pdexta

What is considered a "safe" AFR for NA cars?

ShocK

Depends on the car IMO. There are a lot of variables.

Safe Air Fuel <14.0:1 anything higher starts melting stuff

thorax

but as a bmw tech i know 14.0:1 is called lamda 1 but i think the 335 is lamda 2 which is two times leaner

ShocK

Beats me, I've read up a lot in the NA threads and everyone says anything above 13.9:1 is unsafe. With my vafc I run about 13.8 throughout the rpm range.

.MM

i have the 70RR, J's Header and stock intake and i was tuned by Giles as well with emanage.

i was told, i was running very lean up top too, like over 15:1

something is wrong with your car because my AP1 on giles dyno made 232whp

my current AP2 on his dyno with the above mods, made 247whp

hub dyno

.MM

even 13.8 is too lean

my car is tuned at like 12.5:1 and it made almost 250whp

devs2k

Hey, that's my J's stuff

How are you liking your tune? The NA tune by Giles was pretty fun

iDomN8U

This is concerning, since there are tons of people running I/H/E without any tuning.

More input would be appreicated!

devs2k

It is concerning! The saving grace is that at the end of the day, it is still NA and therefore the effective compression ratio isn't nearly as high as a FI set up. Also, the overwhelming majority of people fill up on 93 octane, slightly higher than the recommended 91. This helps prevent detonation. Also, if detonation begins to occur, the knock sensor will send a signal to the ECU to pull timing (and I think dump fuel as well, not sure about this one). The only problem is knock must occur first, and the damage is already being done!

There have been some cases of blown engines (spark plugs melting and destroying the cylinder alls and pistons) due to a prolonged lean condition. How many of the blown engines out there are due to a lean condition? Hard to say.

Also, most people that they their car is fine probably do not conduct regular compressions tests to see what is going on. Even FI guys will not notice a loss of power but see the true results from a compression test and evidence of internal damage.

Bottom line is, why risk it?

Hero

the header is generally the biggest culpurate to running lean.

if you install anything other than an intake and exhaust your afr is going to start getting out of line. how much is up for debate and dependant on your combo of parts, but it is something to be aware of.

i had my setup tuned with an emu. all bolt ons exect a header, tuned to 12.9 /13.1 perfect ratio for n/a. after installing my rick's header i went for a re-tune...afr jumped up to 14.5ish. not good.