Spark plug location versus power/economy and emissions.
 

http://smrmicro.com/re-ky.pdf

Something's up with my PDF viewer on this machine, so I'll check it out on another machine later, as the information I'm looking for might still be in there.

I was reading it last night with a friend and it seems interesting that the spark plug location changes your NOx and HC emissions. It also changes power and economy...

Interestingly, power and economy are packaged together and are traded for emissions.

Now, I know they changed the location of the spark plugs in the S5 RX-7. Were there any changes to the location of the spark plugs in earlier rotaries, say the 13B from the REPU or the RX-2, 3, 4, etc?

Was this change to meet stricter emissions standards, or to increase the power/economy from an inefficient engine?

Basically, I need someone who has a stack of rotor housings from various 13B's laying about that can look at them and tell me where the spark plugs are located in regards to the crest of the little curve in wards in the rotor housing.

Mine, inside the housings, have a tiny hole were the trailing plug goes (top), and a big hole were the leading plug goes (bottom).

Yes, all of them do... However, if you stack an S4 or earlier housing next to an S5 or later housing, you'll see that the spark plug holes are spaced apart different.

the spacing of the spark plugs has a huge impact on the flame proplaglination durring combustion and this is effects how the fuel is burned thus determining the exhaust emissions. Off the top of my head I believe the S5 has the spark plugs slightly further apart.

Did they only move one or both plugs? According to the article, the relation between the plugs and the little ridge in the side of the inside of the rotor housing is the key factor.