Guran's NA6 "Little Reddy"

[evil_weevil]

save money and keep flogging little reddy mate - you are doing a great job with her!

Im scared to enter an event with you now as you'll be quicker LOL!

[Guran]

14th August 2011

Eastern Creek Supersprint Round 7

It's often the little things that make a big difference. Who would have thought that an extra 4km/hr would have such dramatic consequences? That small margin was the only difference between comfortably negotiating turn 1 at Eastern Creek on 22nd May, and experiencing a scary 5th gear drift at 170km/hr on 14th August.

Here's some data to digest ...


Turn 1 0226 0410 0522 0814 by Guran5, on Flickr

Red = 26th Feb 2011 best lap 2:01.72
Blue = 10th Apr 2011 best lap 2:00.76
Green = 22nd May 2011 best lap 1:59.81
Black = 14th Aug 2011 2nd best lap 1:59.41

The red line shows how I used to have a slight throttle-lift before turning in, which washes off a bit of speed but also sacrifices precious time. In April (blue), I took a brave pill and tried turn 1 without lifting, and you can see how much more speed I was able to carry through. In both cases, I was shifting into 5th gear at the 100m marker. In May (green), my car was making better power in the conditions so I turned in with 170km/hr and carried even more speed through turn 1 (and braked much later for turn 2). The car felt really planted too. But this Sunday, my car was making heaps more power than usual (more on that later), such that I had to change to 5th gear much sooner at the 200m marker and after getting a fast entry onto the straight, I turned in with 174km/hr. Another 150m later and the rear started to overtake the front! I kept the boot in and counter-steered, holding a massive ~170km/hr drift for about 100m before the car settled again. Boy oh boy, was that an eye opener! You can see it all in the video below.

OK, back to normal service ...

ARDC ran this round and there were only 86 entries, way down on the usual 100 drivers. Something to do with the high entry fee perhaps? There were up to 6 runs on offer (3 flying laps each), but for various reasons (including running low on fuel), I called it a day after my fifth run. So not many laps, but I still was absolutely delighted with the result. Better than the half dozen drivers who crashed out in a day of unusually high carnage! We also had the opportunity to see firsthand the results of the first stages of new track that have been constructed.

The day started with a cool 8C and soon warmed up to a maximum of 17C. Better still, the atmospheric pressure was quite high at around 1025hPa - good news for stock naturally-aspirated engines! The BOM had forecast scattered showers but they never arrived.

Run 1 started after a long delay to recover a couple of cars that crashed out. I went out near the end of the Blue group (1:55-2:01). I was passed by a HSV Maloo at turn 8 on the first lap (2:02.9282), but then caught up to him again by turn 8 on the second lap. He must have had problems because he pitted on that lap. Unfortunately, his slow exit to turn 12 forced me to run wide on the exit and I clobbered the leading edge of the concrete runoff-pad. The compromised lap (2:02.9679) meant that I was then passed by a Ford Capri GT down the straight. This guy subsequently missed every apex by at least five metres but pulled away on the straights such that I had no chance to overtake, ruining my last lap (2:05.4518). It was a very disappointing run. Patience grasshopper.

Run 2 was much better and I had virtually no traffic other than getting passed by the Maloo again. I had laps of 2:00.7085, 1:59.6598 and 1:59.6634. A new PB already, and I was still tweaking the tyre pressures!

After a lunch break while more crashed cars were being retrieved, Run 3 started with a 2:01.3470. I was starting to catch up to Rudi Frank's Beetle - his usual Class 4D Beetle had broken down so he was driving a mate's substitute. It was hilarious watching this thing lift a front inside wheel in the corners! At the start of the second lap, I clipped the ripple strip on turn 1 and got a bit loose but managed to catch it. The rest of the lap went smoothly and ended with 1:59.2883 - another new PB ! Next came the abovementioned testicles-in-throat moment in turn 1, then I braked too early for turn 2, had another moment in turn 4, and finished with 1:59.4063. Still plenty of room for improvement.

Run 4 began inauspiciously when I saw Lindsay Burke crash Robert Kai's RX7 into the concrete wall on the inside of turn 12. After a couple laps under yellow flag, the run was red flagged. But not before the Capri GT lost a wheel and crashed out at turn 8, plus a Civic broke a gearbox. So with three cars requiring retrieval there was another long delay. It was great to see that Lindsay was totally OK - he had been another victim of that concrete step exiting turn 12.

Run 5 started following Tony Williams' Class 2A NA6. I began with a 2:00.6845 lap, but then couldn't bring myself to take turn 1 flat. I'd seen too much carnage with other cars that day, and had memories of Paul Bowers' XR4 inserted into the concrete wall at turn 1 during the last round. So I lifted for turn 1! Even so, I finished with laps of 1:59.7273 and 1:59.8843.

