SR20DET My Air/Fuel Ratio (Suggestions)

[Edyz7s]

Just installed my AEM AFR gauge and sensor today. I am new into having this and have done some research on how it works..
I would like to know from you guys if my AFR looks okay:

https://www.dropbox.com/s/6xardzky6em9mt0/Video%20May%2001%2C%208%2008%2027%20PM.mov?dl=0

I have no tune and I feel it might be late to get one since I did a compression test and all around it was at 120s.
I have my timing at 17 btdc, running 91 octane always and my tps voltage is currently 0.45 and at WOT it reads at 4.08. I still have stock FPR with walbro 255 fuel pump.
Normal driving is arould the 14s. WOT is pretty rich, 11-10s, it feels like I loose power when I push it but if I have it mid throttle I feel the power.

[Kingtal0n]

Stock engine?

12:1 is fine for stock turbo boost. Any richer is a waste of gas usually.

I found that many stock ECU are fine, its the MAF that is inconsistent. I've swapped out 3 different mafs and gotten 3 different WOT a/f ratios before. You might consider playing the swap-a-maf game to find one that gives you around 11.8 or 12:1 but not 12.5 or higher. 11-10 is why you probably feel a drop in power. that and you might be knocking with poor fuel and too much timing.


Timing needs to be 15. 15 is for the stock engine in Japan, where they have 98 octane and 30*F weather or whatever sometimes. You bring that motor here to constant 90*F and 93 octane and its a damn miracle it runs the way it does. Now you're putting 91 octane in and advancing the timing? good luck brah

[oLemurs]

Stock engine?

12:1 is fine for stock turbo boost. Any richer is a waste of gas usually.

I found that many stock ECU are fine, its the MAF that is inconsistent. I've swapped out 3 different mafs and gotten 3 different WOT a/f ratios before. You might consider playing the swap-a-maf game to find one that gives you around 11.8 or 12:1 but not 12.5 or higher. 11-10 is why you probably feel a drop in power. that and you might be knocking with poor fuel and too much timing.


Timing needs to be 15. 15 is for the stock engine in Japan, where they have 98 octane and 30*F weather or whatever sometimes. You bring that motor here to constant 90*F and 93 octane and its a damn miracle it runs the way it does. Now you're putting 91 octane in and advancing the timing? good luck brah
actually the japanese gas isnt 98 octane, it uses a different rating scale known as RON which is the equivalent to 93 octane

[Edyz7s]

Kingtal0n,
Care to explain a little bit more on timing/octane/weather? I stay in the SoCal region

Going more in depth with my stock motor, i upgraded my cooling system with Koyorad Radiator with 350/370 Z radiator cap(1.3 bar), running mishimoto thermostate, got P2M radiator hoses with autometer water temp gauge that reads 150 to 180 the most in my SR, running Mishimoto Z-line intercooler with CxRacing intercooler piping with Greddy BOV sitting on the throttle body side, recirculated. I use 10w-30 vavoline/mobil-1 full syn oil

[Kingtal0n]

They get better gas at their pumps. Maybe not 98 but its at least 95 octane. They label as 100.

its all about temperature when it comes to gasoline. If the engine was just started parts are cool and gasoline has trouble vaporizing. anymore than it does from a metal table in a room. As the metal heats up the gasoline reacts different to it- it won't even touch it anymore, just instantly poofs into gaseous state as it barely touches the surface. The gasoline absorbs energy, heat, and now there is more space between gaseous molecules, they are moving with more energy. Consequently collisions are more frequent and of greater magnitude.

Chemical reactions are all about collisions. Collision rate, reaction rate, there is some number of collisions per unit time with sufficient energy and force to cause a reaction and generate products. In this case its CO2 and H2O of course. The question is, how do we adjust the rate of successful collisions? Well for starters we can turn down the temperature. Is there any other way?

Molecular shape. If I use a more highly branched hydrocarbon structure, it will be more sterically hindered and there should be fewer collisions that result with successful reaction. This is the major difference between ZERO octane gasoline and 100 octane gasoline, the ZERO octane gasoline has 8 carbons in a straight chain, whereas the 100-octane molecules are 2,2,4-trimethylpentane which has 3 side chains. It also happens to release less energy per molecule in a reaction because of this difference in bond energy/shape. This is why higher octane fuels give less fuel economy overall, while also imposing a slower number of successful reactions per time at some given temperature which makes the expanding gas's pressure differential (the rate at which pressure is increasing in the constant volume chamber before the piston can get out of the way) slow down, which gives the piston more 'time to move' so to speak, thus avoiding a catastrophic explosion which blows the head gasket if you are lucky, or puts a hole somewhere else if you are not.

So to recap and sort of go over that last part again to make it clear: the suddenly dangerous explosion happens because of chemical reaction rate. We can lower rate with lower temperature or by changing molecular fuel source and using it to adjust rate. If the rate is too fast, pressure builds too quickly and parts get holes in them.

Even if you time the spark right, if the temperature is too high, the sudden explosion will still ruin the engine. Spark -> KaBOOM! like a bomb in there. Pressure just rises too fast if its too hot, or with too poor of a fuel.

That said, if you are getting hotter, you want less timing. Start the spark much later so that the increasing rate of pressure doesn't get out of hand. Most cars have IAT sensors so the computer can pull timing when things get hot. The higher hotter temperature is increasing the rate of the reaction so they start the spark later and still wind up with the ideal pressure when the piston/rod is in the best position to accept it. They have assured this because they have properly chosen the correct compression ratio, and associated chamber technology to provide this consistent reliable situation at Earthly, wide range of ambient temperature values. If you've screwed with any of that stuff: compression ratio, expected octane, timing, head gasket, anything, you just had better know what you are doing, the consequences of those actions. Upgraded head gasket + hot day + boost can = blown engine instead of blown HG. For example.