Port and polish

[rajeev2liz]

OK I have a 99 Mazda miata and am thinking about porting and polishing the head. My question is would this really make a big difference in HP?

[kung fu jesus]

not without supporting mods, like an ECU, decking, cams, tuning, etc.

[HarryB]

And even then, it will make a little difference.

[AndrewG94]

I would say it depends on how much miles are on that head done.
I´m just porting my poor NA head with nearly 130k miles on iit and there was tons of carbon buildup on exhaust side.
with only that cleaned there have to be gain + some port on exhaust side polish and portmatching on intake side and you should see few HP I believe. Will see that on dyno, but I don´t have dynoed my car yet so, nothing to compare it to.

[kung fu jesus]

I wouldn't expect a gain from a carbon cleaning, perhaps more response or regular use performance.

The idea to headwork is improving airflow, so while maybe a couple of HP might be picked up on everything else being stock, porting and polishing alone isn't really worth the expense. Raising the compression through milling would be more beneficial in that aspect of modification, within reason.