Evinrude vs Mercury

[dieselcat]

Re: Evinrude vs Mercury

For some reason I'm still not getting the 5500-6000 rpm at WOT,this motor is only hitting 4500-4600 rpm.When i was running it at 3500-4000 the boat was on plane.I have a friend who has a 90 vro on a 20ft boat he gets his best mileage at around 4000 rpm's with a 17 p prop,my dad also has a 120 hp vro on a 18ft aluminum bass boat with a 21 p and says he gets his best around 4200 rpm's anything over he said he might as well run it WOT cause it sucks it down.my dads 120 gets better than my 88hp[90],there has gotta be something that is causing this thing to suck gas like it is.Carbs have been rebuilt,fuel pump has been rebuilt,new head gaskets,new rectifier, new thermostats,and a new water pump impeller.I love how the motor runs aside from the gas it drinks and not getting the rpm's it's supposed to and would like to keep it,but I'm not going to keep feeding it all this gas it is drinking,there has gotta be a solution.If i knew for a fact it would fix everything i would rebuild it and put all new electronics on it,i got a hell of a deal on the motor IMO,i paid $1450 for the motor plus $300 for shipping,so with everything I've done to it i got around $2100-$2200 plus my time of doing everything.

PS.I'm going out today and will top off tank before and after i go and let you know the results,miles traveled,rpm,and fuel consumption,Thanks to all!!

 

[56 rude]

Re: Evinrude vs Mercury

try a 17p aluimium prop,you,ve got a heavy 19 p stainless on there which is a lot of mass to turn.i tried a 19 stainless last year and my rpms dropped a lot ,more so than if i had of went with a 19 al.if i remember correctly i was in about the same rpm range as you are with the 19 .thats way too low for full throttle.im sure you will find a 17 al will get you up where you should be then when you back off the gas you will be a lot more efficent.your lugging big time with that prop.

 

[56 rude]

Re: Evinrude vs Mercury

dieselcat i might add that im friends with a prop repair wiz and ive tried lots of props so im just not blowing smoke here.im sure that a 17 p al prop is going to be very close if not dead-on.give it a try.

 

[jay_merrill]

Re: Evinrude vs Mercury

If you are only turning 4,600 rpm at WOT, it sounds to me like you are overpropped. That would result in high manifold pressure and increased fuel consumption. You may need to go down to at least 17", which should give you about 5,000 rpm at WOT.

There are many opinions here about WOT range, with some saying to exceed the manufacturer's stated range, and some saying to stay within it. Some also feel that a motor should always be set up so that it runs at the top of the WOT range in typical load configuration. To these folks, anything less is viewed as "lugging" the engine. There are also all sorts of opinions about lugging and build up of coke on the rings, etc.

I run my motor at a WOT of 5,100 rpm. I use BRP Engine Tuner on the motor about twice a year and have not had a problem with deposits. I do use high quality oil though. I'm about to pull my motor and put it on another boat, so, I'll probably not buy another prop (less pitch) for it. What I am doing now works for me and is giving me decent fuel economy, so I'll leave it alone until I see what the best setup for the new boat is.

Let us know what your numbers turn out to be on the next run. From that point, we should have some ideas on helping you.

 

[dieselcat]

Re: Evinrude vs Mercury

Ok,I went out today put 10 galons of gas in the boat went roughly 43 miles at WOT almost the whole way and when i got back to dock i had about the same as i did before i put the 10 gal in,didn't top it off after words,but i know i didn't use much more if anymore at all than the 10 gal i put in it.Had 1/8th tank when i filled it and when i got back had bout 1/8th tank.
As far as to much prop not sure,boat launches really good but i will try a 17 p and let you know.

 

[56 rude]

Re: Evinrude vs Mercury

Ok,I went out today put 10 galons of gas in the boat went roughly 43 miles at WOT almost the whole way and when i got back to dock i had about the same as i did before i put the 10 gal in,didn't top it off after words,but i know i didn't use much more if anymore at all than the 10 gal i put in it.Had 1/8th tank when i filled it and when i got back had bout 1/8th tank.
As far as to much prop not sure,boat launches really good but i will try a 17 p and let you know.

let us know how many rpm,s your turning at wot with the 17p .your saying you went roughly 43 miles at full throttle and used roughly 10 gallons which doesnt sound far off seeing as that motor should use approx 9 gallons a hour at full throttle more or less.of course other factors come into play such as design of boat ,weight ,trim,current ,and water surface.mine ,trimed out and at full bore hits approx 5650 rpm with the 17p at slightly past 40 with a slight chop.one other thing also ,is the tach on the right setting?i know sometimes theres differnt settings for differnt motors,4pole 6pole etc.i cant remember of merc and rude had the same settings maybe somebody else that has acess to the tach charts that come with them could chime in.

 

[56 rude]

Re: Evinrude vs Mercury

ok was just reading tach instructions for teleflex tachs and the settings for 4 and 3 cylinders are differnt!did you switch yours to the 4 cylinder setting.if you didnt then your proably getting the wrong tach readings and we will have to start again.teleflex has pdf instructions for tach,s.wether you have a tel or not the same principle should apply.

 

[dieselcat]

Re: Evinrude vs Mercury

56,yes i actually just put a new tach in last year and it is a teleflex omega.My merc is a 4 cyl,as is the erude and if i remember correctly it is set on the 6p,i will look and see for sure what its set on if i remember next time I'm out.
Pretty smooth waters on the river yesterday sept a couple barges i ran into.I always trim the boat to the max without getting the bow hopping,trimmed out going down river i get right about 45mph, up river about 35-37mph.BTW the prop on the erude is the same prop from my merc,i just bought a new hub instead of buying whole new prop.I would think if the 75 hp merc did good with this prop then the 90hp erude should only do better?I am still going to try a 17 p,and if it works good then I'll just have my stainless re pitched.

