Power train loss

thunder1 · #1 (**permalink**) 04-18-2006, 05:54 PM

Was wondering what the power loss in the drive train is, on the standard drivetrain.
I dyno my car on a dynojet and put down 264 hp & 282 torque, I have a 302 with Elbroke 202 heads which I was told put out 350 hp.
My question is, is the power loss the same on a bigger engine as my small block I would think it would be the same since you are moving the same mass?

scottj · #2 (**permalink**) 04-18-2006, 06:31 PM

The answer to your question is no. Gear set efficiency is expressed as a percentage of power. The more power that is put through a drivetrain the greater the power loss.
Scott

DAVID GAGNARD · #3 (**permalink**) 04-18-2006, 07:32 PM

If your motor does make an honest 350 hp at the flywheel then your loss thru the drivetrain is about 25%, not that good but not that bad............it all depends on a lot of variables of your drivetrain...... and how it's set-up........different transmissions absorb different amounts of hp,likewise for rear ends.......then you also have your water pump, alternator and any other acces. hanging on the front of the motor...........
Lightened, polished rear gears such as found in NASCAR will make a difference as well as how they are set-up.......same goes for tranmissions..........too many varaibles for a "blanket" number to go by......

with that said, I should be able to tell you in a couple of weeks what my 65 Mustang road race car will do........I've had the engine on an engine dyno and in a couple of weeks will be going to a chassis dyno....... I'm running a custom built road race toploader thru a 9" rear end with an aluminum driveshaft connecting the two, on the front I only have a high volume aluminum water pump and a 60 amp alternator all with race under drive pulleys.........

I'll report back on the findings as soon as it's done............

David

jeffko · #4 (**permalink**) 04-19-2006, 06:18 AM

There are certainly variables to be considered, but when I had my car on a chassis dyno the guy told me that most cobra setups loose between 60 to 90 horsepower. Evidently he has dynoed numerous cobras with crate engines and dynoed engines.

Cashburn · #5 (**permalink**) 04-19-2006, 04:05 PM

With those numbers depending on your transmission and air cleaner setup your motor is probably closer to 310-320HP. There are a lot of different ways engine builders today make their HP claims. A "California Dyno" for instance would be open pipes, no front accessories, electric water pump, etc. or it might just be a piece of software

mrmustang · #6 (**permalink**) 04-19-2006, 05:10 PM

Ed,

Drivetrain loss is usually 17-22%, it can vary from car to car, even fluids used in your engine, transmission, and rear end, not to mention the transmission and rear end used in your vehicle. I have seen as little as 11% loss (circle track car using all sythetic fluids) to as much as 27% on a 302 crate engined Cobra replica. Do the math and you can find your high and low averages based on this.

Bill S.

thunder1 · #7 (**permalink**) 04-19-2006, 06:19 PM

I work in a machine shop and rebuild gearboxes also, when we rebuild them with new bearings and set preload ,we do what is call a breakaway reading at each set of gears and bearings with a torque wrench, could be inch pounds,
no matter what is hook to the gearbox,"electric motor hand crank "the amount of torque should be the same .So way the percentage?

Cashburn · #8 (**permalink**) 04-19-2006, 06:54 PM

Yeah but you were told 350 HP, not a specific torque right? So that's what we are looking at.

What do you have for an air cleaner?

mylesdw · #9 (**permalink**) 04-19-2006, 07:53 PM

Quote:

Originally Posted by thunder1

I work in a machine shop and rebuild gearboxes also, when we rebuild them with new bearings and set preload ,we do what is call a breakaway reading at each set of gears and bearings with a torque wrench, could be inch pounds,
no matter what is hook to the gearbox,"electric motor hand crank "the amount of torque should be the same .So way the percentage?

Your breakaway reading measures the residual friction in the bearings and seals. It is a good way of measuring the 'stiffness' of a new box and I guess you are right that it will remain fairly constant.

In addition to this, each pair of gears generates friction proportional to the loading (torque) applied so here is the 'percentage bit'. Any pair of gears (and especially helical type) involves pairs of teeth 'rubbing' together and the friction of this uses energy to produce heat. The harder you load the gears the more they rub...

thunder1 · #10 (**permalink**) 04-19-2006, 08:19 PM

Thanks myles C-W
load of the gears is from the weight of car and torque applied, Thanks ,never thought of it that way but that make sence, and thanks for everybodys replies

Cobracraig · #11 (**permalink**) 05-05-2006, 08:36 AM

Thunder1,
As a very general rule, rear-wheel horsepower on a manual-transmission car is about 15% less than SAE net, and rear-wheel horsepower on an automatic-transmission car is about 20% less than SAE net.

jdean · #12 (**permalink**) 05-05-2006, 09:05 AM

Along with air filter and any other accessories, you would be surprised how much power is lost through the side pipes. The efficiency of Cobra type side pipes varies a great deal, and can cost up to 30-40 horses. A lot of times when an engine that has been dyno'd with headers only is put in the car and then taken to a chassis dyno, this muffler restricted loss is lumped in as drive train loss.