port burns more than starboard...

Lifes Good · September 2013

hi everyone

I am looking for your input on why my port engine burns about a half a gallon more per hour at 3800 and a gallon more per hour over 4100 than the starboard.....?

both engines run strong and reach 5000 rpm with no problems. both props are tuned and drives are 2 years new. oil is clean and no burning oil.

so what could be the reason?

thanks in advance!

LG ~ Mark

212rowboat · September 2013

Swap regulators and see if the problem follows..

Black_Diamond · September 2013

I chased that goblin for awhile. My Starboard engine pulls a bit more, went thru everything and no change. I can even them out with a tiny throttle adjustment and still be synched within 100 rpm. Just takes a little feathering. I can change it ~4gph doing that.

Capt Ron · September 2013

My boat never burns the fuel evenly.... just make sure you have all the gas valves opened and they will equal out... don't forget, if you have a generator and are using it a lot, that will lower one of the tanks easily... I wouldn't worry too much about this issue... they all do it..

Michael T · September 2013

Hey LG, I was talking to one of the guys at the old Mercruiser engine building plant in Stillwater Oklahoma years ago. One of them, some of you guys may know him, Rocky said "you know we test some of these guys off the line from time to time and you can take two off the line right beside each other and they can have differing HP by up to 5%, that's just the way it is". I've been told that the % difference is less in the "hand built" 6.2s and 8.2s. MT

Lifes Good · September 2013

thank you guys! I figured as much but ever since the dpx days I have been ultra sensitive about anything that just seems off. the good news knock on real wood.... all systems are working perfectly. well I do need a new horn... air horn that is!

thanks again...

Black_Diamond · September 2013

Once you have fuel flow monitors, you pay attention to the little things like this. It's normal and just sets your baseline. Enjoy!

Capt Ron · September 2013

The real important part is how you broke in the new engines. If you follow proper break in rules then you will have a better engine performance than one that wasn't. This was on of the big reasons I buy new.

Michael T · September 2013

Exactly, Ron! MT

frodo13056 · September 2013

Being a former machinist, I can tell you that when GM makes an engine block, head, crankshaft, camshaft, piston, or any other engine component, they make them in "lots" and lot sizes range from maybe a hundred to several hundred depending in anticipated demand. So, they "set up" required tooling / machines that will perform all of the machining operations for each specific feature - boring, milling, drilling, taping, etc. As tooling wears down, tolerances will vary and if you select a block that was run early on in the machining process, the tolerances will be much tighter than a block that was machined later in the lot run - still within tolerance but a little looser than the first blocks in the run. Those minor differences in tolerances are the differences you'll see on the final assembled product which in turn affect cylinder diameter, roundness of the cylinder, cylinder finish, piston diameters, and so on - all of which will create differences in fuel burn, oil burn, vibration at various RPMs, etc.

Michael T · September 2013

Beautifully said! MT

Lifes Good · September 2013

thanks again for all the great information. I love the detail. I checked my engine serial numbers and they were made in line together. no gap between them. so their specs should be nearly exact. maybe when I had my props tuned one of the blades could be off slighly. she gets haulded out on sept 1 for cleaning, zincs and painting. maybe I should have them spec'd again. whats a couple hundred more bucks.... 8-}

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