2003z

iTrader: (7)

On all of my dynos and on other modded cars my shop has dyno'd the a/f ratio has been right at 14.7:1. On the piggyback ecu thread, the stock was anywhere from 14-16:1.

Question is, why does everyone think this should be pinging, when the perfect a/f ratio for economy is 14.7:1?

From 'How Stuff Works':
A gasoline engine burns gasoline in the presence of oxygen (see How Car Engines Work for complete details). It turns out that there is a particular ratio of air and gasoline that is "perfect," and that ratio is 14.7:1 (different fuels have different perfect ratios -- the ratio depends on the amount of hydrogen and carbon found in a given amount of fuel). If there is less air than this perfect ratio, then there will be fuel left over after combustion. This is called a rich mixture. Rich mixtures are bad because the unburned fuel creates pollution. If there is more air than this perfect ratio, then there is excess oxygen. This is called a lean mixture. A lean mixture tends to produce more nitrogen-oxide pollutants, and, in some cases, it can cause poor performance and even engine damage.



12.5:1 is the desired af for performance, but 15:1 is not excessively high. And for the 1 or 2 folks out there who constantly put down technosquare, we think we have a perfectly reasonable explanation for my 'no gain' dyno's, and its not that their program doesn't work, but won't put that out until its confirmed sometime soon.

SlamMan

Have you tried testing your A/F on another dyno?

If you are getting near 14.7/1 you would be making maximum power with the near perfect burn but also running very hot. This is obviously not good. Tuners usually shoot for 12.5/1 for boosted cars. I would think you could get leaner for an NA car but not in the 14s'

failsafe

Leaning out under hard throttle causes temperatures to rise, which causes lean mixtures to to pre-ignite. The lean mixture leads to increased temps which can lead to detonation.

johnsZ

this is a lean mixture situation with an advanced timing situation or a hot engine, or combination of these situations.
the computers do a pretty good job of keeping this down, along with the sensors read by the computer. Also, with premium fuel it is pretty hard to get this situation, or it might ping one or two cylinders before the computer detects and alters the situation.
Just for fun, and if you have a few extra dollars, find the gas station with the "good stuff"- the purple gas with 101-104 octane, then put the throttle down after the engine is warm- it will start hard, but the computer can go to full advance really quickly without knocking.

j's350z

MY question to all that have had your cars dyno'd and A/F measured??.. Where and how are they measuring your o2 readings? If they are just sticking a probe in the exhaust, then thats as accurate as you smelling the exhaust! To get an accurate o2 reading, you need to weld in an o2 bung pre-cat and use a wide band o2 monitor and measure. I am not sure if my car was running lean before the ecu due to the CAI, but it is possible. Also, the shop that does my tuning has a $8,000 wide band set up, so I would think its pretty accurate. This reply wasn't meant to be harsh in anyway, I just wanted to know how people were reading the A/F ratio's. I don't know many people that took out their manifold or cat pipe to install a o2 bung....

2003z

iTrader: (7)

I have not had a bung installed, (yet???) but my shop uses a Hariba wideband sensor. My shop actually just conducted a wideband sensor shootout for Grassroots magazine, and the Hariba was the best.