AirFuelRatio question
11-25-2008, 01:05 PM
#1
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AirFuelRatio question Just wondering what your guys' afr's are at in upper boost. Mine are about 11.5 up in the 4000 range, 12.0 around 5000, and the only spot of concern is 12.7 at 6300. Its a little lean I know but just wondering if you guys think its too lean and I need to add some more fuel to get it down in the 12.0 range?
Reason I ask is when we did add more fuel, we also seemed to lose power. About 20 hp to be exact.
Reason I ask is when we did add more fuel, we also seemed to lose power. About 20 hp to be exact.
11-25-2008, 03:07 PM
#4
You didn't mention octane or if you are running alc or meth injection.
Most fi guys like to be more like 11.0 to maybe 11.5. 12.0 mabye with alc injection/meth would be ok leaner than 12.0 don't think a very good thing. Are you out of pump or injector?
Most fi guys like to be more like 11.0 to maybe 11.5. 12.0 mabye with alc injection/meth would be ok leaner than 12.0 don't think a very good thing. Are you out of pump or injector?
11-25-2008, 03:30 PM
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Well it sounds like I will be back on the dyno soon to tune it and get it down in the mid 11s range. We were shooting for around 11.5 but got really good numbers with this tune and I wasn't sure how much 1 point of AFR would matter. Duty cycle is around 75% and theres still plenty of pump. It was ran on 94 octane street gas.
Oh and I havent hooked the meth kit up yet, but I have one. The 12.7 was without meth and in reality we only saw that high number on one of the runs, it was usually about 12.5 above 6000 rpms. The AFR #s came from the dyno itself and not my wideband.
Oh and I havent hooked the meth kit up yet, but I have one. The 12.7 was without meth and in reality we only saw that high number on one of the runs, it was usually about 12.5 above 6000 rpms. The AFR #s came from the dyno itself and not my wideband.
11-25-2008, 03:40 PM
#6
Gaining 20hp is not really worth it for the risk. A pound more boost but safer afr or a big more timing can easily make more than that. Lots of guys seem to run split like 11.5 to peak torque and 12.0 to peak hp.Not sure why guys don't run more like 12.8 till the turbo starts spooling also.
Course with speed density you can tune for on boost and off much easier than maf tuning.
Course with speed density you can tune for on boost and off much easier than maf tuning.
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11-25-2008, 07:42 PM
#8
Just wondering what your guys' afr's are at in upper boost. Mine are about 11.5 up in the 4000 range, 12.0 around 5000, and the only spot of concern is 12.7 at 6300. Its a little lean I know but just wondering if you guys think its too lean and I need to add some more fuel to get it down in the 12.0 range?
Reason I ask is when we did add more fuel, we also seemed to lose power. About 20 hp to be exact.
Reason I ask is when we did add more fuel, we also seemed to lose power. About 20 hp to be exact.
11-25-2008, 08:17 PM
#9
12.7 and you will pop a head gasket or pound the bearings out of the motor.
Doug
11-25-2008, 11:42 PM
#10
Yep, I'd tune for min 11.8 across the board, then add the meth with a target of about 11.0, then start testing adding some timing back in. When I add my meth I am going to run my MSD multi-step retard box so that if the meth ever stops working, the timing gets retarded about 4-6 degrees immediately and a light goes on. You never want your AFR to be unsafe if the meth fails.
This is all on-boost advice. For off-boost, low throttle cruise, I've got mine tuned to run closed loop at like an AFR of 15.5:1 with timing up in the 42-44 range. It's letting me squeeze and extra 3-4mpg out of it safely, which helps even with gas at $2.25, never mind $4.79!
Jim
This is all on-boost advice. For off-boost, low throttle cruise, I've got mine tuned to run closed loop at like an AFR of 15.5:1 with timing up in the 42-44 range. It's letting me squeeze and extra 3-4mpg out of it safely, which helps even with gas at $2.25, never mind $4.79!
Jim
11-25-2008, 11:58 PM
#11
I don't know if this option is only available with speed density but you can retard your timing based on intake air temps instead of buying an expensive MSD box. You can have the timing retard say 1*for every 10* of intake air temp added. If your meth fails and IAT's go up 50*, it retards 5*.
11-26-2008, 12:03 AM
#12
94 Green, no offense but if you're tuner doesn't know that almost 13:1 a/f is bad on a turbo car, he shouldn't be touching your car. He should know what kind of timing and air/fuel to run throughout your powerband. He can tear up all kinds of **** and you not even know it right away. You can bandaid a lot of tables and metrics in a tune and it run for a while then one day you change your oil and it looks like someone poured gold glitter in your engine or your rod punch a hole in the side of the block.
And if you have a meth kit, why don't you add it now vs. tuning a second time without meth and then a third time with it? That makes no sense unless you have a friend tuning for free or cheap or you're just ballin' like that.
And if you have a meth kit, why don't you add it now vs. tuning a second time without meth and then a third time with it? That makes no sense unless you have a friend tuning for free or cheap or you're just ballin' like that.
11-26-2008, 09:24 PM
#13
I don't know if this option is only available with speed density but you can retard your timing based on intake air temps instead of buying an expensive MSD box. You can have the timing retard say 1*for every 10* of intake air temp added. If your meth fails and IAT's go up 50*, it retards 5*.
11-26-2008, 11:55 PM
#15
I don't know if this option is only available with speed density but you can retard your timing based on intake air temps instead of buying an expensive MSD box. You can have the timing retard say 1*for every 10* of intake air temp added. If your meth fails and IAT's go up 50*, it retards 5*.
That's a good idea. My Holley 950 Pro will allow tweaking like that, but I never thought of changing the settings to use it as an alky-problem safety net.
Thanks,
Jim