i have a question...my 91 civic dx manual says that it requires 91octane now i've been putting 87 in it for awhile...should i be putting the 91octane in or is regular just fine?

 

The manual actually says 91 octane? It shouldn't, that engine is designed for 87.

 

the manual says:

"gasoline requirements
your engine is designed to operate on unleaded gasoline with 91 research octane number or higher. using gasoline with an extremely high octan rating would be an unnecessry expense with no appreciable improvemment in performance"

im still going to continue using 87 i was just wondering if i really shouldnt be.

 

Research Octane Number (RON) is higher then the octane number shown on US and Canadian gas pumps.

91 RON is equal to 87 (R+M)/2 octane gas. The manual says to use 87 octane gas in somewhat misleading terms.