Jump to content
SAU Community

Are My Calculations Correct ? Rwkw>rwhp>hp

robots

By robots,
in Engines & Forced Induction

 Share

Recommended Posts

robots Experienced

robots

Posted
Posted (edited)

I always assumed that rwkw = rear wheel kw, rwhp = rear wheel hp

kw = flywheel kw, hp = flywheel hp.

Now all the dyno sheets on SAU read in RWKW.

This means rear wheel horse power, right ?

Lets say I got 220rwkw. It means I got 220kw at the rear wheels.

Or 220*1.34=294rwhp and 294*1.1(drive train loss coefficient. 10% is low, but anyway.) = 323hp at the flywheel(crank)

Are my calculations correct ?

Edited by robots
The Dan Grand Master

The Dan

Posted
Posted
I always assumed that rwkw = rear wheel kw, rwhp = rear wheel hp

kw = flywheel kw, hp = flywheel hp.

Now all the dyno sheets on SAU read in RWKW.

This means rear wheel horse power, right ?

Lets say I got 220rwkw. It means I got 220kw at the rear wheels.

Or 220*1.34=294rwhp and 294*1.1(drive train loss coefficient. 10% is low, but anyway.) = 323hp at the flywheel(crank)

Are my calculations correct ?

I'd say it would be closer to 365-370 engine hp

robots Experienced

robots

Posted
  • Author
Posted

One thing I don't understand is than. Lets you got hks2530 turbo. 320hp turbo. And you get 210-220rwkw from it. Which equates to around 340hp. So is there a mistake in the calculations or happy dyno ?

tridentt150v Grand Master

tridentt150v

Posted
Posted

Yeah, 15-25% so say 20% average unless your a Holden or a Ford then the factory will make it more like 30-40%.......lol. The 307kw Holdens don't dyno test at 307kw [that figure is a little optimistic].

Depends on your gearbox, diff and/or CV's, wheel bearings, clutch anything that produces friction and heat in the drive train. The more heat the greater the power loss between crank and wheels.

simpletool Mentor

simpletool

Posted
Posted

I use 20% for driveline loss and 0.746 for hp to KW.

So 350hp engine = 280 hp at wheels = 209 kw at wheels.

350hp x 0.8 x 0.746 = 209 rwkw.

In your case that's 220rwkw/0.746 = 295rwhp or 275kw at engine or 369hp at engine. BUT that 20% drivetrain loss becomes less as you get more power with the same driveline. So 369hp might be a tad high. Isn't this a metric society? So you have about 275kw and likely 450Nm of torque maybe a touch more.

cankas Contributor

cankas

Posted
Posted

Isnt the 20-30% drivetrain loss for a standard car?

206kw flywheel skyline - 25% drivetrain loss = 154.5rwkw which is about right is a drivetrain loss of about 50kw

If the drivetrain doesnt change and all you do is increase engine kw the drivetrain loss figure shouldnt rise very much.

A 300rwkw skyline with an upgraded clutch and flywheel wont change the drivetrain loss much

Therefore 300rwkw + drivetrain loss of 50kw (generous) is only 350 engine kw

If calculate a 300rwkw car at 25% your way off, its a 25kw difference and it grows as the numbers become bigger

TTT Grand Master

TTT

Posted
Posted (edited)
I always assumed that rwkw = rear wheel kw, rwhp = rear wheel hp

kw = flywheel kw, hp = flywheel hp.

Now all the dyno sheets on SAU read in RWKW.

This means rear wheel horse power, right ?

:banana::huh::):huh::P:huh::blink::huh::blink::huh:

edit.. I had more emoticons to make my point but..

THE FOLLOWING ERROR(S) WERE FOUND

You have posted a message with more emoticons that this board allows. Please reduce the number of emoticons you've added to the message

lol... owned by zee germans of old

Edited by GTST
PM-R33 Grand Master

PM-R33

Posted
Posted (edited)

Isn't AWKW in a GTR pretty much the same as RWKW. As under normal driving conditions while accelerating, most of the power goes to the rear wheels anyway? So say if a R32 GTR makes 250kw in AWD it will make like 255kw in RWD? However i suppose with engine power there would be a bit of a difference as you would lose a bit more power through an AWD drivetrain with an extra diff/transfer case etc. compared to RWD.

So therefore it would be a bit more at the engine when comparing a 300RWKW car and a 300AWKW car. I think it will be just stabs in the dark to guess how much extra power those components take away in power loss through heat and noise.

Edited by PM-R33
W0rp3D Grand Master

W0rp3D

Posted
Posted

At the end of the day unless you put it on an engine dyno its only estimated, its what is read at the wheels that counts.

An easier conversion from horse power to kilowatts is that 100hp = 75kw, its not exact i know but its easier to do a quick conversion with those figures.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • Turbodoc
      Noobie Stagea owner..

      By Turbodoc · Posted

      Hey Dave, welcome aboard! Good to see another soon-to-be Stagea owner here. The wagons are awesome — plenty of space, still got that Skyline DNA, and loads of potential if you’re into mods. Definitely post up pics when you get it, everyone here loves seeing new builds. What model/year are you looking at?
    • GTSBoy
      Duncan's V37.......race car?

