Rough piston dish calculation help needed.

[Will]

I ordered a new set of oversize pistons for my L18, and the dish looked a little bit deeper that the pistons that are in the engine now - probably shipped me a set of the L20B pistons I figured - I wanted to do a quick calculation to find the volume of the dish using the depth of the dish and the radius measured to the center of the slope of the dished area.

 

Current pistons: dish is .8mm deep, 34mm radius - 2.99cc

New Pistons: dish is 1.7mm deep, 34mm radius - 6.35cc

 

It seems pretty unlikely that I've wound up with two sets of pistons with weird amounts of dish, so I was wondering if anyone knows why calculating the dish using the depth and radius can be so far off from the normal values for these pistons? (4.36cc for the L18 and 11.36 for the L20B)

 

Here are some pictures of the pistons that came in the mail:

 

 

...and the current pistons:

[banzai510(hainz)]

Can one still find L18 pistons??????? I wonder if being sold as a L18 replacement. Side of box specs is wrong?

 

Im thinking l20s in the photo

[zed]

I measured volume of a Mazda piston valve reliefs by covering them with a piece of plastic and injecting water through it with a syringe/needle. Sealed the plastic onto the piston with grease. not very accurate, but its a start

[DAT510]

You can also put drill two small holes (with in the dish of the piston) into plexiglass seat the piston on the plexiglass and CC it that way, HRH did this I believe.

 

EDIT: He did it to find the CCs of a cylinder head! i'm sure it'll work for this too!

http://community.ratsun.net/topic/38349-build-thread-for-l20bl20de-lzka2024e-something/page__st__100#entry631449

[Sealik]

I measured volume of a Mazda piston valve reliefs by covering them with a piece of plastic and injecting water through it with a syringe/needle. Sealed the plastic onto the piston with grease. not very accurate, but its a start

 

Thinking the meniscus might raise the plastic a bit...........increasing volume

[Will]

Thanks for the tips - I heard back from the seller & these new pistons are for a L20B. He said that he's going to try and track down L18 pistons, but I doubt that he'll be able to find any.