What are you guy's A/F at idle and cruise
#1
What are you guy's A/F at idle and cruise
Just wondering what you guys run at.
I have GT35R and my idle A/F is around 12.8 and cruise is around 13.5, I believe it's a little rich. I always thought idle should be in the 13's and cruise should be in the mid 14's. From my understanding that's with stock twins and as far a logic allows me it should be the same for a single right?
Feedback greatly appreciated.
M-
I have GT35R and my idle A/F is around 12.8 and cruise is around 13.5, I believe it's a little rich. I always thought idle should be in the 13's and cruise should be in the mid 14's. From my understanding that's with stock twins and as far a logic allows me it should be the same for a single right?
Feedback greatly appreciated.
M-
#2
Rotary Enthusiast
iTrader: (9)
Join Date: Sep 2006
Location: Nashville, TN
Posts: 1,003
Likes: 0
Received 0 Likes
on
0 Posts
I have mine to idle right at 13afr but at cruise its alot leaner. Mine sits at about 15 afr if its at a constant cruise speed. Works perfect, It seems to be able to cruise as lean as high 15's without any problems but 16's and it stutters.
#3
_________________________
iTrader: (3)
My 1/2 bridge idles much smoother in the mid 12s than it does in the 13s. I had it in the 13s for a while, but the idle would become strange at times. It would lose the brap and idle funny. it wasn't missing, it was just odd. I moved it back down in the 12s and it will maintain a very healthy brap that shakes the car.
#6
Rotor Head Extreme
iTrader: (8)
At idle and cruise, your engine is in a vacuum state (which basically mean it's NA). So why would you think either turbo would have an effect on your A/F ratio? If your engine is ported for more overlap, that will have the biggest effect on the accuracy of your A/F ratio reading. More overlap will allow more unburned fuel to exit the exhaust port. Also some don't realize that with more overlap, it's possible to get the impression the engine is running too rich when it really isn't. Think about it!
#7
rotorhead
iTrader: (3)
What kind of porting do you have?
I have found on a couple street ported motors that idle stability really decreases when you go much leaner than 13:1 on the wideband. If you carefully datalog hot starts you will see that the motor will always pull a little less vacuum (putting you in a different cell on the fuel map) and the IAT sensor will heatsoak to a degree (leaning out the mixture).
If you still have your ISC installed you may then experience surging as a result of this. If you don't have it installed, it will just start to idle low and maybe have unpleasant vibration. I aim for a range between 12.5 - 13:1 on these street ported cars (street ported FD and big streetported FC). That way when you hot start it doesn't get too lean (assuming your air temp correction is set up properly to account for heatsoak). You MUST account for hot start situations. It will drift always drift a little lean , unless you just overcompensate for the IAT change and then live with running rich under boost when it's hot out. It becomes a very tricky balancing act if you want a lean, stable idle under all weather conditions. There is a reason why they use O2 sensors on factory ECU's.
My cruising AFR's get leaner as vehicle speed increases. Under about 45-50 it's in the high 14's, and on the highway it's in the high 15's. That's on a streetported FD and a big streetported s4 T2.
I have found on a couple street ported motors that idle stability really decreases when you go much leaner than 13:1 on the wideband. If you carefully datalog hot starts you will see that the motor will always pull a little less vacuum (putting you in a different cell on the fuel map) and the IAT sensor will heatsoak to a degree (leaning out the mixture).
If you still have your ISC installed you may then experience surging as a result of this. If you don't have it installed, it will just start to idle low and maybe have unpleasant vibration. I aim for a range between 12.5 - 13:1 on these street ported cars (street ported FD and big streetported FC). That way when you hot start it doesn't get too lean (assuming your air temp correction is set up properly to account for heatsoak). You MUST account for hot start situations. It will drift always drift a little lean , unless you just overcompensate for the IAT change and then live with running rich under boost when it's hot out. It becomes a very tricky balancing act if you want a lean, stable idle under all weather conditions. There is a reason why they use O2 sensors on factory ECU's.
