is this true? some guy on the IS forum said that if you multiply the whp times 1.21 and 1.24 then you get crank hp. therefore that means if you divide the crank hp by 1.24 then it should give you a good idea of what whp should be. if thats true then a stock CLS should be about 209. is that right or whats going on here?

 

According to that a CLP stock should be putting 181hp to the wheels..... Dunno if that's true but I'll take it....

 

1.21 assumes a 21% drive train loss, as 1.24 assumes a 24% drivetrain loss. If you know what your drivetrain loss is for sure, it'll be pretty accurate. Otherwise it's just a ball park figure.


No..

So you know your drivetrain loss is 24%. Hence only 76% of the power is making it to the wheels.

260=hp @ crank
.76=76%

260*.76=196.7 whp

209hp would be a 20% drivetrain loss.
(209/260)*100=80%

 

oooooook
so is 196.7 what we should make stock? if it is then this way actually works?

 

Like Siggy said, it may work sometimes if this number just happens to correlate with the drivetrain loss. But not always with all cars, take for example the 6 spd, it's loss is less than the auto, so it should put down more hp.

 

It also depends on the manufacturer. While 6MT Acura's might lose around 24%, BMWs have much smaller losses, closer to 9%. So it all depends. Manual cars could lose anywhere from 15%-20%, while Auto's could be anywhere from 20-25%. Again, these are estimates and they will vary. AWD cars lose even more power to the drivetrain also.

 

That's all fine, but why do you say "1.24 assumes a drivetrain loss of 24%"??? It all depends how that number it's used, in Italian's decription, it's being used to multiply wheel HP to get crank HP. This is an usual, kind-of backwards way, but it's equivalent to assuming 24% hp GAIN at the crank with respect to the wheels.

In fact, if you want to convert it to go the other way:
CRANK = WHEEL * 1.24
WHEEL = (CRANK) * (1/1.24) = (CRANK) * 0.806
= CRANK * (1 - 19.4%)

So a 19.4% loss. While it might be true for the lexus boards, that's a bit low for our cars, we actually do lose more like 24% like you said. In Italian's units, the equivalent multiplier number would be:

1 / (1.00 - 24%) = 1 / (0.76) = 1.32


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ADDENDUM:

This whole discussion about how much loss our cars have is the the AUTO. The 6MT has significantly lower loss, it seems like; didn't Titan19 dyno at 219hp stock?

If that is so, our loss is "1 - (260-219)/260" = 15.8%, and
our equivalent GAIN multiplier is: 1.19

That # very close to the 1.21 that was spoken of earlier.

 

Ya i see what your saying... thats correct.

Actually my calcs will be off quite a bit as it didn't take into account starting HP.

 

truly a ball park figure...

I dynoed at 189whp (on a mustang dyno) so that means 27% through the drivetrain. So not only do our trannies suck ass, it sucks up lots o' power.

 

I fixed my equation... LOL it was way off...

This works, plugin any drivetrain loss % and WHP and it will give crank HP. Of course it'll be off a lil bit. But shouldn't be much if you know the true drivetrain loss.

So a 6MT CLS dyno'd at 219hp and we think it has a 16% drivetrain loss....

WHP=219
drivetrainloss%=16

(100/(100-drivetrainloss%))*WHP=crank HP

(100/(100-16))*219=
(100/84)*219=
1.1904*219=260

lol, ya I dunno what I was thinking before...

thanks for correcting me!