MSefi.com read only forum (Jan.15,2018)

Total newb question here.

I'm finally getting ready to properly tune my project (tired of not having any real power thanks to my laughable first "tuning" efforts), but I have no idea where to start with my AFR table. I've got the cruising area of the table pretty well sorted, but it's the upper end that I'm stuck on. The manuals say to use ~13.0 at peak torque and ~12.5:1 at peak hp.

I've never dyno'd this engine (even if I had ready access to a dyno, I'm not going to get accurate results without a decent tune to start with) and it's been pretty heavily modified from stock, so it's effectively unique. How on earth do I figure out where peak torque and horsepower are?

Thanks guys.

With a sufficiently rich mixture, i.e. one that consumes all available oxygen:

Torque is proportional (relatively) to the air mass ingested per cycle.

Stated differently, but equivalent:

Power is proportional (relatively) to the mass air flow rate.

Knowing the fuel flow rate (duty cycle), and the air/fuel ratio (wideband sensor), the mass air flow rate can be determined.

Get a datalog of a WOT pull, and stick the above values into Excel. You should be able to generate a power curve.

Note that you won't get an actual power curve from this method - but the chart you make in Excel is going to be a scalar multiple of the actual power curve (more or less), so it's still useful to determine at which RPM the peak torque and power are located.

Remember that power is the product of speed and torque.

Those AFR setting guidelines are just that, guidelines. Every engine is a little different in what it wants for AFR to create maximum HP/Torque. The difference between 12.5:1 and 13:1 is fairly small and I would bet that the dyno won't show much of a difference either. If this is a NA engine set the WOT AFR for 12.5:1 across the top and tune the VE table to that. Then when you get the VE table dialed in you can try adjusting the AFR at WOT to see is you get more torque/HP or not. If it's a turbo motor then you might start richer for safety, maybe 11:1.


C|

Thanks guys. Should have it dialed in after a few more driving sessions.