Q about the secondary fuel injector diffusers
 

Can someone who has had experience with both S4 and S5 TII and N/A motors please tell me the difference between the secondary fuel injector diffusers.

My S5 TII came with a "double stack" diffuser that had two rubber o-rings on it. But then I had some spare "single stack" with only one o-ring diffusers laying around the garage. So, are the double stack diffusers a S5 thing, or are they a TII thing?

To ask the question more specifically...are the diffusers the same accross series for N/A to N/A (so, S4 n/a is the same as S5 n/a and S4 TII is the same as S5 TII), or are they the same accross engine type from S4 to S5 (where they are the same S5 n/a is the same as S5 TII and S4 n/a is the same as S4 TII)?
Thanks,
-a