100 Octane?
 

My friend in buying a new 38 ft.performance boat with twin 525s..The dealer has told him he needs to run 100 Octane every 3rd tank and 93 the rest of the time...
What is the reason behind running the 100 octane?..Doesn`t make much since..

Re: 100 Octane?
 

Are they the new Merc 525's or the SC's?

Re: 100 Octane?
 

Hotter burning fuel will help keep injectors clean. Not an absolute necessity but it is not a bad idea.

Re: 100 Octane?
 

We need more info

Re: 100 Octane?
 

The higher the octane in gasoline the cooler it burns. It burns slower. That's why higher octane can handle higher compression. Compressions side effect is heat.
Secondly, the amount of heat in the combustion chamber has nothing to do with how clean your fuel injectors are or aren't. It's the additives in the fuel that keep the fuel system free from rust and scale. The filter is supposted to take care of the dirt.

Third. The same additives that do the above job are in 87 as 93. They may or may not be in the 100. Depends on where you get the fuel.

If the motor can handle 93 without detination, that's all it needs. There would be no reason for the 100 octane.

DAVE

Re: 100 Octane?
 

Dave F is right the higher the Octane the higher the flashpoint. Therefore higher octane burns cooler. High octane is for preventing detonation on motors with a lot of compression and/or timing. It does not makes boats/bikes/cars/etc faster. In fact, it makes them slower! Less heat=less hp.

I could see them asking to MIX 100 octane with 93 to get to a certain number(ie 5 gals of 100 mixed with 5 gals of 93=96.5 octane) but every third tank? That makes no sense at all.

Re: 100 Octane?
 

100% correct. higher octane burns cooler. The injectors aren't even in the clyinders they are in the intake so temp has nothing to do with them, it aint a diesel ! the only benefit would be lower clyinder temps and pressures resulting in extended head gasket life. The every third tank bit make no sense at all though. that engines is mapped for 93 octance and runs the best on it. Along with the lower clyinders pressures and temps will come less power. The motor was designed to run on 93 and that's what you should run.

Re: 100 Octane?
 

I have 525sc's and it says right on top run 93 plus octane. Spoke with merc and asked about 92 since in some areas that is all you can get, and they said it would not hurt it. Dont know why they would say 100 but you can run it. Do they own the marina and sell that fuel, maybe that is there way to sell more fuel :D

Re: 100 Octane?
 

They are new 525 EFIs...Tnx for the input..sounds like someone wants to sell some 100 octane....