[TitaniumTT]

Originally Posted by Rotary Evolution

take his suggestion with a grain of salt, every car reacts differently to different AFRs and 16AFR cruising on most 2nd gens simply wont happen because the car will want to fall on its face to even keep up with itself, perhaps he runs a smog pump which skews his figures up or runs an AEM with a crappy bosch wideband sensor which also seems to have figures a bit off..

Few other things matter as well I've noticed. Exhaust, intake, and plugs will all slightly effect how the engine reacts. I've not noticed a huge ramp up between .85L to 1.05L... in fact, aside from the engine sensors, you really couldn't tell engine was running any differently.

Originally Posted by Rotary Evolution

at any rate, lean the AFRs out as much as you can first while cruising that can maintain speed while having a steady foot on level ground. then advance timing up to about 45 degrees of advance with a 8 degree split. you don't need wideband figures at all, the engine will tell you where it wants to be because it will begin to lose power if you push the AFRs too far on the lean side, on the rich side the engine will not hate you so much before it starts losing power. when leaning out AFRs there is a radical ramp you will reach when the engine doesn't like what you're feeding it.

Originally Posted by RETed

First, if we're going to assume the AFR #'s are off, then why even bother mentioned #'s at all?

Second, I've run a 13BT past 16.0, and it did not "want to fall on its face".
This was at 4kRPM+ and EGT's were creeping past 1,000C or over 2,000F.
The engine will push ultra lean mixtures like that but EGT's are just too hot to be comfortable.
There was no hint of lean surge - see below - and the car kept running with no hiccups.
Granted, we were cruising at a spritely speed of over 100mph on the expressway...



Those in the industry call this "lean surge".
I guess you can call it "lose power", but it's more like a hesitation.
It's more likely an ignition misfire, cause you don't have a coherent burn inside the engine.


-Ted

Psh, if only I could be at 4k rolling down the highway I was at 4k around 80-85....

Anywho, like Ted said, I really wouldn't tune a car like that (ignoring sensors) for the reasons that Ted mentioned. Granted my EGT's were up there (1700 at cruise) to begin with but I woudn't blindly tune by just cruising down the highway waiting for lean surge to happen without monitoring EGT's.

For what it's worth, advancing the timing will allow you to run leaner, and it'll bring the EGT's down as well.

Like just about anything related to tuning an engine, there is a sweet spot withen the cruise to keep the EGT's down, and I feel that it's rather difficult to find it running blind