I’m thinking about having the cylinder head skimmed.
But how much should i skim it by??
I have read loadssss. some people have done 50 thou, 40 thou, 30 thou, 20 thou etc. But this is what i’m puzzled about… What should i go for?
Also, as the head will be off for skimming, i’m going to have it ported/polished - if that makes any difference to the size skim it should undergo?
The car is in use daily and i plan to do some trackdays too.
Thanks!
Firstly, there is not much point in having your head ported and polished unless you are going to have it done properly and checked on a flow-rig to ensure consistancy between cylinders, most professional head-porters will charge around £350-500 to port a head properly and test it.
There isnt much scope for fitting larger valves in these heads 
A good way to gain horsepower on these engines is to have your camshafts re-profiled (removal of metal from the heel of the cam lobes and the cam lobes re-ground to give higher valve lift and better duration), also to get the best power you would need to go to a solid-lifter cam follower rather than the hydraulic type you have currently, you will also need to use Vernier camwheels to get the best results from the cams.
Piper Cams will do them to one of their performance profiles for you for a one-off job price of around £150-175 per cam (you have to sort the lifters)
As far as raising the compression ratio by skimming the head, most competitors in the MX5 race series seem to take 40-50 thou off - but remember
they will be using super-plus 99 octane fuel, if you are planning to stick to the cheaper fuels like ordinary un-leaded then you may need to retard the ignition timing a bit and 40 thou ought to be the most you would want to remove to avoid pinking or detonation turning your engine to scrap pretty quickly.
Hope this helps?
Dr. Eunos
I run the high octane fuel anyway 
advance the timing to 14-ish deg.
I’m thinking a 20/30… = 25 thou skim then?
Do you have a link to the solid lifters? I can get access to a flow bench anyway, think i might check it first to see if its really needed or not, i have heard they are quite good flowing heads anyway
Are the vernier camwheels worth the hassel? I don’t fancy paying out for a days dynoing just yet!
Is there anything else that i can do? De-cat pipe? 4-2-1 manifold with a flexi?
What’s your aim with these mods?
It’s a project car and i’m just looking at options
One goal is to make my eunos “mine” if you get me 
There are other things to first before i even start on the engine, i’m just gaining some info so i can have a good think about things before i do it.
Ah yes, fully understand that
I took the same approach when I bought mine 11 years ago. So long as you’re not expecting huge power gains without spending a lot of money, you can have a great time with the engine, I’ve done it many times on things from Minis to twin cam fords, this time I took the short route and bolted on some FI
I figured that haha, what mods can i do to improve the performance without going too pricey?
I used to own a mini, sadly the shell warped and at the time i didn’t have any time or patience to put her on a jig and straighten it, so shes in the scrapyard in the sky.
I’d love to fit a turbo on the '5 but i can’t afford to at the minute, i probably will at a later date
A decent intake system, manifold and exhaust system will free up a few BHP, but to be honest the gains against cost are not very good .
Just had a look at MX5 parts for the bits
Manifold £280
Front pipe £153
Cat? not listed
Back end £327
Intake system £178
Well over £900 for a gain of maybe 10 bhp
It seems that superchargers seem to be very expensive over in the UK, just looked at Moss and over £3k
I paid $3k for my complete system with all the extras.
Captain Muppet one of our drift specialists put together a Turbo for I think £500, been running reliably for about 3 years, so food for thought there mate
There’s a guy in this thread who has skimmed his head http://www.mx5oc.co.uk/forum/forums/t/25199.aspx?PageIndex=108.
Maybe have a chat and see what his dyno figures are
Have a look into what Mazda did with the 1.6 in the M2-1001 (raised compression, changed pistons, higher lift intake cam, exhaiust, intake); 130PS. Bob Hall, ex-Mazda North America, claimed Mazda did put together a CARB-legal NA 1.6 Miata with a reliable 150hp in 1990. Using a Mazda MPV hotwire MAS was part of the change.
There are inexpensive kits now available to fit the ex-MINI Eaton chargers;
http://www.trlanefabs.co.uk/SUPERCHARGER-PARTS.html
My long term ambition is to do a normally aspirated 200bhp 1.8
Dr. Eunos
It went on at the end of the 2007 season, and apart from a split oil drain hose (I must stop using parts recovered from skips) it’s been trouble free. I’m running low boost - 6psi. It should be making something in the region of 150-160bhp.
My other car (not an MX5) had a 120bhp 1.8 which has been ported, tweaked and fettled with comedy cams and big valves up to 160bhp. The turbo engine in the MX5 adds significantly more drama to the driving experience and cost a tiny fraction of the money.
That said - I needed that much power and had a tiny budget for the MX5. If I just wanted to play with an engine I might do things differently. I think my light weight flywheel changed the driving experience more than 10 or 15 extra horsepower would.
Made my own backbox up 
it’ll do for now, £30 all in, sounds really sporty now
Pipercross cone filter fitted (+ heatshield - quite naff, i’ll make my own up)
De-cat pipe is on its way, hopefully it will be here tomorrow, along with some vents to make a cold air feed
Set of Denso TT plugs fitted
Will change the oil again while i have it in the air, and filter this time
Will take some pictures of it all tomorrow - this is all of course if it stays dry and i get what i’m after at the scrapy!
N/a tuning is pretty popular especially in the US, google is your friend.
I would say do a 40 thou skim, exhintake mod (if a 1.8), mild port and 3 seat valve job. Blink motorsport have good results, talk to Nikpro over on MX5Nutz.
Later on try cylinder re-bore and oversized pistons and better cams, but first you’ll benefit from a better flowing air intake (ARC or JRCAI) and exhaust.
Megasquirt will have benefits of saving fuel and increasing power.
P.s You will really need to use verniers to get your timing spot on after a skim, I’m doing a GB over on Nutz if you’re interested.
http://www.mx5nutz.com/forum/index.php?showtopic=86543