Can the timing belt squeak on Merc 1500?

[Zac Penn]

Chris,
So you say i can run regular 87 octane gas at 21 BTDC? If so then I am wasting a lot of money using 93 octane

Update...
I ended up bringing out another prop with me and with a 3-blade 17 pitch prop I can get up to 5300 rpm and 32 mph on my gps. With the 4-blade 19 pitch I am stuck at 4300 rpm and 29 mph. I do have a 3-blade 15 pitch prop as well but I haven't tested it out yet. Here is a fuel economy question for you...

Do you think the fuel savings would be measurable between WOT at 4300 RPM vs WOT at 5300 RPM?
Am I causing damaging stress on the motor running the larger prop at lower RPM's?

 

[Chris1956]

I would say you are wasting money on premium fuel, as the motor does not require it.

As for RPM, the motor will run best if propped to get into the recommended WOT range (usually 5300-5800), with a normal load. Running a motor with too much pith on the prop will lug that motor, raising wear and tear and using extra fuel. Remember, best economy is when the motor is being held at a speed by the amount of throttle opening. When you lug an engine, the vacuum in the manifold drops, which is an indicator of poor economy.

 

[emckelvy]

Am I causing damaging stress on the motor running the larger prop at lower RPM's?

A resounding YES! You need to rev that engine and 5300 is probably on the low side of its "happy place". 5500 would be better and you'd probably get it with the 15-pitch prop.

The 1500 has porting which makes more power at the high end of the rpm range, and it does need to rev. You must be pushing quite a large load, judging by the speed & rpm. That same motor on a 15-16' ski boat will produce speeds in excess of 50 mph!

The WOT rpm testing ensures that the engine is not over-worked ("lugged") at lower speeds with more load. If you "lug" the engine by overloading it with too-large of a prop, it can lead to detonation and piston failure. Not to mention fuel economy will in many cases be Worse, since the engine isn't up in its powerband.

Anyway, I bet you'll be happy with the 15P on there, especially if you typically carry a lot of extra load in the boat. Don't worry about overrevving that 1500, it'll be happy to spin right up to 6 Grand without complaint! Only just do that for the WOT test, not all the time (in deference to its age, if anything else).

HTH........ed

 

[Zac Penn]

Tanks guys. I couldn't figure out if I would have better fuel economy at a higher rpm range at WOT. I am going to try the 15 pitch and see what happens.

As usual you are the best!