articfriends

iTrader: (1)

I do know on mefi 3 stuff i tuned w 502 mpi i closed up the afr gap even though you cant tweak individual cyl fiel trims by double firing the injectors vs once per 4 cycle revolution

Gimme Fuel

I was surprised to see that a dual plane manifold was just as imbalanced. I was going to suggest you try one until I read that you did. Those are some absolutely horrible AFR imbalances! Is Norm scratching his head too?

Has anyone tried a old school dual quad low-rise manifold on the dyno to see if that evens out the AFR? Would be interesting to compare that to tunnel ram results.

AllDodge

iTrader: (1)

I was thinking mine my be running a little fat (seeing black soot build up on tips), but after reading this I may be in the "safer" place

SS496

Given your knowledge Im sure you have thought of this....but I will say it anyway just in case.

Are you SURE the lean readings are from a lack of fuel to that cylinder.....are you SURE it isnt a misfire causing a false lean condition?

EDIT: looking at the graphs all the transitions appear smooth....usually false leans (from misfires) show up as erratic jumps...however I do not know what type of data conditioning that DAQ is using.

Do the plug readings per cylinder correlate with your wideband readings per cylinder?
Have you switched the widebands around to different cylinders?

Im not saying you dont have an imbalance issue...im simply encouraging you to double check so you dont chase your tail if you dont.....

articfriends

iTrader: (1)

Ron, we put so.much fuel into it w performer to try to get #3's afrs below 14 at wot that we drove #2s afrs below 10.5 to point where bsfc was in the .62 range and #2 was breaking up. We thought the vic jr was bad, the performer was worse, we gained 20-30 ft lbs tq sub 4600 but none of that matters if you have a cylinder thats 15-1 to get rich cylinders to run.

Gimme Fuel

Well this would explain why Mother Merc's setups are so pig rich! Trying to keep it together through the warranty!

What was the AFR spread when you dynoed the MPI intake with even length runners?

articfriends

iTrader: (1)

Ss496, yes, i swapped 02 sensors, free air calibrated them etc. Plug in #8 when we started out looked mightly lean and lean cylinders moved when we swapped to dual plane. These uneven afrs are nothing new, just most dynos dont read individual cylinders. The real question is, how lean can these hot cylinders really be because you cant add fuel to point the rich cylinders wash rings and foul plugs. In past, before the 8 02 setup,we always used tailpipe readings. Like shown with yhe averaged numbers, you could easily see 12.5 and have cylinders in 10s, low 11s and cylinders in 14's but when you add all 4 up, divide by 4 you have a number we all feel is "safe". How many people have torched # 7 or 8 w open plenum intakes and thought it was "bad gas"?
i would love to dyno a bone stock, good running carbed hp 500 and see what THOSE numbers look like, im confident its real similar!

articfriends

iTrader: (1)

Ron, i remember seeing afr spreads of +2 leanest to rich, certain ones started out lean, others rich, matched up somewhat in 4000 to 4800 range THEN flip flopped, rich went lean, lean went rich from there up. Blamed ecus, harnesses, swapped a million things around. When i configured the mefi ecu to double fire the injectors (once per revilutuin vs once per 4 cycle revolution) it got much better. I had to increase the pw accordingly because of having 2 sets of dead bands vs 1, ie, pw is 10 ms, 1 ms of dead band/latency, you have 9 ms of actual flow, fire injector twice f0r 5 ms, now you have 2 ms of dead band w 8 ms of flow, you change it to a total of 11ms in table to compensate to over simplify it

SS496

This is exactly why I love the megasquirt 3 pro systems with CANegt.....individual cylinder fueling control at different RPM/loads.

Im not knowledgeable in the MEFI systems. However, if they are anything like OEM SFI automotive systems the "factory" calibration corrects for these imbalances per cylinder and the "aftermarket" tuning software do not bother to unlock those features.

The cylinders I would be most concerned about would be in the ~13.7-14.7 areas @ WOT....However, there are some factory calibrations (gasoline trucks) that stay in closed loop/stoich all the time versus entering power enrichment.....but their specific power output is far less.

As with many things...there isnt one answer....it is application specific.....like the undergarmets...it depends....haha

articfriends

iTrader: (1)

Ss496, your giving mercruiser mefi too.much credit, lol, its blind speed density w batch fire, it basically looks at rpms, map and a knock sensor
Its tuned pig rich from mercruiser, for good reason!