Need an explanation of rpm behavior

[Bondo]

Re: Need an explanation of rpm behavior

The motor is a Mercruiser 140. I plan on doing the electronic conversion and an MSD style box. How much speed does a hydrofoil usually cause you to loose?

Chris

Ayuh,.... Look into the Delco EST ignition,...

It's what Merc is now usin', 'n is a Great ignition,....

Reasonably cheap too,...

 

[Chris_94_Sprint_TX]

Re: Need an explanation of rpm behavior

I have run the boat without the foil. It planes sooner/easier and at a lower speed as best I can tell from the short trips I've had.

Thanks Bondo, I'll look into it. Will the distributors from a newer 3.0 work in my 85? Seems maybe swapping one in may be better/easier. The Summit Racing ignition box sounds tempting at $150 to add along with it. According to their tech line it can be used on a boat but its not CG approved, however if I use it I plan on mounting somewhere dry (have a few places in mind).

Chris

 

[CharlieB]

Re: Need an explanation of rpm behavior

A simple cost effective ignition improvement for the 120 - 140 series is the Pertronix unit. Replaces the point plate with an electronic unit, much hotter spark, quicker start, smoother idle, small increase in power and acceleration, often picks up a few RPM at WOT.

You can replace the coil with a little hotter one but it is not required.

 

[Tail_Gunner]

Re: Need an explanation of rpm behavior

Use your automitve backround with a few exception's do not trust the tach...boat tachs are eye candy no more no less..use gps to determine your speed..again boat speedo's are eye candy. Once you verify things with accuracy paost back with the gearing and pitch on your out drive things will clear up quickly.

 

[Chris_94_Sprint_TX]

Re: Need an explanation of rpm behavior

I don't know what the gearing is on my outdrive. I bought this boat used and the PO didn't know much about it, he always had it serviced by a shop close to him. All the plaques/stickers on the outdrive are gone. I am using my auto knowledge, I have hooked up a Stewart Warner tach and verified readings within about 100 RPM or so of my boats tach. I was going to use my multi-meter but I am unable to locate the needed attachments at the moment.

Chris

 

[Bronlonius]

Re: Need an explanation of rpm behavior

In regards to finding the gear ratio, this thread might be helpful, assuming you have an alpha 1 like you signature http://forums.iboats.com/mercruiser...a-1-outdrive-has-wrong-gear-ratio-442997.html