Dilema: Switch to 95 Octane and retune, or detune" it for regular petrol?

2nd Hand Yank · Post by **2nd Hand Yank** » Wed Sep 14, 2011 9:14 pm

So it sounds from forum members that my engine is probably getting detonation at low rpm sometimes.

I'm using regular petrol, but I could switch to 95 octane. (or higher if need be)

I haven't done a full tune-up yet with my EA82 though,
I've only owned this '93 L Series for 2 months.

Today I bought what could be my last full tank of regular petrol,
in case tuning it for regular petrol is the best idea.

*Question* - Can my old EA82 actually see performance or economy gains by tuning it for higher octane petrol?

It would be a waste to end up with the same amount of power and economy and be paying more per-Litre.

Thoughts?

taza · Post by **taza** » Wed Sep 14, 2011 9:26 pm

I can't help but I will say that I use octane 95 Petrol in my Forester (EJ202 manual) and I get about an extra 80-120km to a tank compared to standard octane 91. Plus the engine seems abit more lively..... just

Taza

Venom · Post by **Venom** » Wed Sep 14, 2011 9:34 pm

It will be more fuel efficient and will have a bit more power if it is properly set up for a higher octane fuel. However i think its pretty well established that it is not more economical finacially, but if you see value in the performance benefits then that would change the equation. There are probably other things you can do to compliment the higher octane fuel too, like a more powerfull ignition system.

I reckon try it for a tank and see if it cures that particular problem you have, thats a pretty simple and quick way to see if it is a pinging problem. Plus you get to try a higher octane fuel, although your car might not be getting the most out of it.

Gannon · Post by **Gannon** » Wed Sep 14, 2011 9:57 pm

You will only see a difference if you adjust your ignition timing to suit the higher resistance to knocking. You could also raise your compression ratio, but it isnt really worth the effort.

woody.t · Post by **woody.t** » Wed Sep 14, 2011 10:17 pm

apparently 91 is or will be phased out over the next few years to make way for a ethanol based replacement as the new cars on the market are not rated for such a low octane fuel . . . just what i was told not 100% sure on its validity and on personal experience the extra fuel economy almost accounts for extra cents and the boxers seem to like 98 better.

discopotato03 · Post by **discopotato03** » Wed Sep 14, 2011 11:02 pm

Is this an EFI or a carburetted EA82 ?

A .

sven '2' · Post by **sven '2'** » Wed Sep 14, 2011 11:13 pm

2nd Hand Yank wrote:So it sounds from forum members that my engine is probably getting detonation at low rpm sometimes.

I'm using regular petrol, but I could switch to 95 octane. (or higher if need be)

I haven't done a full tune-up yet with my EA82 though,
I've only owned this '93 L Series for 2 months.

Today I bought what could be my last full tank of regular petrol,
in case tuning it for regular petrol is the best idea.

*Question* - Can my old EA82 actually see performance or economy gains by tuning it for higher octane petrol?

It would be a waste to end up with the same amount of power and economy and be paying more per-Litre.

Thoughts?

PULP = Slightly better response. Slightly smoother. Better economy makes it worthwhile to run on PULP. Much better behaved in summer.

Re-tuning to a better grade fuel is a waste of time in NA L-Series though. Just switch and enjoy.

Sven

Davidov · Post by **Davidov** » Wed Sep 14, 2011 11:17 pm

In an EJ25 does octane 95 make much of a difference to running it on 91? Ive been using 91 but the manual highly recommends 95.

d_generate · Post by **d_generate** » Thu Sep 15, 2011 1:25 am

No EJ should be running on 91 period, if it was mine it would be on 95 minimum. I have to run both my Lib & WRX on 98 as they have JDM computers and should be on 100 but I wouldn't use anything else unless I was driving a HQ Belmont.

2nd Hand Yank · Post by **2nd Hand Yank** » Thu Sep 15, 2011 2:21 am

^^ The only reason I'm running 91 is thats what the motor was designed for.

If my noises are detonation,
then my right foot really can't ask it too much without yelping.

I'm not expecting it to be immediately more economical,
but if it's 10 cents more a Litre (7-8% more expensive) and it goes 2-3% further,
that means I don't have to fill up quite as often
or can get a little further on a full tank.
A marginal increase in power would also be VERY welcome.

I'd just hate to switch if the noises aren't causing long-term damage,
I won't get better economy and my power won't change.
It'd be silly to switch for that.

2nd Hand Yank · Post by **2nd Hand Yank** » Thu Sep 15, 2011 2:23 am

sven '2' wrote:PULP = Slightly better response. Slightly smoother. Better economy makes it worthwhile to run on PULP. Much better behaved in summer.

Re-tuning to a better grade fuel is a waste of time in NA L-Series though. Just switch and enjoy.

Sven

PULP? Is this like fermented gum chips?

littlewhiteute · Post by **littlewhiteute** » Thu Sep 15, 2011 5:17 am

2nd Hand Yank wrote:PULP? Is this like fermented gum chips?

PULP = Premium UnLeaded Petrol

revmax · Post by **revmax** » Thu Sep 15, 2011 6:19 am

2nd Hand Yank wrote:^^ The only reason I'm running 91 is thats what the motor was designed for.

