WOT Matching

[mawyatt]

Anyone with the new digital throttle control check engine matching at WOT. Today my starboard engine ran about 4500rpm while the port would achieve only 4250rpm. My dockmate has the same 38DA but with regular throttle control and his engines match to within 20rpm at WOT.

 

[Jackie J V]

Are you sure it's not just the gauges? On my current boat, the faria gauges can give false readings from time to time. If your boat was out of sync by 250 rpms, you should be able to both feel and hear the condition.

Paul

 

[osd9]

The 38DAs come from the factory with two different size props....from memory....I think one is 23" pitch and the other is 22.5" pitch. Have the props been played with?

 

[mawyatt]

Are you sure it's not just the gauges? On my current boat, the faria gauges can give false readings from time to time. If your boat was out of sync by 250 rpms, you should be able to both feel and hear the condition.

Paul

I have the Smartcraft digital display unit as well as the guages. Both show port engine lower WOT by about 250rpm. I have the DTC which eliminates the linkage issues.

 

[mawyatt]

The 38DAs come from the factory with two different size props....from memory....I think one is 23" pitch and the other is 22.5" pitch. Have the props been played with?

Dom,

Nothing changed on props. Boat was purchased new off showroom last year March 2008 and only mod is the cockpit TV whichis now a 32".

 

[Sea Gull]

Did both engines hit 4500 the last time you ran the boat last?
Is 4500 the max rated WOT for your engines?
When was the last time you had the bottom/running gear cleaned?
Are the fuel filters clean? How fresh is the fuel?
Has any work been done recently on port engine or the controls?
Is a plug wire loose on the port engine (assuming gas)?

These are the first things I would check before looking at anything more involved.

 

[mawyatt]

Did both engines hit 4500 the last time you ran the boat last?
Is 4500 the max rated WOT for your engines?
When was the last time you had the bottom/running gear cleaned?
Are the fuel filters clean? How fresh is the fuel?
Has any work been done recently on port engine or the controls?
Is a plug wire loose on the port engine (assuming gas)?

These are the first things I would check before looking at anything more involved.

Good questions Sea Gull. I checked the oil and everything before we went out (my usual visual) and noted nothing unusual.

I am not at the boat but think the WOT for the 8.1L Horizon engine is around 4500rpm, will check this when I return to the boat. I remember both engines being able to reach 4500rpm in the past,but I don't run WOT except every so often just to vary engine speed/load and such and is just for a short burst (5min). Gas consumption goes way up!!!

I have a very reliable diver (does most boats at marina) and he keeps things clean underneath, visits at least once a month.

The fuel is new (filled up last week) although fuel filters have ~50hrs.....maybe time for new filters. Since tanks are different the port filter could be partially clogged and not the stbd filter. Good point..thanks.

I am in the engine bay every time I visit the boat (read often usually every other day) and have not noticed anthing unusual. I have been trying to trace a water leak (another issues and many posts to such).

MM did a water pump repair to the port engine their last visit to correct water leak problem. I checked everything after MM visit and didn't spot anything unusual. Good point though I will revisit and do a more through check.

Thanks for the pointers Sea Gull,

 

[Hampton]

Did I miss it? Have you ever tested them at WOT before now? I had to tune my props twice to get the WOT's to match. I wonder if there could be variations in the props other than the planned differential for transmission gearing. 250 is kind of a lot, if it's real, but mine were worse after having them tuned by an apparently unscrupulous shop in West Palm.

Mine were really bad at cruise. The starboard engine used about 2 GPH more than the port. That was my first clue. Can you verify the differential through fuel consumption?

 

[mawyatt]

Did I miss it? Have you ever tested them at WOT before now? I had to tune my props twice to get the WOT's to match. I wonder if there could be variations in the props other than the planned differential for transmission gearing. 250 is kind of a lot, if it's real, but mine were worse after having them tuned by an apparently unscrupulous shop in West Palm.

Mine were really bad at cruise. The starboard engine used about 2 GPH more than the port. That was my first clue. Can you verify the differential through fuel consumption?

John,

I remember both reaching 4500rpm in the past, my dockmat has a 2006 38DA and said he could reach 4500rpm on both within 20rpm. I am not that concerned (don't run WOT very much) unless something is wrong with the port engine.

 

[Hampton]

John,

I remember both reaching 4500rpm in the past, my dockmat has a 2006 38DA and said he could reach 4500rpm on both within 20rpm. I am not that concerned (don't run WOT very much) unless something is wrong with the port engine.

Yep. I missed it. Check your fuel flows with RPM matched at cruise. If it's higher on the port, I suspect that prop has more bite than the stbd even considering transmission diffs. If that is the case, then it won't turn quite as fast.

Your target is 4600 RPM in the 370 HP 8.1's.

http://clubsearay.com/forum/showthread.php?t=6461&highlight=props+tuning

http://clubsearay.com/forum/showthread.php?t=6274&highlight=props+tuning&page=2

 

[tobnpr]

If you're supposed to turn 4600, and it's only getting to 4250, you should be concerned. That's a lot of missing rpms- and absent a mechanical problem with the engine it's being overloaded.

 

[osd9]

I just posted this in another thread, but thought you might not see it there....here are the specs for the standard marine 8.1....back in 2004 anyway...they may have change a bit since, but I wouldn't think by very much...note that it is rated at 4600 RPMs but goes a little higher...looks like 4800 or so.