>
>Relying on a rich fuel mixture alone is not good for max HP
>when boosting. Remember, anything richer than 10.1:1 will
>cause detonation also, just as easily as too lean of
>mixture. Then only reason is you can run soo much boost
>pressure without timing retard is becasuse of running on the
>edge of very rich conditions, thats not good for power. IMO,
>you will make more HP, with a slightly leaner air/fuel
>mixture, and retarded timing at higher HP. My EGT's never
>went above 1575 degrees when i was boosting 10 psi. I still
>cracked a piston. We HAVE to pull timing at one point or
>another. Its just plain physics.


not really. if you are getting 15 degrees of advance (like I do with a stock ecu, and no map sensor correction) adn you take out 8 degrees of timing to run over 15 psi.......you are running SEVEN DEGREES OF ADVANCE. that doesn't work. you will MELT valves doing that. you have to know what your timing looks like to begin with and not jsut blindly retard timing when you think it's good to. running leaner than 11.3 to 11.5:1 even with 16 degrees of timing advance on a "well flowing motor" will melt stuff. I had my car tuned PERFECTLY to 12.2:1 at wot on the dyno, and my egt's never went above 1550 either........after I put in the afx ecu and didn't remember to correct for it. (remember the 10 extra degrees of timing). I put a hole in a piston the size of a human thumb. when you get over the hump and start soaking heat into your pistons and head and cylinder walls, egt's go "down". more heat is transfered through the metal, and less is transfered thorugh the exhaust. tuning for Max hp is "not" what you want to do for longevity of yoru engine. it is great for drag racing when extra engines are available, but if you do tune fo rmax hp, you will burn stuff, bust stuff, and utterly break things constantly (I was tuning for max hp when I tweaked the car for 12.2:1 air fuel ratio). if tuned properly, you can make almost as much hp as peak consistantly and safely with the right ammount of fuel and the correct ammount of spark advance. most single turbo supras tune for about 11.3 to one on teh dyno and 11.8:1 on the street (what the load generally caries the number up to) and abotu 16 degrees of spark advance to run 20 psi on pump gas........they most of those guys have NEVER removed an engine due to damage (I talk with a lot of them, because most of the local guys around here have their act together).


>Your theory of tuning is by running so rich, that it cools
>the intake charge enough to avoid serious detonation. The
>stock o2 is by far not perfectly accurate, but its pretty
>close overall IMO. If it wasnt, the the readings it gets
>would be totally inaccurate when just normal driving around,
>and your engine would run like crap, and get horrible gas
>milage. The o2 alone is what sets the Short term fuel trim,
>and Long term fuel trims on our cars. It HAS to be somewhat
>accurate at oxygen measurement. Not perfect, but close.


the oxygen sensor is pretty stable and consistant "if it stays at a relatively consistent hot temperature". if you run without a cat, or run open exhaust, etc. etc. etc. really rich mixtures can cool the exhaust so much that the 02 sensor becomes inaccurate. this usu. happens at wot runs with a cool car. this is usu. the time when something will mess up. I have acutally seen cars run so cool that once ran as soon as the o2 sensor reached operational temps, the exhaust knocked it back in warm-up mode (even wide band sensors). on a relatively stock car, that is pretty much in tune from the factory, the o2 sensor has to do very little. on a heavily modified car, the o2 sensor has to usu. adjust much more, and that's where you start to find inconsistencies. I have seen my o2 sensor in my stealth read .98 on the dyno and .95 on the dyno and have the "exact same air/fuel ratio" via a wideband sensor and a logged graph. it is possible to have glitches, and less backpressure in the exhaust (lack of cat) increases that risk.



I just wish my theories could be tested out using a dyno. Try
>mega rich fuel mixtures for high boost. THEN try retarding
>timing and leaning out fuel mixtures to where they really
>should be. I'd be willing to bet money that higher HP will
>result with leaner fuel and retarded timing. It makes sense
>anyway..

I have. retarding timing decreases hp output from my car. (with the accell dfi and no pressrue sensor clamp, my wot timing is abotu 19 degrees). leaning the car out also increases power. that is very blatant on the dyno. it also makes it rattle 'slightly' on the dyno, and rattle "extremely" on the street.......causing holes in pistons (personal expierence)


>The J&S can pull timing from each cylinder. We have 2 coils,
>one for cylinders 1 and 4, the other for cylinders 2 and 3.
>BOTH of these sets of cylinders fire at the same time, BUT
>only one cylinder is on the compression stroke, and the
>other is on the exaust stroke. So lets say cylinder 1 fires
>and gets detonation. The J&S reads the knock, and knows that
>cylinder 1 just fired, and it will remember to start to
>retard cylinder 1 NEXT time IT fires. So it "knows" to SKIP
>the next following spark trigger signal for the same coil,
>because now the next following signal is going to spark
>cylinder 4. The next spark signal after cylinder 4 is back
>to cylinder 1, so only then does it retard spark. Make
>sense? The unit listens for knock over 100 times a second.


that is pretty smart .


>
>Let me ask this also. How many of us boosted 420A guys run
>at 15+ psi of boost, and have actually dyno tuned our cars,
>using timing retard and A/F ratio adjustments? I think we need to retard
>timing, and run closer to a consistant 12.1:1 to 12.5:1 A/F
>ratio under boosted conditions, or slightly richer, but
>thats it. Of course, this is all my theories anyway


I think people not going to the dyno is the main cause of engine failure from this board. but it isn't going to be solved running 12.5:1 air/fuel ratio and 2 degrees of timign advance. I think everyone should learn how to do things, but I just feel bad knowin for a fact that something bad is goin to happen. if you run 12.5:1 air fuel ratio past 15 psi, you "absolutely will" burn something half to death. if you don't retard timing, you will melt your pistons (aftermarket) or crack ring lands (cast pistons) and if you retard timing at that air/fuel ratio, you will melt your exhaust valves and burn up your valve stem seals. been there. done that. got about 7 dead pistons of experience.

A.D.P.
"...If you do too much, people become dependant. If you do to little, people loose hope. If you do it right, people won't be sure you've done anything at all."
bring it on............

A.D.P.
"...If you do too much, people become dependant. If you do to little, people loose hope. If you do it right, people won't be sure you've done anything at all."
bring it on...........