I need help figuring out how to match the correct rods to the pistons I'm looking to use in my build. I searched the site and didn't really come up with any threads quite on point, if I missed something please point me in the right direction...

I have a 90 Miata with a now torched 93 engine. I am having the block bored to .020.over. I had originally been looking at some Supertech pistons, but they called for rod length of 5.228" with pin diameter of .787" (20mm). It seemed like I could not locate any H beam rods that would fit that bill, so then started looking at other pistons.

I looked at Wisco .020 pistons with part no K554M785, only to find out they call for the same rod specs as the Supertechs- 5.228" with .787" pin....

I have seen on ebay several sets of these Wiseco pistons (of the same part number aformentioned) matched with a set of Eagle rods with part no CRS5233M3D...

If I'm not mistaken, that is a 5.233" rod.... How can that work? it seems like if the pistons call for a 5.228" rod, running one that much longer could cause interference with the valves and/or head? Or is it just going to up the compression ratio??

Any thoughts or help on this issue would be much appreciated!

 

So, even though I didn't get any input, I found that the Wiseco .020 pistons actually call for a 5.234" rod. And the CR is quoted at 8.5:1 with that setup (located this striaght from the source - Wiseco).

So running the Eagle 5.233" rods should actually lower the CR slightly. But Since I'm going to have the block decked, I figure it should almost even out. Stock CR for the 1.6 appears to be 9.4:1, so i figure this should still be an ok setup since I'm currently running about 8psi boost, but hoping to up it to 10-12 psi so having a lower CR should actually be ok.


So a follow up question I have if anyone is reading this and knows, is about the head gasket: I measured a spare stock head gasket I have laying around and it looks like it is 78mm.... so if I'm boring out to 78.5mm, it doesn't appear a stock sized head gasket will work... correct???

I have searched the internet for cometic gaskets and they seem to only list 80mm bores for their Miata 1.6 gaskets... I'm at a loss for what head gasket I need to get to not interfere with my larger pistons, but not go so big as to adversly affect the CR...

 

Stop it and build a 1.8 block.

 

Too late, i'm already ***** deep in this one! My pistons and rods are showing up tomorrow.