TB993tt

Surely the lower the lambda number the richer the mixture ie less air so more fuel

So on mine at 4050rpm lambda 1 is 0.75, lamda 2 is 0.79 and I have 1.17 bar boost and a CR of approx 8.5:1 so the mixture is 11.6:1.... so pretty rich ?

JBL930

Anything under 0.79 is rich i think, i was commenting on you saying "it hovers between 0.81 and 0.87 reving up to to 7000rpm".
0.87 is lean Toby, really lean.

TB993tt

Told you I didn't know anything about the lean/rich thing - us Motronic boys do not need to be concerned with such things

Well in that case I must be ready for melt down as lambda 2 is at 0.87 from 6000rpm peaking at 0.91 at 6900rpm - probably why the bloody thing uses so little fuel - average (inc city traffic/blasting) 17mpg (imperial) and struggle to get less than 19/20 on a run.......

JBL930

Does it make any difference if it's the sensor before the cat or after the cat?

Felix

But all it takes in one cylinder to go lean and burn its piston while the lambda across your 6 cylinders still looks OK. Motronic has individual knock sensors for each cylinder that will help protect the engine.

JBL930

Hi Phelix
That's why i'm sticking a 993tt engine in my 930
Retro + Engine safety =

Phelix, do you know anything about the "guideline" AFR or Lambda for motronic tuned engines? Do Toby's figures sound lean? I don't doubt it's absolutely as it should be with what RS have done, hell i've been in the thing at 190mph+, it just sounds like the numbers go way outside the widely accepted parameters. Is there something else going on that i'm unaware of.
Sorry all, i'm just a stickler for info

Felix

Hi Jonathon,

Given that Toby's engine has survived extremes of performance I'm inclinded to think his AFR figures are fine. But I'm not sure we can compare AFRs between single and twin plug engines quite so directly; I think the twin plug engine can run leaner without harm. I think logging Martyn's AFRs would be more relevant to the engines of the mere mortals among us.

regards,

Felix

eclou

The pre-cat sensor is the most valuable reading. If worried about burning up a piston, running an EGT on each primary exhaust tube would also help.

JBL930

I knew there would be something Felix, cheers

Eclou, not worried about burning a hole in a piston as it's already happened, my new engine won't ever be as extreme as Toby's or Martyn's. Ok, never say never

Greame, sorry for buggering up your thread, from what has been said though you should ask whether you should be richer at peak torque, even Toby with his twin plug Evo heads runs 0.77 Lambda at that point, so yours does look a bit lean there, at least on the face of it. Would be interesting to see the fuel graph from a stock GT2 ECU

graeme36s

No problem as detonation is all our worst fear. Matty the mechanic from Fearnsport and the chap who now owns the company that runs the dyno where happy with the lambda readings. (I have not got a clue). G Force where into Porsche's, the new guys are into big HP japanese stuff. Dave who owns the shop, very nice guy runs a 600bhp 350Z. When Fearnsport booked the cars in they mentioned a GT2 and an Evo. After running the other GT2 he started moving all the cables around as he thought the next dyno car was a Mitsubishi
Scottmellor if I ever get the opportunity to get the GT2 flat out it will be flat out and thats a promise.

JBL930

Sorry Graeme, i'm about to do a bit more thread buggering, i'm really interested in the whole AFR thing, i'm sure others are too, and it seams a good opportunity to get some answers.
I've done a crude scribble over your fuel graph, one guessing what Toby's fuel is doing and the other what i thought your fuel would look like. I've used the word "Optimum" but i think a better word would have been "Safe".



I know Jean runs rich to keep things cool, i don't suppose you'd chip in mate and tell us what your ratios are at peak torque and WOT? And Martyn, if you have your data to hand it would be good to see what yours is on single plug.
I guess also with the Secans on your engines you get away with running leaner as the IAT are so low.
I'm probably going to be close to Graeme's numbers when i get my engine up and running, and i'm a bit paranoid about fuel, which i suppose is understandable

As an aside, can Graeme fit better/quicker actuators to reduce the sudden drop in boost after peak torque, or is it purely down to needing better ECU programing

TB993tt

Jon
I have been looking at various engine dyno sheets (mainly from RS) and I may have to revise my assertion that the slow wastegate/ECU mechanism is solely responsible for the big dip seen in Graeme's boost curve.

It is certainly the ECU sensing the onset of knock and abruptly pulling boost and (on modified cars) because the boost is much higher than the stock 0.7/8 bar (at peak torque) the pull seems to be much more abrupt however there are examples where the "hole" is quite subtle which does make me think (as you guess) that ECU programming can smooth this out to a great extent.

I am not sure exactly how the Motronic attends to knock but could it be that on a "non optimally" tuned ECU there is a high knock count (at peak torque) due to the tuner allowing too much boost (for the engine configuration) so the ECU reacts more aggressively pulling a higher percentage of boost - compared with an engine which is designed to take a ceratin level of boost and the knock count (or sensing the approach of said knock) is much lower allowing the ECU to signal for a more subtle actuation of the wastegates and making the "hole" less obvious ?

There is very little data available with boost traces, but here are mine taken from my dyno data sheet (the procurement of which was like getting blood from a stone !)
You can see a well controlled transition from peak torque boost following knock curve - this results in a smooth power curve without any holes (no you can't see that ) -I have included the lambdas 1 & 2 for you also

People with fixed boost set ups should take a look at this and think maybe "why" the boost likes to wiggle up and down like that and why Bosch designed the system so it can do that ?

JBL930

Toby, I guess you go quite rich at peak boost/torque to cope with the 1.2bar, maybe Graeme being lean at peak torque is accentuating the knock and therefore (at least part of) the reason for the quite massive hole with the ECU sensing danger, logic would say richen that area up and it would help some don't you think?

Still can't get my head round your engine dealing with those lean numbers at WOT, it must be made from unobtainium

graeme36s

I will double check with And. I am seeing him Saturday and I will make sure that the we are not running lean. I think my problem is that the boost shoots from roughly 0.5 bar to just over 1 bar within 500rpm and the actuators cannot deal with it. (bare in mind they are brand new). By running a more gentle boost increase should help the actuators and stop the drop in boost. I'll let you know what the experts have to say as the hole has to go.

Stummel

Pls dont get me wrong. I admire your car and especially driving it on the track.

But I do not quite understand why you would bring it back to the "experts" after it still has a "hole" in its torque curve. Trial and error on a GT2?
You would NEVER ever get a sub-perfect engine tune for a 993 GT2 from RS-Tuning or Manthey for example. And they would not see any need to call it an EVO for whatever reason.

Just can not see NOT going to the best of the best with this piece of art and Porsche history.
Even or maybe more so if it is a standard 450hp engine.