MazdaManiac

iTrader: (3)

OK. I get it.
SoCal is representative of every RX-8 I have ever seen.
Excellent.

You are truly the master of small-sample causality.

sinned2545

fixed ^

this also has some good Ideas of numbers
https://www.rx8club.com/showthread.p...light=Dyno+day

R80MAV

it seems this is an argument that has been brought up time and time again. it seems that the 192 (4ports) seem to get closer to their specified output. does anyone know why the numbers are way off what the factory spec is?

RIWWP

iTrader: (2)

I think you are forgetting the very critical piece of the pie that some of the engine's power is used to move things and fluids around. This all encompasses the "drivetrain loss" number.

"True" wheel horsepower will always be lower than "true" crank horsepower. And if a manufacturer over-rates an engine (like Mazda did) the WHP is going to be even farther off. If they under-rate an engine (like some Ford and Chevy engines in the past) the gap will be narrowed quite a bit farther.





I'm sure Mazdamaniac can correct me on anything wrong in this next bit. I typed it up previously, though only got some corrections on the actual terminology used.


________
Drivetrain loss is neither a flat % nor a fixed number.

Rotational-only components before the transmission (such as flywheel, crankshaft) soak power, but only when RPMs change. They do not soak any power when the RPMs remain constant. Higher mass (weight) parts increase the power soak. This is one reason people go after lightweight flywheels. There is no difference between a lightweight and a heavy when you keep the RPMs the same, but the heavier one resists engine change more, which steals a bit from acceleration, but can also be of a benefit when you want to maintain momentum (typically not an issue for performance oriented driving, but a common factor for commuter cars)

Rotational-only components after the transmission (such as driveshaft, axles, wheels) soak power, but only when the vehicle speed changes. They do not soak any power when the vehicle speed remains constant. Higher mass (weight) parts increase the power soak. Carbon fiber driveshafts improve engine response, but are really tied to vehicle speed, not RPM, so they have a greater impact when the speed change desired is the greatest. Smaller vehicles of the same drivetrain configuration typically have less loss from this aspect since their driveshaft, axles, and wheels are typically smaller. It's the mass of the parts that matter though, not the size (different materials can make larger parts weigh less than smaller ones of a heavier material)

Mechanical linkage before the transmission (such as the e-shaft gear in a rotary, input gear on the transmission, alternator, pulleys) soak power at an increasing rate as RPM increases. This number can easily change for cars based on lubricating fluids and surface treatments. Race teams apply REM and WPC treatments to gear contact surfaces specifically to reduce drivetrain losses, and it works.

Mechanical linkage after the transmission (such as the output gears, diff gears, axle joints, wheel hubs) soak power at an increasing rate as vehicle speed increases. This number can easily change for cars based on lubricating fluids and surface treatments. Race teams apply REM and WPC treatments to gear contact surfaces specifically to reduce drivetrain losses, and it works. The frictional surface area matters here as well. For example larger wheel bearings generate less heat and drag than smaller ones (of the same material and velocity).

Fluid and air pumps before the transmission (oil pump, water pump, any vacuum drag from emissions components or the engine itself, power steering pump if you have a fluid system) soak power based on RPM at an exponential rate. The rate of loss increases dramatically as RPMs increase. The viscosity of the fluid and pump efficiency can make dramatic differences as well. For example, the RX-8 OEM water pump uses flat vanes on the impeller to push the water through, and a common upgrade is to go to a spiral impeller design, and this has been proven to increase measured WHP between 5-8whp. Obviously it doesn't do anything to the engine's output itself, it's just reducing some of the drivetrain loss.

Fluid pumps after the transmission (diff) soak power based on vehicle speed at an exponential rate. The rate of loss increases dramatically as the vehicle speed increases. Power losses are also impacted by fluid viscosity. The dyno difference of an RX-8 on the same dyno/same day between cold diff fluid and hot diff fluid is around 5-7whp. Again, zero impact on what the engine is actually producing, just changing how much power is being lost to move the fluid around.


Some components have more dynamic drivetrain loss explanations, such as the transmission fluid. Part of it's loss is based on RPM, part on vehicle speed. Some components also change based on ECU or triggers. For example the A/C compressor on an RX-8 soaks lots of power, until you pass a certain point in engine load, and then it internally shuts itself off on command from the ECU until engine load drops back under the threshhold.

There is also loss from the tires themselves, somewhat based on vehicle speed, but it's more dynamic than that, due to the change of shape a tire undergoes as the speeds increase, and every tire is different based on internal composition, sidewall flex, tread squirm, etc...

Brettus

iTrader: (2)

Not So Cal at all - this is the RX8club dyno thread .
I could do the middle pages as well then add them all up and average them if you like ?

Me - data
You - words

MazdaManiac

iTrader: (3)

Fixed that for you.

Brettus

iTrader: (2)

OK - I'll take that on the chin .

All the publicly available data would support my numbers - what happens in your world is obviously another thing.

R80MAV

I do understand transmission losses but i thought it was generally a fixed percentage between most cars, around 10-15%

But as youve stated mazda have over-rated the renesis which i was unaware manufacturers did, i always thought it was more likely that engines were over-rated to keep consumers pleased when they got their vehicles tested. its good info though and thanks for sharing.