Det with 11.1-1 AFR's
 

I carried out the airbox (resonator removal+larger inlet to airbox)mod on my Bugeye,which did show the AFR's leaning out a bit more to 11.4-1 on the SECS, at points in the revrange due to the increased airflow.But is usually at 11.1-1 when on boost.
It has caused the knocklink to show a bit of amber activity,even with the AFR's showing a decent level if richness and inlet temps only 1 deg above ambient(which is better than the std setup temps).The knocklink quietens down with it put back to std.
This is on a STD ecu.

Basically,why does it show a bit of det with all the figures looking good?

Gary

The reason the AFR leans out a bit is due to the measured airflow signal being weaker, ie the ecu only supplies fuel to match the lower 'measured' signal. This reduced signal also determines the ignition advance, lower loads generally run more advanced timing.
So you now have less fuel and more timing for the same airflow.
These engines run on the edge of det by design so you are eating into the ECU's knock sensor activated safety margin if you are seeing knocklink activity.
An AFR of 11:1 is leaner than most std bugs run on full boost.

Andy

Thanks for the advice Andy.

Why do you say that it has a reduced signal,when in theory it should have more air going in due to the increased airbox intake size,which i thought would mean a higher signal.
Its quite a learning curve when you start monitoring these things.

BTW,John Banks advised that 11.5-1 or lower was rich enough when i was first finding out about AFR's-im a little confused now.

Gary

The factory wideband on original calibration is not accurate enough to be sure you are not leaner than you think.

11.5:1 usually is OK, but as Andy says, your timing is likely to be too advanced. You can run 9:1 and still det with advanced timing.

What Andy is saying about the signal, is that in changing the intake you have changed the gas flow pattern over the MAF sensor. This often makes it read LOWER for the same mass of air. So it runs leaner and invariably more advanced timing. This can make power to a point, then it causes detonation.

Small changes in airflow patterns over a MAF can be dramatic. For example my APS cast elbow which sits about 6 inches before the MAF, makes it under-read airflow by about 20-25%, you could easily blow the engine within miles if this is not corrected for. Your example is less extreme.

Forgot to say, the SECS/Delta Dash wideband display from the OEM sensor saturates rich at c.11.1.... so you could have easily gone from 10:1 to 11.4:1 for example.

Thanks John.

That makes it clearer now.Does it require a remap to make the wideband lambda calibration more accurate then?

It may well have more air going in but the actual measured signal can be altered due to the resonator removal, most alterations to the induction result in a reduced maf signal.
11.5 is not necessarily too lean for a properly remapped car if the boost is moderate and timing adjusted accordingly but if you combine the effects of the advanced ignition timing and leaning out then you can get closer to the det point.

Andy

Edited to say JB is faster on the keyboard than me :D

Bob Rawle reported some successful recalibration of the new age front wideband against a MoTeC PLM, not sure if he now trusts it to map with or not.

It might also take a while to learn around the change and drop the timing, especially just for ambers... how many miles did you give it?

You could use a splash of NF octane booster with (presumably) Optimax? Then you will add to your gains.

What is meant about the "saturation" level on the lambda?

Also,would it be best to reset the ECU so it can start the learning process again for the knock correction,so it doesnt advance it too much?

Thanks for the speedy replies-its greatly appreciated,as i am keen to learn about this stuff :thumb:

Its run on Optimax,and has had about 150miles with the mod.
edited to add-it only had about 20-30 miles on spirited driving though;)

Resetting would bring the ignition down temporarily, but the bugs are quite quick to learn anyway, so reset of dubious value.

Saturation - I mean if it goes richer than 11.1 you won't know, it still shows 11.1.

Ah...i understand now-i have to admit,i did wonder why it would go to 11.1 and stay there without any fluctuation.
Probably time for a remap soon then-ive just been reading the 2.5 conversion thread,would it be better for me to get a power fc @ £700 from Andy?It does seem a very reasonable price compared to a Tek3.

The Apexi Power FC is currently not an option for the new age cars I'm afraid............... a free Tek3 may be though !!

Andy

Im all for freebies;)

Just read your post about the free Tek3.
Oh how i wish i read more into the last bit,i thought you was referring to my "free airbox mod". :(

PS my car also has decat UP/Down pipes-PM me if you feel the need for another lab rat ;)

PPS,did a reset,all is quiet on the knock front at the mo.

Gary