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og
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Discussion Starter #1
well had the car dyno tested sat eve and it turns out that in order to maintain the a/f at ~13.7 we needed to lean out from ~3500rpms on up at wot. at 7000rpms it's leaned out to 10%. we figured the hp gain (sae corrected) is approximately 5hp for a properly tuned s-afc... and the hp figure came up at...

183.7 fwd hp! i can't remember the torque, somewhere around 202 ft/lbs IF memory serves but i'll get back with those figures.

anyway, i was psyched, higher than either hans or i expected. this of course gave him LOTS of room to bust my balls about my 15 flats, altho hopefully after this saturday i will shut him up :D

well it also dispelled the thought that higher injectors will help and the 360cc injectors did NOT go in nor will they be going in until the supercharger gets installed in january (ordered in december, merry christmas to me, 4-6 weeks shipping=january install). anyway, hans n i did put a plan of attack together... by ocean city... well, we'll just leave it at that :D anyway, just wanted to let y'all know if you were curious, safe travels.

- mike
 

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To produce the most power you always want to maintain a stoichiometric (big word, +10 points)mixture of air and fuel at ~13.7. Running rich reduces performance and running lean is a good way to blow a piston. You want to run that perfect balance as close as you can get it. By leaning the car out in the higher RPM range, you can net a few ponies (if its running rich in the first place). Most cars will get a little rich at WOT (wide open throttle) because the injectors go static and they dump all the fuel they can, which is usually more than you need.

To tune it you'll need an Apexi S-AFC fuel controller so you can adjust the air/fuel mixture. Just slap it on a dyno, hook up a datalogger, and run it. Then just adjust the AFC and run it again. Thats what tuning a car is all about :)

.jon
 

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The Wizard Of Aaahhhhh's
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jon3k said:
To produce the most power you always want to maintain a stoichiometric (big word, +10 points)mixture of air and fuel at ~13.7. Running rich reduces performance and running lean is a good way to blow a piston. You want to run that perfect balance as close as you can get it. By leaning the car out in the higher RPM range, you can net a few ponies (if its running rich in the first place). Most cars will get a little rich at WOT (wide open throttle) because the injectors go static and they dump all the fuel they can, which is usually more than you need.

To tune it you'll need an Apexi S-AFC fuel controller so you can adjust the air/fuel mixture. Just slap it on a dyno, hook up a datalogger, and run it. Then just adjust the AFC and run it again. Thats what tuning a car is all about :)

.jon
Stoichiometric is 14.7:1 not 13.7:1

Stoichiometric is a compromise between max power AND max economy.

If the goal is to get the max power, all of the oxygen in the mixture must be burned, because the power output of any engine is limited by the amount of air it can pull in. To be sure that the oxygen combines properly with the available fuel, extra fuel must be provided. This increases the air fuel ratio (makes it richer in fuel), resulting in some fuel which remains unburned.

During wide open throttle the A/F ratio will be forced rich by the ECM for maximum power. During this time the oxygen sensor outputs a voltage that corresponds to a rich A/F ratio. But the ECM ignores the oxygen sensor signal. The ECM is now in open loop, and relies on factory programmed maps to calculate what the on time of the fuel injectors should be to provide a rich A/F ratio for maximum power.

Chris
 

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og
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Discussion Starter #5
hey chris,

pretty sure stoich is 13.7, that's what my car was tuned in to on the advice of a number of people, including hans and the guys running the dyno.

also, running too rich causes you to lose power: i was running too rich on my first dyno run and it came in at 180.1hp, second and third leaned it out and tuned it in to 13.7, runs came in at 183.4hp and 183.7hp. as far as i'm aware, stoich is the top performance for your engine, the perfect air/fuel ratio, burning all the oxygen but not using too much fuel. i need forced induction, dammit, i hate being limited by natural aspiration. soon but not soon enough :D

- mike
 

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NO.

The best performance is normally seen with little bit to the rich side, so that explains the 14.7:1 is the stoich.

if you had more ps with little leaned out, that means you had really TOO much fuel in there.

So, now you have a little rich, but not stoich engine.

Trust me, I learned this in the Engineering course.(I am an Engineering student)
 

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The Wizard Of Aaahhhhh's
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Stoich is definatly 14.7:1

Yes, running too rich will cause you to loose power, but running stoich at WOT is way too lean for max power and it is dangerous to your engine. Most engines will make maximum power at an A/F ratio of between 11.8:1 and 13:1.

Most tuners always recommend to begin programming from a known very rich initial setting and carefully leaning until torque falls off slightly, then going back richer to the point of max torque.

To burn all of the oxygen, you have to have enough fuel. If you don't how is all of the oxygen going to burn? It won't just burn by itself, will it? YES, under pressure it will, it's called knock or detonation. And that's what you want to avoid at all costs.

Just think...it's even harder to get it tuned right with forced induction. Consider yourself lucky. ;) :D


Chris
 

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Mike, what are your settings, we have similar mods, i want to see where your rpms are set at, and what your -XX% is at in those ranges, i want to compare what i got to what you got!
actualy i dont have a dyno near me, so i want your settings... :(
 

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og
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Discussion Starter #9
after some research you guys were on the money, stoich is 14.7. what i am doing is running leaner than the stock fuel map but still running rich.

my s-afc settings range from +4% at 2000rpms to 0% at 3500rpms to -11% at 7000rpms; it's a straight line from the +4 to the -11. hope this helps, lemme know if you need more specific info, safe travels.

- mike
 

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hey mike. i kinda wanna know what your rpms are set at.. can you give me specific rpms and %tages... along with throttle position percentage too! thanks.. i leaned mine out a bit more and it seems even more punchy. i want your settings to test..
:) cheers
 

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og
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Discussion Starter #11
i'll get you the exact figures either this afternoon or tomorrow, i'm sitting in my office right now but i'll write 'em down next time i'm in the car. safe travels man.

- mike
 
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