takahashi

Got some video. Mastered my RaceChrono data overlaying skill, not the driving skill though. It is still pretty crap.

http://www.youtube.com/watch?v=93dpl4CA_As&fmt=18

Revolver

Nice work Taka...like the overlay of track graphic, etc.

Good to see the weather lifted a little for you guys...pity it didn't stay that way...

takahashi

Thanks Dave.

Sorry that you cannot stay a bit longer. I have for the first time this year use up all my fuel on the race track and had to fuel up in Euroa before coming back to Melbourne.

One very good observation comparing my data from last Winton day which is wet and the dry day I had earlier. I found the corner speed is reduced... (yeah really). But the interesting thing is I am 13 kmh down say at the back straight coming out of the double right, but I am only 2kmh down at the point of braking in the wet track. So the slope of accleration, bearing in mind that I cannot apply throttle earlier in the wet track compare to dry, is steeper. In other words, I had prove of having more power.

I ask myself why. The tyres is the same, perhaps less grip. Same engine oil (not changed yet), same fuel (Ultimate 98)... the only difference is the spark plug being new. I have not taken the picture of the old one, they are less than 10000km old and changed Aug last year and only had .... 6 track days since. I have not taken a picture of it (it is being clean at my mechanics atm - I am going there this arvo to look at it), but they look fine to me, not foul.

So my bottom line is change them frequently to gain max power from an NA engine. I am going to clean the old set and swap them frequently (every 6 months or so). It will last longer if my 8 is a track only car.

The graph is linked in my blog
http://taka-rx8.blogspot.com/2008/12...and.html#links

Revolver

Two of my plugs have done about 40K and another two have only done about 15-20K, so i'm going to hang onto my new set for a while. Car's done 53K all up. Might throw them in at 75K...

takahashi

Leading plugs show far more deposits generally then trailing. So I guess leading plugs are the ones to change if power is slightly lost.

Revolver

Yep, it was the leading plugs that got changed when my first set of coils shat themself.

DavidM

comparing my data from last Winton day which is wet and the dry day I had earlier - I am 13 kmh down say at the back straight coming out of the double right, but I am only 2kmh down at the point of braking in the wet track. In other words, I had prove of having more power.

Hi Taka, I have no idea whether you have more, less or the same power. But what you're seeing in the plots is perfectly normal. Being down on speed in a corner does not necessarily translate to being down on speed at the end of the straight. ie. the speed at the end of the straight at Sandown will be very similar whether you fly thought the leading corner as quick as you can, or whether you stop at the apex and start from stand-still.

I know that is hard to picture, but look at it this way. If you can carry (let's say) 60kph through a corner, then on the following straight you'll be accelerating from 60kph until you reach the end of the straight and brake. Let's say that you're reaching 200kph at the end.

Now look at what happens when you stop at this exact corner and accelerate from stand-still. It will take you only ~30m to accelerate from 0 to 60kph so realistically speaking, it takes you only 30m to catch up to the speed that you were previosuly carrying through the corner. Yes, you you needed 30m to do so, and in turn you now have 30m less of straight to accelerate (from 60kph onwards) before you hit brakes, but that 30m does not make much difference in terms of speed at the end of the straight. ie. at 200kph you're traveling at 55m/s so you'll cover 30m in about 1/2sec. In 1/2 sec you will be lucky to accelerate 2kph at speeds around 200kph. Even at speeds of 160kph you'll only accelerate ~3kph in 1/2sec.

Another exampe is the 400m drag-strip. Your terminal speed at the end of the run is not that different whether you get a bad or good launch. Though, you'll see a big difference in the ET (ie. time). Same thing at the track / straight - You see a big time difference depending on how well you enter a straight, but you don't see much difference in terms of the speed you're reaching.

Speed at the end of the straight is driven very much by the way the car accelerates. Corner exit speed has only a small impact here.

Also keep in mind that to accelerate from 0 to 100kph, you only need ~7sec and about 100m. Though at 200kph you'll cover 100m in less than 2sec and in that time will increase your speed by only about 5kph. So speed difference at low speed is not related at speed difference at high speed.

I'll give you another example - we have a 100m straight, and 2 identical cars. One is lined up (stationary) at the start-line while the other gets a runup at 100kph. When the car with a runup crosses the start line, both cars floor it. Do you think 100m down the road (ie. at the finish line) there will be 100kph difference between the speed of the 2 cars?

What will happen is that the stationary car will cover the 100m in ~7sec and will reach ~100kph. The other car (that had a 100m) runup would have covered the 100m in 3.6sec even if it was not accelerating. So it had less than 3.6sec to accelerate from 100kph onwards before it crossed the finish line. It takes about that time to accelerate from 100 to 130kph (for a car like RX8).

So the 2 cars crossed the finish line at ~100kph and ~130kph respectively ... 30kph difference here even though the difference at the time the 'race' started was 100kph. The longer the straight, the less difference you'll see at the end.

