*Parasitic loss*

[IJ.]

Does anyone have any hard numbers on the loss through the drivetrain in a Mk3? ie: Crank HP V's RWHP.

I've read often that it's 15% but don't think that's right my thoughts would be it's a given number not a percentage as I can't understand how a stock GTE would lose 35hp and a 1000hp monster would lose 150?

 

[Blue87T(Dan)]

Everything I have read says between 12% and 15% for a manual trans and higher for an auto.

I will be interested if you find something to the contrary.

Dan

 

[americanjebus]

yea no shit my auto losses "20%", i for one think thats bullshit. oh i know its true its just bullshit.

for one i use my g-meter to measure hp and on all the stock cars i've tested it on the numbers come back accuratly. before i did anything and was still totally bone stock my 230hp rated car put 191rwhp. last i checked it was 228 at the wheels but unknown crank.

 

[IJ.]

I'm sure someone out there has some hard data on this so yep it'll be interesting!

I would imagine if the stock GTE drops 35hp then the 1000hp motor would lose the same 35hp.

 

[89Turbo]

brought back from the dead, looking for a good answer for Automatic power loss.......

 

[Supracentral]

I'll tell you, that's a hard question to answer.

Auto's behave strangely on the dyno. I've run cars on the dyno that can't seem to make the power they should, and then you take them to the track and the trap speeds tell a different story.

For stock cars it's pretty consistent. However, once you start pushing a slushbox, things sometimes get wierd. I've seen cars that can flash through the converter on every pass on the dyno, yet don't have a problem on the track.

And as for percentages, it works, as a "ballparK" estimate, it's not scientific.

I'll give you an example, my drag car from two seasons ago.

She never made more than 1200 RWHP on the dyno, and it was a bitch to get it to read that.

The cars best trap speed was 189 MPH in the 1/4.

Do the math.

If you consider the following axiomatic:

then you will see that in order to obtain that trap speed, you'd have to put down northwards of 1528 horsepower.

Do a 20% drivetrain loss on that number, what do you come up with?

1222.4 HP - almost exactly what she read on the dyno.

These estimates have been around for years, and they are pretty damned accurate in my experience.

 

[JustAnotherVictim]

I always heard it was about 15% so I guess with that formula I could actually find out once I go run.

 

[whenmunkysfly]

lol thanks for the eqation it helped me finally figure out the power to waight ratio..... 12.75 pound equals 1 hp.

 

[Insidious Surmiser]

Does anyone have any hard numbers on the loss through the drivetrain in a Mk3? ie: Crank HP V's RWHP.

I've read often that it's 15% but don't think that's right my thoughts would be it's a given number not a percentage as I can't understand how a stock GTE would lose 35hp and a 1000hp monster would lose 150?

i was under the impression it was somehwere around 12ish percent for manual and 17-18 percent for auto... more or less for wear and tear, and so on and so forth

 

[cjsupra90]

The reason for the actual losses increasing as the power increases is because as the input power increases, the friction generated in the entire drivetrain also increase due to the high input loads and there for uses up more power to overcome the friction.

This can easily be tested and verifed by monitoring the oil temp in the tranny and the diff.

Do a series (we'll say 4) of pulls back to back with little to no cooldown time with a stock setup car and at the end accurately record the temp of the oil in the tranny and the diff.

Now that same car just highly moddified doing the identical same test and you will see high readings for the oil temperatures.

This increase in temp is due to an increase in friction, and any increase in friction will requier more power to overcome this friction. Therefore the higher power losses with high input power.

Overall, chassis dynos are only good for tuning and nothing more. There are to many variables that can cause false or inaccurate readings.

Here are two really good links

http://www.pumaracing.co.uk/power3.htm
http://www.pumaracing.co.uk/coastdwn.htm

 

[IJ.]

Chris: I can understand the loss increasing to a point but would imagine there has to be a point where the part either stops deflecting or breaks I just can't "get" that the loss is a universal % at all power levels.

Had an interesting discussion here when I decided to go 9" that went along the lines of if there would be a noticable difference in power on the dyno with the diff being the only change.

My stance on this is that the 9" is so much more ridgid that it wouldn't deflect as much so at power should be line ball with the G series.
(unloaded cruising may be different due to the long hypoid gear form of the 9")

 

[cjsupra90]

most of the frictional losses are in the gears and the diff. It the drag from the gear tooth contact that does it. The bad part is in th diff itself, the power has to make a 90 deg. turn. This is why FWD cars have a lower lose.

No matter how much you try to over come it, the more power input, the more friction generated and therefore the more power lost to overcome this friction, but the precentage does stay the same for the most part.

Tranny gears like anyother gears do have efficiencies and these efficiencies do dictate how much power is lost to turn them. IIRC, the two main reasons why race application typically use straight cut gears is because for one, they are stronger by design and two, are more efficient therefore generate less friction and therefore less power loss.

 

[tig321]

.
the two main reasons why race application typically use straight cut gears is because for one, they are stronger by design and two, are more efficient therefore generate less friction and therefore less power loss.

I Remember reading somewhere a very long time ago, that helical gears were stronger than straight cut. This was due to having more surface engagement/teeth touching at one time. However that and also the thrust loading due to the angled cut caused too much power loss (friction) for a racing application. I think?

 

[cjsupra90]

I Remember reading somewhere a very long time ago, that helical gears were stronger than straight cut. This was due to having more surface engagement/teeth touching at one time. However that and also the thrust loading due to the angled cut caused too much power loss (friction) for a racing application. I think?

Yes, the greater contact area does cause more friction and therefore more loss but straight cut gear sets are stronger. The thrust loading is also something that causes a strength issue. A straigh cut gear is flat out better and cheaper to make and the only reason why auto manufactures dont use them is cause they are noisy as hell. If it wasn't for the noise, every tranny would have them.

 

[figgie]

I Remember reading somewhere a very long time ago, that helical gears were stronger than straight cut. This was due to having more surface engagement/teeth touching at one time. However that and also the thrust loading due to the angled cut caused too much power loss (friction) for a racing application. I think?

they are quiter not stronger. The metal chosen is what dictates the gears strength.

 

[Nick M]

That and a slight variance in weather on a turbocharged engine will vary your output noticably. Giving you a different reading.