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AFR vs Power 

 

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 Post subject: AFR vs Power
Posted: Sun Aug 26, 2012 2:23 pm 
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Hey,
Does anyone have some dyno power graphs comparing the power output at different AFR's? preferably for a SOHC engine but it doesnt realy matter. Was wanting to see at what AFR these engines make the best power. Cheers.

 

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 Post subject: Re: AFR vs Power
Posted: Sun Aug 26, 2012 2:36 pm 
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Dunno if this helps much, but it is something.......

 

 

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 Post subject: Re: AFR vs Power
Posted: Sun Aug 26, 2012 5:15 pm 
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shyun wrote:
Hey,
Does anyone have some dyno power graphs comparing the power output at different AFR's? preferably for a SOHC engine but it doesnt realy matter. Was wanting to see at what AFR these engines make the best power. Cheers.


AFR is a reading that tells you that you Air - Fuel ratio is correct, ie not running too rich or too lean.
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 Post subject: Re: AFR vs Power
Posted: Sun Aug 26, 2012 6:13 pm 
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SWC wrote:
shyun wrote:
Hey,
Does anyone have some dyno power graphs comparing the power output at different AFR's? preferably for a SOHC engine but it doesnt realy matter. Was wanting to see at what AFR these engines make the best power. Cheers.


AFR is a reading that tells you that you Air - Fuel ratio is correct, ie not running too rich or too lean.


I know what AFR is, i just want some decent numbers/dyno data showing what's the best value for maximum power in these engines, instead of the generic somewhere between 12-14.

 

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 Post subject: Re: AFR vs Power
Posted: Sun Aug 26, 2012 7:35 pm 
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usually max power is made around 12-12.5 afr
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 Post subject: Re: AFR vs Power
Posted: Mon Sep 03, 2012 10:56 am 
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The books and manuals I have for EFI tuning consistently say that best power is achieved at 12.5-13.1 AFR for naturally aspirated engine. Any leaner and you risk damage from pinging/detonation. Any richer and you are just wasting fuel. Though it is far preferable to waste a little fuel than it is to burn your pistons.

A more central spark plug does best at the leaner end of the range - the "hemi" SOHC is pretty good on this score. Batch fire injection likes the richer end, sequential injection likes the leaner end - I think up to EL is batch, AU onward is sequential (stand to be corrected). Max cylinder pressure is reached at peak torque (prob 3000-3500 rpm) so this is where it needs to be on the rich side (say 12.5), but AFR can increase with revs above that (to about 13.1). Aluminium heads (like the Falcon) like it a bit leaner and cast iron heads like it a shade richer. A sequential-injected 4-valve-per-cylinder DOHC alloy-head engine might do peak power as high as 13.5 AFR.

Most engines are not very sensitive to AFR and anything in the range of 11.5-13.5 will make little difference to power, as long as it is not detonating. See the video titled "Ignition Timing vs Air Fuel Ratio" at http://www.haltech.com/index.php/suppor ... cal-videos for a comparison of dyno runs at various AFRs (and ignition timings). Power is defintiely more sensitive to ignition timing than it is to AFR. If the engine is pinging, it is losing power (and doing damage); running richer will make more power as the extra fuel cools the charge and supresses the detonation.

The above is all about power at wide open throttle. Idle, part throttle, and overrun are another story completely. Hope this helps.

 

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 Post subject: Re: AFR vs Power
Posted: Wed Sep 12, 2012 12:49 pm 
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efxr6wagon wrote:
The books and manuals I have for EFI tuning consistently say that best power is achieved at 12.5-13.1 AFR for naturally aspirated engine. Any leaner and you risk damage from pinging/detonation. Any richer and you are just wasting fuel. Though it is far preferable to waste a little fuel than it is to burn your pistons.

A more central spark plug does best at the leaner end of the range - the "hemi" SOHC is pretty good on this score. Batch fire injection likes the richer end, sequential injection likes the leaner end - I think up to EL is batch, AU onward is sequential (stand to be corrected). Max cylinder pressure is reached at peak torque (prob 3000-3500 rpm) so this is where it needs to be on the rich side (say 12.5), but AFR can increase with revs above that (to about 13.1). Aluminium heads (like the Falcon) like it a bit leaner and cast iron heads like it a shade richer. A sequential-injected 4-valve-per-cylinder DOHC alloy-head engine might do peak power as high as 13.5 AFR.

Most engines are not very sensitive to AFR and anything in the range of 11.5-13.5 will make little difference to power, as long as it is not detonating. See the video titled "Ignition Timing vs Air Fuel Ratio" at http://www.haltech.com/index.php/suppor ... cal-videos for a comparison of dyno runs at various AFRs (and ignition timings). Power is defintiely more sensitive to ignition timing than it is to AFR. If the engine is pinging, it is losing power (and doing damage); running richer will make more power as the extra fuel cools the charge and supresses the detonation.

The above is all about power at wide open throttle. Idle, part throttle, and overrun are another story completely. Hope this helps.


Yeah that's good. Suprised it made so little difference on that honda. Pretty sure i've seen dynos of falcons where just changing the AFR made a reasonable difference though. I run my car at 12.7:1 becuase it seems to be the most widely accepted value, but i'm suprised noone has actually tested this on a dyno.

 

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