TB993tt

Excuse the multiple posting of this:
How Porsche tuning has grown in the last 20 years is an amazing thing, I have watched it from the early days of Motronic when only a handful of people could even access the code to today when people casually talk about a “flash” as if it is something as simple as an air filter.

Those who may have read my ramblings over the years will know that I am very biased towards the tuning done by race engine builders RS Tuning who have a sophisticated, expensive engine dyno set up and many years of ongoing experience of working with that tool to produce the best performing Porsche race engines in the world. Their road engine packages benefit directly from this experience but they are hideously expensive and are only available if you buy the complete “kit” which goes against the “modular” form of tuning which has grown in this industry where for obvious reasons (which are both financial and for the fun factor) people like to bolt bits on and get a “re-flash” to suit.

We did some data logging at the airstrip a few weeks ago with some generous owners allowing me to plug the Durametrics into their cars to see what was actually happening and what exactly the “flash” was doing to their motors……

The results were quite interesting.

The ambient temperature of the day was about 17 degC
Reading the data in the pics below, unfortunately I haven’t lined up all the columns to read in the same order but you can read them if you look:

We have:
Time, this is the first column always and shows the elapsed time of when the reading is taking place, usually there is an updated reading every 10th of a second or thereabouts.

Engine speed is in RPM, sometimes you may notice that a spurious reading creeps in there – that should be considered a “spike” and not actual.

Mass air flow – this is the amount of air the engine is ingesting in kg/hr, basically the more air, the more power all else being good

IAT is intake air temperature, this is the temperature of the boosted air in the inlet tract, these cars (two 997tts and a 997GT2) work well to 55 degC which is said to be the point where timing starts to be retarded. The GT2 IAT is always higher since the GT2 runs much higher boost (1.6bar) in the inlet which is reduced by the action of the expansion intake manifold so the actual air entering the combustion chambers is not boosted so high and is cooler.

Ignition angle – this is the degree of advance which the engine is running at, basically higher advance number the better and a steady number shows a more balanced engine tune.

Vehicle speed is in KPH so for mph divide by 1.6….. so 200kph is 124mph

The lambda banks 1 & 2 are the readings from the lambda sensors and indicate the air fuel ratios. If you multiply the lambda readings by 14.7 it gives the AFR ie a 0.70 lambda is 10.29:1 AFR.

So to the data:

First up is a 997tt with sports exhaust and 200 cell cats and a “flash” from a BIG and well known German internet tuning house.
This car was fast up to 100mph setting IIRC a 3.4s 0-60mph on the way, the problem for this car was that the aggressive boost led very quickly to high IATs at 68DegC, at the gearchange 5th to 6th there is a good amount of timing advance ~14 degrees but varying quite a bit showing the ECU is working hard to keep the numbers good and AFR around 11:1 which is all good. It has a Mass air flow of 1486kg/hr peak at 6860rpm which represents the air it is using at peak power.
After the gear change the revs drop to 5521 and things start to turn nasty, the high IAT forces the ECU to take some action, the ignition advance is held way back and the mixture is richened to 10:1 to protect the motor from knock onset….. EGTs are well controlled.

This car slowed considerably over the 250kph mark in its physical acceleration and the data graphically shows us why.



Next up was a 997tt Cab with just a flash from a well know UK “flasher” who has sold a lot of his product in the UK market.
This car appeared very fast chirping its tyres as it changed 1st to second and with the owner reporting wheelspin changing 3rd to 4th gear !!! The acceleration data again showed it started to slow dramatically over 100mph.

Take a look at the data – it is not at the same speed points as the previous run because the owner was changing gear way before the red line.
So we see he changes gear 4th to 5th at 6093rpm IAT is high at 63DegC but the ECU has already been richening the mixture to cool it down with AFRs at 10:1 at the top of 4th gear.
Now checkout the chaos as 5th gear is engaged, possibly because of too high boost, the timing advance goes to pot and is all over the place even retarding the ignition for a couple of readings and the AFRs get as rich as 9.8:1 to cool things down – it appears the ECU does its job and the IAT starts falling – all this activity results in much slower acceleration.


