New ct20b record. 365rwhp @ 22psi. Gen2 3sgte

[sergei]

alright, now accelerate the driveshafts and diff(s)

input shaft to 8000 rpm
in my case i dynoed the car in 5th (.807), with a 4.11 diff ratio

(was hitting the torque limit of dyno in 4th)

ended up overall ratio of 3.32:1

theoretical wheel speed was 284kmhr

in 8 seconds
the driveshaft reached approx 10000 rpm, the half shafts etc 2500 rpm

Give me mass and diameter of the shafts, I assume half shafts are solid and drive shaft is hollow.

It is all possible to calculate.

What I am saying even if you add inertia of the drive train to the equation there is no where near 100Hp being lost like on those British charts you see all the time.

remember things doing 2000rpm contain 4 times less energy than things doing 4000rpm. Additionally drive shaft is of relatively of small diameter, thus does not have near the same inertia of the flywheel (increase in radius also has quadratic effect).

[strx7]

this thread proves one thing - dont read too much into dyno figures, unless they are for your own car, on the same dyno, in which case you'll know if you have lost power, or gained power - which is what they were designed for to start with. but as for the true actuall amount of power, well that is still anyones guess.

[saft]

compare the drivetrain loss between a fixed run (say held at 5000rpm)

and a ramped run (the way most dynopacks are run)

the "drivetrain losses" in the first example are a lot smaller than the "drivetrain losses" in the second

like running a slower ramp rate, you get smaller "losses"

[saft]

Give me mass and diameter of the shafts, I assume half shafts are solid and drive shaft is hollow.

It is all possible to calculate.

What I am saying even if you add inertia of the drive train to the equation there is no where near 100Hp being lost like on those British charts you see all the time.

remember things doing 2000rpm contain 4 times less energy than things doing 4000rpm. Additionally drive shaft is of relatively of small diameter, thus does not have near the same inertia of the flywheel (increase in radius also has quadratic effect).

do a calculation on the inertia of the pair of wheels/tires as well for the british ones

im not saying their numbers are accurate, im saying the "losses" arent going out as heat and noise

[saft]

i'll measure the halfshalf and driveshaft lengths and diameters next time im under the car

[Luke - BZG]

I'm going to dyno my car which will give me a number...

I'll make modifications to the car to make more power...

I'll take it back to the same place and dyno it again... and if everything there is set up the same as last time, I'll hope the number gets bigger.

[strx7]

I'm going to dyno my car which will give me a number...

I'll make modifications to the car to make more power...

I'll take it back to the same place and dyno it again... and if everything there is set up the same as last time, I'll hope the number gets bigger.

Wise man Luke.
is your car is sorted and back together?

[blindnz]

do a calculation on the inertia of the pair of wheels/tires as well for the british ones

im not saying their numbers are accurate, im saying the "losses" arent going out as heat and noise

So what your trying to say is that if you put massive wheels on your car/massive inertia you will get higher hp numbers because the dyno has more energy to dissipate and leads to a higher hp number?

[saft]

no, massive/heavy wheels with a normal ramp rate will lower the power figure

[blindnz]

Because when its ramped up, it has to overcome generate the inertia in the heavier wheels?

[wde_bdy]

The heavier the objects to accelerate the more energy absorbed and stored in that object, requiring more energy to then slow it down. Energy is not lost, it is stored and released later.

Callum

[RedMist]

no, massive/heavy wheels with a normal ramp rate will lower the power figure

So according to your "theroy" with my massive cast rims and 35 inch mud terrain tyres I have potential energy that'll make my car accelerate long after I take my foot off the accelerator... only in reality it's considerably more throttle responsive than my rally car.

[Grrrrrrr!]

no, massive/heavy wheels with a normal ramp rate will lower the power figure

So according to your "theroy" with my massive cast rims and 35 inch mud terrain tyres I have potential energy that'll make my car accelerate long after I take my foot off the accelerator... only in reality it's considerably more throttle responsive than my rally car.

No, it wont make you accelerate, it'll just take longer/more effort to slow it down. And more effort to speed it back up again.

[sergei]

Let say a wheel weighs 20kg (chromies), radius 318mm (18" FTW), it does 500revs/km at 300kph it works out ~ 43revs/s.

Lets assume a tyre is a hollow cylinder so the moment of inertia = 20 * ( 0.32)^2 = 2 m^2 kg

The potential energy stored in 1 wheel is : 0.5 * 2 m^2 kg * (43 rev/s)^2 = 1850J

Total energy in 4 tyres is: 7400J (7.4kJ).

To accelerate that in 10s it requires 740W, which is incidentally ~ 1Hp.

Can anyone estimate how heavy is the drive shaft (RWD/4WD long bit that turns the rear wheels)? My guestimate it is about 10kg.

moment of inertia for drive shaft of 10kg and 0.04m radius is : 10 * (0.04)^2 = 0.016
The energy at 10krpm (167rps) is: 0.5 * 0.015 * 167^2 = 210J

To to accelerate that in 10s to 10000rpm requires 21W.

Halfshaft? Sweet $&#$% all energy in them - they rotate very slowly, not of that great diameter, and relatively light.

[Scottie]

does car make more hps on uphill dyno(aka treadmill dyno) or flat dyno?

[sergei]

does car make more hps on uphill dyno(aka treadmill dyno) or flat dyno?

makes no difference. It could be upside down and make same power (as long as the wheels don't slip).

I assume they angle the dyno to help with traction?

[Scottie]

[RomanV]

but as for the true actuall amount of power, well that is still anyones guess.

My car makes 300 Horse power.

It's totally legit because I calibrated how much one horsepower is, by running a shetland pony on the dyno.

For sake of thoroughness to see how the power measured at the hooves compared to measured directly, I also said "Kali Ma Shakti de" while I tore its heart out through its chest to count the beats per minute.

[Akane]

Nah, remember last time we had this argument, Akane is wrong, your gearbox consumes 25% of your bullshit HP, and 30% if your car is a 4WD!

[strx7]

Nah, remember last time we had this argument, Akane is wrong, your gearbox consumes 25% of your bullshit HP, and 30% if your car is a 4WD!

do you know where those figures came from?

from memory FF&R mag in the late 90's early 2000's
engine dyno'd something (ej20T from memory) then put it onto a dyno dynamics 4wd dyno and it did read 37-40% less power at the wheels than it did at the flywheel.

once again, its not that it is loosing that much power through the drivetrain, it is that that is how much less power than flywheel hp, that a dyno dynamics 4wd dyno reads.