I know that the 14 deg timing modification is quite popular with NA / Mk1 owners, but understand that the standard mod can’t be done to Mk2 onwards due to a change in the way that the timing system works.
I’ve noticed DoctorMX5 near Southampton sell a modified timing trigger plate that advances the timing on a Mk2 / Mk2.5 by 4 degree (which I understand brings it to 14 degrees as the factory setting is 10 degrees - is that right?):
Is it worth doing? Do you get the same / similar benefits in a Mk2.5 when running on higher quality UK fuel (I tend to run my car on super unleaded anyway) or does the ECU in the car get the ideal timing anyway making this superfluous?
For those not familiar with the timing on the Mk2.5, this done by a plate mounted behind the main crankshaft pulley. To get at it you have to remove aux belts and pulley (just 4 small bolts not the main crankshaft bolt.
I modified my timing plate some years ago. It’s easy enough to with a small round file to slot the bolt holes. I slotted it for about 4 degs.
Does it make any difference? Not much, all I can detect is a small improvement in fuel consumption about 2%, no pinking or anything else though and using standard fuel.
If I was doing it again I would slot the plate for up to 8 degs and try that. With a slotted plate you can freely adjust the timing without removing belts or the pulley, just slacken the 4 bolts and move the plate round ( anticlockwise to retard back to standard, clockwise to advance).
I did it as part of a cambelt change and I like to experiment.
I have done a good few Mk2 cambelts and I have never got the pulley off after removing just the 4 off 10mm AF, M6 bolts. I have always had to remove the large 22mm crank bolt and separate the pulley and back plate off the car and clean up rusting on the mating surfaces.
You appear not to have had this issue Razor.
I can also advise this was the way it has been done on all the Europen MK2 cars from 2008 and I believe also on the US supplied Miata’s from the phase 2 Mk1 cars. At a guess from late 2006.
The reason for the change is that sharing the fuel injection, valve timing and ignition timing with once sensor did not give accurate feedback for the Misfiring fault checkin as reqquired by the ODB2 specification,