2017 4.3L 180HP MPI

[briangcc]

Boat: 2017 Chaparral 19H2O Ski & Fish, published weight is ~2600lbs
Motor: 2017 Merc 4.3L 180HP MPI currently with a whopping 8.2 hours on it. Yes this season has been poor weather wise!
Outdrive: 2017 Merc Alpha One, 1.62 gear ratio
Prop: Unknown 4 Blade, 14.25 x 19P

Disclaimer: Yes I am fully aware I am still in my break in period and the below really should have waited a touch.


Had (2) adults, (2) kids - age 5 & 3, and safety gear on board as well as about a full 30Gal of 91 ethanol free gas. Before I go charging into the marina I want to make sure I'm not going nuts or missing something. For reasons I won't get into, we tried briefly running WOT and ended up at 4400RPM with I want to say either 42 or 44MPH. I still had throttle left and nudging it further did not increase RPM or speed. Rev limiter was not going off at the time, all other gauges were normal, no porpoising, outdrive was trimmed out - I want to say the first line above all the way in/down, engine did not sound as if it picked up any additional throttle either.

Selling marina claims boat should come in around 50MPH and I've seen a Youtube video with same boat and a 4.3 190HP TKS top out right around 50MPH so I would think I should be somewhere close to that ball park. The RPM's have me concerned as they seem to be on the low side of the engine operating range. Couple that with the extra throttle available but no increase in speed.


Question: With these new fangled engines, is there some sort of logic built into them that says, Hey dummy - you're under X hours so you can't exceed X RPM's So after let's say 10 hours some logic gets freed up to allow further increases in throttle?


Just curious before I go storming the castle at my selling marina.

Thanks!

 

[alldodge]

The big issue is the new boats have catalyst exhaust so your motor has 180HP, the previous TKS and EFI models had from 190 to 210HP. Cannot use older motors without cats as your baseline.

BTW your slip is at 9.9 % not bad

 

[tpenfield]

boats never seem to go as fast as advertised. . . but may be worth looking into. Any guidance in the Merc owner's manual about break-in and related expectations :noidea:

 

[tpenfield]

BTW - when I go to sell my boat, I'm taking everything out of it and only keeping about 1/4 tank of fuel in it . . . should go like a rocket

 

[alldodge]

Since its new, will they let you try a 21-3 blade?

 

[Bondo]

Ayuh,.... Did ya trim it out,..??

 

[briangcc]

To answer a lot of questions here...


AllDodge - it's actually a non-cat engine. You can still get them non-catalyzed albeit in limited supply. As for the prop, not sure I would go to the 3 blade as it's got a heck of a hole shot right now, very peppy. I would consider dropping the pitch a bit to get the RPM's up but my bigger issue is the throttle left on the table without any increase in speed. Weird that it'd be propped wrong from a marina as it doesn't match my previous experiences - even with a yahoo dealer who thought it was normal for a boat to take on water they still managed to get the prop right!

TP - nothing in there about expectations on engine break in. Not my first rodeo on this as been the rounds with a Force Outboard, Honda Outboard, and Volvo Penta I/O. Strange that I still had throttle left but pushing further didn't increase RPM or speed any. Trim had no effect other than to introduce porpoising so I backed that in a touch to get back to a smooth ride.

Bondo - Trimmed out as far as it would leave a steady ride. I tried a bit further but porpoising ensued so I had to tuck it down a tad.


Looks like I'll just add it to my list of things for the marina to address under warranty if after a few more hours on her doesn't improve things.

 

[bman440440]

also your gear ratio should be 1.81 on a v6

 

[alldodge]

OK, not cats, but its still less HP vs more HP, don't know why it would have less HP other then detuning do to emissions, but just guessing

 

[briangcc]

also your gear ratio should be 1.81 on a v6

Published data is 1.62. I'm not next to the boat currently but I can confirm tonight.


AllDodge - sure, I could see a significant difference if I was comparing a 220HP 4.3 TKS to a 180 MPI but we're talking 10HP difference between the 180 MPI I have and the 190 TKS. I understand there will be a little difference in MPH due to the lesser HP on my boat but in my humble mind, and I admit I know next to nothing, it shouldn't be that significant - maybe a MPH or two?

Bigger issue for me is the lack of increase in RPM with still more throttle to go. Something's amiss here and I think this is the major contributor right now.


I'll know more once I get some more runtime on it and cross the magic 10 Hour mark. Probably won't be this weekend as wife is working both days so I have to watch the boys - 5 & 3 yrs old. Not exactly the kind of assistance I need launching and retrieving the boat - in a couple years, you betcha!

 

[wahlejim]

To get the top speed on these boats, you have to run in optimal conditions. For example, you as a solo rider, conditions conducive to trimming all the way up, minimal weight, and propped for speed. You say you love your hole shot, but that will sacrifice top end speed. Top end speed will sacrifice hole shot.

My guess on how your marina trip will go: You will complain about top end speed. Mechanic can go out by himself without all of your equipment, give it a go and come in at 48mph at 4600 RPM. That is most likely within range on the engine for WOT. He can then offer to sell you a prop to gain 2 MPH.

Just one other note, if you approach it nicely with the marina instead of storming the castle, explain what you are trying to achieve and ask for their help in dialing it in, they are going to be much more willing to work with you. They should be able to help you dial in a 'speed' prop based on your numbers. Then you can have a prop for towing and a prop for cruising, as well as a spare onboard.

 

[briangcc]

Umm we seem to have drifted into a discussion on max speed.


