Octane Plug

[KITT]

When using optimax fuel, do you need to change the octane plug around?

Anyone found any benefits from using optimax?

[richie00boy]

Re: Octane Plug

The octane plug is only on 8V models. You don't have to change it, but if you leave it on the 95 setting the ignition won't be advanced to take account of the extra octane available.

If you have a 16V with lambda sensor in the exhaust manifold then it should adjust itself, not sure if it adjusts up to 98 octane though, I heard it was ceiling at 95.

[cielo20]

Re: Octane Plug

Hi Richie no its not only on the 8v model as i have one on my 16v !


The octane plug on my 16 valver has A side and B side! I leave that on the B side as the car is a lot faster and you can feel the extra power even if here we have crap fuel (possibly not even 92ron fuel)

[richie00boy]

Re: Octane Plug

Apparantly it's not an octane plug on the 16V, it selects different maps for emissions.

[cielo20]

Re: Octane Plug

When i purchased the engine they told me it was for 95ron (A) and 98ron (B) fuel and it sure make the engine different on the B setting

[DarrenH]

Re: Octane Plug

.....

Octane coding
Because of the sophistication of the ECU and timing control an octane coding plug is not considered necessary for the 20XE & C20XE engines. Octane adjustment is automatically selected according to operating conditions. Motronic 2.5 is programmed with two different timing maps. These are Low Octane Number Map (more retarded timing) and High Octane Number Map (more advanced dwell angle). The ECU selects the appropriate map according to the following conditions. Once knocking combustion of more than 50 have occurred, the ECU switches to the Low Octane Map. Once approximately 8.5 minutes of knock-free operation have passed, the ECU switches to the High Octane Map.

[BigGraz]

Re: Octane Plug

so it doesn't matter which way round this plug is
I've also heard stories of a 'legendary' red octane plug that gives you more power, anyone heard of this

[Addz]

Re: Octane Plug

Side A is the better side isnt it? I always thought B was for some European rules or sommit about noise and emisions?

[Ross_Mk2]

Re: Octane Plug

mine is red an says 95 on one side, and 98 on the other! I have it on 95 and using normal fuel

[Brett]

Re: Octane Plug

doesnt make any noticebale difference IMHO which way round you have it.

I've been out and been told many time to swap it round to gain 20bhplmaolmaolmaolmao

[cielo20]

Re: Octane Plug

But on mine you can feel the difference when you change from A side to B side!(well not a 20 bhp difference maybe ) but you feel the engine revs up faster

[Addz]

Re: Octane Plug

mine is red an says 95 on one side, and 98 on the other! I have it on 95 and using normal fuel

Aye on the 1.6, change it to 98 and use Super. You will see a difference....slightly

[Ross_Mk2]

Re: Octane Plug

Aye on the 1.6, change it to 98 and use Super. You will see a difference....slightly

Super? you mean the stuff thats like 3p dearer? Does it matter whos super petrol i use, which do you find the best?

[Addz]

Re: Octane Plug

Super? you mean the stuff thats like 3p dearer? Does it matter whos super petrol i use, which do you find the best?

I used to find Optimax was good with my old Weber 32/34 carb, and with the RON plug on 98.

Any super unleaded will be better though. Personally, id run the old 95 petrol still in the tank right down and then fill up at least half the tank with Super. (Actually coasted to the petrol station on what must have been fumes, although I think i was being over cautious! )

Then drive it back home and then switch the plug over (blowing out any white powery residue that may be in there, there was loads in mine).

Dont expect miracles, but i found it was slightly pokier, and it got rid of almost all the flatspots i had.

Just remember to use Super all the time, otherwise it will start pinking. I think you can use 1 95RON petrol to every 4 98RON fillups, but i just always used Super until i sold the car

[richie00boy]

Re: Octane Plug

The 1 95RON to every 4 98RON is actually to do with leaded petrol and lead retention on the valve seats. If you have changed your timing to suit 98 fuel you must use 98 fuel at every fill up.