Unleaded 91/98 on my 1992

Archives of Posts to the NZ MX5 List back in 2003
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Daniel

Unleaded 91/98 on my 1992

Post by Daniel » Sat Aug 16, 2003 9:47 pm

hi

i am just wondering if i can fill up my 1992 Jap import mx5 with unleaded 98?
will that improve the preformance at all if any?

thanks

David & Judy Kerr

Unleaded 91/98 on my 1992

Post by David & Judy Kerr » Sat Aug 16, 2003 10:17 pm

Daniel I have been running my 5 on the 98 for quite some time now with the
timing set to 14 deg. 2 Yrs ago she burnt a valve while I was travelling the
South Island, the dealer that I took it to in Dunedin didn't have an answer
for it but did state that it appeared to be running too lean but upon checking
the fuel system and the computer they ruled this out. The shop Forman did
state that he thought 91 to be unreliable and suggested that I run 96 for a
while and monitor any changes.I have found that I get better mileage now than
I did running 91 and the engine runs cooler and performs better ; more
responsive. I changed to 98 about 6 months ago and had the injectors checked
out of curiosity a couple of days ago and was told that they looked great, not
bad for 167,000 KMs.

Cheers,
Dave.

Chic & Morven

Unleaded 91/98 on my 1992

Post by Chic & Morven » Sun Aug 17, 2003 12:55 am

It's unlikely to improve performance without a corresponding timing
change. Normally, I think, you would go to 16 or 18. You just need to
try it out and see what works best on your car. PS On 91, If you are
still running at 10 degrees, moving to 14 will be a noticable
improvement. People claim it adds 6 horsepower. -- Chic & Morven,
us@lynchz.com on 08/17/2003 On Sat, 16 Aug 2003 21:47:30 +1200, Daniel
wrote: hi i am just wondering if i can fill up my 1992 Jap import mx5
with unleaded 98? will that improve the preformance at all if any? thanks

lou Girardin

Unleaded 91/98 on my 1992

Post by lou Girardin » Mon Aug 18, 2003 8:00 am

The engine's designed to run on 91. If you advance the ign timing to 14, 16 or
18 degrees you may need to use 96, this varies between engines. Otherwise
there is no benefit in running higher octane than necessary. Having said that,
there is a difference in fuel quality, eg; Gull, BP ultimate, Caltex seem to
have better additive packages than others. My car and bike both run smoother
on these although it is rated for 91 octane with 11.3 comp ratio.

Martin Harms

Unleaded 91/98 on my 1992

Post by Martin Harms » Mon Aug 18, 2003 8:56 am

I have had to run 96 on my (slightly) advanced timing '90 NZ new because
it pinged on 91. About 6 months ago I discovered that Gull sells 92
octane. I first tried half 92 half 96 per tank, then 92 alone. No
pinging. I have used the 92 exclusively since then - a saving of 5 cents
a litre...

Martin

jeff

Unleaded 91/98 on my 1992

Post by jeff » Mon Aug 18, 2003 9:38 am

hi Daniel

as others have said, the engine is designed for 91
octane and running a higher octane shouldn't make a
difference in performance.

FWIW, more octane would be needed if the engine had
higher compression - either naturally aspirated (eg
S2000) or forced induction (turbo or supercharged).

If it 'knocks' on 91 and the timing is set to the
standard 10*, the engine could be a bit clogged with
carbon in which case it just needs to be cleaned!

hope that helps.
Jeff

** MazdaSpeed exhaust - still looking for a good home
**

--- Daniel <shek@xtra.co.nz> wrote:
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