Article: BHP vs HP vs kW and other power conversions

[o_man_ra23]

watch it and you will learn brett... basically the trueno engine got changed from a stock AE86 7000+rpm 4AGE to a suzuki motor sports AE111 4AGE silvertop capable of 11,000rpm+. Thus, shift points were changed, and as such the car was more sluggish on takeoff, but faster higher in rpm. A shorter diff would have pulled this back to normal, but max speed would have been sacrificed.

Cheers, Owen

[crowncustom]

No worries I'm with it now.just didn't know what initial D waz.Like it is you cant have the best of both worlds.
Cheers Brett

[Fish]

Great contribution Strad...

If you, or anyone, has the time to do some more research ...
I'd be keen to see a reliable flywheel to rearwheel conversion formula & vice versa.

:

When i calculate RWHP i use flywheel kw. What the engine produces in Kw at the motor for example 300Kw i expect it to be 300Hp at the wheels.

thats my guide and i'm sticking to it.

[o_man_ra23]

thats fair, the conversion there is about 30% and that would be what you would expect in a usual RWD format with LSD. If anyone can check what their drivetrain loses (ie, stick ya motor on an engine dyno, test power, then slot into car, and test on rolling dyno), then you would prove a great help to the rest of us in our guestimations. Of course, drivetrain layout, component weight, and service condition will play big parts in this.

Cheers, Owen

[Fish]

i rember street machine did one a while ago using a 202 blue motor. It made 192Hp on the dyno ad when in the car witha trimatic bolted to it it made 150 hp at the wheels. So roughly 40Hp lost to the drive train.... 192-150/192 x 100 = 22% lost in drivetrain.

[Hen]

dont forget that because the HP reading is factored with RPM, a longer geared low rpm motor with more torque but less power can out accelerate a short geared high rpm motor with more power.

No, if the power curves have a similar shape (ie the high power, high rpm engine isn't really peaky) and the gearing is matched to each engine then the more powerful car wins. Regardless of whether it makes more torque, or whether it revs higher.

I agree that a car's gearing must be matched to its power curve. It sucks to drop out of powerband whenever changing up (like Datsun 2->3 shift).

However this has been discussed and argued about plenty before, so I don't want to start it all up again.

Making a program to integrate under a dyno graph would be pretty simple, plus you could enter your gear ratios and get it to optimise the shift point for each gear to maximise area under the curve.

Hen

[Fish]

sorry but a car with better torque will win. for example and proven a 200sx Vs a S2000
S2000 has more Hp and apparently better gearing. Also lighter.
The 200sx has less Hp but more torque. The 200sx is quicker down the straight and around the corners......

Hen i am so confused that at the end of day doesn't matter how much power or torque that you make, that first across the line always wins.

[Hiro]

You still have to take into account weight, gearing etc, you cannot make a pure comparison between different cars based just on power and torque

For instance:
Formula 1 car, 600kg, 500-odd kW, about 350Nm
BMW M5, 1700kg, 370-odd kW, about 520Nm

Guess which one wipes the floor with the other. The higher torque car gets demolished.

Power-to-weight, gearing, and torque curve are the important things. For acceleration you want low power-to-weight, a matched gearbox to the torque curve, and fat flat torque curve (for response)

[Fish]

thats a very big difference there Hiro

Yes but i was showing for two cars easily available everyone on this forum(maybe) that torque does play a part in everything.

the two cars i listed has one lighter and one heavier have a guess there... one has more power and one has less power. One has torque and one doesn't.

[Hiro]

I was just demonstrating that you can't base an assumption on purely one statistic/figure. They all have to be taken into account, and one may have a greater bearing than another too. It's very complicated

[Fish]

yeap thats why i belive i this now

at the end of day doesn't matter how much power or torque that you make, that first across the line always wins

[o_man_ra23]

You still have to take into account weight, gearing etc, you cannot make a pure comparison between different cars based just on power and torque

For instance:
Formula 1 car, 600kg, 500-odd kW, about 350Nm
BMW M5, 1700kg, 370-odd kW, about 520Nm

Guess which one wipes the floor with the other. The higher torque car gets demolished.

Power-to-weight, gearing, and torque curve are the important things. For acceleration you want low power-to-weight, a matched gearbox to the torque curve, and fat flat torque curve (for response)

From your comparison there though, the torque to weight goes well in favour of the F1 car anyways. Whereas the 200SX to S2000 is power to weight in favour of the S2000, but torque to weight in favour of the 200SX, and the 200SX wins.

Both cars in the Nissan Vs Hoonda comparison have comparable drivetrains (RWD, LSD, manual cog swapper... usually etc), so that is a pretty good comparison when looking at the power and torque curves compared with weight. Also the S2000 has better aerodynamics, so again there are more factors in favour of the losing car. All the better for the argument that torque is more important than power.

Cheers, Owen

[Hiro]

From your comparison there though, the torque to weight goes well in favour of the F1 car anyways. Whereas the 200SX to S2000 is power to weight in favour of the S2000, but torque to weight in favour of the 200SX, and the 200SX wins.

Both cars in the Nissan Vs Hoonda comparison have comparable drivetrains (RWD, LSD, manual cog swapper... usually etc), so that is a pretty good comparison when looking at the power and torque curves compared with weight. Also the S2000 has better aerodynamics, so again there are more factors in favour of the losing car. All the better for the argument that torque is more important than power.

Cheers, Owen

True, but then again a F1 car beats basically anything on a xxx/weight ratio. I was however referring more to just torque and not torque/weight, and the winner was immediately obvious. It helps to do an exaggerated example instead of one where a lot of people would struggle to see major differences between the cars (eg 200SX vs S2000).

As to the argument that torque is more important than power, weighting has to be applied to them otherwise a direct comparison cannot be made. Now I don't have dyno charts or specs sitting right in front of me, but could it be that the 200sx has a shed-load more torque than the S2000, whereas the S2000 has a little more power? Give the S2000 as much of a power advantage as the 200SX has torque advantage and would the result be the same? Who knows, but saying torque is more important is irrelevant until you describe how much of an advantage it has over power. Assuming all other things are equal, is a car with 5kW less but 5Nm more going to be faster? Or does it have to be 20Nm more to be faster?

[o_man_ra23]

All depends on where the torque is produced. 2 cars making the same amount of torque, same weight, and perfect gearing for the motor, one makes the torque pretty much between 2000rpm and 5000rpm, the other makes the torque between 5500rpm and 7000rpm. The second car has a much narrower (half even) torque range, but will produce a lot more power due to it being much further up the rev range. However, the first car having the longer torque band will win due to it having a more drivable rev range. So yeah, torque placement within the rev range, and its torque band have a lot to do with a cars driveability and performance, moreso than the power it produces.

Cheers, Owen

[myne]

Perhaps.

But if the first car has 3 gears and the second one has 6, the theoretical differences might be reduced.

At the end of the day, what ultimately matters is the torque at the wheels right up to the cars top speed.
And then, even that really only applies for straight line driving.
For the twisties it's all about having the torque at the speeds you spend most of your time at.

As we all know, gearing can increase torque at the wheels at the cost of RPM.
Make more power up top, you've naturally got more torque to multiply.
So power does mean something, but it's more important to have a package that fits the task than it is to go after peak numbers of either torque or hp.

A wide band might suit one task, a narrow band another. High RPM+power might suit something while a low revving torque monster suits another.

Think about the task. Then develop the car as a package to suit.