Good target AFR for slow acceleration

vrracing · 08-05-2012, 08:08 PM

We spent most of our time tuning for WOT but the car isn't smooth when slowly accelerating as it bucks a bit. Here is a Zeitronix log from the left marker to the right marker its about 7 seconds.

The rows are:

AFR
RPM
Vacuum
% of WoT
Narrow Band TPS in volts

You can see the closed loop mode until the second marker at which point I accelerated from 3000 to 5000 rpm. You can't see it from the charts but it didnt accelerate smoothly.

The AFR rose a little from closed loop from 14.7 to a bit less than 15. Seems like the AFRs should richen up, right?

Thanks

Zak Rabbit · 08-28-2012, 06:37 PM

You'll always get a lean spot on tip-in, what are you using to tune? Also, what method are you using?

88turboii · 08-28-2012, 07:04 PM

in open-loop vacuum, i usually tune to mid 13's AFR and it makes for pretty smooth acceleration, with quite a bit more power than if you kept it at stoich. it makes it feel a lot more torquey and responsive during acceleration. if you keep it lean, it will feel sluggish, imo. I have it come out of closed loop at 25% throttle

vrracing · 08-29-2012, 08:26 AM

Monday night we were going to fatten it up a bit at low load but first we wanted to reset the idle. So we set the ISC and disconnected the BAC, used the idle linkage stop to get the idle to around 775rpm and brought the TPS back to 1v (it was at 1.12 well within spec). Disconnected the ISC and plugged in the. BAC and were happy to see the rpms jump 200 or so when the a/c was turned on.

Then we went out to fatten it up (RTek2 for S5Tii and Zeitronix w/b) and it didnt need it; the transition out of closed loop was fine. The engine will still die if the a/c is on and he lets of the throttle suddenly from 3krpms or so but doesnt if the rpms are around 2k; which suggests we need to crank down on the dashpot (brand new as a couple of years ago).

Thanks for the tips.

08-05-2012, 08:08 PM	#1
vrracing Rotating Assembly Join Date: Oct 2008 Location: TX Posts: 102 Rep Power: 17	Good target AFR for slow acceleration We spent most of our time tuning for WOT but the car isn't smooth when slowly accelerating as it bucks a bit. Here is a Zeitronix log from the left marker to the right marker its about 7 seconds. The rows are: AFR RPM Vacuum % of WoT Narrow Band TPS in volts You can see the closed loop mode until the second marker at which point I accelerated from 3000 to 5000 rpm. You can't see it from the charts but it didnt accelerate smoothly. The AFR rose a little from closed loop from 14.7 to a bit less than 15. Seems like the AFRs should richen up, right? Thanks __________________ 90 S5 Vert. JDM Tii with BNR Stage1 turbo. Pineapple Racing street port. Bonez cat-forward. Corksport cat-back with Vibrant UltraQuiet resonator. RTek 2 wZeitronix w/b. HKS EBC. Vis CF Tii hood. 3000GT wing. Ground Control coilover kit with KYB AGX shocks. Red and Black leather RX8 seats. Corksport Odura lip & bumper caps, OEM Tii skirts

08-28-2012, 07:04 PM	#3
88turboii destroy, rebuild, repeat Join Date: Feb 2008 Location: Charleston, SC Posts: 395 Rep Power: 18	in open-loop vacuum, i usually tune to mid 13's AFR and it makes for pretty smooth acceleration, with quite a bit more power than if you kept it at stoich. it makes it feel a lot more torquey and responsive during acceleration. if you keep it lean, it will feel sluggish, imo. I have it come out of closed loop at 25% throttle Last edited by 88turboii; 08-28-2012 at 07:09 PM.

08-29-2012, 08:26 AM	#4
vrracing Rotating Assembly Join Date: Oct 2008 Location: TX Posts: 102 Rep Power: 17	Monday night we were going to fatten it up a bit at low load but first we wanted to reset the idle. So we set the ISC and disconnected the BAC, used the idle linkage stop to get the idle to around 775rpm and brought the TPS back to 1v (it was at 1.12 well within spec). Disconnected the ISC and plugged in the. BAC and were happy to see the rpms jump 200 or so when the a/c was turned on. Then we went out to fatten it up (RTek2 for S5Tii and Zeitronix w/b) and it didnt need it; the transition out of closed loop was fine. The engine will still die if the a/c is on and he lets of the throttle suddenly from 3krpms or so but doesnt if the rpms are around 2k; which suggests we need to crank down on the dashpot (brand new as a couple of years ago). Thanks for the tips. __________________ 90 S5 Vert. JDM Tii with BNR Stage1 turbo. Pineapple Racing street port. Bonez cat-forward. Corksport cat-back with Vibrant UltraQuiet resonator. RTek 2 wZeitronix w/b. HKS EBC. Vis CF Tii hood. 3000GT wing. Ground Control coilover kit with KYB AGX shocks. Red and Black leather RX8 seats. Corksport Odura lip & bumper caps, OEM Tii skirts

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08-28-2012, 06:37 PM	#2
Zak Rabbit The Newbie Join Date: Aug 2012 Location: Orange, CA Posts: 2 Rep Power: 0	You'll always get a lean spot on tip-in, what are you using to tune? Also, what method are you using?