1997 MX-5 (B61P) top end rebuild (with port work and head skim)

So having sold my 2003 MX-5 Nevada back in the summer, I bought a 97 1.6 MX-5 which after doing a bit of mechanical work on it to make it a good daily, I soon found myself thinking of ways to make it faster. I was very surprised how quick it felt for a supposed 90hp engine, which originally I thought would be a massive let done coming from 146hp to just 90. 

So I did some research and found that by fitting the cylinder head from an earlier MK1 1.6 (115hp) it would take you over 100hp. This followed by a quick search on eBay and £55 later I had a complete cylinder head with cams and valves etc. I could have bolted this straight on but… well… I didn’t. 

Working in the industry I have access to the right knowledge and equipment to make it better than original, which I was surprised to find there is not much you can do to make them better without going mad and throwing money at it. Having suspected it had been skimmed before I got it, I CC’d the cambers to get an idea of compression ratio which I am yet to calculate. The CC hovered around 39cc per chamber (+/- 0.5cc). 

So over the course of many lunch brakes I have been smoothing out the inlet and exhaust ports without taking too much out seen as it will be a mild daily. 

I also plan to have the head skimmed, hence why I need to calculate compression ratio. Any advice on this will be greatly appreciated as I haven’t looked into this a whole lot. I know most people go for a .040 shim but I have a feeling its been skimmed before so I need to be carefully I don’t over do it. 

Having bought the head, I then looked at my engine bay a thought ‘everything but the engine looks pretty good’ so back onto eBay and a few days later a cam cover arrived on my door step followed shortly by a can of VHT red crinkle finish paint. I went back to the drawing board… well the engine bay and thought ‘well if i do the cam cover, the inlet manifold will get jealous’ so one of them turned up on my door step too (It has since been port matched to the head for less interrupted flow) . Then I realised (if you’re still reading, thank you!) the bits attached to the manifold will standout if I don’t do them too so I now have a throttle body, Idle Speed Controller and fuel rail too. Someone could have told me how addictive this MX-5 stuff is!

The plan is when I swap the cylinder head over, I will give the whole engine bay a tidy up with all the extra bits I have then sell the bits I take off. 

Pictures will follow when I work out how… what ever happened to copy and paste!




Hi Jake,

Roadster Robbie told me that the Minimum cylinder head height is 133.8mm, for a 1.6 engine.

That should help you establish if the head has been skimmed.

Hi, I’m not in a position to help or advise but I am interested in what you are planning so hope you keep posting.


Does that mean the minimum you can skim them to? I measured mine today (only with a vernier caliper) and was getting values between 133.85 and 133.99 but it was hard to find points on the head where you could measure. Tomorrow I will put it on a surface plate and measure it properly. 

I have struggled to find values for the factory head chamber CCs which would help but the head thickness should work. 

Have you done something like this before ?