To determine how much horse power is made at the wheels do you subtract 12% or 20% from the actual horse power?

depends on the engine. different cars loose different ammounts because of friction in the driveline. until they create a frictionless driveline than all cars will loose power.

yeah, there's not really a formula to do something like that because there are so many variables. transmission type, gears, 2wd/4wd, Dif... the weights of these parts (rotating weight), resistance.... you get the point. it all comes down to how much resistance there is between the flywheel and the wheels... and it's obviously different on almost every car. but you can use rules of thumb with percentages like you have mentioned above.... as far as those percentages being right or not... I don't know

Thinks for the info. I was going to ask if the percentage subtracted was effected by whether the car was FWD, RWD, or AWD. How much does dyno testing cost? Im sure it cost more to run a dyno for a car thats 4 wheel drive but does anyone know a general price for dyno tests?

i just thought around 20-25 hp loss at wheels..but thats me...

in okinawa you can get your car dynod for 5000 yen. about 47 bucks US. I've seen some places for like 30. If you are evaluating a project make sure you use the same dyno.

This can be calulated by using the 1/4 mile time and vehicle weight.

-you convert the weight of the to kg. (lb > kg...multiply the lb.# by 0.4536)

- then you find the acceleration, use d=1/2 at^2 (1/4mile=402.2meters)
{distace = [1/2acceleration*time]^2}

note distance must be in meters, acceleration must be in meters/seconds^2, time must be in seconds

- then you find the Force, use F=ma
{Force = mass*acceleration}

note Force must be in Newtons, mass must be in Kg, acceleration must be in meters/seconds^2

- then you find the Work, use W=Fd
{Work = Force*distance}

note Work must be in Joules, Force must be in Newtons, distance must be in meters

-then you find the Power, use P=W/t
{Power = Work/ time}

note Power must be in watts, Work must be in Joules, time must be in seconds

-then you find the whp, which is what you look for right?
{1whp = 746watts} meaning you take what ever you got for P and divide it by 746. This will give you a close estimate of wheel horsepower.

if you didnt understand here is and example of a R34 Skyline GTR that does 13.7 in the 1/4mile and its weight is 1560kg:

d=1/2at^2
402.2=1/2a(13.7)
a=4.28 m/s^2

F=ma
F=(1560)(4.28)
F=6676.8Newtons

W=Fd
W=(6676.8)(402.2)
W=2685408.96joules

P=W/t
P=(2685408.96)/(13.7)
P=196015.25watts

1whp= 746
196015.25/746
whp=262whp which is really close if you do the Enlapsed time method which is also usefull, and comes out to 264.3whp by using the ETmethod, if you use the Trap Speed Method than its a bit higher and comes to 297.5whp overall is 280.9. Actual HP the BNR34 has is 277hp so its close. :bigthumb:

in my area, its about $100/hour(as many runs as you can get in) for a DynoJet. but ive hooked up deals like $400 for a hole evening/afternoon of fine tuning.

I just had mine dynoed for £25, or $43.

GTR drive line loss is around 22-25%

GTSt manual will lose around 17-20%

Normal manual tranny will lose around 17-20%

Autos will lose around 23-26%

This can be calulated by using the 1/4 mile time and vehicle weight.

-you convert the weight of the to kg. (lb > kg...multiply the lb.# by 0.4536)

- then you find the acceleration, use d=1/2 at^2 (1/4mile=402.2meters)
{distace = [1/2acceleration*time]^2}

note distance must be in meters, acceleration must be in meters/seconds^2, time must be in seconds

- then you find the Force, use F=ma
{Force = mass*acceleration}

note Force must be in Newtons, mass must be in Kg, acceleration must be in meters/seconds^2

- then you find the Work, use W=Fd
{Work = Force*distance}

note Work must be in Joules, Force must be in Newtons, distance must be in meters

