Cheap Performance Meter

[A80Avant]

yes you are right! mistaken it for 2nd gear already!

[Prophet_dlx]

So it looks like it might be possible to make a 0-60 sprint in 5s on a K24
all those running gt2871r or 3071r should be under 4s with 120 bhp more ...
Sorry its a little bit off topic :/

[Rusty]

I gotta get you under 5s Andy - pretty darn good though... Whats your launch tactic - dumping hard from 4k - 5k - what ?

Yeah, for these sorts of launches about 4.5k and then bring the clutch to bite and let the boost build then bring it up as hard as you dare. Best launches get a chirp from the rear tyres

I think the V stream was a repeatable 5.3s and with some weight reduction (see Project Alpinweiss II) i.e. 1400kg, it'll be in the mid 4s. Easily worry RS2s with that performance

[S2central.net]

I had a VERY fraught hour of roadtests yesterday afternoon - only got a couple of safe / flat stretches of tarmac near me suitable for launches and power runs.

Loads of flat-capped traffic made it hard to get lots of tests done, but I got some... I know Andy wanted some hard launch data with a G meter like my GTech RR but was unable to shift into second gear on multiple occassions... First time I thought I was just kak, second unlucky but after that its apparent I have some sort of gearbox, clucth problem - more of that it in a separate thread - I have a notion what it is.

Attached is a PDF with some comparative analysis of two power runs taken yesterday on the T-Stream in cold weather - versus two taken last summer on N-Stream. The higher run of those two might have had the RS2 airbox fitted - I can't recall for sure.

Note the weight of last year runs is 40lbs heavier due to WWF spec RS6 alloys - yesterday was on stock Avus with winter rubber - approx 5kg lighter per corner.

I've included a G-graph from a half decent launch - interesting to see how the slope of that tails off. Also another power run taken in 2nd which was on the smoothest piece of road - really nice graph.

If it hadn't been such a frustrating test I'd have done some back to back tests of N-T-V streams in same weather but thats going to have to wait. I need t sort the clutch first.

[S2central.net]

Just checked my data here - those runs from last summer had the RS2 airbox fitted - so same mechanical setup. Fuel then was likely 95RON plus a two shots of booster... But I've since taken to BP Ultimate 97 as the best thing I can get here direct from the pump - that maybe explains a little hold back circa 4000 that appears in some runs - you can't feel it. I'll have to investigate that as well - I need a test pilot so I can tweak in real-time.... Just so hard to find enough time at the moment.

[Rusty]

For the record I did some second gear 30 to 60 runs and recorded some steady times at the 3.3s mark. This compares to 2.9 for the S4 and that will now be quicker due to an FMIC and more boost. Those BiTurbo cars are damned fast. Prefer the S2 tho even if turbo lag is an issue for the 30 to 60 run

Be interesting to compare to GTech data there Paul.

This GPS jobbie is really repeatable on the move. With the S4 data there were 4 runs within .01s and 6 within .05s. The S2 data wasn't on the same road as I logged my journey home and gave it WOT from 20mph when possible. Doing everything in 2nd keeps the speeds and losses low. I think it's about 10-15bhp losses at 60mph.

[Rusty]

Paul, do you thing you could send me speed vs. time for 0-30mph hard in firts please? Perhaps in excel? Also, be interesting if you have any 30 to 60 or 35 to 60 runs, same data. The accelration data off the GPS is noisy an requires some work to smooth it out at this stage.

[Rusty]

Basically what I want to see is how sharp the transition between speed = 0 and speed = 5mph is. I have assumed for my 0 to xx runs that it's sharp but this is obviously incorrect. As my GPS is running at 5Hz the transition from 0 to moving takes place in a space of 0.2s, on average the start poin will be in the centre of this transition range and so I've decided to add 0.1s for now to make things more realistic.

[Rusty]

Here's the sort of thing I mean, basically GPS and stationary don't mix so you have to use a threshold value. For me this is the first definite non 0 value, usually between 2 and 5 mph and its previous point. If you were to use the next point then the error is greater still. It seems like my idea of 0.1s isn't that far out TBH.

[A80Avant]

andy if you are still interested to get the g-tech im selling mine.Look at the items for sale page

[Rusty]

Bit late now, I've spent the spare money on a BMW . I'm sure it'll go as I know a few people were looking for one...

The GPS unit is great for everything except standing starts (and even then it's not too bad). It just needs some knowhow in the Excel / maths department to get the best from it, more fun as you're involved in the calcs and so understand the assumptions made and variables used.

[Rusty]

I've created a power curve for the S2, I only have RR data to compare it to and it seems to be quite close although there's the issue of my runs being in second gear and the RR losses not being completely linear. Overall it's close.

Weight was 1650kg
Air density 1.25kg/m^3
Cd 0.32
Frontal A 2m^2
Wheels to fly @ 3000rpm = 1.15, @ 7000rpm 1.35, assumed linear
7400rpm = 68mph

Here's a pic:-

[EspenW]

For the record I did some second gear 30 to 60 runs and recorded some steady times at the 3.3s mark. This compares to 2.9 for the S4 and that will now be quicker due to an FMIC and more boost. Those BiTurbo cars are damned fast. Prefer the S2 tho even if turbo lag is an issue for the 30 to 60 run

Be interesting to compare to GTech data there Paul.

Doing everything in 2nd keeps the speeds and losses low. I think it's about 10-15bhp losses at 60mph.

I have been away from the computer over the weekend, but will get some velocity/time data for you now. IM your email and I will send an excel file. What kinds of increments and what ranges do you need?

Approx 11 hp loss to aero at 60mph in my car. 2nd will provide lower aero losses, but losses to inertia will be higher. I calculated approx 45hp loss to inertia in 2nd vs approx 22hp loss in 3rd.

What is the 40-60 time for yours and the S4? On E85 on a freezing day, I recorded 2.37s 30-60mph, but that was with hesitation due to too much fuel, and did not start to boost until 36mph. 40-60mph is comparably better due to the fact that the entire interval is made on boost. 1.26s 40-60mph. Gotta low the eco fuel.

[Rusty]

Cheers EspenW, I'll calculate 40-60 times and get a PM off to you.

[S2central.net]

GTech RR speed data from that fraught launch attached. Amazing what that 12in rollout does by timeshifting things