Bhp From The Engine?

[KEN-R34]

Hi Guys,

I have a R34 GT-T making around 410rwhp with a GT3076r.

Can you work out how much HP is coming from the engine only knowing the wheel horse power?

Cheers,

Ken

[The Dan]

490-500hp at the engine

[PM-R33]

Yep sounds about right, approx 500BHP give or take if it is a manual. If it's an auto, than a little bit more.

[KEN-R34]

It's a manual, do you just add 1/4 of the whp??

[The Dan]

It's a manual, do you just add 1/4 of the whp??

No. there is approx 80-90hp loss through the drivetrain in a manual 34.

[KEN-R34]

Ahhh ok! Thanks guys

[R31Nismoid]

No. there is approx 80-90hp loss through the drivetrain in a manual 34.

How do you work that out?

Just wondering as no-one has ever really posted any motor on dyno vs car on chassis results best my knowledge.

Some people use percentage, others fix figures, always different

If someone has actual data to aid speculations that would be good

[PM-R33]

I do it this way.

We all roughly know what a standard RB25DET is rated at the engine and we all roughly know what they make at the wheels standard. There's about a 60-80HP loss give or take depending on the condition of things.

So depending on the extra power (say an increase of 200HP at the wheels), i re-ad the 60-80HP loss (since you aren't going to magically lose less power through the drivetrain as power increases unless you have done something out of the ordinary). This will give you roughly your minimum amount of power at the engine. Then i take into account that as power increases, losses through heat, noise, friction ect. increase. Depending on the added power i say it might lose an extra 10HP or something like that.

It is rough, but atleast you know roughly what it would be.

Edited January 6, 2010 by PM-R33

[The Dan]

^^ +1

This is exactly how I work it.

Percentage loss is incorrect. You can all argue til you're blue in the face about it but it is simply wrong.

Auto gearboxes are close because they have fluid vs centrifugal forces in the converter but it still only goes so far at being close, then the more hp you make, the less accurate your percentage will be.

Most manual gearboxes + medium - heavy diffs will lose anywhere between 70-100hp from the engine. Autos are about another 20% on top of that, that's as far as the percentage will get you.

Of course it's different for each gearbox but we're talking 10-15hp difference and it's about as accurate as you are going to get without engine dynoing.

[KEN-R34]

How do you work that out?

Just wondering as no-one has ever really posted any motor on dyno vs car on chassis results best my knowledge.

Some people use percentage, others fix figures, always different

If someone has actual data to aid speculations that would be good

To be honest I always thought it was a percentage added, depending on what car.

Never knew it was fixed figures.

[The Dan]

If someone has actual data to aid speculations that would be good

And if you want to pay the labour costs I'll happily do the comparo for you

[gmx]

I do it this way.

We all roughly know what a standard RB25DET is rated at the engine and we all roughly know what they make at the wheels standard. There's about a 60-80HP loss give or take depending on the condition of things.

So depending on the extra power (say an increase of 200HP at the wheels), i re-ad the 60-80HP loss (since you aren't going to magically lose less power through the drivetrain as power increases unless you have done something out of the ordinary). This will give you roughly your minimum amount of power at the engine. Then i take into account that as power increases, losses through heat, noise, friction ect. increase. Depending on the added power i say it might lose an extra 10HP or something like that.

It is rough, but atleast you know roughly what it would be.

No. there is approx 80-90hp loss through the drivetrain in a manual 34.

I beg to differ. It's not linear as power increases.

A % is a better tool, but still not accurate.

Fluid viscosity and simple gear mechanics have a lot to do with it. There are engineering articles out there if you'd like to read up on it.

[Revenge]

Converting engine bhp to rwhp has to be a around a set HP amount like 70-90hp (what PM-R33 said).

Anyone who stats a percentage is on crack, as this would mean the more HP you make, the more HP you lose. Example based on 10%, @ 300bhp you lose 30hp and @ 500bhp you lose 50hp, BS!!!!!!

[The Dan]

I beg to differ. It's not linear as power increases.

A % is a better tool, but still not accurate.

Fluid viscosity and simple gear mechanics have a lot to do with it. There are engineering articles out there if you'd like to read up on it.

It's closer to a fixed figure than it is to a percentage. Unless you are talking about engines producing under 200hp, then both will be extremely close.

The whole idea of power loss has everything to do with gear mechanics and fluid viscosity, yes, but once it gets to a certain point, the percentage figure becomes more and more inaccurate, the further away from it you move.

Plus you'll need to provide a link to any article you are referencing so I can read it.

[KEN-R34]

And I thought this was a quick question

[The Dan]

Converting engine bhp to rwhp has to be a around a set HP amount like 70-90hp (what PM-R33 said).

Anyone who stats a percentage is on crack, as this would mean the more HP you make, the more HP you lose. Example based on 10%, @ 300bhp you lose 30hp and @ 500bhp you lose 50hp, BS!!!!!!

Try doing it for 1000hp or 2000hp. The gearbox has exactly the same counter force no matter how much extra power is turning it. The only thing that can change that is if the fluid changes viscosity (which it does - but ONLY to a certain point), the gears don't become any more resistive.

[PM-R33]

I beg to differ. It's not linear as power increases.

A % is a better tool, but still not accurate.

Fluid viscosity and simple gear mechanics have a lot to do with it. There are engineering articles out there if you'd like to read up on it.

I never said it was linear.

You know what the car losses through the drivetrain from factory.

Example, the old GTS HSV Monaro's. Rated at 300kw, make about 220-240kw@wheels.

Standard GTST, rated at 180 odd kw, make anywhere from 120-140kw@wheels.

So if the same GTST makes another 110kw@wheels to 250kw@wheels, we re-add that 60-40kw loss, so it pumps it up to 290-310kw@engine. However the engine is now producing more power, therefore everything is slightly increased in loss. This is the figure that can not be given by a percentage, or a fixed linear figure. It varies. I'm sure there would be a close equation you could do to work it out more accuretly. The more power you make, the higher the additional loss through friction, fluids, heat etc.

So in a bit of a maths equation.

kw@motor = kw@wheels + original factory loss (say 50kw to be a nice number) + 'unknown variable' (additional loss as power increases)

= 250kw@wheels + 50kw original loss + 'x'

= 300kw@motor + 'x'

This 'x' value is one that you have to guess logically. It aint going to be 100kw, it aint going to be .5kw. A good educated guess in this case could be 5kw. It will obviously slightly increase with the more power you are making. at 1000kw@motor it might be 50kw.

That is about as accurate as you can get with guessing, and for most people i think it is good enough to have that minium value and a little bit extra. I'd rather under qoute something than over qoute.

Edited January 6, 2010 by PM-R33

[SECURITY]

at the end of the day, who fucking cares?

Edited January 6, 2010 by SECURITY

[PM-R33]

I like to know it due to conversation with people that aren't that into cars. Since most manufacturer's qoute engine HP figures and all modified car owners qoute @ wheel figures it makes discussions with people that aren't into cars difficult.

Classic case, talk to some one that bought a brand new HSV "My HSV makes 307kw, what does yours make" "My car makes 280kw@wheels" "....Haha my stock HSV has more power". Therefore if you are talking to some one, say your friends parents or something, i always use engine HP figures cause by the time i start explaining drive train losses they will tune out and the discussion will be over.

Edited January 6, 2010 by PM-R33

[Duncan1]

at the end of the day, who f**king cares?

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