Got some video. Mastered my RaceChrono data overlaying skill

Thanks Taka. Can you elaborate on the Civic Type R? In some parts of the video it looks like it's pulling away from you in the straight. I would have not expected that ... or is that just an illusion?

takahashi

I have no idea what you are talking about DavidM. I really don't.

I cannot picture at all what you are saying. I am a very simple man really.

Acceleration is meter per second square or ms^-2 (labrat help).

so it is m/s (or speed) divided by time.



There I have a graph speed vs time. The slope of the graph is acceleration. The upper graph is dry and lower graph is wet.

I think the lower graph has a sleeper slope = more acceleration = more power

Cronullarx8

Before this technical discussion gets too overwhelming let me just pause to say a big thank to Taka, Andrew and Stu for making the day happen. It is these efforts that keeps the RX8 spirit alive. We NSW gang will always do our untmost to support you guys (we almost feel obligated!). Looking forward to our next outing. Suggest we keep an eye out for a Wakefiled day and with plenty of notice we may be able to get some of the VIC crew up. (Nats??)
p.s. Taka - I was impressed by your speed in the wet!

takahashi

Coming from you ... thanks for your kind words Rod .

Wakefield day in early October right?

DavidM

I have no idea what you are talking about DavidM. I really don't.

LOL Taka ... just read the examples that I listed and that should make it clear. I did try to keep it as simple as possible. Though, the point here is that you can't look at the speed different in the corner and then look at the speed difference at the end of the straight and conclude that it is due to improvements in acceleration.

Here are some key points in terms of acceleration, and how it relates to entry and terminal speed ...
1. Acceleration for cars is not linear.
2. Acceleration is greater / stronger at lower speeds and weaker at higher speeds.
3. To accelerate from 0 to 60kph takes ~3sec, and ~30m.
4. To accelerate from 100 to 160kph takes ~10sec, and ~400m.
5. The start / entry speed onto a straight has only a small impact on the speed at the end of the straight.
6. No matter what your start / entry speed is, the top speed will be exactly the same if you have long enough straight.

There I have a graph speed vs time. The slope of the graph is acceleration.
I think the lower graph has a sleeper slope = more acceleration = more power

Yes, the slope / gradiant represens acceleration in the graph that you have posted here as this is a time vs speed graph. The ones posted on your blog are distance vs speed graph, so the slope / gradient there does not represent acceleration. What I posted above was in relation to your original posts, which references the graphs in your blog.

Still, looking on the new graph / plot that you posted, it does seem that there is improvement in acceleration between the 2 plots (despite your original logic not being correct). Looking at the 100 to 150kph speed increment, we have:
- dry = 91.5sec to 100.5sec, which is 9.5sec
- wet = 93.0sec to 101.0sec, which is 8.0sec

So if we go just by this, then you're accelerating 1.5sec quicker from 100 to 150kph (ie. 8 vs 9.5sec). Whether it's power, wind, or weight related I don't know. If you can cut out a similar graph / slice on the back and front straights, then we should be able to at least eliminate the wind.

takahashi

Haha I understand now I have used the wrong graph in the blog.

Yes there is more than power factor in the increase in accleration. Wind is something that I had not thought of. As I posted in my blog earlier in the Sandown day. I was having 5kmh short at the back straight because of wind. But I don't think it was that windy that day at Winton.

I don't think there is that much weight saving either. I have relocated the battery that 10kg and I had tonsillitis that I could not eat well for a week, but still

Here is the cut out of the "back straight", you know the one after turn 10 and before the 2 right handers to the front straight.

DavidM

Here is the cut out of the "back straight", you know the one after turn 10 and before the 2 right handers to the front straight.

Hi Taka. Looking at the back-straight, and acceleration from 80 to 135kph ...
- dry = 67.4sec to 75.5sec, which is 8.1sec
- wet = 68.8sec to 76.3sec, which is 7.5sec

So again a quicker time in the wet. ie. 0.6sec quicker from 80 to 135kph (7.5 vs 8.1sec). This would validate that the wind did not have much impact on what we're seeing in the graph as there's no variation in either direction.

I don't think there is that much weight saving either. I have relocated the battery that 10kg and I had tonsillitis that I could not eat well for a week

hehe. So 10kg all by itself is not major, but I do know that ~75kg of extra weight in my car will add about 0.35sec to my acceleration time in the same increment.

Do you know much much fuel you had on board (comparatively speaking)? Though, I can't see there being more than 40kg difference due to fuel even if you were full in the dry and empty in the wet.

So it looks like you did have more acceleration in the wet ... though the odd thing is that more acceleration usualy means higher top speed on the straights (without regard of the entry speed). I do notice that you were braking a few secords earlier, which would account for a couple kph. Still, did you (on any of the laps) reach higher speeds on any of the straights?

