MC suggests 89 octane for my new X1. However, the marina near by only has 87 octane. Anybody have any experience using an octane booster and is it worth it?

Here is the truth. Octane ratings are the fuels ability not to diesel or what most people refer to as "knock". If your X1 does not knock under heavy load with 87 octane you will NOT benefit by using a booster. However, if you here "knock" you should use the additive to prevent pre-detenation wear.

I throw some octane booster after winterization. Just b/c, even with Sta-bil the fuel still loses some of it's Octane rating.

Also if the octane booster says it will give you 3 points higher, its actually .3, so if you have 87 and throw a tanks worth of booster in there you are now a few dollars shorter and running a strong 87.3, not 91, so really its not worth it, unless for a winterization perspective which would make sense. <BR> <BR>Also if you have fuel injection it should have an O2 sensor which should (via the computer)alter the air/fuel mix to stop the detonation, my truck says use 87, but it has 140000 miles and when towing when its hot I put in 89 and it cures my knock issues, it has fuel injection but obviously can't compensate

dont know about mastercraft but with the mercury verado's we rig, using 87 over 89 can result in speed losses in the neighborhood of up to 9mph on the top end,they are supercharged though. Long as you dont hear knock i wouldnt worry about it.

I believe Mastercraft uses the term 89 RON and that equates to 87 octance... RON is a international term I guess?

RON is one formula for working out the Octane number of a certain fuel, or anything else probably, of which there are quite a few. It stands for Research Octane Number. <BR> <BR><a href="http://en.wikipedia.org/wiki/Octane_rating#Definition_of_octane_rating" target="_blank">http://en.wikipedia.org/wiki/Octane_rating#Definition_of_octane_rating</a>