do the 575 sci's take 91 0r 93 octane...or maybe 87

i was told you can run 87, but they like 91 and love 93, i always 93 and have never had a problem with mine, plus they are bumped up a little

I know on the newer SC 600 and 700 you can put the crap 87-89 in them and it will nock/ping and pull the timming back and HP but you can run it but I don't know if the computer on the 575 is good enough to not do harm on the 91 or higher fuel. It's not on their web site ?

Fuel Type - Unleaded Premium - Minimum Posted Octane 91
(r+m)/2 or 96 RON * Mercury Racing does not recommend gasolines containing alcohol ---This imfo came from my Mercury Racing #8 575SCI Service Manual. I have been using 92 with 10% ethanol for several years now with no ill effects yet. I would never run fuel less than 91 octane except if nothing else is avalible, then only enough to run home using no boost and minimum RPM. Using less than 91 octane can reduse the block and heads to junk along with waiting too long to change the head gaskets. I have seen this twice now in the last 2 years on my friends boats.

Originally on the early versions it was 92 octane and then later reduced to a 91 octane requirement. This is per Merc.

You can run anything with 87 as long as it is 0 boost.

how about a 10.5:1 motor !!!!???