As i was sitting in my meaning less physics lab measureing the acceleration due to graph -
I started day dreaming-

somehow i arrived at this-

Why is drivetrain loss dependant upon horsepower?
shouldn't it take Xhp to turn everything x times per min?
if anything, shouldn't it be dependant upon speed relative to the ground (not engine).
the gears, wheels, tires and driveshaft are spinning more and more the faster you go.
ie
the wheels spin more and more at 3000rpms as each gear goes up.

i can see rpms, more stroke, more speed, bigger rear, tq converter, auto vs manual- too
but why with more power?

technicaly in accordance with this theroy-
wouldn't you not need a min amount of power/tq to spin the driveshaft?
it takes x% of your power, not 10hp to twist it or whatever it is?

isn't it kind of saying-
you have these heavy shoes-
this strong guy runs and this weaker guy runs-
they are heavier for the stronger guy

maybe bad example -
maybe i'm stupid wrong and missing something very obvious
but




challenge everything
(except the acceleration due to gravity )

 

1 thing that may make it take more power from stonger motors is friction.as you make more power you are accelerating the gears faster and harder causing an increase in friction of the rear gears and the trans planetaries.dont know for sure but it may be because of that?

 

hmmm
i doubt that could be the reason for an extra 25hp i'm losing...

 

Trey, I had never considered that drivetrain power loss was proportianate to HP. Am I reading that correctly? So then the hp loss is a percentage of engine hp, or maybe a derivative, not a flat percentage? So just throwing out numbers, a 300 hp/tq motor and a 500hp/tq motor will lose different amounts of power to the rear wheels?

Either way, all the more reason to get that carbon fiber driveshaft. Hmmm... do they make carbon fiber rearends, axle shafts and wheels yet?

Nate

 

Some of the losses are proportional to rpm and some are proportional to power transmitted, and some are proportional to acceleration of the components.

Rpm: bearing friction is the best example, but it's only a small % of the loss. Windage, or flailing around of the oil in the trans and rear end should also be rpm dependant. Tire deformation at the road/dyno roll is mostly this, but maybe some power related. So would higher tire pressures give higher RWHP? Probably.

power: gear friction. Hypoid bevel gears as found in the RWD rear end have lots of sliding friction between the meshing teeth. The more power they transmit, the more fricton and heat they generate. Winston Cup cars have rear end coolers just for this reason. RWHP increases can often be measured when changing to synthetic rear end lube. 9 in. Ford with it's high amount of offset of pinion and ring gear axes (compared to 10 or 12 bolt GM) is a big offender, but it's also very strong. Trans gears have the same effect, but to a lesser extent. Running in 1:1 ratio (direct) or 4 th in a M6 is probably least loss.

acceleration: every component with mass (which means most of them) have inertia which resists being accelerated. The faster the acceleration (on the road or dyno) the more power is consumed accelerating components. Because inertia is rpm related, those things turning the fastest have the greatest effect.
Also, inertial is higher when the mass is farther from center.

Lightening a flywheel is at about 3 times as effective as lightening a driveshaft the same amount when running in direct. If you are in the lower gears, the lighter flyweel is many times more effective.

If you are going to lighten things to get more RWHP, the biggest offenders are engine speed related items, especially flywheels. Wheels and tires are big inertial hogs, but they are only turning a fraction of engine rpm.

Factory power and torque ratings are taken at steady state or on a "step" dyno test, where inertia doesn't matter, so acceleration power numbers on a chassis dyno will always be less. Fortunately aftermarket engine dyno tests are most often run ar some acceleration like 300 rpm/sec. It's a lot easier on the engine also.

Most (but not all) chassis dynos can only measure power/torque when the vehicle is accelerating. They are "Inertial Dynos" because what you are doing is accelerating a large drum with a known inertia. A vehicle putting down 450 RWHP accelerates the dyno drum much faster than a ricer putting down 100 (FWHP?).
Most are rated at 1000 hp. I've never seen a 1000 RWHP run but the test wouldn't last very long!

I won't even get into torque converters. If you had a lockup converter that would take all your engine's power, you'd get higher RWHP numbers running the test with it locked and in 3rd gear[1:1] .

My $.02 [edited for spelling]

 

Trey:

You know where to start:

[SEARCH]

We have flogged this subject several times, with numbers.... .

 

Oldsstroker:

As usual, a very articulate post.

You should it and cut n' paste it every time someone uses a simple constant to back up their statement that their car has "x" hp at the crank because it was "y" at the rear wheels.

Thanks.

Rich Krause

 

I've seen the ones in LT1 tech and they are nothing but worthless rants that end up being personal pissing contests.
I decided to stop here.
I dont come in here often, I usually cant understand your crazy mumbo jumbo.
maybe one day i will be smart

 

Listen up in physics class. Couldn't hurt, might help.

 

As was mentioned, a great deal of it is inertia. A physics term you should read up on.

 

Mikael and treyZ28, thought questions for you:

How does piston mass effect rotating inertia? (We could include the small end of the rod, piston pin and rings also.)

How does a high stall converter effect rotating inertia?

 

i know inertia

its when you guys get into cams and flow and stuff that i'm lost-
didn't take fluids yet

 

Things you should add to the Torque Converter question.

What SIZE and Weight(wet)

What Stall

last but not least what STR

Every one of these has a effect on the inertia spin up

 

Sorry. I didn't say that right. I am interested in general how a high stall effects rotaing inertia of the engine and it's effect on vehicle acceleraton.

Here's my take: if your TC stalls at 2500 and you shift at 6500, the engine has to accelerate 4000 rpm during first gear which may be 2 seconds or less. That's about 2000 rpm/second.

If it stalls at 4500 and shifts at 6500, the engine only accelerates 2000 in those 2 seconds for 1000 rpm/second. That's a huge difference "inertia wise". In each suceeding gear the tight converter drops rpm farther, so the effect continues. It doesn't really matter how fast it accelerates to stall speed prior to launch.

Of course, the multiplication, efficiency, etc. of the TC also factor in to determine final results, but I was just looking at engine and TC pump, (the largest part of the TC) which is solidly attached to the engine.

 

All I want to know is how much I need to put out at the flywheel to hit a magical 400 at the wheels through a T-56