With less than an eighth of a tank of fuel left, and with about half a dozen badly mangled cars accumulated in the pits, I decided to pack up and skip the sixth run. Discretion is the better part of valour!

My time of 1:59.2883 was a new PB by 0.5244s, and improved my old Class 1A record for NSW Supersprints . Having taken so long to crack the two minute barrier, I was really pleased to find that all except one of my clear flying laps had been faster than my old PB of 1:59.813.

Natsoft Results

Video of the last two laps from Run 3, including my 1:59.2883 PB.


I finished the day 2nd in Type 1 behind Saba Hanania's C63 AMG (1:52.596 PB & 1D record), and ahead of Glenn Thomas NB8B (2:01.149 PB), and Keith Monaghan NB8B (2:04.825 PB). I was the only entrant in Class 1A again. Fastest MX-5 was Patrick Bramston with PB of 1:48.378 (turbo NA with slicks).

After Round 7, NSWRRC (777) have retained the lead of the club championship. But the MX-5 Club of NSW (754) have halved the gap to second, and ARDC have fallen further behind (668). With only two rounds to go, there's a good chance we can snatch the title, provided we maintain a good turn-out of drivers.

[NitroDann]

And you wonder why I want to get in your passenger seat

Dann

[Guran]

The Winter 2011 issue of Club Torque is now available as a PDF for download from the club website (just click on the cover image below). If anyone did not receive the printed magazine and believes they should have, please let me know.

[Guran]

A few weeks ago I showed a graph of my club trackday laptimes at Wakefield Park, as a function of the date during the year. There appeared to be a trend suggesting faster laps in winter and slower laps in summer. Originally I thought this must be due to temperature, but then this technical paper got me thinking that it might actually have more to do with atmospheric pressure. So I did some digging into the BOM archive and came up with these two new graphs covering all my dry trackdays over the last 12 months (the free BOM archive is limited to 12 months):


9am MSLP data is from the Goulburn Airport BOM site which is just over the hill from the track. Very reliable data. I've sketched in some "best fit" curves that seem to match the overall trend, and divided them into two groups depending on which tyres I was using. The one outlier at 1012hPa is from 5th Sep 2010 when the track had a trickle of water across the apexes of turns 2 and 10. It's interesting to see that the difference between RE001s and RE55s seems to be bang on 2 seconds in like-for-like conditions (which I've never actually tested on the same day).


9am MSLP data is from Badgerys Creek, which is about 15km to the south-east of Eastern Creek. I've split the data into two halves corresponding to before and after I started to take turn 1 flat throttle (seems to make 1.0-1.5s difference). In this case, I've fitted straight lines. I don't know which is correct - but more data from future trackdays will answer that.

The atmospheric pressure at both sites tends to be lower in the summer and higher in the winter, just like temperature. But the correlation against temperature was much weaker. Furthermore, MSLP can occasionally get as high as 1035hPa, especially in June and July.

Sooooo ... if the planets align and I happen to be at the track at that time, I'm predicting that I might eventually get down to something like 1:16.5 on RE001s / 1:14.5 on RE55s at Wakefield Park, and 1:58.5 at Eastern Creek . That'd be great ... but it sort of takes the gloss off it if the weather is such a strong contributor.

Maybe Dann or someone else with technical knowledge could pipe in here with a theory as to why this trend might be happening? I'm thinking that it might be related to AFR, with the engine running slightly leaner as MSLP increases. Is that feasible?

[manga_blue]

I tried to tell you last time. You're developing dodgy scientific hypotheses to explain laptime variations then massaging the stats to support each one. The one true reason for any variation is emotional, not scientific. Here's the corresponding and much more meaningful analysis of manga times.

I'm storing the helmet somewhere special in preparation for the next outing.

[NitroDann]

The afm will account for both air pressure and temperature, so it shouldnt be leaner.

But, cool air is denser, and high pressures are denser again.
What im saying is that if you get a litre of air and cool it, it will be now less than a litre(lets say 900cc), and so denser, then if you add more air, inside that 900cc space, this respresents your higher pressure. Now you have, lets say 1100cc of the original temp/pressure air in a 900cc space.

Long story short, cold air is less pressure, so having cold air And high pressure is a lot more air than you might realise.

But you wont be leaner.

You may make 2-3% more power though.



If you really want to run a 1:14, take mine for a lap sept 4th, im sure youd be able to manage it

Sorry, tired, huge ramble.

Dann

[Guran]

Phil that's just too funny. But you can keep your stinky helmet! I'm sticking with the science. BTW, I also have logged data showing faster straight-line acceleration on these high MSLP days.

