AFR's why tune so rich??

[Rhyno]

Hey Worldwalker,

As far as I understand the BEST way is to measure AFR with an individual Wideband 02 sensor, installed in EACH exhaust primary pipe; that is one per cylinder about 2 foot down from the cylinder's. In a real world situation this is quite an elaborate and expensives set up, and I imagine most tuners wouldn't be able to tune it.

So the best normal way is just one wideband where your exhaust mani joins up to the tail pipe.

When I was learning the basics I found this very useful, very infomative video's with graphs. Should answer all your questions

Innovate Videos :: Engine Tuning Resources

Its worth making a cup of coffee before clicking through, they go for a few minutes.

In particular this video: sniffer

And this one was pretty good too: Innovate

Hope this helps!!!

[worldwalker]

Great thats the info I was looking for. I've spent the weekend on google and all I can find are a lot of people trying to sell me stuff and a lot of contradictory "evidence".

[boxh34d]

OST
I'm not sure on specifically head porting, but from what I've seen, and my tuner has said the same thing, the more efficient an engine is at actually getting a complete burn, the less timing that it needs to make power. Greater efficiency = less time to do the same job. I imagine this is true with getting complete evacuation of exhaust gas etc in your porting case.
The theory can sometimes be a false economy though. Ie, I was mucking around in the shop when he did some back to back testing of a turboed engine before and after fitting a thicker headgasket to drop the compression from 9.8 to around 9.3:1 (IIRC). Although in (really really simple) theory the high comp engine should have been more efficient at a given boost pressure, the act of lowering compression (without raising boost) and dialling in more timing actually made more power everywhere, and was a lot less critical of AFRs in peak torque. With then running leaner in the period prior to peak torque, which was not possible before pinging with the high comp, even more bottom end power was made.
The fact that he did this without a second thought suggests he has seen it plenty of times before.