-then you find the Power, use P=W/t
{Power = Work/ time}

note Power must be in watts, Work must be in Joules, time must be in seconds

-then you find the whp, which is what you look for right?
{1whp = 746watts} meaning you take what ever you got for P and divide it by 746. This will give you a close estimate of wheel horsepower.

if you didnt understand here is and example of a R34 Skyline GTR that does 13.7 in the 1/4mile and its weight is 1560kg:

d=1/2at^2
402.2=1/2a(13.7)
a=4.28 m/s^2

F=ma
F=(1560)(4.28)
F=6676.8Newtons

W=Fd
W=(6676.8)(402.2)
W=2685408.96joules

P=W/t
P=(2685408.96)/(13.7)
P=196015.25watts

1whp= 746
196015.25/746
whp=262whp which is really close if you do the Enlapsed time method which is also usefull, and comes out to 264.3whp by using the ETmethod, if you use the Trap Speed Method than its a bit higher and comes to 297.5whp overall is 280.9. Actual HP the BNR34 has is 277hp so its close. :bigthumb:

Now, call me collect at 011819090684207 and try and explain that to me in layman's without reading it like dicatation. I found the same damn thing on google in 8.5 seconds.

okay forget all of that here is a site where you just type in your cars info and it will tell you everything. This is not 100% accurate but it come close:
http://www.imoc.co.uk/qm/view.asp?ID=83

Great this sucks, forget about my last post, the page seems to be deleted for some reason.

1. grab a calculator

2. here is the forumula (reallly short):
hp= weight(in lb.)/(1/4 time/5.825)^3
this is the ET method

3. this is the formula for the TS method:
hp= weight (in lb.)*(trap 1/4 mile speed/234)^3

If you dont understand this tell me.

Does automatic transmissions necessarily create more friction? Everyone seems to suggest subtracting a higher percentage with an auto than with a manual.

i think it's a rotating weight thing? not sure though.

i think it's a rotating weight thing? not sure though.

the gears in an automatic are a bit larger....especially the overdrive. thus causing more friction.

M will always remain the same. As long as M on the tarmac is normal them M will be too. unless if it rains or other reason.

forgot to add M= force of friction.

I heard in a magazine that in every car generally 20-22% horse power is lost by the time it reaches the wheels. Its probally a starting point if you are trying to get a general idea of how much power is made at the wheels if accuracy is not the goal.

thats wrong info, the dodge srt4 has 230 crank, and it puts 250 to the wheels. Im not sure about the info, its from the top of my head.

thats wrong info, the dodge srt4 has 230 crank, and it puts 250 to the wheels. Im not sure about the info, its from the top of my head.


thats phsyically impossible. a car cannot make more at the wheels than it does at the crank. the crank = no friction, wheels = power after the friction from the drivetrain. it makes about 250 at the crank, and about 220 at the wheels.

my mistake: it was 250lb of torque

my mistake: it was 250lb of torque


i hope you are agreeing with what i said though, because horsepower is only a way of measuring usable torque....still cant make more at the wheels than it does at the crank.

acording to physical calculations it can match it or get even higher. The ET and TS methods are to calculate an approx of what the hp might be. The Skyline GTR has 277hp and it got an average (TS, ET @ 1/4 mi) of 280.9hp. Could it be to the wheels.......looks like its to the crank. But if i do cars like a Celica GTS by using the same method i get an average of 145.5hp.........know its seems like its to the wheels doesnt it?

it cannot match it or even higher, unless they somehow invented a new frictionless drivetrain since the last time i checked. it averages 280 at the wheels yea, at the crank they get about low 300's.

What is the actual HP of a Skyline GTR <R34>? (Lets begin there)

nissan claims 276 at the wheels for GT-R's, while i read an independant study where GT-R's are around low 300's at the crank.

