To answer the question at hand, you will be fine.
Merc does indeed rec 91/2 oct. It is not necessary, you can get by with 87 ( if it is fresh and ethanol free ). Not that I would, but you are not going to hurt your motors, at least not with detonation.
If you want a booster that actually works, get TK-7. It is the ONLY octane booster that actually helps.
As and owner of a 225 carb bridgeport, a 240hp EFI bridgeport, a 245 carb 2.5, a 260hp 2.5, a 280hp 2.5 many 300PLUS hp 2.5 drags, a few 300 pro max's and a 300x... and a licence to work on them, I can assure you I know more about them than the stump who clearly forgot more than the rest of us!.
If you want a booster that actually works, get TK-7. It is the ONLY octane booster that actually helps really
Ya gotta love it with all the wisdom on these forums....
Any hydrocarbon with a higher effective octane rating can be mixed homogeneously into a "base fuel" hydrocarbon with a lower effective octane rating with the net effect of raising the octane of the base fuel. It isn't limited to a particular brand name or chemical makeup.
93 octane fuel is regularly mixed with 87 octane fuel IN THE PUMP ITSELF to deliver midgrade 91 octane into your car.
Toluene is, and has always been, an effective "octane boosting additive" to pump gas.
There are, however, OTHER MAGIC CHEMICALS (remember tetraethyl lead???) that, when added in small amounts to unleaded base stock, can improve "octane" dramatically by inserting themselves in the long chain molecules and providing a "buffer" action in the flamefront behavior.
No need to argue whose octane booster is bogus, and whose is glorious. Many of the AutoParts brands of octane improvers, however, are MINIMALLY effective. When they speak of boosting your octane by two POINTS, they are talking about going from like 90 to 90.2 - keep that in mind.
And I hope we ALL are firmly aware that OCTANE is an empirical measurement of how RESISTANT a fuel is to uncontrolled combustion. It isn't a measure of the energy content (heat content) of a given fuel. High octane fuel can be run at a higher pressure and temperature while providing detonation resistance. You want a fuel that burns evenly rather than explodes - that's the goal. As a hard and fast rule of thumb, given a low octane gasoline and a high octane gasoline, the lower octane gasoline will contain MORE energy per ounce than the higher octane fuel. Test after test will show that running the lowest octane fuel that will stave off detonation in your engine will deliver the best fuel economy and power - when all other engine parameters are identical. All of us who have cars that run "better" on premium are experiencing what happens when the computer avances the ignition curves to take advantage of the higher octane fuel we've poured in. If we had non-computer motors, we would have a NEGATIVE performance gain when adding higher octane (although not enough to feel).
In the case of a 300 ProMax, it's a motor that's happy on midgrade fuel.
Ethanol in your fuel? Yeah, it will show that it runs leaner in your motors, but unless you are running a race tuned motor, there is generally enough fuel metering leeway to ignore the difference. Generally, that is.... I have a 68cc 2 stroke Scooter that belongs to my son, but I ride to the shop occasionally. It's tuned to the edge of life, and runs impressively. Add ethanol in the fuel and cool weather, and it will no longer start when cold, and requires a jetting change. You won't have that issue on your 300 ProMax.
A 300X is a smaller, more highly tuned motor. Requires better fuel.
And cranking compression on a 2 stroke motor doesn't mean much by itself. Unlike a 4 stroke motor that has an "intact" cylinder bore, a 2 stroke is perforated with ports. These ports let pressure escape, ESPECIALLY at cranking speeds. Two different 2 stroke motors cn have the same cranking compression with one being a low rpm low performance mtor with low octane requirements, and the other being a racing motor with wild porting that requires higher octane.
Sure, given the SAME motor, raising the compression also raises the cranking pressure, but raising the exhaust port lowers the cranking pressure. I've got a 2.4 Merc that had 135 psi at baseline. I reshaped the compression chambers and brought the compression up to 185, then I raised the exhaust ports .060" and it dropped to 170. You get the idea. Cranking compression doesn't mean much in a two stroke. Combustion pressure at operating rpm is what matters.
Bridgeport Mercs have a larger exhaust port opening that is "too big" for the piston ring to remain stable. For that reason there is a bridge in the center of the port to support the ring. When you REALLY start modding those motors for serious power, the bridge gets too hot and "melts" out of the way because there isn't enough beef behind the bridge. Then you lose the cylinder. We had better luck going wild with standard finger ported oval port blocks when we started going nuts with them. Good luck to anybody running a Bridgeport who starts spraying nitrous, etc. Better hold your mouth just right and live & die by the fuel pressure warning light.
Now why are all of us fussing at each other?
If there are people on here who have "forgotten more about something than somebody else will ever learn" then maybe they need to take a memory course. Why the crap are they forgetting so much, and if they are, why do they want to brag about it.
There were probably people on here who were "building motors when I was crappin yella" but what is that supposed to prove? All I can tell it means is that they learned how to put together an old motor when I was eatin strained peas. Big deal. Seniority is not necessarily a valid qualification for the guy you want keeping your modern motor running right. Neither is forgetfulness.
Back to the thread - it's a shame that our fuel is full of alcohol, not cause it will blow up our motors, but because we don't go quite as far on a gallon, and because the rubber parts in our fuel system harden on exposure to alky.
I see London, I see France...
Mc,Very impressive,what a great post,thanks.Enjoyed the read. "Peace,out" been a while since I've seen that one.Memories.....Kinda made me smile. Bob
Great post MC, a lot of info in a few short paragraphs that even I can understand. I know now I didn't hurt the engines and am grateful for all the imput by everybody and know the course I will now follow. Thanks again, all of you.
Alum Metal Fab
Custom Marine Sales
Dave's Custom Boats
Diamond Performance Parts
Double R Performance
Elton Porter Insurance
Fastboats Marine Group
GGB Exhaust Technologies
Grand Sports Center
Ilmor High Performance Marine
Lake Cumberland Marine
Lake Havasu Boat Show
Marine Technology Inc
McLeod Design Group
Performance Boat Center
Performance Marine Trading
Potter Performance Engines
Ron Sporl Performance
Speed and Custom Marine
Total Dollar Insurance
Teague Custom Marine
Wake Zone Marine Insurance
Young Performance Marine