Is Drivetrain Loss Constant?

[greatone61]

I have a quick question, say with a stock truck your losing about 18% hp through the drivetrain. If you supercharge that same truck are you still losing 18%???

 

[ViperTruck2933]

Good question and your probably going to get several different answers. :dontknow:

 

[SilvrSRT10]

I have a quick question, say with a stock truck your losing about 18% hp through the drive train. If you supercharge that same truck are you still losing 18%???

Yes and no. Your power is still going through the same drive train with the same amount of drag or robbing the same power from the engine. So that remains approx. the same. Now even though a SC creates more HP. It also robs the engine from some power to turn the SC. It's just that the SC creates more HP than it robs but I would guess that the percentage changes when you add accessories to the engine. Someone will chime in and make your head spin in a little while.

 

[RedSrt007]

For simplicity, yes you will still lose the same amount. But as the numbers go up, your power loss will also increase (500hp=425 roughly, 1000hp=850..etc..). Different mods will help in decreasing the amount of drive train loss...flywheel, viscosity of oil, lightweight syncros, etc...

a general rule of thumb -

FWD is typically 10-15%.
RWD (RC) is typically 15-22%.
AWD is typically 20-30%.

Im sure everyone has there own opinions and reasonings...but those are mine..take it for what its worth

-Red

 

[AWDisuzu]

opinions are not worth much..... anyway, your drivetrain does not magically rob more power when you add power to the engine. it's a mechanical constant.

 

[ViperTruck2933]

Okay, lets do some hypoteheticals here then............

If a bone stock RC puts down 425 rwhp (500 flywheel per manufacturer) thats a 15% loss or loss of 75 hp. Let's say the motor gets a N/A build with stock pulley's and no external power robbers anywhere else.

Now let's say the truck puts down 575 rwhp after the build. Would he have 575 + 75 = 650 at the flywheel or 575 + 15% = 661 flywheel hp?

 

[RedSrt007]

15%...from what I have talked to Chris about and read, the percentage is consistent....so you would be at 661 @ crank. I cannot see how it would be a 'set' number on drivetrain loss, it wouldn't make sense, its based on percentage.

If so, lets use this for example:

Stock 500hp crank / 425hp wheels
Im sure if you were to get 2000 hp (crank) out of it, you would loose more then 75 hp in drivetrain loss. You (in approx theory) would be @ 1700 wheels. Im sure it would taper off at some point, and could be plotted out, but thats where it gets too technical for me lol....

Once again, IMO

-Red

 

[Nowwhat]

the drivetrain loss percentage will begin to decrease at a certain point.....


if you are losing 18% at 800 crank hp

you will not lose 18% when that crank hp is boosted to 1200 hp

 

[greatone61]

Here is my problem:

2006 SRT-8 Charger made 360 rwhp stock....425 crank hp.


Supercharged it made 540rwhp. Only thing that was changed in the drivetrain was a Limited Slip Differentrial. What do you guys think he's making at the motor with the supercharger?

 

[ViperTruck2933]

Here is my problem:

2006 SRT-8 Charger made 360 rwhp stock....425 crank hp.


Supercharged it made 540rwhp. Only thing that was changed in the drivetrain was a Limited Slip Differentrial. What do you guys think he's making at the motor with the supercharger?

Well that's a 15.3% drivetrain loss in stock form. If the percentage holds true then it should be 622 flywheel hp after the S/C. :dontknow:

 

[greatone61]

Well that's a 15.3% drivetrain loss in stock form. If the percentage holds true then it should be 622 flywheel hp after the S/C. :dontknow:

Thats what my and my buddy have a disagreement on...he says you don't do the percentage calculation you just add the stock hp loss back in and you get your new flywheel hp. So in this case the stock hp loss was 65, so the new flywheel hp would be 605....I still think thats not right......

 

[ViperTruck2933]

Thats what my and my buddy have a disagreement on...he says you don't do the percentage calculation you just add the stock hp loss back in and you get your new flywheel hp. So in this case the stock hp loss was 65, so the new flywheel hp would be 605....I still think thats not right......

I think it's safe to say he's between 605 and 622 fwhp, lol.

 

[Bone]

the drivetrain loss percentage will begin to decrease at a certain point.....


if you are losing 18% at 800 crank hp

you will not lose 18% when that crank hp is boosted to 1200 hp

I agree, it's not completely linear with loss. The percent may be somewhat close but a little less (in percent). I imagine there are plenty of variables involved.

 

[rab986]

I agree, it's not completely linear with loss. The percent may be somewhat close but a little less (in percent). I imagine there are plenty of variables involved.

Yes.. many variables. You can't expect to get flywheel hp by simply plugging in a number. More horsepower will create more heat in the drive train which will also rob more power. I can change numbers on my dyno by simply tying the car down too tight or something as simple as incorrect tire pressure even the fan being slightly askew. I chassis dyno is only as good as it's operator.

 

[AWDisuzu]

and in an automatic, you could get more loss due to slippage in the torque converter