HC pistons from corksport

[twilightprotege]

since we're talking about custom rods - why not just get custom rods that are longer than stock. that way you dont have to even buy new pistons, you just reuse the ones you have!

i have been thinking of this myself, but would really need to see what mods to the block and oil jets are required...

 

[Gen1GT]

A longer rod with the same piston would decrease your deck height, and during high RPM running you could hit the cylinder head, or get valve interference. That's why you might not be able to use the FP rods, since the FS stroke is longer.

You wouldn't want to use the BP rods either, since they're shorter than the FS ones. The last thing the FS needs is a shorter rod. Too bad, since the BP has forged rods.

When you buy rods, they're custom most of the time anyway. Just have them make a rod with FS specs, but to accept a 20mm wrist pin. You'll have to measure the BP pistons to see what the length is from the middle of the pin bore, to the top of the piston. Subtract that number from the same number of the FS rods, and that's how much longer you can make your rod.

Oh ya, in case you guys didn't already have this one...

http://members.aol.com/FE3N/rods.html

 

[Gen1GT]

since we're talking about custom rods - why not just get custom rods that are longer than stock. that way you dont have to even buy new pistons, you just reuse the ones you have!

i have been thinking of this myself, but would really need to see what mods to the block and oil jets are required...

Because you can buy Miata 10:1 pistons for like $30 each

Doesn't the FS have oil jets?

 

[twilightprotege]

yeah the FS does have jets

but with the longer rods hitting the head, why would that be any different to HC pistons? we're only talking a few mm here i guess

 

[twilightprotege]

i should clarrify - i was meaning what mods to the block and what mods to the oil jets are require to make it work

 

[Gen1GT]

Actually, standard deck height for my car is 1mm. Which means if the piston were to travel 1mm more up the bore, it would hit the head. High compression pistons are domed in the middle, but the outer edges are the same. The dome makes the air/fuel squish into a smaller area, which is why they're a high compression piston.

If you notice on the rods page, the Compression Height of the BP pistons is 1.108". Not very much. So whatever it is for the FS pistons, subtract it from the BP number of 1.108, and that's how much longer you can make your rod, while maintaining the stock FS deck height.

 

[twilightprotege]

i get you now...dont know what i was thinking about when you were saying deck height

that's interesting about the comp height. they have the lowest distance out of all the pistons listed....hmmmmm.....i wonder what the FS has...

another possibility - the head gaskets. you could go for the 0.09" thick gasket instead of the 0.04" stocker. there's a bit more room.

but then again, with the large stroke v bore, we want to reduce the rotational mass as much as possible

 

[Gen1GT]

But with a larger gasket, you lose compression. No point in getting higher compression Miata pistons if you raise your deck hight.

They had to shorten the BPs compression height a bit, because the BP is really just a stretched B6, and with it's longer stroke, and pretty short rods, they had to move the wrist pin up in the piston some....

But like I said, it would allow for a longer rod on the FS(assuming the FS has a larger CH), which would definitely be a good thing. Since the FS rods should be replaced right off the bat, this could be a good mod? Who's doing it?????

The Toyota 7MGTE/7MGE 3.0 L6 pistons are 83mm too, and they have a super large 22mm wrist pin, but compression wouldn't be very high. 2.0 VW engines also have 83mm bore....still think the Miata pistons are the best bet though, and might as well keep it in the family....