Also on another topic - Can you elaborate on the Civic Type R in the video? In some parts it looks like it was pulling away from you on the straights. I would have not expected that ... or is that just an illusion?

WAY

Hey Taka, just watched the video. Great to see some footage of the day! I am surprised you said my tyres had more grip. I thought the Dunlops has the better wet grip? I certainly was struggling big time for grip especially on the outlap where you overtook me. From your in car footage, I would say that you were doing it much easier than me as I was on tippy toe the whole time. It also took me the first couple of laps to adjust to the sudden extra 100kg in the car compared to all the previous sessions! (Andrew was in my car in that session for those weren't there). Guess my 1:51 lap wasn't too bad considering the extra weight and stuck behind you by the back straight. It was bloody bad timing for the rain to come back too because as you can see on the video I had just cleared that supercharged Type R and ready for a serious assault on the lap time. Andrew was sensible enough to advice me not to go for it in that next lap when it started spitting down.

WAY

The Civic has a aftermarket supercharger on it. I think it puts out 260kw atw! Struart can verify that figure. Not sure if I remember it right.

takahashi

DavidM,

Thanks for your thought on that. Fuel will be similar if there is any will be 10L-15L difference.

That Civic is supercharged. There is a great "wine" from the charger. I thought it has 200kw atw.

WAY,

No because it is a softer compound that it needs more heat to get grip. Colder temp in hard compound tyres are much better. In semis it is not the all pattern, it is all about heat on tyres.

I only manage to get about 25-30 degree on the tyre at the pit.

I am on limit as well. I am just smoother coz it is my nature.

MACCAA

Er no.....softer compound requires LESS heat to get grip-hence the soft compound wets that overheat rapidly as the track dries out.The harder the tyre,the more heat it requires to get "sticky",so it's more durable.
That's why they run super soft tyres in qualifying,because they come in quickly,but go off just as quick-usually 1-2 laps..Then they run a harder comound in the race.
Cheers
Len

takahashi

Totally agree with what you said Len.

Oh I should rephrase my point. (I use the wrong word, I should have said "the softer compound needs a higher operating temperature to get grip")

I am getting the same surface tyre temp in the slightly softer compound than the RE55S SR2 in WAY's car.

My point is, say both tyres are running at 25 degree on the track. Which one will get more grip? The softer or the harder compound. Mind you the operating temp in semis are around 60 degree.

Remember both are dry tyres. From my experience and my readings from the tyre tests in Japan. Yes, the softer compounds take less heat to get to operating temperature. But the operating temperature of softer compound is higher than the harder compound. I don't have the actual figure (or the Japanese are too selfish to share).

So my point in the wet... although I am still guessing that is the fact... that in a very low temp, the harder compound MIGHT have an advantage.

I am also guessing here, but I really suspect that the wet semis are operating in the very low temp.

Well ... if I guess right that is.

takahashi

Haha.... I have done a silly thing to google and search my Jap mags about running our semis in the wet. Of course, there is no such info on that....

I guess we should not guess what a dry compound semis will do in the wet . It is just a silly thing to do.

DavidM, what do you think? You seems to have a lot of experience on that .

takahashi

Oh I sort of find this.

http://www.tracksideperformance.com/TireBreakIn.htm

Hey I did a wrong thing by lowering pressure to 29psi before the wet day. I should have left it at 32psi. Normally my semis after a track day is about 27psi when cold.

auzoom

Way, when I was riding with you I was really suprised at the level of grip you got.

Was also amazed at the grip you had on braking. Did you have traction control or ABS on or off?

Cheers

Andrew

auzoom

Hey guys a favour to ask. Did anyone pick up a Racing Beat gauge pod? It was in a blue plastic bag. I have just unpacked my car finally and its not in there

Cheers

Andrew

WAY

Traction control and ABS was both on. But as you experienced yourself, even with them on it still allowed a bit of slip angle.

DavidM

DavidM, what do you think? You seems to have a lot of experience on that

Hi Taka. Not sure how much help I can be here. I have had more than my share of wet track days over the last year, and I can safely say that RE55s have close to no grip in those conditions .... that is at least for me. In the wet it's not unusual to for me to wheel-spin them in 4th gear ... not just on the straights, but also coming out of ~60kph corners. Road tyres have 10x the grip levels in the wet. On the other hand Toyo RA-1s were unbelievable in the wet. As long as there was no standing water, they were possibly the grippiest tyre that I've experienced in the wet.

That's about all I can help with. I would think the more 'focussed' the tyre, the worse it'll work in the wet.

That Civic is supercharged. There is a great "wine" from the charger. I thought it has 200kw atw.

OK. In that case I'm surprised how little it's pulling away from you and how well you kept up with it on the straights.

WAY

December's Motor mag tested both our tyres (and a couple of other semis too) and the wet lateral G on your tyre was way higher than mine (something like 1.07 vs 0.92). But then again, we have no idea the temp of the tyre or the track when they made it wet...