My main issue is that I hit 4400RPM with more throttle to give but yet increasing the throttle had no effect on either RPM or speed. This is on the LOW end of the operating range and I was curious, since I had throttle left but no increase in RPM or Speed if there was some sort of limiter kicking in due to the low hours on the boat thus far. Since it appears that this isn't the case, I'll first try adding a few hours of use and see where that gets me. If not, then it's off to the marina to find out what's amiss as it isn't right currently - either due to setup error, adjustment, or bad propping.



**Water was glass smooth with no wind so we can take that out too.

 

[wahlejim]

Wide open throttle range for that engine is 4400-4800 RPM. There may be a rev limiter kicking in to prevent you from getting higher RPMs. I would imagine it would limit you at different points in the throttle with different props and different weights, but always at the 4400 mark. The marina may be able to adjust that for you so it kicks in at 4600, but I am just shooting at the hip here as I am not 100% familiar with the 2017 MPI setup

 

[briangcc]

Just a quick update....Drive is stamped 1.62 for the drive ratio.

I ran the boat combo through Merc's prop selector and it's saying I should be at 14 x 18P giving me a WOT of 4660 at 48.8 MPH. So the prop I have may very well be correct, or close enough, once I get the throttle issue squared.

Won't be back on the water for a couple weeks to confirm all this.


WA - I think you're right that some sort of limiter is in play here, just not sure where. No audible alarms were going off while I was at 4400RPM which seems right as it's within spec, albeit on the low end. All gauges were normal and the ODB light was off (ie. not lit) on the dash. I gotta get it back on the water where I can open it up to see what's going on and how much throttle position I have left after hitting 4400RPM.

 

[Dave-R]

I have run a few four blade props, and always the top speed drops a little. You keep saying you have a lot of throttle left. I doubt it. What you don't have, is enough hp. to let the engine achieve full rpms. If you ran a 3 blade 19 or a 21 stainless pitch I think you might do a little better. Some props perform better than others. 44 mph is pretty good where I run at 5000' elevation. Good luck Dave-R

 

[rderenzy]

1997 merc 4.3 here
I've hit 50mph on gps with my POS, 1997 19.6' boat and its super heavy
wife and I
4400-4600 rpm

not sure on prop pitch, but prop is just a entry level and its kinda beat up

 

[briangcc]

Just stopping back to update my original post.

Currently sitting at 16.2 hours on the motor. Last pass with my wife and two oldest boys was at 4600RPM and 48MPH according to the speedo. Seems respectable to me. May try something with the prop down the road as the Merc prop selector is saying I should drop to an 18 pitch to gain a couple mph.

May also speak with the selling marina as the last few hundred RPM's required a lot of throttle travel so something might be amiss there. Will cover that with the 20 hour service.

 

[achris]

also your gear ratio should be 1.81 on a v6

bman440440 Earlier V6s, yes, 1.84:1. But the later ones, and in particular, injected engines Merc supplied 1.62:1... That's normal, and as spec... Nothing to see here.

 

[achris]

Published data is 1.62. I'm not next to the boat currently but I can confirm tonight.

No, you are correct, 1.62:1 is the normal ratio supplied with an MPI engine.

AllDodge - sure, I could see a significant difference if I was comparing a 220HP 4.3 TKS to a 180 MPI but we're talking 10HP difference between the 180 MPI I have and the 190 TKS. I understand there will be a little difference in MPH due to the lesser HP on my boat but in my humble mind, and I admit I know next to nothing, it shouldn't be that significant - maybe a MPH or two?

Main questions.... What are you measuring revs and speed with? If you're using the dash instruments, not unusual for them to be out by as much as 10%. You need to use a CALIBRATED shop tacho and a GPS, and as wind and current also effect speeds, you need to do the run in both directions.

Bigger issue for me is the lack of increase in RPM with still more throttle to go. Something's amiss here and I think this is the major contributor right now.

That can be easily explained by the mechanisms within the control box, and the way a throttle butterfly works. You may be moving the lever, but the mechanism inside has already reached maximum travel. Confirm this by removing the flame arrestor from the top of the engine and have someone watch the throttle plate. Once it reaches full open, see if there's travel left in the lever... Also, once that throttle plate is about 95% open, it's pretty much at full... Unless the engine is dramatically underpropped, you're not going to see any increase...

I'll know more once I get some more runtime on it and cross the magic 10 Hour mark. Probably won't be this weekend as wife is working both days so I have to watch the boys - 5 & 3 yrs old. Not exactly the kind of assistance I need launching and retrieving the boat - in a couple years, you betcha!

Also, at 8.5 hours, that engine is still tight. Don't be too concerned about performance until you have at least 50 hours on, and 2 oil changes done...

Chris........

 

[achris]

Wide open throttle range for that engine is 4400-4800 RPM.

Correct.

There may be a rev limiter kicking in to prevent you from getting higher RPMs. I would imagine it would limit you at different points in the throttle with different props and different weights, but always at the 4400 mark. The marina may be able to adjust that for you so it kicks in at 4600, but I am just shooting at the hip here as I am not 100% familiar with the 2017 MPI setup

The rev limiter is fixed at 5,000rpm for these engines. It's not adjustable by anyone, not even people with the proper diagnostic software. (I know, I've tried)...

At 4600 rpm you are right on the maximum power. Dropping prop size will increase your top RPM, and DECREASE your actual power output. It's a war of diminishing returns. And yes, a 4 blade prop will always drop a couple knots (really seamen use knots, not mph, that's a land-lubbers unit of measure ) off the top speed. For best speed, use a 2 blade prop... Just saying...

Chris......