Well it's about 30-40 degrees colder in Florida this morning than it was when I got my Vortech S/C tuned in South Carolina a few months ago.

I've read posts on my350z.com about ECU stabilization upgrades and wondered how it would apply to our rather drastic temperature swings so I waited for a morning like today with some nervousness. On the way into work the temp gauge pegged 51 degrees the whole way and I thought I'd do a little experimenting. I carefully and curiously decided to take a gander at the a/f gauge to see what types of deltas I would see from 3000rpms to near redline (under WOT) and I was a little surprised at what I saw.

Previously I would hit a/f #'s in the 11.2-10.6 range at WOT in 3rd gear and now I'm seeing 11.6-11.2 with a slight dip right into the 11.0-10.8 right at redline.

The odd thing is that the numbers are staying right around 11.4 pretty consistantly (with a few flashes of 11.6 and 11.2 scattered around) from 3k to about 6k rpms and the numbers used to be quite a bit lower. It was very common for me to see 10.X after 4500 rpms and now I'm about 0.5 a/f higher.

I don't think this is a big deal, but am more concerned as to what's going to happen when the temps hit the low 30's or high 20's. Does anyone on here have this upgrade and can they explain how it works? If I get the ECU stabilization upgrade would I need to get a retune? TIA

Also, guys who were running mid to high 11's before (g8tor20 and turbomaxima are two that I know of...) be careful and keep an eye on those gauges. Guys w/o gauges also be careful. If you were in the high 11's before you could be nearing mid 12's and that might not be exactly what you want.

 

So, it means you are running lean? What can happen if you a/f is too high?

 

Boom... simply put.

 

High A/F means too much air, hence lean, correct? If more air, why boom? Wouldn't all the fuel burn off more quickly?

Sorry, I am a noob at FI, I know.

 

You need more fuel to prevent detonation. People lean out A/F ratio to make more power, as you dump fuel that can cause loss of power or make less power.

 

Neff,

Did you email your concern to your/our tuner and see what they say?

It was about 50 degrees yesterday.....so I'm good to go!

 

it's sorta unrelated, and i hope neffster doesn't mind, but what happens when one goes too rich on the A/F?

And can someone elaborate a little more on running "lean" A/F?

 

If you go more rich than 9.0(or there abouts) you risk washing through the piston rings and getting fuel in the bottom of the block. This gas will go straight to the rod bearings and trash them in short order. As far as running lean just remember that under load the engine gets so hot that under compression it can actually ignite the gas itself with no spark. These irratic flame fronts hitting each other is what we know as detonation. Their is also a related condition called pre-ignition that occurs only because of the heat in the cylinder and can push the piston in the opposite direction that it is trying to go but we won't worry about that right now. Because gas engines burn most efficiently at 1:14.7 fuel to air molecules this also makes it the point that it is easiest to ignite(see detonation). Having a lower AF ratio helps the engine ignite the fuel at the point intended(by the spark plug). Different tuners have different theories on how to tune fuel and ignition but it is safe to say that in an FI application somewhere between 11.0 and 12.0 is the best AF under boost for pump gas. Leaner than that and you could have detonation. Hope I helped.

 

thanks so much djniknala.

 

Well.....I'm liking this cooler air!

This morning as I WAXED a guy in a 2nd gen M3......

My Zeitronix logged 8.3 lbs of boost and AF of 10.5.

 

At 38 degrees this morning I hit 10psi!! This car is even more of a monster! GRD says I'm still safe, I'll cross my fingers.

 

So does that mean that the AF for every gear should be between the 11-12 mark? So over 12 would be too lean and under 10 would be too rich? And this is only at WOT that we should be worried about right? So what about under normal driving conditions?

 

at normal driving (not boosting) i've noticed a/f to be in the 14's.

 

this is more consistant with colder air...you tend to run rich in colder air than lean...this is why it is rec to have your car tuned for safety during heated conditions so as the air cools down, you'll richen up...what you're seeing Neff is uncommon based on my knowledge of this...try resetting your ECU for 12 hours and driving the car aggressively and see if your result is the same...

 

Neff,

I had the same thing happend today. I usually run 10:1 at wot and today ran 12.6:1 each time and never hit 10.~:1 or 11.