Ok, a couple of months back I dynoed my car (205 Hp) and it had a A/F ratio of 13.6 across the board with a nasty spike to 14.5 at 6500 rpms. Mods were testpipe and HKS drop in filter. No VAFCII was employed.

installed invidia cat-back yesterday and went to the dyno. horsepower dropped to 202, but what really concerns me if my A/F ratio: 14.8 -15.3 across the board with a spike of over 16 at 6500 rpm.

I then installed (rather plugged) a VAFCII, and started lowering my A/F ratio to 13.8, but the closer I got to 13.8 the less Hp I made (190 when very close to 13.8)!!!!!

Frustrated, I reset all values to zero and headed home.......

My questions are:

are the above events normal??

Is it possible that the Invidia had such a leaning effect on the A/F mixture??

Am I a victim of heatsoak, since the closer I got to 13.8 the less Hp I made??

Also, VTEC was was set at 5200 as it's where it eliminated the spike /drop in the Hp curve. Is it to low (remember guys its an F22C)??


Any input will be greatly appreciated

 

How are you measuring the AF ratio?

 

I wouldn't be too concerned about 15.3:1 AFR.

 

All measures were taken with a wide-band oxigen sensor. From what ive heard isnt 13.8 as the optimum, when tunning with A VAFCII?
.

 

Where was the 02 installed, before or after the Convertor?

AF readings taken at the exhaust outlet are usually a full point or more leaner than readings taken upstream of the Convertor.

 

I have a testpipe so theres, no converter. I astill insist those readings were very high, and trying to lower the A/F to 13.8 resulted in power loss!!!!!!!!

 

higher AFR should produce high HP numbers to a certain level.

 

Please answer if the measurement location was consistent in the two different dyno sessions.

 

Yes to about 14.7:1... anything over 14:1 is dangerous in my conservative opinion. I tuned my turbo car to 11.2:1 and it was very happy there. I tune my NA Mazda motor to 13:1 at the leanest peak. I'm new to S2000s so I don't know if Honda intended for them to run somewhat lean for maximum power and fuel economy.

You could be losing power adding fuel because your piggy-back computer is fighting against the stock ECU for control. Like I said, I'm new to S2000s but not to cars and engineering in general. You can change one parameter on the VAFC but it could be causing issues with another variable that you didn't touch.

For example... in cars equipped with a MAF (mass airflow sensor) generally piggy-back computer tap into and disrupt the signal flowing back to the ECU. They trick the computer into thinking something is happening that really isn't... like with a flapper door MAF it will tell the computer the door is open farther than it really is (for fuel enrichment). In doing so, the computer also compensates with the ignition timing also since you are now on a different point on the map. So it's possible by adding fuel, you are also retarding timing because the ECU thinks it's under more load than it really is and thus pulls a few degrees of timing to avoid a knock condition.

That's my educated guess.

 

Yes, measurement location was the same!