woulddug

What is the average loss (%) of HP and Torque from Flywheel to Rear Wheels, with a stock trans and differential

BOB EAGAN

Roughly 55 hp/tq on a manual and 65 hp/tq on an auto. When adding power it pretty much stays time same.

///DarkSide\\\

~11%

SpinMonster

I'm in this camp. It isnt a percentage since the power it takes to spin the driveline is a set drag on the engine. It isnt going to icrease the power it needs as your engine power grows. So 50-55hp makes sense.

A Z06 dynos 460 and is rated 505
A base LS2 dynos 350 and is rated 400
A LS3 dynos 480 and is rated 430-436.

A 1000hp car will dyno 950rwhp.

Dan Wendling

I think the answer is close to the fixed loss in hp but does include some percentage that is a function on applied engine torque. I expect but can't prove that the loss through the torque converter at stall is in part a function of the torque level. Must be that any given converter slips more at stall with 600 tq then it would with 300 tq. More slip means more heat means less power.

Seems like all other poser losses in the drive train are speed/rpm related so if you don't go faster then these losses should be fixed.

On the other hand if quicker is the goal then the losses to accelerate the masses of the drivetrain will be higher the faster you try to accelerate them. Not sure how this translates into hp?

haljensen

LS2 and LS3; Forget percentages

55 (+ or - 5) HP loss flywheel to rear wheel Standard trans.

65 (+ or - 5) HP loss flywheel to rear wheel Automatic trans.

Go back over the HONEST Dynojets (Smoothing 3, SAE correction)posted here in this Forum in the last 4+ years.

Wah

I'm a mechanical engineer and I don't believe the loss is a percentage. Just because an engine produces more power, the loss becomes larger. It's also a ploy to show a higher number of power at the flywheel.

I agree that's the loss is in the 50-55hp range.

PowerLabs

What you said is true, but it can only be extrapolated so far...
The ZR-1 dynos 540WHP and is rated 630SAE HP BTW 90hp loss.
Show me just ONE single 1000HP car that loses only 50HP going through the transmission

I'm a mechanical engineer too, and I agree with you, but I will add that as the horsepower goes up, losses DO go up some. First of all power losses in a transmission go up almost exponentially with RPM, so if you make peak power at a higher RPM than a stock vehicle, you are also losing more power. The loss may still be a fixed number, but it'll be a bigger number because it happens at a higher RPM where windage and viscous losses are higher.
ALSO, if you are making more peak HP at the same place you did before, then torque must also have gone up. With more torque, there is increased contact load on the individual gear teeth; more contact load = more deformation = larger contact path = larger losses.
FINALLY, if you are using a non load bearing dyno (Dynojet for example), with more power the acceleration rate goes up. The higher the acceleration rate, the higher the internal losses; this is precisely the same mechanism by which cars with taller gears show lower dyno numbers...

SOOO... It is neither a fixed number NOR a percentage. It is closer to a fixed loss than anything else, but the truth is that trying to guess crank hp numbers from dyno whp data is a crapshoot

glass slipper

The ZR1 dyno numbers are all over the place to begin with. They have different ring and pinion gears than the other 3.42 C6s causing different HP loss characteristics. Peak HP of the LS9 occurs at 6500 RPM vice 6300 RPM for the LS7 and 5900 RPM for the LS3 and as you stated above, higher peak HP RPM will have an exponential impact on HP loss. As you know (since you're SC), the correction factor typically used for SAE HP can't be applied to supercharged engines. I believe that's one of the biggest reasons the HP numbers are all over the place. Ambient conditions would be the other big contributing factor with lower temps causing less timing to be pulled and allow the LS9 to operate closer to certified HP conditions. Also, your point about more HP loss due to inertia for high HP cars on a DynoJet chassis dyno will certainly apply here. But I agree with you in general about the 1000 HP engine and the 50 HP loss...not going to happen. I think Spin was just exaggerating to make a point.

Your analysis of HP loss to gears in a manual transmission on a chassis dyno is good with one exception...the HP loss to gears in the transmission will always be zero. There is no power flow going through gears in 4th gear, the input and output shafts are locked together for a straight through power flow. You will of course still have HP losses to oil windage, bearings, and seals.

One other thing, the DynoJet chassis dyno is a load bearing dyno...the engine has to be loaded somehow. In this case, the engine has to overcome the inertia of the roller but it is still a "load" as far as the engine is concerned. I think you're confusing the terms "inertia" and "absorption" with "loading" and "non-loading". Chassis dynos with rollers only are pure inertia dynos with the inertia of the roller providing the load but storing the HP as kinetic energy in the roller. Eddy current chassis dynos are pure absorption dynos in that they dissipate all of the HP generated by the engine as heat. The hydraulics of the Dynapack is an example of another absorption dyno with the hydraulic fluid dissipating the HP as heat. Then there is a mix of inertia and absorption (Mustang and the newer DynoJets). But all dynos "load" an engine, even the lowly Prony brake dyno.

Your last paragraph does an excellent job of summing everything up, I agree completely.

Mez

With Dyno's numbers so widely quoted, I don't even try to convert it to flywheel power anymore. Who on this forum has a flywheel dyno test?

oldmansan

I always like when glass slipper chimes in.

San

PowerLabs

marc8090

I'm no expert on transmissions but I don't think the input and output shafts are "locked" together in 4th gear. They are at a 1:1 ratio but the power still goes through the gears on the counter shaft. If it wasn't for the counter shaft with the synchros and shift forks there would be no way for the power to transfer from the input to output shafts. Power is transmitted through gear teeth in all forward gears, and reverse.

Walt White Coupe

Like you said: "I'm no expert on transmissions"

oneblackvette

I'm not a "mechanical engineer", but I did stay at a Holiday Inn last night.

glass slipper

Would you like to place a small wager of $100 on your last statement?

Please consider doing this as I need money for lunch next week.

Craigster05

Maybe these pics will help, it was the simplest example I could find. Rich (Glass Slipper) is correct.

This set up of locking input and output shafts was common in early 3 and 4 speed transmissions. Then along came "over drive" 5 and 6 speeds. In those transmissions, fourth gear is still accomplished by locking input and output shafts together, but fifth gear was an over drive - it just used another set of gears on the countergear and output shaft, and another synchronizer assembly. The difference was that the gears ratios caused the output shaft to be "over driven" - to be turned at a higher rate than the input shaft - therefore the term overdrive transmission was used.

mirage2991

I'm another kind of engineer, but I surely would like to know, if it takes 55hp to turn the transmission, then how in the hell can you turn it by hand...unless, it's a percentage lost...I seriously doubt you can make 55hp with your hand turning the input shaft.

It is a percentage because it involves drag (through liquid) and friction and acceleration through time.
You can hook up a 3hp engine to a T56 and it'll turn it just fine...so clearly the static 55hp loss is not accurate. It is a percentage.

Dan Wendling

The discussion is relative to the peak hp rpm. Clearly at lower input shaft speeds the losses are less and so is the hp.

PowerLabs

OK, now turn your transmission to 6500RPM by hand
While you are at it, explain to us that air resistance is also minimal because you can wave your hands through the air without feeling much resistance...