great fuel debate

Originally Posted by jonboy

I'm running CR9Es to compensate, which I hope will be enough.
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This is becoming nicely circular....

I don't know enough about NGK heat ranges to confirm, but my guess would be that they would do. However, the plug only "records" what it sees...and everything else in the combustion chamber will be getting a tad hotter too. Like, valves. More importantly, at the limits, the overadvance will precipitate detonation.....to counter which, requires a fuel with a higher octane rating (fanfare of trumpets!) - embee will probably confirm that.

My personal experience has been that, for road use, you might gain a little extra by going beyond manufacturer's ignition settings (because of safety margins and tolerances), but not very much and usually with some nasty penalty. Given the efforts put in to set it up right to start with, I personally never messed with maker's timing settings.

[embee]

Ref the above post.

As said by others the SV is calibrated on 91RON, and I'd guess that at 11:1 CR it's going to be quite heavily knock limited up to resonably high revs (wouldn't like to guess where) on that. It probably isn't knock limited at max power though.

If so it would mean that the ignition at low/mid speed and high load will be pretty retarded from MBT (max brake torque), so a blanket shift of a few degrees (stepped key) will have the most effect at low/mid speed (which dyno curves do indeed show), but relatively little effect at max power.

95RON will allow ignition to be set to significantly nearer to MBT, hence the 4degrees.

The only question mark really is whether you end up "over-advanced" anywhere, i.e. places where the std ignition is at MBT already.

As for the plug grade, I'm pretty confident that one grade colder will be sufficient if the 4deg is the only significant mod. Japanese manufacturers are pretty conservative and there's a decent safety margin in standard specs. Plug grade is as much down to the head structure and cooling galleries (i.e. the heat path) once the chamber+CR are fixed.

Adding ignition advance (up to MBT anyway) will actually reduce exhaust gas and exhaust valve temperatures.

FWIW I have the slotted pick-up holes which give 2degrees. You can certainly notice the low speed effect, much snappier pulling away. Never heard any knock (unlike my old BMW!).