The two factors are not mutually exclusive.

Center Line came out with some wheels about 10 years or so ago called Convo-Pro (I believe). Their deal with these wheels was that for every 10 lbs of unsprung weight you remove, it's like removing 100 lbs of sprung weight. Each wheel weighs 2 1/2 lbs (total of 10 lbs) less than some of their other popular wheels, without a reduction in strength. I can see where this would also benifit the inertial losses that were talked about. Accelleration and decelleration would be improved. If you take this into account throughout your drivetrain, by reducing a pound here (aluminum or composite drive shaft) and a pound there (aluminum or reduced weight flywheel), the inertial savings are going to add up. There are some areas that could be looked at, I would think, that could really assist in the loss department.

More food for thought.

[Blown1993Z28]

Originally Posted by Paulster2

Okay, this helps me understand what is happening. I guess you need to take all of the factors into account

Something that I think you need to take into account is that as you reduce your inertial load, you will reduce your frictional load. The two factors are not mutually exclusive.

I know this is an ancient thread but instead of starting a new post and pissing people off I searched all the old threads for this previous discussion.

Trying to calculate fWHP from rWHP I came across the "percentage problem" After doing tons of research on it, Inertia Loads vs. Frictional Loads accurately describes the non lonear parasitics loss of the drivetrain. No argument the inertial load is a constant. While the Frictional Loads do increase with RPM, they are no way near 1:1 (non linear) Assuming ALL your drivetrain has decent bearings the actual efficiency of oil lubed metal to bearing efficiency is about 98%. That means doubling your Horsepower would cost about 2 more % or 96% efficiency.

Really trying to keep the math here simple, if a stock Z28 has 275 fWHP and assuming 15% parasitic loss of the M6 (41 HP) you get 234 rWHP. Doubling your fWHP to 550 HP the new parasitic loss is 2% more or 41 x (1.02) = 42 HP. Thats WAY FAR OFF from assuming the percentage way of 82 HP new parasitic loss. I know we all want to brag about how much HP our engines make but unfortunately we were inflating the numbers.

Its still debateable what % the drivetrain losses are but 15% Manual and 20% Automatic seem to be accepted. Variables like aluminum driveshafts or synthetic fluids can be calculated but honestly rotational inertia and fluid dynamics are beyond what I can explain (I actually passed both in Engineering but I don't know them enough to explain) Consider the parasitic loss a Tax you pay on the stock drivetrain. Any upgrades making more rWHP do not enjoy the extra 15% or 20% we assume out fWHP is making. Basically if you used the % method to determine you were making 550 HP you are wrong by 40 HP (you were only making 510 HP)