Same Motor, Same Prop, Losing speed??

[Steamboatbonner]

Hey gang.I have quietly absorbed the knowledge this site provides for some time now... but this one stumps me. I have an 88 SeaRay Seville, 20 CC, 3.0 Merc with an Alpha1 Drive.. I recently had the motor replaced with an identical 3.0. Before the motor swap I could cruise about 40-42 mph (Speedo AND GPS). Since the motor swap I have a hard time getting past 32 mph. (Speedo AND GPS). The Tach is also reading a lot higher on the new motor but Im thinking the tach is no longer accurate and needs replacing. Any insight on where my speed loss is coming from???.







Or should I move this to the engine forum?

 

[Sea Rider]

Welcome to Iboats,

Your wot rpm is needed for both trials. Were props same when swapping engines ? Were both trials conducted with lightly loaded boat on flat calm no wind sea cond ?

Happy Boating

 

[Steamboatbonner]

Engine was swapped, everything on the lower unit stayed the same (except impeller). WOT rpm will take some time to acquire as the Tach is likely at the end of its service life and needs to be replaced. However both trials were in the same waters, in the same weather, in the same conditions and cargo. The only difference is I could do 40+ with 1 passenger. Since the new motor was installed, I've only been out by myself and have never exceeded 32 mph.

 

[Sea Rider]

Is the second engine undergoing break in period ?

Happy Boating

 

[Steamboatbonner]

Wasn't a new motor. came out of another boat. So I'd have to say no. I made sure to pump out the old fuel and use fresh, checked all the filters, fresh fluids, carb is sparkling clean, it sounds like its running the same as the previous motor, but again, without an accurate tach I cant be 100% positive.

 

[Maclin]

Did you do a compression test?

 

[Steamboatbonner]

Hmm... Good Call! Never even though to do one. I'll do it first thing Saturday morning. Those run right around 140 or 150 per cylinder correct??

 

[steelespike]

I wonder why you would change motors when you had a setup that was right at the top of the expected speed.
range You seldom see a 3.0 over 40. Usually those that make 40 struggle with loads and or water sports.
I wonder if the throttle opens all the way and is the timing set right and advancing as it should.
I would think 140-150 would be the max.Important to be within 10% between cylinders.

 

[Maclin]

I was also wondering what made the engine swap necessary, what happened to the old engine to make it fail.

 

[Steamboatbonner]

The block was cracked on the old motor. I felt replacing it was a better option than repairing it.

 

[steelespike]

Perhaps you can transfer the old motors guts to the replacement motor block.

 

[Steamboatbonner]

I thought about trying to salvage a few parts off the old motor, but once it came out and I got a good look at it, and after seeing the fluids that came out of it, I decided to cut my losses and leave it to the mechanic that did the swap in hopes that he would have more use for it than me.

 

[swaycleveland]

my thoughts are this..... new ENGINE ( motors are electrical lol) came from a boat. However, unless we can be sure that the engine was prepared for a boat and not swapped INTO that boat from a car, we can be sure that its up to the task at hand. What i mean by this is that the new ( to you) engine might not have a cam in it suitable for boat purpose. That would drop you right down into your problem area. just my $.02

 

[Steamboatbonner]

Interesting theory. I don't know the complete history about the boat that this new "engine" came out of. I guess anything is possible. I was led to believe that the engine was original to the boat that it came out of.

and not to split hairs but: If "motors" are electrical, wouldn't BMW and GM become BEW and GE?:laugh:

 

[Maclin]

Pretty obvious that the replacement engine is down on power, just need to find put why and perhaps lead to a fix.

 

[Steamboatbonner]

Ill do a compression test Saturday as well as connect a shop tach to try and get an exact rpm. Ill post back my results towards the end of the weekend. Thanks all.

 

[Bondo]

my thoughts are this..... new ENGINE ( motors are electrical lol) came from a boat. However, unless we can be sure that the engine was prepared for a boat and not swapped INTO that boat from a car, we can be sure that its up to the task at hand. What i mean by this is that the new ( to you) engine might not have a cam in it suitable for boat purpose. That would drop you right down into your problem area. just my $.02

Ayuh,..... Considerin' the 3.0l GM motor has never been used, other than marine or industrial applications, ya barkin' up the wrong tree,.....

 

[alangore]

by definition a motor is anything that creates movement or motion. by definition an engine is something that takes one form of energy and converts it into another, or something that produces some sort of work or energy from a given input.therefore a car engine can be referred to as either. lol btw the chevy 409 was referred to as the mystery "motor" even by the factory engineers.

 

[QC]

Come back with the compression numbers and we'll move this to the proper section (might be here for that matter). Good luck!

 

[Steamboatbonner]

Well this weekends maintenance didn't go the greatest. The compression gauge I had was not in functioning order. I did notice that the plugs looked to be burning very clean and evenly. With the long weekend coming up I will be borrowing a new set of gauges and doing the test before heading out on the lake for the 4th of July festivities.

Just curious, how much change in performance should I expect to see between 87 grade with 10% ethanol, and 89 grade with 0% ethanol?