what oil type / grade is best for a mk1 5 for trackdays, ie fully synthetic or semi synthetic. want to give my engine the best chance to survive a sustained thrashing…
The MK1 especially before about 1995 did not have an oil cooler also the 1.6 engine even with an oil cooler after 1995 still appears to be suspect for oil cooling according to those that claim the knowledge.
I have never done a track day!
An oil has an upper tempreture limit based on the second viscosity number.
So for a 10W/40 we are intersted in the 40 number.
The higher that number the better for high tempreture protection but too high and there are lube problems as it has issues getting into small spaces in the big and small ends.
So if you want both belts and braces buy an expensive 10W/50 fully synthetic oil and .change it after the track day.
If your car has a large oil cooler then plenty people use a sythetic 10W/40 for track days but you would need an oil temp guage to check the oil is not getting over tempreture.
If you google for used oil analysis miata, you will come across people who track day their cars in the states and then get an oil analysis done after some track days to see if it is still in spec.
The cost of the UOA is approx the cost of a oil change circa £25 to £30.
If you decide to do it more than a few times a large oil cooler than the standard and a tempreture guage is starting to be a good idea
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1639346&page=1
http://www.nasaforums.com/viewtopic.php?f=39&t=42852
The bit to look at is at the bottom of the report page re viscosity as it shows the oil viscosity is below the lower limit after track days.
I just got one done on my Impreza after 9,000 miles and it was still well in spec long runs and no track days.
Got the report back within a week from Blackstone Labs.
Oh if you use a 50 oil even it shears down it will still be at a 40 grade but even then it suggests other things will be happening so time to replace.
Ive used either 5w30 or 10w40 and changed it every 6 months or so even when supercharged. lots of trackdays and a good bit of road mileage.
Worry less and enjoy your driving !!
I only fitted an oil cooler when i was reaching 110-115 degc on one very hot trackday but the car engine is still very good and uses hardly any oil…a lot of fuel though.
Alan
I’ve used 5w40, 10w30 and 10w40 both fully and semi synth for track days. All have been fine - if you have a nasp car I doubt you’ll have any issues with any of these.
FWIW, I have settled on fully synth 10w40 as I think its the best for track days.
Thanks for all the detailed replys. thats very helpful. will go fully synthetic. BTW that oil filter is a sod to get at. its the 1st oil change ive done on my mk1 and still have not managed to get the filter undone. theres just no room to get any tools in there to undo it. will be back on the case this weekend to get it off.
Yes taking the cylinder had off does improve access to the filter!
no need,
a firm grip whilst wearing a pair of rubber gloves should do the trick.
and then just do it up hand tight.
but i find it easy cos ive got girls wrists and can grip it behind the manifold !!
oh and a sanwich plate for the oil temp and another for the thermo takeoff for the cooler
an old belt pulled around it and doubled back with the long end out can help to free it up.
Alan
A firm Grip… Do you get angry and turn green to get it off 
I dont go green but the air turns blue if it sticks a bit !
Alan
A friend has similar double jointed wrists and can remove and replace MX5 oil filters by had with ease. I have the cup sockets that are driven by a quarter in ratchet but even the the Mazda branded filters come in two different sizes just 2mm different in diameter and you need two different size cup sockets to cover being able to get them on and off.
Even the Mk3 filter is a touch difficult to get at.
With any oil cooler ensure you fit one with a thermostat, no point in having oil temps constantly low in cold weather or short journeys 
I would worry less about the type and brand and more about clean and toped up.
Synthetic oil is long life oil designed to go a long time between changes, however it does not stop it getting dirty. It is over kill for track day driving and frequently is too thin for the engine and therefore the oil gets burnt.
Change it frequently and Tesco’s value oil will do.