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R34 Gtt Fwkw To Rwkw

TR33GT-001

By TR33GT-001,
in Engines & Forced Induction

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TR33GT-001 Collaborator

TR33GT-001

Posted
Posted

Hello all.

Hope 2013 finds you well.

I have read a lot about owners believing that there was a magic percentage of 25%, for drivetrain losses, to allow a conversion from flywheel kW to wheel kW in a RWD platform.

I had always thought this was bunk.

Was suprised to compare two dyno sheets from my car over a three year period.

The 25% was pretty close.

Maybe it's just my car though.

Attached is a spreadsheet which progressively matched the dyno runs.

This is NOT the gospel, it's just what happened for my car.

Jim

KW to HPx.pdf

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https://www.sau.com.au/forums/topic/419425-r34-gtt-fwkw-to-rwkw/
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wolverine Grand Master

wolverine

Posted
Posted

Oh noes!! :no:

I think this will go on for a few pages. Those who mistakenly believe that there is a fixed percentage will get increasingly angry at those who believe there is a relatively fixed loss (with a very small increase in losses due to friction etc as power levels rise).

IBTL

GTSBoy Grand Master

GTSBoy

Posted
Posted

I say the "losses" are largely at the tyre/roller interface (it's the only place where you can liberate 50 - 200 HP where there is sufficient cooling to take the heat away). And in general, on a DD dyno, it's about 25% (including the real losses in the drivetrain, however small they are).

TR33GT-001 Collaborator

TR33GT-001

Posted
  • Author
Posted

so, pray tell, how did you get flywheel power readings from after you've upped le boost?

Hi xALmoN

Hope all is well.

The FW power noted, is only approximate.

It was proportioned to the original dyno run, when stock.

We slotted in the originally claimed 206FlyWkW, with a 154.4 RWkW actual dyno run, and kept the ratios the same all the way down the chart.

The interesting outcome, was keeping the same percentage of FWkW to RWkW on the second dyno run, resulted in exactly the right amount of RWkW.

Don't forget please, that I only posted this as a result for my car only. Not a gospel on how to convert FWkW to RWkW.

To be honest, there is so much involved in that conversion, I would have no hope of figuring it out (I'm a bit challenged)

It was just an interesting result.

What could actually be happening here is that the FlyWkW is going up or down faster as the power increases, and I wouldn't know it.

Trozzle Grand Master

Trozzle

Posted
Posted

I think that the fact that a 'fixed percentage' can be debunked by eventual melting of gearboxes when you're in the 1000s of HP is a fairly certain indicator that it's not correct.

Perhaps for a given gearbox design, it's a percentage loss until a certain point? Who f**king cares anyway.

t_revz Grand Master

t_revz

Posted
Posted

Subscribed :)

Look forward to checking this after work.

I generally tell ppl the Hp I make at thd wheels is about the kw it makes at the flywheel. While I don't believe its a fixed percentage most ppl are just looking for a number to compare to their car and its close enough and they have no idea what their car makes on a dyno so its much easier

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