More timing questions

[trader]

I have been running my 1.6 (non turbo) at 14 degrees TDC for some time now and like its snappiness on Premium. I recently bought a book Miata Universe by Jay Lamm. In it he says \"never use premium gas in your Miata (unless you've radically altered your cam timing). Regular fuel (87octane) has got the correct volatility for the Miata's fuel injection system\". When he refers to Cam timing I'm assuming he is talking about base timing and not changing cams. Has any one tried running at more than 14 degrees? I've been told that I can go up to 18 and thats where I'll find low down power improvement on premium.

[SuperMazdaKart]

87octane? Must be an American book. Regular unleaded in Australia is 91 octane using the Euro standard of octane measurement instead of the U.S. standard.

[Juffa]

I ran my original NA at 14 and later at 18 degress. I found that I need to use 98 octane fuel as she would ping like crazy on the lower stuff when running at 18. At the time Shell was the only one selling 98 octane, which shows how long ago this was.

I do remember a seat of the pants 'peppines' but it was a few years ago now, and my memory ain't waht it used to be.

What really made a difference was the fitting of a Loch Stewart cold air intake and exhaust.

J

[Steampunk]

but it was a few years ago now, and my memory ain't waht it used to be.

J

same goes for your speeling

Trader, I think what the guy meant was that the RON requirements of regular unleaded(87 sounds suspiciously low) is the "optimum" for a stock or mildly modded engine.

The best power that a car can make is on the verge of detonation.

In other words, whilst high compression, turbo/super charged cars pretty much need higher RON fuel because they have high cylinder load/pressure and thus lower detonation threshold, stock and mildly modded cars do not.

My car (mild mods) would probably make better power running 91 RON, but I am erring on the side of caution and running 98.
I would much rather produce less power and more durability rather than more power with a chance of detonation.

[Juffa]

but it was a few years ago now, and my memory ain't waht it used to be.

J

same goes for your speeling

no, actaully it's the same as ever.....not good that is

ps. Are you trying to get Miata's job as my primary school spelling teacher

J

[Steampunk]

but it was a few years ago now, and my memory ain't waht it used to be.

J

same goes for your speeling

no, actaully it's the same as ever.....not good that is

ps. Are you trying to get Miata's job as my primary school spelling teacher

J

Nah, I'm just a bit pedantic that way

[trader]

Sorry I put this in the wrong area. Like you Juffa I'm too old for this. Yes it was an American book. For the moment I think I'll put it back to 10 degrees as the Canberra club is doing the Targa route in Tassy next month and I'm not sure if you can always get premium down there.Dw

[AJ]

you can get premium pretty much anywhere you go on the Targa track, Trader, & even the backwaters have 95ron

[adamjp]

One of the reasons the book refers to 87 Octane is that the yanks use a slightly different fuel rating system to the rest of the world (what else is new).

But a little recognised fact is that higher octane (in any measuring system) fuel burns slower. The flame front in the compressed fuel/air mixture will move slower in 98RON than it will in 91RON if the mixture is compressed to the same amount.

The more the mixture is compressed, the faster the flame front moves.

So the point of spark timing on your engine is to have the flame front generate best pressure in the combustion chamber at or just after top dead centre.

If the engine is otherwise the same, adding higher octane fuel without advancing the ignition (starting the burn earlier) will generally cause a drop in power as peak pressure will occur after the piston has started down the bore anyway. However, advancing the timing (in this case the static timing) will not necessarily require higher RON fuel.

On a stock engine, running 14deg advance will work fine on 91RON in pretty much any condition.

[GP]

never use premium gas in your Miata (unless you've radically altered your cam timing).

This has nothing to do with Ignition timing. Does the 5 have an adjustable cam gear or something?