are RWKW overrated

[glen73]

I have a question, now mine has 126.3 rwkw.
i was sitting down the other day working out my friends power to weight ratio compared to my power to weight ratio.
if i have worked it out wrong then please correct me.


126 multiply by 1.22 for the lose during drive train which equals roughly 154KW's at the flywheel.

now i have worked my power to weight ratio to be 171 kw per tonne.

POWER divided into WEIGHT multiplied by 1000 = ?kw per tonne

now my friends VT series two CLUBSPORT has 260kw at the fly.
his tare weight is 1740 kgs
now his power to weight ratio is 149kw per tonne

now mine should leave his car behind but i feel it wouldn't.
this draws me to torque. while my motor puts out 126 rwkw it doesn't feel as though it has the push back in your seat of a strong V8.
Has my car been tuned for KW's. is it possible to sacrifice KW's for torque?
my theories could also be very wrong, if so please correct me
and it could be a case of I'm just really used to the power.
either way i want more boost.
can anyone set me straight on Torque versus overall Kilowatts?

[Sheck]

Pretty sure, if you have worked out the power to weight correctly (not sure on common drive train loss numbers) then you would beat him.
BUT
I think you would only have him until around 130-150kmh at which point he could/would start catching and then overtaking you. Thats only becasue power to weight only goes so far (from what i've read) and after a certain velocity your amount of power wont be able to push your car through the friction of areodynamics, and all that, as fast as old mates commy.

So 1/4 mile you should beat him easy, but top speed run he'd have you.

I'd say with some tuning of the cam gears you could move the power band down a little which would give you more torque by sacrificing power, but not much. I dont think you could tune it any different (if it has been done properly in the first place) to get more torque. Maybe get a better turbo that spools up quicker - that'll give you more boost sooner = more power + torque.

Well, it looks like you'll have to test out these theroys of mine with a couple of races!!!! at the track of course

dave

[glen73]

ok i'm pretty sure the mx5 has 22% loss from the fly to the wheels. another guy that races mx5's told me this.
this is all in theory of course and im not trying to insight a drag race or anything

[glen73]

tare=900

Kerb Weight 955kg

mine is a 1989 model

[Matty]

factor in driver weight and fuel, oil etc and you can add about 100kg to each car.

As for rwkW, the number you got depends entirely on the dyno you did it on, no point comparing with others unless the dyno operator has a known benchmark.

Also factor in the turbo spool up and launch technique. If you're off boost, your friend has a good chance of beating you.

You can play with the boost vs rpm curve to alter the torque curve, but there are driveability limits.

[Sean]

Why not just race him and find out?

I hate to say it but you'd probably take a loss to him, not by much though...

Get him on the start and you should be able to hold him off over 400m

Let him get the jump and I doubt you'll reel him in.

Get him on a twisty road and your car should wipe the floor with his if you have similar skills.

[Techno]

Hi Glen73

Over the past 4 years at club dyno days the results have consistently shown that there is a 32% loss between the manufacturer's claimed KW (DIN) and RWKW{on the Dynamics Dyno we use}

A stock 1.6 will put out around 59rwkw, a NB8a is around 66rwkw, a NB8B is around 72 rwkw.

The SP.s put through have been around 110 to 114 rwkw (one there was a 118. Recently I did a 131 RWKW (with the $2.30 mod).

SE's have been around 96 to 104 rwkw.

Assuming a linear relationship between flywheel and rwkw then the algorithm is RWKW X 1.4706 = Fly.

So a NB8A with 66 rwkw = 97 at the fly.

An SP with 114 rwkw = 161 at the fly (Mazda claimed 159 in post production releases)

So with 123 rwkw on the dyno we use that would put your flywheel estimate at 180.

given the weight of the car is 980 kg then you would have 5.417 kgs per kw or 184 kw per tonne.

The Clubsport would have around 9.6 kgs per kw or 148 kw per tonne.

BUT it is how you use the power/torque when you drive. While you may make high kw at high rpm the rate of acceleration is governed by torque and mass.

I had a lovely time mixing it with a BMW M5 on a club drive 2 Sundays ago. That car has 400Kw against my 190 Kw. But the ability of the SP to build torque from mid to high rpm, change gear and do it again ... while the M5 just grew pace at a steady pace was a good example of knowing when to change gear to maximise the torque available.

Just be aware of the differences between Dyno's. There is a dyno in Sydney that the NSW Club uses that give results much higher than the Vic Club's dyno. See the $2.30 SP mod topic and see how a NSW un modded SP gets 130 rwkw and a Melbourne SP gets around 114. With the $2.30 mod the NSW car gets 160 rwkw and the Vic one gets in the low 130's.


I know that the SP can handle the Clubsports quite well, up to a point.... but the Clubsport just keeps on going. I'm running out of power at around 195kph but the CS is still accelerating. The SP is right in the power band between 80 and 110, does this in 2.9 seconds un modded and I would estimate around 2.6 seconds with the $2.30 mod ... much faster than the CS and anything else that is generally available.

the best way to test mods is to pick a suitable stretch oc road, 3rd or 4th and go from 3,000 to 7,000 rpm. Time it, mod it, time it again.

Regards

Rob

[Boags]

Over the past 4 years at club dyno days the results have consistently shown that there is a 32% loss between the manufacturer's claimed KW (DIN) and RWKW{on the Dynamics Dyno we use}

I understand this is fairly general, and from your equations it works quite well for low kW cars. However, as it has been said before, I cannot imagine a 1000kW Skyrine losing 320kW through the drivetrain...

Just another anecdote, not evidense.... I was next to my mate who had borrowed his brother's Supercharged Ford V8 Ute(The Brett Stevens "Kitten" Burn-out Ute) and I (in my stock NA6) thrashed him from standstill to about 3rd gear. As soon as i popped third he flew past at a squillion miles/hour, but the enormous weight difference let me get in front up to about 80km/h.

I would also like to point out that it was probably mainly a driver difference as well as him not wanting to SMOKE the tyres... But it took him 3 gears to catch me.

Boags

[sabretooth]

It would be proportional. More torque = more friction - so therefore you're generating more noise and more heat. Unless you've got an extremely efficient drivetrain then your losses are going to be linear to the amount of power being generated. Your diff, gearbox and other inertial losses are all going to count and are only going to get worse the faster you want to go. A 1000KW Skyline is going to be losing a lot of power trying to drive all four wheels.

[OMY005]

It would be proportional. More torque = more friction - so therefore you're generating more noise and more heat. Unless you've got an extremely efficient drivetrain then your losses are going to be linear to the amount of power being generated. Your diff, gearbox and other inertial losses are all going to count and are only going to get worse the faster you want to go. A 1000KW Skyline is going to be losing a lot of power trying to drive all four wheels.

So drive train parasitic losses are like the tax man then. The more you put in the more you loose.

I found this info.

Andrew.