Target Afr values
Thread Starter
TECH Apprentice
Joined: Oct 2015
Posts: 310
Likes: 24
Target Afr values So I have been searching for a while and cant find anything on wot target Afr values for stock ls motors.
I have found 14.7 seems to be the norm below wot. Does anyone have target values for 87,93 octane at wot. The settings in the Holley HP for a stock 5.3 are at 12.5 and it runs a little rich. I was wondering if that value should be in the 13 range.
I would love see some fuel tables.
I have found 14.7 seems to be the norm below wot. Does anyone have target values for 87,93 octane at wot. The settings in the Holley HP for a stock 5.3 are at 12.5 and it runs a little rich. I was wondering if that value should be in the 13 range.
I would love see some fuel tables.
A naturally aspirated engine will make good, safe power around 12.8 AFR. It will make more power at 13.x. How lean you feel is necessary is your call as a tuner. For a dedicated track car running excellent fuel and short dragstrip passes, you can probably set it more on the lean side. My advice to you is start at your current 12.5 and slowly lean it out to find best power without melting parts in the combustion chamber.
Thread Starter
TECH Apprentice
Joined: Oct 2015
Posts: 310
Likes: 24
Thanks for the info. Does the fuel you use help with lean conditions? This is a track only build. I threw a stock lm7 in an s10 and built the rest of the truck to handle 900HP. I want to learn the tuning end before adding power adders. Been trying to find a book or a decent tuner to lean on for advise.
The danger with running a lean AFR is heat. Additional fuel from a rich (mid to upper 12s AFR) mixture helps cool the combustion chamber. If you lean it too much and the temperature spikes you will start to melt spark plugs and pistons. Lean AFR and high temperature typically also promote detonation which magnifies the destruction. The type of fuel you use will affect the resistance to detonation. Higher octane will be more resistant. However, the octane for gasoline fuels will not make much difference in the combustion temperature. Now if you switch to E85 or straight methanol it's a different story, as they burn much cooler than gasoline.
ethanol in fuel also wants a richer mix according to some of the more knowledgeable guys on here (ie it might like 12.6 more than 12.8 or leaner if you run pump gas that is up to 10% ethanol)
I typically shoot for around 12.7-12.8 anyway and just get no-E gas when I can. Doesn't seem to make a huge difference either way so I quit stressing about it so much and focus on more important things.
I typically shoot for around 12.7-12.8 anyway and just get no-E gas when I can. Doesn't seem to make a huge difference either way so I quit stressing about it so much and focus on more important things.
