99_SS_LS1

iTrader: (4)

I have a few questions regarding drivetrain loss.

For starters, I've always heard that 12-15% loss is about standard for a manual trans.

Being a WMU alumini and still keeping in contact with my old professors, I get the benefit of going back to the facility to run my car on their dynojet. A few months back, I put down a run with my peak horsepower being 360rwhp at 6k rpm. After I ran it up to redline, my teacher told me to throw it in neutral and let it coast down to measure drivetrain losses. At the equilvent speed of 6k in 4th gear, while in neutral the dyno shows a lost of 30.6 hp. So my teacher claims that shows my drivetrain loss. Doing the math 30.6/360 = 8.5%

Seems pretty low.

For instance, I was talking wtih a guy with an 05 ls2 gto m6 the other day. With headers and a tune he put down 345rwhp on a mustang dyno. The ls2 being a 400 hp stock engine with headers, i estimate would probably be closer to a 20% loss. Which equates to about 2.5x as high as my supposed loss. What gives?

Just hoping to get some answers, or if nothing else spark an interesting conversation.

Would also love to have some ammo to fire back at my teacher (he's a ford fan btw)

fuseone

well i was always told 15-20% was for auto trans. and as for the ls2 having 400 thats bhp as to where he dynoed 345 that would be wheel hp and not all chassie dynos are the same a mustang dyno i my self think shows bit more accurate a number as compaired to a dynojet.

qqwqeqwrqwqtq

I believe 8-12 % is on the more realistic side of what driveline losses actually are, depending on many factors and assuming it's manual trans or locked converter.

Fwiw my stock 07 ZO6 which is rated at 505 crank hp put down 463rwhp. (matches your 8.5% driveline loss).

Of course, even with no changes to the driveline, losses will not remain a fixed percentage. With higher horsepower comes higher losses to friction and inertia.

Stang's Bane

iTrader: (22)

I completely agree, but I would say that even though the losses increase as HP goes up, I would say that the percentage goes down. Just my own little theory..

99_SS_LS1

iTrader: (4)

So it's probably a pretty good bet that watching a dynojet coast down with the car in neutral will give a good idea of horsepower loss due to drivetrain?

DrkPhynx

I've always heard/known/went by the "15% for manual" ideal.

I had my car dynod on a Mustang dyno, and it put down 300rwhp in stock form (showroom stock, right down to the tires). If the loss is only 8.5%, then that puts the crankshaft at about 327.86. And that is right around the stock WS6 rating. However, that seems ludicrously low for a 346ci engine with all the tricks and this one has. Plus, I thought it was pretty well known in this community that GM underrated the F-Bodies, and that actual power output was in the 350hp range. And with a 15% loss, that would be about right for me (352.94).

TT632

iTrader: (3)

I have had one car that i followed from the Engine dyno to a dyno jet. With a loose 4500 race converter it showed a 25% difference.

topend

I believe drivetrain loss is more of fixed number than a percentage.
People say 15% drivetrain loss for manual transmission.Now if your engine make 1000 hp your telling me your going loses 150hp to friction.thats alot of heat for the drivetrain to handle.

jermzz

iTrader: (18)

what....?

DanO

Here is a basic summary as to why you are seeing the low numbers

First, the power loss is a function of Normal Load and coefficient of friction under that condition.

1st, you have different loading conditions and half your transmission s not even being measured

2nd, its going to be related to load, not just speed. some components in the transmission can be related to speed alone (i.e. seals) but bearings and gear friction are a function of load and speed.

Lots of testing is completed in the automotive world to "Map" the losses of the transmission. there are conditions where it is fairly efficient, and other loading conditions where it is very inefficient.

FASTFATBOY

iTrader: (23)

Thre are so many variables it can never be a set percentage, here are just a FEW.

Rear end type
Rear gear
Rear tires
Driveshaft AND angle of driveshaft
Trans type
Converter effeciency
CLutch and flywheel weight
Oil temp
Coolant temp
Trans fluid temp
Correction factor used
Type of dyno used

No way it can be a SET percentage.

AUSTRALS1A

Good comment
I'd add to that comprehensive list one more.... RPM

My recent experience for drive line loss on a 383 ls1, 5500 stall 4l60e, 4.11 irs rear through radial tyres was 610horse engine dyno > 427hp chassis dyno.
That's roughly 1/3 loss (33 odd percent- sorry dont have calculator for exact figure) To lose 100 hp on an engine that only made say, 300hp would not be workable; its more like a 70 hp loss - the percentage is variable depending on the power level and those listed variables above.

melchoir

iTrader: (4)

With higher horsepower comes higher losses to friction and inertia. In physics a lot of the losses are due to friction, and friction losses are proportional to the forces applied, the more force, the more friction loss.

BAKED

iTrader: (14)

Wouldn't the amount of friction be relative to RPM? If that is the case then a 383 that makes 400 Hp @ 7,500 RPM will robbed of more power than a 454 that makes 500 HP @ 6200 RPM's