 

[56 rude]

Re: Evinrude vs Mercury

keep us informed dont give up on the rude theres no way it should use 2x the gas.though mine will hit 5650 rpm i back it off to around 4800 and it gives good fuel milage for a 90 hp pushing a glass boat and i could really go to 135 or 140 hp on that boat but the darn thing runs so nice i dont want to for the marginal increase in performance id get.but if a good deal came up id shoot for max hp.

 

[jay_merrill]

Re: Evinrude vs Mercury

I think there are really two issues here - that of fuel consumption and the fact that the motor will only turn up to 4,600 rpm at WOT. If you are saying that you had exactly the same prop on the 75hp Merc (different hub) and had the boat loaded the same way, there is something wrong. It doesn't make sense that the Merc would turn up to a much higher rpm.

I would start with figuring out why this is the case.

 

[Fl_Richard]

Re: Evinrude vs Mercury

Could the gearcase gearing be higher in the Merc? This would account for the prop difference.

 

[Silvertip]

Re: Evinrude vs Mercury

Don't you have a post on the prop forum wondering about the fact rpm was only 4700 @ WOT? You answered your own question. Overpropped requires too much throttle opening. If an engine is propped wrong at WOT it is propped wrong at thottle setting less than that. The 19P prop you took off the 75 Merc if fine for that engine and I know that because I also have one. It is probably wrong for the Johnny/Rude because there is gear ratio difference in these two engines. 2.33:1 on the Merc and 2:1 on the Rude which I explained in the other post. And yes, optimize the setup.

 

[dieselcat]

Re: Evinrude vs Mercury

Don't you have a post on the prop forum wondering about the fact rpm was only 4700 @ WOT? You answered your own question. Overpropped requires too much throttle opening. If an engine is propped wrong at WOT it is propped wrong at thottle setting less than that. The 19P prop you took off the 75 Merc if fine for that engine and I know that because I also have one. It is probably wrong for the Johnny/Rude because there is gear ratio difference in these two engines. 2.33:1 on the Merc and 2:1 on the Rude which I explained in the other post. And yes, optimize the setup.

So if the merc is 2.33:1 and the erude is 2:1,which is the lower geared motor?I am assuming the merc is a little lower geared.I don't know how gearing in a boat works vs a car.I know 411 are lower that 373

 

[56 rude]

Re: Evinrude vs Mercury

So if the merc is 2.33:1 and the erude is 2:1,which is the lower geared motor?I am assuming the merc is a little lower geared.I don't know how gearing in a boat works vs a car.I know 411 are lower that 373

mecr is lower geared thus it can turn a 19 p prop with more rpm.again before you give up try a 17p on the rude.ive gone through this with my boat with a dozen different props and configurations and have always ended up back with the 17.i might add thuogh i got a glass boat ive tried the 90 on a al boat that weighed next to nothing and fooled around with props on that also ,guess which one seemed to work best ,yup the 17p.

 

[dieselcat]

Re: Evinrude vs Mercury

I'm pretty sure i need to move the motor up a hole or 2.My friend that has the 20ft boat with the 90 vro,his motor sits up off of the transom about an inch and a half,17P aluminum prop,WOT right at 5500 rpm.Also i can't trim motor up very much before the bow starts bouncing,motor trimmed to max without bow hop is almost level,but if i stop and try to take off with out trimming it back down it starts spinning almost immediately.With my other motor after i had it trimmed to max,and would stop,then go again i wouldn't have to touch the trim unless i had a good load in the boat.

 

[jay_merrill]

Re: Evinrude vs Mercury

Where is your cavitation plate in relation to the bottom of your boat?

 

[alangf]

Re: Evinrude vs Mercury

I had a 20' Robalo with twin 88 SPL's on it. The SPL's were incredibly piggish on fuel. I went 25 miles offshore and of course 25 miles back and burned 55 gallons! I was not comfortable with only a 60 gallon tank. I checked locally and found out that everyone with SPL's agreed they were gas hogs. I now have a 22' ProCat with twin 100 horse 4-stroke Yamahas. A trip 65 miles offshore and trolling all day burned 75-80 gallons.

 

[dieselcat]

Re: Evinrude vs Mercury

Where is your cavitation plate in relation to the bottom of your boat?

Not sure am going to check it later and will let you know.I think it's either dead even with it or maybe a little below,boat is a slight vee all the way back,does that matter?

 

[jay_merrill]

Re: Evinrude vs Mercury

If the cavitation plate is slightly below the transom at the keel, I don't think you need move the motor up on the transom.

The best explanation that I have heard for your low rpm issue, is the gear ratio situation. Frankly, I didn't pick up on that as a concern, because I don't fool with anything but old OMC outboards. It just didn't occur to me. Then again, that's why having all these experts at iboats is such a great situation.

Absent some problem that is causing your engine to develop less than full power, you seem to have a prop pitch problem that you must correct. Until you do, you are not going to get a reasonable view of what your motor should be burning in gas.

 

[Silver Heels]

Re: Evinrude vs Mercury

Just a word on gas gauges, you can take it for what its worth. On my boat, I would run to "E" on the gauge and fill up at a station or a marina when that happened. I would always pump in just shy of 20 gallons leading me to believe for years I had a 20 gallon tank. Boy, was I surprised when I pulled up the hatch on the floor and dusted off the data plate on the tank. The actual fuel capacity is 43 gallons! My point, as you already may know is these gauges simply cannot be trusted