F1 2.5 mercury 260 hp 1995 fuel oil mixture

[stretch123]

I want to change my oil to a "better oil" maybe synthetic and octane boost. I need some recommendations for oil type and racing fuel or pump gas.....I want to get the most out of my F1 mercury 1995 260 hp ......thanks veterans.....I run just 32:1 standard outboard oil and super unleaded.......

[Raceman]

First of all, an F1 and a 260 are not the same engine.

That having been said, Ive always run my 2.5 Merc stuff at 32:1 with full synthetic. I like Klotz, but there are other excellent choices as well. It may be worthwhile to do a search on oil. It's a subject that's drawn a lot of opinion (and controversy) around here in the past.

As far as octane, it really depends on what heads you're running. Also, not all octane boosters are compatible with all 2 stroke oils. If higher octane than pump gas is required MY OPINION is that you're better off adding some race gas to your fuel mix than experimenting with octane boosters. A common myth is that adding octane increases performance. Actually using a higher octane than the engine needs does nothing for performance and in some cases may even hurt the performance somewhat.

[stretch123]

Thanks raceman.....would you recommend pump gas or 100 octane? getting 130 to 135 in each cylinder.....new reed valves motor is strong......

[Raceman]

Generally speaking I would think that 93 octane Super Unleaded pump gas would be sufficient to support 130 to 135 lbs of compression, but of course there are variables................. timing, the way the compression was checked (accuracy of guage as well as technique). I wouldnt want to see you risk a powerhead on my GUESS as to what octane you'd need, especially given the fact that I've always been conservative with my own stuff.

Do you know what CC your heads are?

[stretch123]

no i do not know the cc's....I was told that the engine is an F1 , but to double check what do I look for?

[Raceman]

I'm not an expert on the history and all the variables of Merc F1 engines, but its safe to say that stock 260 powerheads were never used in F1. From some time in the mid 90s, the F1 powerhead, or S3000 is closer to what is also known as the 300 Drag. There are differences between these two also, but it's mainly bolt ons and changeable.

All F1 Mercs from the late 70s foward had counter rotating powerheads and the timing mechanically locked at full advance. I'm not sure how deep the description of F1 that someone gave you goes, but all complete F1 motors had 12" mids (actually a full 10" shorter than std mids) and non shiftable Speedmaster type gearcases. Of course that too is easily changeable with bolt on parts. There've been various changes in electronics over the years between F1 stuff and other high perf Mercs, as well as head CC's.

In any case, F1 and 260 are contradictions as far as engine description goes. The two do not overlap, and are probably more accurately described as first cousins.

If you post your serial number, somebody around here can probably tell you exactly what it was when new if it hasn't been changed.