Don Sliger, riding a machine built by Jimmy Enz with two Royal Enfield Interceptor engines mounted one in front of the other set a record in Bonneville in 1970 of 203.16mph. It was the first time 200mph was breached on a naked bike. To keep it in perspective, no commercial bike achieves such speed even today! The feat did not constitute an official record, since that requires two runs in opposite directions and in the return run Sliger experienced clutch problems. The bike ran on nitromethane. According to the Interceptor Owners Page, the machine is now the property of Les Power in North Carolina. They have a very small picture of it, shown in the left. However, Royal Enfield Japan's Website has this picture from the National Motorcycle Museum in the UK,
with the Double Interceptor. The engines were connected by gears, not chains, on the right hand side. So it is either a replica or Les Power has loaned it or donated it to the museum. More pictures of the bike in the museum are
In addition to this, a poster in a Cycle World bulletin board has this picture of yet another Double Interceptor,
where the engines seem to be linked in the primary, on the left. The rear engine seems to have the head turned, with the exhausts in the back.
Finally, again in the Interceptors Owners Webpage we find this Double Interceptor Chopper with engines side by side!
So I guess several bikes can make the claim of being the most powerful Royal Enfield!