We have 87 91 93 and Sunoco has a 94 octane too. When I can I put in 94...my gas mileage actually increases over the 93 which goes in if there is not a Sunoco around. My owners manual says that you need atleast 91 octane for the GSR. It may be 10 cents more than 87 per gallon, but on a GSRs 10 gallon tank the most that would be is a whole dollar. Plus your gas mileage will probably go down more with the lower octane and you will need to fill up more often which will cost more. If you are worried about saving money do what Acura recommends, otherwise you might break something that is a lot more costly.