Rx-7 plugs
 

Ok, I got a set of NGK FD plugs to replace my OEM plugs. I thought I read that you needed to put some sort of washer on them to make them the same length as the stockers?

Any help would be appreciated

On my RX-7 I actually remove the washers to get the electrodes a little bit closer to the engine. They don't hit the apex seals on 13B's. Not sure about the Renesis but I don't see why they would. Those washers are actually seals. I've never had any issues without them though.

which FD plug is the trailing?

It will be marked with a "T" on the plug.

I used them in my 05 with good results. The 04 is running the ones it got during the recall.