Hey guys,

Just got a dyno graph back with the AFR imposed on it. This dyno was shown to be losing about 40%, which means I'm making about 233Kw at the engine (which is not unrealistic for a mildly modded car, that started out at 206Kw I suppose)

But I'm concerned about the AFR. Isn't 11:1 - 10:1 a bit rich, even for a 1.1bar turbo?

Any comments?

Thanks.

 

That's rich as hell, but totally common on Evos. The ECU dumps fuel to prevent detonation. Use an AFC to get it back up to 12:1 in the upper RPMs and you'll see big power.

 

That's the scary thing... I've got a Air/fuel/Ignition computer in already, and that's supposed to be dyno tuned. Did he do a bad job?

I don't have access to the ECU (locked) but could I theoretically lean it out by increasing the boost levels?

But thanks for your help...

 

I agree you want to be at 12:1 as stated. Question is, did these A/F numbers come from a wideband? Just want to verify that they are accurate.

 

Uuuuhhh, Lost me there already...

Sorry, all I know is that it's the one that's normally fitted to the Dyno Dynamics Dynamometer. (Say that 5 times fast!). If anyone knows whether it's wide band or narrow band, I'd much appreciate it.

I am going to get it retuned on a Dynapack Dynamometer (more accurate) in a few weeks, after a few more mods have been made.

 

It is probably wideband. Most places sell it as wideband O2 tuning on the dyno.

 

So I'd assume it to be accurate... Thanks...

Okay, so back to one of the original questions. Can I lean it out by adding more boost, or will the computer just compensate for that and add yet even more fuel?

 

How much boost are you running now? I think I would lean it out before just adding more boost.

 

First question was this on pump gas. Second is this a stock s2000, cause if so I wouldn't change a think considering the high stock compresion ratios and the fact you are running pump gas. You might actually have to run that rich to keep from detonating. Your chart looks really smooth and I would for see any real gains you would get from leaning it out much more than 10-20hp. But by leaning it out you could risk loosing the motor, not worth it in my opion

 

Doug,

Thanks for your response, but it's actually a Evo VI running on 95RON octane (91 r=m/2) I have a slightly better graph running 98 octane (93) but it doesn't show AFR.

Mayhem, I'm running 1.1 bar boost.

 

You could proably run a bit more boost, but that's not the best way to use up that extra fuel. Do you have a dyno graph with RPM instead on wheel speed? You really need to use that to start pulling fuel with whatever fuel computer is available. If this is tuned, he didn't do a very good job IMHO. 12:1 is widely accepted as a safe A/F ratio on pump gas and you are running better gas than most of us do it on.

 

There are different procedures to enlean the mix. Boost, fuel map, and timing will all have an impact on AFR. Most of the 03 US EVOs I have seen tuned are staying a bit richer than 12:1 just to be safe and to prevent the engine from pulling timing from impending knock from cheap pump gas. If you are tuning to 12:1 using 98 RON make sure you always use that octane.

Not positive about ECU timing and knock sensor function for EVO VI compared to US EVO, but desired AFR should remain the same.

 

Thanks JFH,

I cranked up the boost tonight to 1.2bar (18psi) and it kept hitting the fuel cut defender. Looks like proper tuning is the only way to do it.