Replacement Engine not Performing

[fishga]

My former mechanic replaced my 1979 Mercruiser 228 (305 GM, 4bbl) with a 305cu in Grooms Marine rebuild. The Mercruiser 228 with an Alpha 1 Drive and 14x19 stainless prop on my 20' Mark Twain did the following:
2600rpm = 26MPH
3000rpm = 30MPH
4400rmp = 48MPH WOT Trimmed
The Grooms engine with the same outdrive, boat and prop does the following:
2600rpm = 30MPH
3000rpm = 35MPH
4000rpm = 50MPH WOT Trimmed
The carburetor was trashed off of the old engine so we have replaced with a rebuilt Rochester Quadrajet that is suppose to be identical to the original. The old engine had much better hole shots and acceleration for water skiing. What would be the differences??? I'm really not happy with this new engine's performance.

Addition. We replaced the 19 pitch stainless with a 17 pitch aluminum.We did get much better hole shots and performance at the low end and reached 30MPH at under just 3000RPM - closer to the original Mercruiser. Unfortunately WOT trimmed did not give any noticible increase in RPM and lowered top speed to 45 mph.

I don't have a whole lot of information on the Grooms Marine engine but my prop guy and new mechanic say it should be safe to reprop for 4400RPM at WOT. But I don't seem to be able to get there. All of the tests were run with 3 passengers and from full to half tank of gas - hardly close to the 1500lb max for the Mark Twain.

The inability to get RPM above 4000 indicates to me that there is just no power in the upper ranges for this engine. I don't know if this is by design or just bad assembly. All in all, I wish I had my old Mercruiser back. Can anyone help me with this problem?? Can I do anything to make the performance of the Grooms engine be like the Mercruiser???

 

[tommays]

Re: Replacement Engine not Performing

If your reaching a real 50 MPH GPS with orginal prop the first thing i would do is check the tack

You cant be going 2 MPH faster with the same driveline and prop at 400 less rpm ?


Tommays

 

[calwldlif]

Re: Replacement Engine not Performing

Tommy has a point.
Rpm is rpm

 

[Bondo]

Re: Replacement Engine not Performing

Ayuh,.........

You're #s just Don't jive,......... Something besides the Motor is Different..........

 

[bjcsc]

Re: Replacement Engine not Performing

Hmmm...given the possible margins of error on both the tach and whatever you used to measure the speed, basically you could be saying that you replaced your engine with an identical engine and are seeing the same performance. Doesn't seem so unusual to me. How many hours are on the new engine?

 

[b00tstrap]

Re: Replacement Engine not Performing

[quote ] you replaced your engine with an identical engine and are seeing the same performance. Doesn't seem so unusual to me. [/quote]

Thats what I was thinking, why would you expect the identical displacement engine to have so much different performance... perhaps the mechanic was a bit overzelous in his performance statements

 

[DHPMARINE]

Re: Replacement Engine not Performing

At one time,any given new engine had to be within 10% of it's advertised rating.A 200 could be 180 or 220.

DHP

 

[fishga]

Re: Replacement Engine not Performing

Thanks for all the responses. Let me answer:
1. We've checked the tach...it is correct
2. My goal is 30mph-3000rpm..wot 48MPH at 4400rpm with power out of the hole for skiing with my 19 pitch stainless props. The exact performace of the old Mercruiser 228.
3. My thought all along is the only thing that is the same in the Grooms rebuild and the Mercruiser is the displacement. I would be willing to bet that the cam and heads are standard automotive. That would explain most everything.
4. I have barely 50 hours on the new engine. The boat was returned in such horrible shape it has taken me almost that long (almost 3 boating seasons) to even get it to perform like this.

 

[calwldlif]

Re: Replacement Engine not Performing

I guess when the outdrive was off
to remove the engine,
the coupler was changed?
This is the only way the outdrive
rpms could be diff from the eng rpms.
would explain the diff performance
at the same tach numbers.
Given the prop wasn't retuned, or the trim
postions are off.
Something in the drive line changed.
engine turning same rpms, but speed, performance
different. The power of the engine to turn
set rpm doesn't matter, if it turns X-rpm,
like the old one turnd X-rpm then the output
speed with same drive, prop would be the same.

 

[DHPMARINE]

Re: Replacement Engine not Performing

How did you check the tach.I think mine might be off and need to check.

DHP

 

[b00tstrap]

Re: Replacement Engine not Performing

The drive wasn't rebuilt or serviced at all?

 

[fishga]

Re: Replacement Engine not Performing

The drive shouldn't have been serviced and looks to be exactly the same. We have checked the tachometer several times and it is a little off at idle but reasonably accurate above 2000rpm.

I am not aware of any coupler that could have been changed in the drive line. If it has anything at all to do with gearing it could very well explain things. I never knew there were any other reduction mechanisms on the back of the engine. I'll ask.

I have always felt the cams in the two engines were different. The cam is the piece that controls the power curve of the engine. Unfortunately without pulling the engine and tearing it down, there is very little way to tell.

 

[fishga]

Re: Replacement Engine not Performing

regarding tachometer check - it was done by my mechanic. He hooked up his shop tach to the engine and compared values to the dashboard tach.

The speedometer is unusually accurate. I checked that against my portable gps navagator.

 

[b00tstrap]

Re: Replacement Engine not Performing

I have always felt the cams in the two engines were different. The cam is the piece that controls the power curve of the engine. Unfortunately without pulling the engine and tearing it down, there is very little way to tell.

RPM is still RPM despite any power curve. I think the gear ratio in your drive "changed" maybe the mechanic accidentaly installed a different alpha drive w/ a different ratio? Do you remember what the original ratio or serial number was?

 

[Bondo]

Re: Replacement Engine not Performing

I have always felt the cams in the two engines were different. The cam is the piece that controls the power curve of the engine. Unfortunately without pulling the engine and tearing it down, there is very little way to tell.

RPM is still RPM despite any power curve. I think the gear ratio in your drive "changed" maybe the mechanic accidentaly installed a different alpha drive w/ a different ratio? Do you remember what the original ratio or serial number was?

I think the Issue will be found in some other direction,.......

Both of these motors require the 1.5/1 ratio drive............