I have a 2001 WRX with the usual de-cat exhaust, filter and remap. The AFR is currently 12.1 (made 286bhp on MAHA rollers). The map is being tweaked to sort out some overboost and have the option of adjusting this also.

Was recommended to me that I run an AFR of 12.5 for optimum performance but was told this is dangerously lean... and it's been suggested that I might even want to run a bit richer than the 12.1 it is at currently.

Can someone please give me some guidance on this issue?

Thanks.

Edit: correct AFR's now!

 

I've recently checked my 97MY UK spec with a wideband and got the following AFR's @ 0.9bar....
13.2 @ 3000rpm
12.5 @ 4000rpm
11.6 @ 4500rpm
These are with std ECU, std Intake and DeCat Exh.

How are you reading AFR? Sounds like your sensors screwed since you'll only see 20+ during backouts - ie. fuel-shutoff. If your AFR is really that lean under load and you have'nt pulled all your spark out, it's bye-bye to your engine.

 

It was measured on a rolling road... was just told this by the operator... wasn't using wideband.

 

gotta be a mix up somewhere. If you're in Essex I could dig up my kit and do a check, would have to be weekend though.

 

Appreciate the offer mate - it's going on another set of rollers this weekend so hopefully will be able to shed some more light on things then.

Thanks

 

21 is not an AFR.

you do not want to be leaner than 12:1 really.

Alex

 

Just re-read my first post... I mean't 12.1 not 21... it's been a long day.

Your figures seem to fit now Mark.

 

ok, makes sense now. running 12.5 at max power rpms might be a bit dodge, you should be well rich up at those speeds to help keep your EGT's down, etc. Probably best to play it safe when it comes to squeezing out the last few bhp at the top end.

 

12.5 or 12.1 is quite lean.

You start to lose power onece you drop into the high 10's which is where a standard ECU tends to be near the redline.

To be safe but to still achieve good power, you really nead to be mid 11's.

The 2.5's tend to run a bit leaner i.e in the low to mid 12's but alot of these are also running headers etc... which IIRC can allow you to run a bit leaner

Have you got a copy of the RR plot with AFR on it, that you can post. Saying it's '12.1' is a bit of a genralisation.

 

What boost?

 

If it hasn't been mapped (which the 1st post seemd to indicate), then I would suspect approx 1 bar (maybe slightly less)

 

!!

 

regardless.. 12.1 is too lean unless you are running meth?

 

I'm wondering about the approximate power gains leaning from 10.2:1 AFR to lets say 11.6:1 on a stock scooby.

I'm running quite rich because I cant feel if the car is really making power at lean afrs like 11.6:1 (RR) I know I need to run it on load type dyno but just wanted to know if could notice any power gains.

 

10.2 is very rich, probably sapping power assuming the gauge was accurate

 

Peanuts, it was just an example. I'm running 10.7:1 at 7000rpm, 14 psi and the wideband(zeitronix) is located in the mid pipe.(turboback without cat)

 

I wouldn't expect to see much difference at all in engine output leaning out to the AFR your suggesting and you really need to be monitoring knock and EGTs when testing this.

 

Cruising around 14.0:1 - 14.7:1
0.0 Bar would be around 13.5:1
0.5 bar around 12.5:1
1.0Bar Around 11.8:1
1.5 bar 11.3:1

I think these are the numbers you should see if the car's been remapped.

 

I get
15.0:1 at idle
14.7/9 at cruise
11.7 at 1.0 bar
11.3 at 1.65 bar
all based on an 18g with headers

I run methanol so will be leaning these out a bit tonight