My cruising AFR's get leaner as vehicle speed increases. Under about 45-50 it's in the high 14's, and on the highway it's in the high 15's. That's on a streetported FD and a big streetported s4 T2.
Trending Topics
#10
Stay tuned...
iTrader: (3)
Join Date: Jul 1997
Location: West Islip, Long Island NY
Posts: 2,917
Likes: 0
Received 1 Like
on
1 Post
Anthony
#12
Will work for horsepower
Now its 4:30 dif and j-spec trannie oh well 21mpg!
#14
Rotary Freak
Join Date: Feb 2001
Location: fort worth, tx, usa
Posts: 1,926
Likes: 0
Received 0 Likes
on
0 Posts
every engine and aftermarket ECU is different on how to set the proper cruise and idle a/f. For example, apexi PFC and Haltech and go pretty close to stoich without and issues. Mircotech and AEM for Rx7 works best at around 13.5-14.0 for cruising. This is on a slightly ported or stock port engine. more aggressive street port and bridge engine require more fuel. I think alot have to do with how the ECU runs the injector phasing and how it stage the injectors. The rpm at which you cruise could vary a/f as well. anything below 2500rpm seemed to run best in the 13.5 a/f range and around 14-15 range at steady state. 13.5 a/f at crusing isn't too bad. You might gain another 3-4mpg by leaning out more but what I find is that the response time may suffer a little on certain injectors no matter how you adjust the throttle pump on the ECU when tuning cruising closer to stoich. The best way to tune cruise a/f is to dyno it on a steady state dyno and find the max hp at the leanest a/f and advance timing. It takes alot of time to do it this way and alot of the facility don't offer a steady state dyno.
Last edited by pluto; 02-05-09 at 04:20 PM.
#15
Eye In The Sky
iTrader: (2)
Join Date: Feb 2001
Location: In A Disfunctional World
Posts: 7,895
Likes: 0
Received 114 Likes
on
66 Posts
Stock intake ports with ported port throats, and mild exhaust porting.
Idle with no load: 12.5
Idle with A/C load: 13.5
Cruise is tuned from 14.5 at about 35mph to 16.5 at 70mph.
20.9mpg at 70 mph with JDM short 5th gear.
The only tuning issue is around 58mph when the secondary TB ports just start to crack open.
It can cause a momentary leaness as primary port air velocity drops. That is tuned 16.
Bad Mazda design between air flow through the ports and when secondary injectors start to work which is about 100mph cruise.
Check it out sometime with a DL if you have a PFC.
Idle with no load: 12.5
Idle with A/C load: 13.5
Cruise is tuned from 14.5 at about 35mph to 16.5 at 70mph.
20.9mpg at 70 mph with JDM short 5th gear.
The only tuning issue is around 58mph when the secondary TB ports just start to crack open.
It can cause a momentary leaness as primary port air velocity drops. That is tuned 16.
Bad Mazda design between air flow through the ports and when secondary injectors start to work which is about 100mph cruise.
Check it out sometime with a DL if you have a PFC.
#16
thanks for all of your responses guys, a lot of useful info in here. So I guess the idea behind the richness is to keep the EGT's low due to the cooling properties of the fuel, thereefore so I won't blow up using this crappy 91 octane that we have here. So the thinking is to start with a lower EGT's before I hit boost.
This is for the time being as once I get my AI there won't any worry about high EGT's at 15 psi with 91.
This is for the time being as once I get my AI there won't any worry about high EGT's at 15 psi with 91.
Last edited by Montego; 02-06-09 at 05:05 PM.
#18
You are correct. But after this thread I questioned my tuner on why so rich, and his reply was "I try to keep the EGT's lower at cruise so when you WOT (whenever that is) the starting temp is lower from the get go". Anyway, thats the logic behind the madness.
Thread
Thread Starter
Forum
Replies
Last Post