G-Tech Pro RR newbie

[S2central.net]

**** - i'm forgetting gearing / distance aren't I ?

[Rusty]

P=F.v (Power = Force x velocity)

F = m.a must be assumed to be true, this includes air resistance, driveline resistance, tyres etc. etc as it's the force felt by the car and also includes the "squat factor" discussed earlier.
You input m and measure a.
You know v from integrating a wrt. t.

Using simple dimensional analysis you get

P = N * m/s = Joules/s = Watts

Any regional variations for mass, power etc. etc. can be easily sorted out.

All i can say is you guys lost me about 10 posts ago

[S2central.net]

Hope the beer helped

No it didn't - something is wrong and I can't get the sums to work... Forget the 0-60 thing with gear changes... Even assuming a run from say 30-50 in same gear... Converting everything to metric I don't get a sensible result.

Power is a measure of work done (Force) per unit time.

The Force, F = mass x acceleration or F= M x A smells right

We can get A from the g reading (or calc from v = u + at if we only know speeds and time interval 't')

Wouldnt Power be equivalent to F/t, or expressed as (M x A)/t ????

But using that creates equally bonkers numbers. I need help (or therapy)


Paul

[Rusty]

I believe it's all standard quattro gearing and wheels/tyres....

[EspenW]

He.. he.. he.. mine pulls .84g in second and 60 comes up in 4.1. could do it quicker but i need third gear for 60.

Yep, with kiddie-like gearing like that, no wonder
The RS2 can reach 68mph in 2nd
What kind of ratios are you running? Wheel size?

[Rusty]

Hope the beer helped

[S2central.net]

Nah doesn't smell right... I need a drink - fugg this.

[S2central.net]

Hell I just got it I think... Take the g reading for acceleration and multiply by 9.8, then divide by 3.93 for feet per second squared.

So 0.4g becomes 0.997 for the 'a' in our calc.

Then divide time in seconds by 60 for minutes. 5.2 seconds becomes 0.086 mins

Power = 3560 (lbs) x 0.997^2 x 0.086 = 304bhp

RIGHT ?

The 0.4g was a guess for 0-60 mph in 5.2 seconds but when you convert mph to metric and use the v=u+at you get 0.391g alright

[S2central.net]

My brain is hosed - I want to play with some numbers on a spreadsheet here and figured ANdy's starting point for the basic calc was sound...

P = F x V

where F = m x a
and V = U + at

meaning P = m x a^2 x t

But what units of time and acceleration are needed to work with lbs of mass to get a sensible number of bhp ?

I need some sleep

[Rusty]

Mine could pull 1g in 6th....



























once

and then 60-0 in 3ft

[DJones]

Yep, 0.5G is more than my Golf, though, seeing approx .43G as max in 2nd in that one. The RS2 pulls close to 0.7G in second, but the E50 turbo is far from properly spooled in that gear Not liking the hot summer weather, car feels like a turd these days. 10% power loss vs a cool day.

He.. he.. he.. mine pulls .84g in second and 60 comes up in 4.1. could do it quicker but i need third gear for 60.

[magarv]

Yep, you need to trigger the accelerometer, but that does not take much effort, a normal start is plenty good.

Exactly my point and quite obvious that it is to trigger the accelerometer A normal firm start is the most accurat, not to easy and not to hard...

[EspenW]

With the Mr. Dyno I can produce perfectly overlaying graphs on consecutive runs. I use it to adjust cam timing, ignition advance, etc. Real world conditions, so I value it more than any dyno graph.

[Rusty]

When I can get to my test route I'll do a number of runs and see how repeatable things are and then adjust teh weight to get a repeatable 240bhp, this is what my setup was producing the 3B FW so it should be close. I can also do runs in 3rd to remove a bit of the squat-skew on the accelerometer. I'm happy to be within 10% of the dyno measured WHP, This means that I can now compare setups, chips etc. to give a rough as hell estimate of any gains or losses when combined with the time honoured butt-dyno.