91 or 96?

Douglas Ormrod · Post by **Douglas Ormrod** » Mon Mar 15, 2004 1:29 pm

Hi Listers

Bought a '93 1800 automatic MX5 a few weeks ago. First time I took it to the
filling station I realised I didn't know whether to use 91 or 96 - so put in
96 to be safe. I then checked in my Haynes manual and it says 86 or higher.
I then asked a friend with MX5 and she said she always uses 96.

So what is the accepted wisdom on this topic?

Cheers

Douglas

Eric West · Post by **Eric West** » Mon Mar 15, 2004 1:42 pm

I run my '94 1800 on 91 Octane with no problems.

I am aware that there is some benefit to changing to 96 and adjusting timing to 14 Degrees BTDC but what benefit or why, nobody has ever explained to me.

Since Douglas has raised the issue, could someone please fill us in (as distinct from fill'er up).

Eric

Gareth Kemeys · Post by **Gareth Kemeys** » Mon Mar 15, 2004 2:12 pm

to advance the timing increases the horsepower slightly, however you need to
run it on a higher octane petrol to prevent "knock"

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The Haynes manual (being US) gives the octane rating based on the US
system of the calculation of Research Octane number + Motor Octane
Number divided by 2, whereas we just use the Research Octane Number here.
NZ 91 RON has a 82 MON, so the US way gives 91+82/2 = 86.5.
This means that our 91 should be OK for standard timing.
Advancing the timing to 14 degrees BTDC (along with other mods such as
exhaust extractors, less restrictive air inlet) does seem to provide
extra power. However, this would need 96 to be sure that detonation
(knock) doesn't occur.

Keith

Nina · Post by **Nina** » Mon Mar 15, 2004 4:46 pm

I adjusted my timing to 14 (was set on factory 10) just before xmas. I'm
now running on 96 and have no problems with pinging at all. Plus she's a
completely different car to drive, I love it!

Nina

~~~~~~~~~~~~~~~~~~~

And the Lord spake, saying 'First shalt thou take out the Holy Pin. Then shalt
thou count to three. No more no less. Three shalt be the number thou shalt
count and the number of the counting shall be three. Four shalt thou not count
nor either count thou two, excepting that thou then proceed to three. Five is
right out. Once the number three, being the third number, be reached, then
lobbest thou thy Holy Hand Grenade of Antioch towards thy foe, who, being
naughty in My sight, shall snuff it.'

Lou Girardin · Post by **Lou Girardin** » Mon Mar 15, 2004 5:33 pm

I ran my 1.6 at 14* and used 91 with no probs. There are variations between
individual engines, so try 91 and see if it detonates.
Lou

Grant · Post by **Grant** » Mon Mar 15, 2004 5:34 pm

Just curious as to what happened to the fuel economy with the timing and
octane change, or were you already using 96? I imagine there would be little
change as you would tend to make use of the power increase anyway (I would).
Also, is your car a 1600 or 1800?
Eric's comment made me come back and read the signature line as I normally
don't bother!.
Grant.

Nina · Post by **Nina** » Mon Mar 15, 2004 5:49 pm

Mine's an 89 and I was on 91 before the timing change. I'm fortunate to have
a great mechanic as a friend and he took her for a test run with me after
the change. Was pinging from a$$hole to breakfast so decided to put 96 in
her, had no probs since. Asfor fuel economy... The way I drive is
definitely not good for fuel economy, 91 or 96. But I enjoy driving the cr*p
out of my car (mind you, going fast on the straights is boring, hillclimbs
around the twisties rules! Had an awesome drive Whitianga-Coromandel-Kopu
yesterday. Still grinning!) and don't mind spending $ on fuel. After all she
was built for high revs and fast corners =)
Nina

~~~~~~~~~~~~~~~~~~~

And the Lord spake, saying 'First shalt thou take out the Holy Pin. Then
shalt thou count to three. No more no less. Three shalt be the number thou
shalt count and the number of the counting shall be three. Four shalt thou
not count nor either count thou two, excepting that thou then proceed to
three. Five is right out. Once the number three, being the third number, be
reached, then lobbest thou thy Holy Hand Grenade of Antioch towards thy foe,
who, being naughty in My sight, shall snuff it.'

Grant · Post by **Grant** » Mon Mar 15, 2004 7:21 pm

I agree the windy bits are what it's all about. Just been sent a fault at Te
Mahia lodge in the Marlborough Sounds for tomorrow so that means a good
drive from Blenheim to Picton, on to Linkwater through the Queen Charlotte
Drive (well over 200 corners in 15km!) out to Keneperu Sound then 30 minutes
work and drive back again. Don't need many spares so it's the MX5 tomorrow
and get paid per km as well. This is one of the great MX5 roads we are
fortunate to have in this region as thos going on the Warbirds run will get
to see for themselves shortly. I'm not worried about fuel economy but just
interested. The run tomorrow is dfinitely not good for fuel econonmy but
sure is good for grins.
Must get hold of Monty Python's Holy Grail. Never got around to watching it
yet. Love their stuff.
Grant in hope it's sunny tomorrow Blenheim.

Lou Girardin · Post by **Lou Girardin** » Tue Mar 16, 2004 7:01 am

Another good twisty drive is; SH16 to Wellsford, on to Brynderwyn and turn
left for Paparoa, right just before Paparoa and follow this to Oakleigh.
Right onto SH1 and carry on till the 1st turn-off for Waipu, then follow the
coast through to Mangawai and on to SH1 again. South to Wellsford and right
onto SH16. 300 km's of good windy roads. Did it yesterday, left at 10.00AM,
got back at 4.00PM including stops.
Lou
PS. That was on the bike, add 1/2 hour for cars.

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