A/F ratio question

[gchronis]

I understand the Ford tune for the 03 Cobra is lean before 3500 RPM and pig rich after that. Custom tuners are trying to get as close to 11.7 or so as possible throughout the RPM range. Too lean is not good for the engine, too rich wastes gas and does not yield optimum performance, though it can't hurt anything. Am I correct till here?

Now, if the stock tune is considered safe, how's that safe if it's like 14 at 1500 RPM? You only don't want to be too lean after a certain number of RPM? If so, why? And what is that magic number above which you are hurting the engine if you are not below 11.7?

Thanks!

 

[capnkirk52]

i heard 12.5 on a blower car??? 11.7 seems rich to me

 

[03gobluecobra]

I have heard that these cars will actually make more hp as you go from 12.5 to like 11.7.

 

[j card]

An AFR of 14 is considered safe at 1500 RPM because there isn't a whole lot of stress on the motor at that point - plus you probably don't have full boost either.

I think some of these guys are getting carried away with the fuel as a band-aid. The "safe" AFR numbers keep getting lower and lower depending on who you ask. Personally, I think if you have to go any lower than 12, then you're probably trying to fix a problem that lies somewhere else - like timing or cooling.

 

[gchronis]

Ok, well, whatever the value is. 11.7, 12, 12.5, it doesn't matter. What I want to know is how come the stock tune is safe at 14 around 1500? And when I refer to magic number, I mean the RPM number above which you are hurting the engine if you are too lean, because apparently it doesn't matter if you are too lean at low RPM. I fon't understand why you can be so lean at low RPM either. Isn't that bad to be so lean even at low RPM?

 

[Chonger]

My AF is a flat 13:1 till about almost 3,500 RPM's. Then it drops like a hammer into the high 11's. I would not worry too much about the AF ratio at the lower RPM range. I never go WOT under 3,000 RPM's anyways. What happens when you make a WOT run? You take it to redline and shift gears. During a WOT run the car never drops below 4,000 RPM's. In my case if I do go WOT at a lower RPM range it is only in that 13:1 ratio for a second at most.

People don't go WOT at 1,500 RPM's. Try that with a pully'd car in 1st gear and you won't go anywhere. If you do go WOT at 1,500 RPM's in a high gear you are asking for trouble no matter what the AF ratio is.

 

[gchronis]

Ok, got it. Sometimes I find myself in 3rd and hitting it around 3K. Guess that's not good. Chonger, what you said makes sense, though. Thanks a lot.