Is there anywhere the "ideal" (yeah I know such a thing don't exist...) graph for AFR across the rev range and in relation to boost?

I mean, all ppl agree that idle and cruising should be as close as pos to stoic. Fine!

Then you have ppl saying that 12 is OK whilst booting it, others say a bit more. And what about half throttle then?
Is there any proper theory to read about?
Also with forged internals, you could go slightly leaner (well rich again, but not down to 12s) on booting as it can withstand heat better, right?

well I was waiting for an expert but since you have now replies I'll throw in 2cents worth

Forged internals are stronger but they are not bulletproof, detonation tends to be the biggest killer of pistons IIRC, and while forged will take more punishment they will still break after a while. you could run an aquamist to suppress detonation.

I've always thought 12.5:1 was meant to be about right for a turbo car, but most go to 12:1 for saftey as you say.

Excessive leaness leads to piston heat and that in turn leads to dentonation. I guess at low/no boost situations piston heat is less so a slightly leaner mixture is O.K. but really have no idea about this with any sort of confidence

I'll pull "forced induction" by graham bell off the book shelf and have a look for you

Cheers

Part throttle can be around the 14.7 area as there isnt really any heat. Ideal for power is 14.7 but this isnt safe. So general opinion is nearer 12 redline for safety. and around 11.8 for midrange to do with the boost level that will be running around there.

Ross

Right,

Did a long run today (well, longish 30miles) using the EVOCARS chip only.

Cruising up to 100mph (vacum 0.3bar) AFR=14.7
moderate accel AFR=13.5
really booting it AFR=12.3-12.5
Never managed to see anything lower than 12.
So all seems to be fine.

HOWEVER (there's always a but...) idle AFR=15.5
Now, the odd thing is that even a 3deg throttle, brings idle speed to stoic.
Now, I did clean the Idle Control Valve last week and I may have got the nut a couple of turns of (did put a mark but the mark dissapeared when I cleaned the fcuker )
Could that be causing the wrong idle - mind you if I swap chips, idle AFR=14.7!

Was this after the ecu reset?

15.5 idle is fine. Im running that at the moment just now. When i've been a run mines settles at 14.6-15afr. Sometimes it leans out slightly to 15.5 but thats fine.

12.5 is cutting it fine dude. Should be slightly richer than that. Is that at redline? And is it 12.3afr the full midrange? Just seems a wee bitty lean.

Ross

Ross, on purpose I didn't do an ECU reset. I'll do tonight and I'll try it again tomorrow.

Mind you, it's not exactly easy to read AFR, check the road, check boost, revs and make sure you don't crash on the cars ahead...

I've got the logged data in comma delimited text files but I cannot get the graphs I'd like to in XL yet. Will try and find another tool for visualisation.

l8r

Done the reset, all remains the same:

idle AFR is 15.4-15.6
others as before.
Considering I'll be on forged internals, I'd have thought that the values are OK. I'll know for sure once I install the EGT probe (at rebuilt time)

cheers

How long did you leave the reset, i.e. the ecu disconnected?

It took mines nearly 100miles to settle down.

Ross

Ross, I started another thread in Tech as I think that it's the ICV cleaning I did last week to blame (mind you after all the driving I did yesterday, I swapped to another chip (abarth) that was behaving b4 and it's again wrong on idle only!
The only dif is that I've actually driven the car a lot, heated the engine properly and so seems like it's cleared up some crap out of the engine...
Will see.
Or it could be that the new tubular manifold I put in (using the old gasket, stupid me!) is leaking at idle messing the AFR on idle only, but cannot see why just touching the throttle it goes to stoic immediately!

V.

because your ICV closes then?

anyway AFR 15-16 is ok on idle, you don't have to worry about that.

Totally agree. The worry gauge has got you!!

Ross