Piston to Bore Clearance using OEM Mazda 83.5mmPistons
 

Hi,

Any suggestions on piston to bore clearance when using OEM Mazda 83.5mm pistons? NA application.

Factory manual I have states standard clearance as 0.0010" to 0.0025", and max as 0.006". Some discussion here Piston to Wall Clearance which seems to conclude between 0.002" and 0.003". I will be using the OEM Mazda .5mm rings, which I have not seen yet, but assume are pre-gapped (i.e. not file back), so the more I open the bore up, the more I will open the ring gap up.

Mostly track usage, and more concerned with max performance than anything else.

Currently I'm thinking of aiming for around 0.002 to 0.0025" which is the towards the upper end of the OEM "standard clearance".

Any input appreciated.

Cheers.

Naturally aspirated with stock pistons? Use stock clearance values. If what you have been reading online is about forged pistons then it is useless if you are using stock cast pistons because the expansion values are different. And if it is for a turbo application then the temperature range will differ as well.

Hi,

Thanks for the reply. I do understand the differences between the requirements of different pistons, and NA vs Turbo.

Mazda set OE clearance values with many factors in mind, many of which I am not concerned about. I am specifically seeking advice regarding optimum bore clearance for NA track car performance using OEM pistons / rings.

Cheers.

Talk to Emilio at 949 Racing if you want some really technical advice for a race engine. There is a big difference between a 10 hour race engine, a 100 hour race engine, and a 2000 hour dual duty track/street engine. Bore clearance, ring tension, and a whole lot more play into it.

Cheers sixshooter, I will try to follow up with Emilio at 949 Racing then.

You are of course correct that there can be a dramatic difference in engine running time between refreshes, depending on a huge number of factors. I would not be overly concerned by a relatively short time between rebuilds if it means reasonable hp extra. However at the expected power density, using OEM Mazda pistons and rings, I think there will be quite a while between rebuilds.

Tried to PM Emilio through the forum but it appears that I can't.

Anyone?

His website?

You could make a telephone call during west coast business hours, maybe?

He'll sell you some better power than stock rings for your application if you let him. And I'm sure he can offer some other suggestions while you have it apart.