      By GTSBoy · Posted

      See if you can thermal epoxy a heatsink or two onto it?
    • Duncan
      Duncan's V37.......race car?

      By Duncan · Posted

      The other problem was one of those "oh shit we are going to die moments". Basically the high spec Q50s have a full electric steering rack, and the povo ones had a regular hydraulic rack with an electric pump.  So couple of laps into session 5 as I came into turn 2 (big run off now, happily), the dash turned into a christmas tree and the steering became super heavy and I went well off. I assumed it was a tyre failure so limped to the pits, but everything was OK. But....the master warning light was still on so I checked the DTCs and saw – C13E6 “Heat Protection”. Yes, that bloody steering rack computer sitting where the oil cooler should be has its own sensors and error logic, and decided I was using the steering wheel too much. I really appreciated the helpful information in the manual (my bold) POSSIBLE CAUSE • Continuing the overloading steering (Sports driving in the circuit etc,) “DATA MONITOR” >> “C/M TEMPERATURE”. The rise of steering force motor internal temperature caused the protection function to operate. This is not a system malfunction. INSPECTION END So, basically the electric motor in the steering rack got to 150c, and it decided to shut down without warning for my safety. Didn't feel safe. Short term I'll see if I can duct some air to that motor (the engine bay is sealed pretty tight). Long term, depending on how often this happens, I'll look into swapping the povo spec electric/hydraulic rack in. While the rack should be fine the power supply to the pump will be a pain and might be best to deal with it when I add a PDM.
    • Duncan
      Duncan's V37.......race car?

      By Duncan · Posted

      And finally, 2 problems I really need to sort.  Firstly as Matt said the auto trans is not happy as it gets hot - I couldn't log the temps but the gauge showed 90o. On the first day I took it out back in Feb, because the coolant was getting hot I never got to any auto trans issues; but on this day by late session 3 and then really clearly in 4 and 5 as it got hotter it just would not shift up. You can hear the issue really clearly at 12:55 and 16:20 on the vid. So the good news is, literally this week Ecutek finally released tuning for the jatco 7 speed. I'll have a chat to Racebox and see what they can do electrically to keep it cooler and to get the gears, if anything. That will likely take some R&D and can only really happen on track as it never gets even warm with road use. I've also picked up some eye wateringly expensive Redline D6 ATF to try, it had the highest viscosity I could find at 100o so we will see if that helps (just waiting for some oil pan gaskets so I can change it properly). If neither of those work I need to remove the coolant/trans interwarmer and the radiator cooler and go to an external cooler....somewhere.....(goodbye washer reservoir?), and if that fails give up on this mad idea and wait for Nissan to release the manual 400R
    • Duncan
      Duncan's V37.......race car?

      By Duncan · Posted

      So, what else.... Power. I don't know what it is making because I haven't done a post tune dyno run yet; I will when I get a chance. It was 240rwkw dead stock. Conclusion from the day....it does not need a single kw more until I sort some other stuff. It comes on so hard that I could hear the twin N1 turbos on the R32 crying, and I just can't use what it has around a tight track with the current setup. Brakes. They are perfect. Hit them hard all day and they never felt like having an issue; you can see in the video we were making ground on much lighter cars on better tyres under brakes. They are standard (red sport) calipers, standard size discs in DBA5000 2 piece, Winmax pads and Motul RBF600 fluid, all from Matty at Racebrakes Sydney. Keeping in mind the car is more powerful than my R32 and weighs 1780, he clearly knows his shit. Suspension. This is one of the first areas I need to change. It has electronically controlled dampers from factory, but everything is just way too soft for track work even on the hardest setting (it is nice when hustling on country roads though). In particular it rolls into oversteer mid corner and pitches too much under hard braking so it becomes unstable eg in the turn 1 kink I need to brake early, turn through the kink then brake again so I don't pirouette like an AE86. I need to get some decent shocks with matched springs and sway bars ASAP, even if it is just a v1 setup until I work out a proper race/rally setup later. Tyres. I am running Yoko A052 in 235/45/18 all round, because that was what I could get in approximately the right height on wheels I had in the shed (Rays/Nismo 18x8 off the old Leaf actually!). As track tyres they are pretty poor; I note GTSBoy recently posted a porker comparo video including them where they were about the same as AD09.....that is nothing like a top line track tyre. I'll start getting that sorted but realistically I should get proper sized wheels first (likely 9.5 +38 front and 11 +55 at the rear, so a custom order, and I can't rotate them like the R32), then work out what the best tyre option is. BTW on that, Targa Tas had gone to road tyres instead of semi slicks now so that is a whole other world of choices to sort. Diff. This is the other thing that urgently needs to be addressed. It left massive 1s out of the fish hook all day, even when I was trying not too (you can also hear it reving on the video, and see the RPM rising too fast compared to speed in the data). It has an open diff that Infiniti optimistically called a B-LSD for "Brake Limited Slip Diff". It does good straight line standing start 11s but it is woeful on the track. Nismo seem to make a 2 way for it.
×
×
  • Create New...