Sr20 Octane questions

[SrS13]

I have a couple quetions:

What is the highest level of octane a stock 13 sr20det an utilize?

If I wanted to run 101 or 110 octane on my stock motor, would I need t retune?

would I need to mix the 101 or 110 with a lower octane fuel?

Other than reducing detonation what other advantages are there from running higher octane?

I appreciate your help and information.

[Nismo_Freak]

I'd say 96 octane is about as high as the stock computer will go for. This is because it will only reduce timing when knock is present, and the ECU is tuned for 100 octane in Japan, which is 96 US octane.

[msaskin]

One thing to remember is that higher octane will let you run more boost without knock, therefore without the ECU retarding timing.

Granted, the T25 is really your limit in this regard. Past 15psi or so the T25 really loses just about all efficiency, and 93 octane will keep knock under control at that boost level. That said, putting in some higher octane gas for a margin of safety can't really hurt.

Out here in the west where we only get 91 octane (yeah, it sucks) i'm running water/alky on the street, and for open-track events i usually throw 3 or so gallons of Xylene or Toluene in the tank, which raises the octane to ~95.4

~matt

[SrS13]

So if the ecu was built for 100 octane.

Will I be able to run 100% 100 octane on the S13 Sr20det?

or would I need to mix it with a lower octane fuel?

thanks

[msaskin]

Run whatever octane you feel like. The ecu was not programmed for a "specific" octane of gas. Run 90 octane or run 116 octane, it doesn't matter.

The ECU does one thing (at least so far as octane would be concerned). It listens for knock through the knock sensor. If it detects knock, it pulls ignition timing back a few degrees until the knock goes away, then it begins advancing ignition timing back along the preprogrammed curve. That's it. If you somehow were able to run 85 octane gas and not get knock, the ECU wouldn't know the difference, it's only when it starts detecting knock that it changes things.

~matt

[SrS13]

are there any sort of horse power increase from running higher octane?

Would I need to tune my S-afc differently if I were to run 100 over 91?

thanks once again.

[msaskin]

hp increases: no, not really. The only time you'll see a horsepower gain from higher octane is if you were knocking and therefore losing power on the lower octane gas. If you were properly tuned on lower octane, you won't see any real gain from going to higher octane gas (provided everything else; fuel trims, boost, etc., stays the same)

~matt

[Def]

Run whatever octane you feel like. The ecu was not programmed for a "specific" octane of gas. Run 90 octane or run 116 octane, it doesn't matter.

The ECU does one thing (at least so far as octane would be concerned). It listens for knock through the knock sensor. If it detects knock, it pulls ignition timing back a few degrees until the knock goes away, then it begins advancing ignition timing back along the preprogrammed curve. That's it. If you somehow were able to run 85 octane gas and not get knock, the ECU wouldn't know the difference, it's only when it starts detecting knock that it changes things.

~matt

Actually, Nissan ECUs revert to Secondary(or Knock) timing and fuel maps whenever knock is detected. They use those maps until the car is shut off. Whenever the car is restarted, it will use the Primary fuel and timing maps until knock is detected. So there is no advancing of the timing with any form of the stock ECU once it detects knock.

Also of note, the ECU only listens for knock in a few cells of its primary timing map and they're pretty far down there in the RPM range(like 2000-4500RPM), and only for high load conditions.

[Hijacker]

def,you made me think of something. i've heard of some cars getting stuck on the knock map and not reverting back unless the ECU is reset.

Has anyone ever heard or experienced that with an SR20?

[msaskin]

Actually, Nissan ECUs revert to Secondary(or Knock) timing and fuel maps whenever knock is detected. They use those maps until the car is shut off. Whenever the car is restarted, it will use the Primary fuel and timing maps until knock is detected. So there is no advancing of the timing with any form of the stock ECU once it detects knock.

Also of note, the ECU only listens for knock in a few cells of its primary timing map and they're pretty far down there in the RPM range(like 2000-4500RPM), and only for high load conditions.

Interesting on both counts. I've dug through the ROM files from the ECU while doing some tuning work and knew about the 2nd set of timing/fuel maps, but I wasn't sure on what conditions the ECU switched between the two.

~matt