Thanks Dann. Let me try again, delving into my 24-year-old memory of high school chemistry!

Ideal gas law: pressure times volume equals moles of gas times gas constant times temperature (PV=nRT). Volume is fixed via the AFM, so this converts to pressure divided by moles of gas divided by temperature (P/nT=constant). If pressure increases and/or temperature decreases, then moles of gas has to increase. In other words, on a cold day with high MSLP, the engine breaths more molecules of air (with oxygen being the important bit). The oxygen sensor initially detects a slight excess of oxygen and starts feeding in more fuel (compared with a hot day with low MSLP), to achieve the target lambda. So the engine makes more power because it's fed with more oxygen molecules and more fuel. Is that how it works?

[manga_blue]

The oxy sensor has no effective role on the track.

On my NA8 the ECU goes into open loop when RPM > 4608 or throttle position (TPS) > 50%. In open loop the ECU supplies fuel according to a pre-configured map based on AFM, TPS and intake air temp sensor (IAT) readings, rather than optimising outputs using oxy sensor values. As Dann says, the AFM and IAT outputs mean the ECU is always given an accurate reading of air mass, independent of ambient temps.

On your NA6 with an on/off TPS I'd assume that you'd go open loop above about 4500rpm or at full throttle. Since these describe your normal driving state then I'd say you'd never see closed loop or use the oxy sensor.

Without doing the calcs I'd say the variation in air mass delivery resulting from air temperature variations would absolutely dwarf those from MSLP variations.

You could try correlating laptime with ambient temps. That's not very easy because low temp means low grip. The perfect day is low temp, no wind but with full sun putting some warmth on the track surface.

[Charlie Brown]

Bryan, I can see numerous variables that you haven’t taken into account.

The effect of the high pressure system on your tyres. The higher atmospheric pressure will tend to lower the pressure within your tyres, this inturn will affect the amount of grip you have on the surface. This is not to be confused with the effect the higher atmospheric pressure has on the entire surface of the car and not just the top, thus negating any additional downward pressure.

Also you need to take into consideration the effect of methane gas being released from the local tip. Methane gas is 40% lighter than air, so the atmospheric pressure over the Creek may be lower than the pressure at Badgerys Creek.

Then you have surplus rubber from Time Attack increasing the co-efficient of friction that allows higher corner speeds.

Ah the list goes on and on. Basically I’m in agreement with Phil. Have a sh*t before the run and reduce weight and just flog the sh*t out of the car.

[evil_weevil]

Ah the list goes on and on. Basically I’m in agreement with Phil. Have a sh*t before the run and reduce weight and just flog the sh*t out of the car.

so THATS what I'm doing wrong !!!

[manga_blue]

If everyone followed your advice, CB, there'd be a methane gas hotspot right beside the track as well.

BTW Bryan, I think I've found a car that'd be quicker than yours in 1A. Yes, it's a stock 1600 NB Coupe.

http://www.goo-net.com/usedcar/spread/goo/13/700055051220100921001.html

[NitroDann]

Yeah bryan thats right.
It doesnt matter that the air is thicker or colder, the density makes the air heavier, carrying more momentum to push that flap open further.
Therefore more fuel is added, making more power.

But I reckon have a shave and go to the toilet is the easiest way to guarantee performance

Dann

[Guran]

BTW Bryan, I think I've found a car that'd be quicker than yours in 1A. Yes, it's a stock 1600 NB Coupe.

Nope. Mazda only made 187 NB Coupes, less than the 200 required to be eligible as a "Production Car". However, the regular 1.6L NB would be a contender. I just hope that no CRXs or Civics show up in 1A!

[Guran]

Thanks for the explanation Phil. Helps a lot!

On your NA6 with an on/off TPS I'd assume that you'd go open loop above about 4500rpm or at full throttle. Since these describe your normal driving state then I'd say you'd never see closed loop or use the oxy sensor.

Yep, when my throttle is pressed, it's pretty much always flat to the floor!

Without doing the calcs I'd say the variation in air mass delivery resulting from air temperature variations would absolutely dwarf those from MSLP variations.

MSLP variation from 1030hPa to 1010hPa is a 2% difference. But the AFM doesn't adjust for this does it?

Temperature variation of 30C versus 10C is a 7% difference (in Kelvin). But you say the AFM adjusts for IAT, so this should cancel out, shouldn't it?

You could try correlating laptime with ambient temps. That's not very easy because low temp means low grip. The perfect day is low temp, no wind but with full sun putting some warmth on the track surface.

Yes, I've tried that correlation but it doesn't fit anywhere near as well as MSLP does.