Author Topic: Stock A/F ratio in M42 engine? (Read 5188 times)

HaNasich · « **on:** March 23, 2009, 07:31:19 AM »

Has anyone taken AFR readings from their stock M42 engines?
im looking for some figures to compare with the AFR readings i've got from my LM-1 after installing DASC kit

thanks

Ron.

1991 E30 M42 · « **Reply #1 on:** March 23, 2009, 09:47:43 AM »

Under load? With you being boosted i would want to see it around 12.5-13, but when you are idling or just cruising it should be in closed loop and you would see your afr ranging up and down, rich and lean.

nickmpower · « **Reply #2 on:** December 09, 2009, 08:31:11 PM »

what values did you see from the LM1?

bbarnumboy · « **Reply #3 on:** December 26, 2009, 02:46:31 PM »

if you are still looking for this. i have a wideband hooked up to my stock m42 and i run about 14.3-14.8 average under cruising and WOT.

nickmpower · « **Reply #4 on:** December 26, 2009, 03:52:35 PM »

Yeah i have a wideband as well. I was looking for the DASC air fuel ratios though.

My car runs a little richer then yours at full throttle but i have a markD chip

HaNasich · « **Reply #5 on:** December 28, 2009, 06:18:44 PM »

BBarnumboy - that is very lean - usual state for stock M42's
my car was showing same figures with DASC and stock injectors.
the thing is that the engine used to ping in certain rev. and certain load
i didnt like the thought of blowing my engine for lean mixture, so i switched to SAAB 900 turbo injectors (could not find Mustsang ones)
no i run richer - 12.8-13.2, the engine does not ping and i hope that im on the safe side

bbarnumboy · « **Reply #6 on:** December 29, 2009, 10:18:00 AM »

i dont notice any pinging. and i just put on a brand new head and had the injectors cleaned and balanced. and it ran that safe ratio before all that. maybe i have some sort of chip installed i did not know about. i was under the impression that on a N/a mid range 14's were perfect? so did those saab injectors work as a direct plug n play?

dcroteau · « **Reply #7 on:** January 08, 2010, 09:37:51 AM »

After melting pistons in my race car and dealing with and tuning an aftermarket ECU for 4 years I learned quite bit about AFR readings.
Truth is an O2 sensors are really only good enough to get you in the ballbark.
The quality of gas (ROM Octane), the compression ratio, cams and where you run your motor - AFM are critically related.
I ran a 13.1 motor with radical cams burning VP 112 gas (which is a very high grade gas) with AFR reading at around 12.5 WOT this is a tad on the rich side but rich is always safer. At the end of the day you ideally should try to keep your AFR at WOT just south of 13.0 around 12.8. You can run leaner if you want to extract every last bit of power out of a motor but you run the risk of off detonation. Also wide open throttle is not alway the biggest engine killer. You have to be look at partial throttle conditions as well this is the area most people don't look at when tuning a motor it also happens to be where a motor can be under signifcant load and suspect to dentonation.
This is the area that was the cause of melted pistions in my motor. - Beware