If my noises are detonation,
then my right foot really can't ask it too much without yelping.

I'm not expecting it to be immediately more economical,
but if it's 10 cents more a Litre (7-8% more expensive) and it goes 2-3% further,
that means I don't have to fill up quite as often
or can get a little further on a full tank.
A marginal increase in power would also be VERY welcome.

I'd just hate to switch if the noises aren't causing long-term damage,
I won't get better economy and my power won't change.
It'd be silly to switch for that.

Detonation is causing long term damage, even imediate for that matter in the form of very small/tiny holes in the piston and combustion crown. It is causing extra load on the big end bearings although they hardly ever give out, eventualy the piston will break around the ring land.
Also detonation/pre ignition is robing your engine of power and economy. The way I see it 91 octane is false economy.
Put a full tank of 98 in it and you will understand.

sven '2' · Post by **sven '2'** » Thu Sep 15, 2011 8:10 am

2nd Hand Yank wrote:^^ The only reason I'm running 91 is thats what the motor was designed for.

No it wasn't.

Was designed for JDM and OS fuel markets, generally much higher quality fuel than the AUDM.

The AUDM Subarus were detuned for for our market - as all (or most) JDM cars are.

You are running technology circa 1915 - ie a carby - therefore the best thing you can do is put the best fuel in.

steptoe · Post by **steptoe** » Thu Sep 15, 2011 8:32 am

Starting to look at fuel numbers again myself (been used to no-choice-but- high- octane LPG) and noticed woolies and caltex offer a product called Vortex in 95,98 and Diesel. Not sure if it was timing or location but ended up paying 3 cpl more for 98 than 95. Think i will stick to the 98 - gave me 10 litres per 100km of varied driving in the EA82TS Vortex

While the knock sensor works on efi they "self adjust according to fuel grade" (Lexus sales pitch

)

On my old EA81 in my Brumby I found to shove ten bucks of 98 on an empty tank it ran better by allowing me to stomp on the loud pedal get more torque down lower, so not needing to rev higher it should give better mileage, yet I never allowed self to fill up on it so cannot tell you to budget for a few tanks of 98 and just try it can I?

Maybe try gearshifts 500rpm lower... actually, what are you hoping to achieve ? performance, economy or a balance?

Wait for the fit a new big zap coil people to come on in

steptoe · Post by **steptoe** » Thu Sep 15, 2011 8:34 am

Detuned for AUSDM - how so?

MTB92 · Post by **MTB92** » Thu Sep 15, 2011 8:56 am

2nd Hand Yank wrote: I'm not expecting it to be immediately more economical,
but if it's 10 cents more a Litre (7-8% more expensive) and it goes 2-3% further,
that means I don't have to fill up quite as often
or can get a little further on a full tank.
A marginal increase in power would also be VERY welcome.

I'd just hate to switch if the noises aren't causing long-term damage,
I won't get better economy and my power won't change.
It'd be silly to switch for that.

just try the 98. its what everyone else on here had to do to see if it made a difference.
run your tank to nothing and fill it up with premium. you will be the only one who knows if it makes a difference to your car. then you can decide if its worth it or not. it will cost you all of 5 bucks, just take an extra bottle of water to work and dont buy a drink or whatever and you will be even anyway.
even better, run it for a couple of tanks and do a L/kms test on it and see if it is more efficient then go back down to 91 (i am almost certain you will feel the drop in power, even if you dont notice the increase as much when you initially filled).
sometimes you have to stop thinking and working out little percentages and just give it a go. in the end it comes down to whether you notice the difference in fuels (i know i do!)

Post by **Alex** » Thu Sep 15, 2011 9:42 am

im going to be different to the crowd

i wouldnt bother. Spending anything but the minimum on an ea82 is still too much.

ive been there done that, tried to get more performance from my old ea82 carby, just a waste of time and dollars.

id just run normal fuel, ea82s are moderately bullet proof, when it dies put a ej motor in there.

itll probably last another hundred tanks if its even pinging, then with the money youve saved on 98octane fuel about 15c per litre extra than 91 youll be 3/4 of the way there for a ej motor.

put simply i wouldnt spend any money an ea82 if it isnt 100% needed.

alex

sven '2' · Post by **sven '2'** » Thu Sep 15, 2011 4:17 pm

steptoe wrote:Detuned for AUSDM - how so?

Differing compression ratios, emission controls, jets etc.

Am sure I read that the JDM service manual specifies a different coil, spark plug gags and timing - maybe that was on USMB, back when I suffered carby syndrome*

In my experience, this is partly why when you buy an import engine, the manifolds etc are changes from your dud motor to the 'new' one.

More modern cars sport a different ECU map

* carby syndrome (noun def) - thinking one can increase the power of a EA82 by tinkering with the carby - most often a delusional state, fixed only by 2,000ml of EJness, and in rare cases, 1,800ml of EA82Tness

Post by **Alex** » Thu Sep 15, 2011 5:09 pm

sven '2' wrote:
* carby syndrome (noun def) - thinking one can increase the power of a EA82 by tinkering with the carby - most often a delusional state, fixed only by 2,000ml of EJness, and in rare cases, 1,800ml of EA82Tness

BAHAHA!

very rare EA82Tness