how lean? or rich?

Blown 91 Bird

Registered User
just curious but how lean (or rich) are our cars with stock motors and a stock tune across the board? I know all will be different being at different altitudes and different air temps... but do they generally run rich or lean?

I saw a dyno sheet for someone on here and the A/F curve looked as if it were somewhat rich throughout the lower RPM range, but got crazy lean (14:1+) near redline. Not sure if this was a stock motor with a stock tune or not though.

Im asking cause ive been thinking about putting a nitrous kit on my car (wet), and will setup the jetting to be on the rich side (and just play with bottle pressure to lean it out when wanted) if these things tend to run lean. I know i could just find out by putting it on a dyno and using a wideband o2, but from my experiences my cars have always ran leaner on the street then they did on the dyno since the loads are different (which is why i will not tune any of my cars on the dyno). So other then going by what an o2 sniffer has to say on a dyno, the only other choice would be to stick a set of fresh plugs in it and make a pass on my test road and pull over and pull a couple plugs out to see what they look like (which is what ill most likely do).
 
my 89 was pretty good in closed loop , about 4 pounds of boost it goes to open loop and seems a little rich but not real bad
 
14+ isn't lean 14.7 or 15 is stoichometric, but I know some if not most OEM manu, do set WOT or heavy throttle to 12.5....

Edit, after watching Thomas Aden set up his nitrous on the dyno and aborting 10+ runs there is no other way in hell I would hook up a bottle without it being setup on a dyno. That is the most controlled environment you are going to get. I would strongly recommend that. It is going to be a lot closer than sniffing plugs too ;) . Then if you really want it tuned use your wideband on the street.

I know the load is somewhat different on a dyno, but I really don't know what that means. Your load is going to be different driving up a hill, or down a hill, or with headwind etc.

50 or 100 bucks for the dyno time would be worth it if you ask me. Espically if your dishing out 900 for a wet kit.

Good luck either way.
 
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400 bucks will get you an absolutely fabulous wideband, it will cost a lot more time and money if you blow the motor. Plus, chicks dig lots of gadgets man.
 
Stock programming on 89-93's are 11.0:1 at WOT. 94/95's are 9.5:1 at WOT. Ideal is 11.8:1 and it is supposed to switch from 14.64 to WOT fuel commands at roughly -0- on your boost gauge. Most SC's are lazy and switch well into boost which is bad.
 
T-bird4vr said:
14+ isn't lean 14.7 or 15 is stoichometric, but I know some if not most OEM manu, do set WOT or heavy throttle to 12.5....

Just out of curiosity, what the heck is stoichometric?? In English please, for us non-engineers.

Ira
 
XR7 Dave said:
Stock programming on 89-93's are 11.0:1 at WOT.

ok, that is what i was looking for. So they are a little bit rich.. works for me.




and tbird4vr... if you dont think anything in the 14.X:1 A/F ratio is LEAN, then id love to see you tune your SC to have a 14.X:1 A/F across the board and make a pass with it. I have some spare pistons you can have after you melt yours. My 94 mustang when i first started tuning it was jumping around in the 13.2:1 to 14.0:1 range (datalogged) once it got up over 4500 and making 14-15lbs of boost and every plug i pulled out had stone white straps. That is LEAN. I dont care what you say. After adding fuel and taking away timing in each RPM table i finally got it to have a pretty flat A/F of 12.2-12.3:1 across the board, and my plugs look like they are supose to (greyish) and the car runs alot better.
 
1FASTSC said:
Plus, chicks dig lots of gadgets man.

i already got a couple of them... just not in the bird :p

ek2oh0.jpg
 
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