I was checking my afrs yesterday with a wideband up the tail pipe, and in the peak boost area I'm running approx 13.2 ( which I know is too lean) - (99ron fuel).

I will sort this out asap but I'm just wondering what are the dangers of running lean?

is it just knock and raised egt's?

Cheers

 

That reading won't be too accurate. The AFR you are seeing could actually be delayed from spool time. Also, there could be up to about 1pt difference in AFR by reading it in the tail pipe as opposed to closer to the downpipe. If you were actually at that AFR, you'd probably be detonating audibly.

 

be ready for a wide variation and strongly viewed opinions.

Knock is the big reason. But technically your best power area for afr is around 12.5.
Gasoline is NOT an effective means of cooling the cylinders. But I guess you could say every little bit helps, thus people / mitsubishi run richer afr.

Oddly the hottest afr region is right at 14.7 (we are talking gasoline stoich) and either side is cooler.

To answer your question, unless you have a pretty special set up, wot 12.5 or lower would be a better place to start. There are a few tuners that tune in that area, I use it with water injection, but nearly everyone runs in the mid to low elevens.

At any rate 13.. is to high without water injection. To run that high the timing would need to be pretty low, that is where you will run into hotter exhaust temps. Its the late timing rather than the high afr.

To keep both within reason one tries to get the most timing they can get while having the afr as low as they can. (at least that is what I do.)

 

does the car have a cat?

 

cheers guys,

there is no cat on the car,

I know the afr will read a bit lean at lesser revs but I'm sure its accurate at higher revs (I'm using the innovate tail clamp)

I don't think that there is much delay in it either as I am picking up 2-3 counts of knock in the same cells.

.....so is det/knock my only real worry?

 

just speaking to a friend who has the same ecu and same ralliart map and was saying his was similar to mine fuelling wise untill he upped the boost level to approx 21psi. - then it was quite good.

mine is currently running 15psi

the ralliart map is a generic map which is mapped for approx (upto) 23psi

so I think I may try upping the boost first to see what happens.

(don't understand why this would be the case but will give it a little tweak to see.)

 

Not true. With a good wideband and good tailpipe connection the AFR's are very close from a wideband installed in downpipe and the tailpipe. With a test pipe I've seen about the exact same AFR between the two on spool through the midrange and about .2 difference after 6500. Of course this depends on the exhaust and muffler design as well. I've tested this on a bunch of Evos with widebands installed in the downpipe. With a good HFC, I see about a .2 different on spool, .1-.2 in midrange and .3-.4 up top.

Now, at idle the tailpipe sniffer will be off as there just isn't enough exhaust flow for accurate readings.

I keep seeing people say full 1pt differences between the downpipe and tailpipe but I have failed to see this on a ton of cars that have been on our dyno. The key to this is having a 100% sealed exhaust system of course.

We use the innovate clamp and and sniffer, http://www.innovatemotorsports.com/x...cat=250&page=2

 

if you are seeing 13 afr during spool up that would be understandable, and once you get to full spool get a richer afr that would a normal.

now you may not want that, it is a function in the ecu and can be altered.

 

I've seen some large differences on our dyno. I'm just saying that I wouldn't 100% trust readings taken at the tailpipe.

 

thanks, thats the tail pipe clamp that I'm using.

you've just backed up my confidence in the readings

.....why do you think the readings are more 'out' higher in the rpm? I would have thought it would be the other way round?

cheers
Mark.

 

+1, Razor, we use the same innovative clamp with our LM-1, I've never seen it read that lean at WOT unless the clamp was installed wrong, exhaust leak, etc. I'm even able to get decent idle AFR readings as long as the exhaust outlet is not too big.