AFR relation to RPM and load?

[zapp168]

Does an engine require a richer mix to run at higher RPM's under light loads? For example, lets say I was driving in first gear and just cruising at 6000 RPM, would I still want to see 14.7 or does the higher RPM require a richer mix?
Thanks

[Supercharged111]

It's my understanding that the load requires a richer AFR to stave off detonation. Low manifold pressures ultimately yield a lower dynamic compression ratio, thereby requiring more timing and allowing for a leaner mixture. Now there may be something I don't know, perhaps it's beneficial to keep it rich across the board up top so there's less of a transition in AFR's? Don't see why that'd matter, that's what the pumpshot's for, but I'm sure someone smarter will chime in to straighten me out.

[zapp168]

The question actually stems from auto VE tuning. If you turn off all (most) of the modifiers to tune the VE table, do you just want it richer at the top regardless?

[mr.prick]

98 WS6, M6, 02 PCM, CO3, SD 2 Bar tune, 416 D1SC Procharger, 60# Injectors, Patriot Lq9 heads, 232 int 240 exh. Lift .595 int .608 exh 115.. header, Intake, AEM WB.

Do you want to be lean at 6000rpm at any MAP kPa?

[Supercharged111]

The question actually stems from auto VE tuning. If you turn off all (most) of the modifiers to tune the VE table, do you just want it richer at the top regardless?

See that's screwing me up too, the tutorial says to set PE mode to 14.63:1. I'm thinking of leaving PE mode at a flat 12.5 and then create a filter in the map that differentiates by throttle position between PE and non PE conditions.


Do you want to be lean at 6000rpm at any MAP kPa?

That's just it, does it matter that you're lean if there's no load? If you cruise at 2500RPM's it's cool to be stoich or leaner, so what makes that different up top? No load = no need for the fuel, right?

[mr.prick]

Lean AFR = higher cylinder temps
PE is your friend at high RPM no matter the load, especially in a road race situation.
Decel maybe a different story.

Check out my engine load PID (http://forum.efilive.com/showthread.php?t=10442) idea.

[poolshark021]

I've been thinking alot about this recently. What is the point of setting PE to 14.63 for AutoVE? Wouldn't the pcm command whatever is in the PE table during PE events and therefore the resulting afr could still be compared to actual afr to get a ben factor? Is there something else that could throw off the commanded afr during PE? If so how does setting the table to 14.63 stop that from happening?

[zapp168]

Do you want to be lean at 6000rpm at any MAP kPa?

Sir, I rarely need to reach 6000 RPM :grin:......
I just want to be more smarter:doh2:
Is 14.7 really lean at 6000 rpm if you are cruising? If you want 14.7 cruising at 2500 rpm, do you really need 12.5 cruising at 6000....?
I personally would get ill trying to set the VE table hanging my car at 6000 RPM. GM has the money to find those numbers..I don't LOL. PE table is safer. Yes lean = higher cylinder temps, but here we are again.....What is lean?

[joecar]

If the motor is not under load then it a richer AFR is not needed...

So, what is "load"...?

At high RPM low MAP (I don't know how you achieve this), the load would consist of:
- pumping/compression losses,
- ring friction on the cylinder walls (increases with piston velocity),
- rotating friction at all the oil/bearing interfaces (increases with angular velocity),
- crank and piston bottom windage (increase with speed squared),
- oil pump resistance (increases with pump speed),
- drivetrain friction (increases with vehicle velocity),
- aerodynamic drag (increases with vehicle velocity squared)("cruising" at 160 mph),
- other stuff (tire resistance).

As rpm increases, those load components increase to significant levels, so the "load" on the motor is not the same as when "cruising" at 60 mph...

so my guess is that in this case the AFR has to be richer than stoichiometric by some amount (my guess would be something like 13.7).

[Supercharged111]

The increased frictional loads you mentioned are up to the oil, not the AFR to cool. I can see these things increasing the MAP, at which point you'd need a richer AFR anyway.