As far as I've known since I've owned S2000's, the actual block casting is the same between F20C1 and F22C1 blocks. The differences in displacement and compression came from the stroke changes and piston design, but I always thought they shared the same bore.

I recently bought a set of F20C1 piston rings for my F20C1 rebuild. Since I started the rebuild, I picked up 2 sets of crank/rod/pistons from both AP1 and AP2. In essence, I have the option to run either in the F20C1 block and it'd be my preference to run the AP2 setup for the added displacement.

I'm tempted to use the AP1 ring set on the AP2 pistons since it's an AP1 block, someone else posted the same situation and noted:
"
the oil control rings are identical, but the spacer is way different. its more "dense" on the ap2

the ap2 2nd ring is the same thickness but has a step on the edge, much like rings i see on aftermarket pistons.

the top rings look 100% the same."

So to my understanding, the AP1 stuff would work, it's just that the design was improved for AP2's (probably why the AP2's burn less oil). Does that sound about right?

 

THIS is a great post!

 

the later model ap2 rings use a Napier style second rings to keep oil out of the combustion chamber at high rpms.

the denser oil ring spacer keeps the oil control rings more stable and also reduces the chances of oil getting into the chambers.

I would recommend using the later ap2 rings

 

just thinking aloud in case someone sees something catastrophically wrong with my idea

 

i'll take that into consideration, i wanna see the actual differences between their designs side by side. when i take em off i'll take pictures etc. and hopefully the next person to attempt a hybrid block will have more info in front of them

 

I bought all 3 part numbers last summer to compare.. i tossed the mess w/o taking pics

I did that because for the oversize short compression height mahle pistons i'm using we have to use honda rings b/c they are the only ones on the planet that make a 2mm oil control ring with an 87.25mm bore.

there are 2 different ap2 part numbers, (dont remember the year they changed it I want to say 05) and 1 ap1 part.

 

I couldn't find the other part# for OEM Honda piston rings, checked 04, 05, 06, 07, 08, and 09 in order and got the same part#'s.

Damn Honda though, that's such a slap in the face to discover they kept selling the old design after a new and improved design was made to reduce oil consumption.

 

my mistake, the ap1's have 2 different part numbers, not ap2's

both ap1 part numbers are "normal" style rings.

 

Very interesting read. I was wondering if i can use the newer style piston rings in my F20C2 and came across this during my search. So has anyone succesfully used AP2 rings in an early AP1?

 

Same block casting and same diameter pistons, yeah you should be able to lol