I am wondering if the sedan being rated for 87 octane would be the reason for the HP difference? I have heard that the sedan engines that were rated lower tested to be pretty much the same HP as a coupe.

 

That's what I thought too.

However, the coupe has a more free flowing exhaust. People who installed the coupe midpipe onto the sedan noted very slight increase in HP. So the coupe with a slightly better flowing exhaust must have slightly more hp than the sedan regardless of octane.

 

With the later sedan and coupe with the same ratings, do they still have the different exhausts? Anyone dyno both back to back?