WolfInSheepsClothing

Good points scorpion

Scorpion

I think you are talking about closed loop O2. And most tuners turn it on, they just set the max correct values at a conservative level in case of O2 sensor failure. Leaning out your WOT by 5% will hardly cost you a motor if done once or twice.

For changes in the enviroment, the car looks at a varity of fuel trim maps. It crossreferances coolant temps, intake temps, baro pressure and so on, and bounces those numbers off the base fuel table to calculate the amount of fuel needed. The only time it looks at AFR is during closed loop.

Hope that helps.

Scorpion

So then how do you tune? How do you know what the exact threshold levels are at each given RPM point?

Most knock tuners I know tune the car until they see knock then back it off a few degrees. I find this to be the worst way to tune. Follow me on this. Think of it like a bicycle. When you are pedeling there is an optimal point in which you push on the pedel that the bike will move forward. If the pedel is all the way at the top and you push staight down on it it's not going to move. This would be the same as detination or knock in a motor. Now imagine that the pedel is horizontal, when you push on it, the bike moves but not far and not fast. This is the same as when your timing is backed off too far. Now on a motor you can't see where the connecting rods and crank are, you only have some numbers to rely on. MBT tuning tunes the car to the point at which the rods are pushing on the crank at the optimal angle to make torque. At that point you shouldn't be close to knock, and your car will be performing to it's potential. Tuning to knock and then backing off sometimes leaves you closer to knock than MBT tuning.

Don't get me wrong, I'm not trying to tell anyone how to tune there car, I'm just trying throw out differant ways to tune. IMO they are better, but each tuner has his or her own methods.

elusiv

^ I'm convinced! Makes much more sense to me now...

Now since i'm a newbie street tuner, mind telling me what MBT stands for?

Scorpion

MBT = Mean Best Torque

Which is why you need a dyno to tune with this method

elusiv

Fine, fine... i'll put the laptop down and step away from the car now...

Scorpion

Just for timing, I do all my fuel tuning on the street

elusiv

Bleh its ok, street tuning is only fun for the first or second pull. 20 pulls later and you just want to throw the laptop out the window and go back to stock lol. Can you tell im sick of it? haha

Evo-L

How do you go about tuning for MBT? Whats the procedure, I use the conventional if it knocks, pull timing until it doesnt. Im obviously a rookie, but trying to learn!

Scorpion

It really depends on the dyno you are using. Best case is you have access to a dyno with load control. The way I do it is I pick a RPM cell, say 3000, then I just hit each cell in the map in the load collum. In each cell add timing until the you don't see any gains in torque and move on to the next cell. Of course this only works for vacuum and low boost states. You wouldn't want to hold the car at 7000rpm at 10psi while you added timing, it'd be alot of stress on both the car and the dyno. For your WOT runs just graph it out, add .5 degrees, graph again and compair them. If you made torque, try it again until you don't. You can use the same technique or vacuum states if you don't have a load-baring dyno. It just takes a little longer.

Be aware that until you are proficiant at it, it will take some time and will cost you some money on the dyno. But once you get it down, it'll go quick. When I attended EFI 101, the instuctor took a blank map and fully tuned a WRX in 45 minutes. One day....I'll be that good