My average was of 280.9hp according to the ET&TS.

at the wheel or at the crank? and its not at the crank, because nissan doesnt have that amazing a drivetrain!

i mean it is possible for numbers at the crank and numbers at the wheels to match, but wheel power cannot exceed crank power. how does it gain more power? obviously not the engine if its exceeding the max power it can give. and the only way that the numbers for the flywheel and the wheel can match (as ive said before) is if there is some sort of new frictionless drivetrain, and the car is floaing on air. mathematically its possible to get crank + wheel numbers the same, but mechanically its not. ive always found that no matter how good your math is, cars seem to be alittle bit off when it comes to calculations about power.

at the wheel or at the crank?
this is what i dont know.

With so many variables and percentages youll never hit it on the dime. Even dynos arent 100% percent accurate.

forget about it then.

this is what i dont know.

those numbers were obviously taken at the wheels, not the crank.

This is a question/debate that has raged for years. Another is with dyno comparisons.

People and even some dyno operators claim a fixed percentage of drive line loss based on drive line configuration. However physics has a much better explanation. How's that? Simply put if you look at a drive line it takes "X" amount of force to turn the wheels of a car. Whether it is static and the wheels are suspended in the air or physically rolling. This power thus is a percentage or fixed value to achive initial motion. Now we want to accelerate that motion to a higher speed. It will take more power but not linier to achive this. It is however still a percentage of the engine's capability.
If you put a car on a dyno, whether it be a hub or rolling road to measure the power there are a series of calculation that the software does to compile a number of what you see. These are based on certain vaiable and certain constants. The easiest way to put it is the software tracks the amount of time it takes to achive maximum road speed, your full run, vs the amount of resistance that is given to the rollers and comes up with the power output you see.
It however is not a fixed percentage that is what we are told to calculate engine hp based on the hp shown at the wheels. This brings me to another point soon to be discussed. Every dyno's software is different well each manufacturer's software is different. Each rely on an engineer's input to specify what sort of numbers to run in order to achive what is perceived to be acceptable.
Getting back now to the beginning. If it takes, lets say 3hp to turn the wheels initially to a speed of 2mph. We then want to turn it double the speed it doesn't take double the hp to achive this, it would take maybe another .3hp. As we continue this the amount will vary to a point increase in a linier amount then it once it reaches a certain point the mount or percentage decreases to still increase speed. As an example lets say it takes 300hp to ahieve a road speed of 150mph. It won't take 330hp to ahieve 151mph which is 10%, nor will it take 360hp to achieve the same. The percentage curve, if you worked it out is shaped like a mount. It increases rapidly then decreases as the input power increases as it doesn't take as much of a percentage of increase hp to ahieve a gain. It is also not linier overall.
Think of it this way, with a block and tackle setup ( rope and pulley ). how much weight does it take to life a given object. Double the resistance weight and you have to double the force to lift it right? So it is a 50% increase of force for a 50% increase in resistance. I thought I would toss that in to boggle your minds for a bit.
With gearing such as that in a gearbox resistance vs force to move or turn them is simular but different. There is a set calculation to achive a given result, but dyno manufacturers can't adjust for all the variable such as wheel weight, wheel diameters, added things to the engine such as aircon, altenator etc. So they use a base figure as a round about value.

Now this brings me to the previous statement about dynos. You can also not compare dyno readings from one to another. People that do that have little dicks and write on walls, in other words children. I've seen this time and time again and the arguements and bullshit still rages today but all the so called "experts". Each dyno uses different software unless they are manufactred at the same time and same manufacturer, they will be different and produce different values. Hub dyno's natoriously show higher figures than rolling roads. They always have an always will. They also who huge and out rageous numbers for torque values. I've seen one that a guy made 330hp at the wheels yet produced over 610 flbs of torue! This was a petrol engine not a desil. I've seen auto's throw nearly double torque numbers over manual's while throwing substantially less overall power. Again this is all software number crunching or fudging as I say. I could write a damn book on this lol and looks like I've done a few chapters here. sorry about that.