OK so the last two were $2000 “flashes” from “tuners”. My “flash” was a program written by RS Tuning over 2 days on the engine dyno (most of which was doing part load programming so not relevant to these full load runs) specifically for the bolt on turbos, air pipes and 100 cell cats and expensive intercoolers which my GT2 engine has.

Mine is a 4th to 5th gear change. At 6902rpm you can see the Mass air my engine is ingesting is 1775kg/hr – what this data also shows is the “overboost” which RS program into their software. If you look at the data when 5th gear is engaged the Mass air for the first reading is still 1746kg/hr and then descends over the next few readings, this is the program allowing extra boost and extra torque as the next gear is engaged, this also happens if you stomp on the gas pedal in the mid range and gives extra performance in this area – non of the other flashes did this……
Next up, the IATs at 51 degC, lower than the others but remember the GT2 runs 1.6 bar in the inlet manifold so the IATs are always higher. The timing advance speaks for itself both in high degree of advance and in consistency. The AFRs are immaculately controlled with little variation at around 12.2:1 on this engine the IATs go lower as 300kph is breached and all the other numbers stay similarly constant…



I hope people find this analysis useful and please feel free to correct me on anything I may have said which is incorrect.
The second car really drove it home to me that some people will think they have really fast “tyre shredding” packages – this car was chirping its tyres as I said, but it is all just smoke screen programming to give the illusion of a fast accelerating car.

Just because the numbers are very “pretty” to my eyes below is the data trail of my GT2 up to 190mph, see the dropping IAT, the 22.5 degrees of timing advance and the steady 12.2:1 AFRs – it is poetry – right up until the rods break !


Not sure what this all really means to us enthusiasts ? Certainly modern electronics are awesome and can cope with whatever is thrown at them as long as the safety bits are left in, but to me it makes me even more cynical about "flashes" ......

bbywu

Toby, what is your current setup that you used to record your data above?

bob

TB993tt

Bigger RS VTGs, RS Carbon air pipes, 100 cell race HJS, BMC, headers, expensive intercoolers and programming.
Full load engine dyno boost curve:


On speaking with RS recently they have had two catastrophic rod failures on tunes similar to mine (at the ~830NM level) which toasted the motors - I am going to get a set of Arrow rods fitted in the next month or so (RS only recommend Carrillo but I am pretty confident of the Arrow products)

TT Surgeon

interesting

TT Gasman

Interesting data points, I would like to see how others compare. For instance, stock, Ruf and GIAC.

TB993tt

So would I, it would be fascinating......

Hoping to get similar logs in a few weeks for a Proto 996tt monster, a 544PS Cargraphic/RS 997tt and a stock tt....... mine won't be there as I am having rods fitted, apparently two RS cars have have bad failures at my level of tune......

LAT

Toby

Have you tried this exercise with you 993tt, the Motronic has some of the same input ability except for Lambda and Exhaust temp.

Interesting to see.

Levino

TB993tt

Hi Levino
No, the 993 has been resting (well between magazine road tests) in a dealer showroom for the last 18 months
It may be coming back out to play soon....

LAT

Toby

Magazine test, tell us more.

Also, do you know if it is possible to convert O2 sensor voltage to lambda or AFR? I have the Durametric Enthusiast version and it will capture O2 voltage.

Levino

TB993tt

There were three, two in mags and this one online:
http://www.pistonheads.co.uk/porsche...?storyId=21254

Will there be a formula you can put in excel to change voltage to lambda/AFR

LAT

If you would, which magazine and issue.

Not clear on your second statement.

LAT

From Pistonheads article.

The list of other modifications runs into next week, but suffice it to say that the result is 580bhp, 587lb ft and an ability to hit 300kph (186mph) form rest in 38.9secs.

Good review and no surprises, she is mean machine with total driveability.
Quick note, I imagine it is a typo, the 0-300kph is supposed to be 28.9 secs. is it not?

TB993tt

yeah typo.

Jiaim

I was sure you went with the akrapovic aftermarket exhaust and headers, so you can resist to the dark side of the force

TB993tt

Too much $$$$$ for me and unknown benefits on the set-up I had already paid for......