1981 merc 200 performance

[jamesbalog]

so ive had the boat in with this motor for about a month now and wanted to share what i was getting numbers wise. I was expecting a little bit of a jump from my johnson 175 but i do not see it. are my numbers normal or what could i do to improve them?

The boat is a 1990 center console 20 sport. The boat has bottom paint. It is ran pretty heavy usually with 45 gallons or so of fuel, a kicker motor, 2-3 200+ pound adults, one 150qt cooler with ice and fish and more rods and tackle than i care to talk about.

im running a 3 blade 14.25x19 aluminum prop

im maxing our at around 42mph gps speed at 5100 rpms trimmed out

getting around 36 mph at 4500

30mph at 3900

26-27mph at 3500

im getting pretty much the exact same numbers as the johnson 175 i had. Im not sure about fuel burn as i pre mix now and have never filled the tank to 100%capacity. It sure seems like im burning less fuel now although its just a guess.

i was expecting more but im not getting it, anything prop wise i could do to improve it?

[smokeonthewater]

So you went from prop rated 175 to flywheel rated 200?
No increase there.

[jamesbalog]

Originally Posted by smokeonthewater

So you went from prop rated 175 to flywheel rated 200?
No increase there.

nice easy explanation smoke, i forgot about that. I just did a bit of reading and found that no one tends to agree what % of HP was gained in motors prop rated vs flywheel rated. Ive saw as low as 3% up to 15%.

Anyone here have a guess on what the actual % is?


also does anyone else think my numbers look low, or is it just me?

[THEFERMANATOR]

What year was your old 175 JOHNSON? As to prop VS flywheel differences, a good example could be the 235HP EVINRUDE basically became a 175HP engine when they went to prop shaft ratings. On the other hand some engines stayed the same as a 150 EVINRUDE stayed the 150. On average you expect to see a 10-18% loss. And if your JOHNSON was made after 86 it was propshaft rated, and your 200 MERC became a 175 when MERC went to propshaft ratings. So you stayed at teh same power levels. And you should be seeing more than 5100 out of that old 2.4L if you want it to perform well. 5100 is lugging it down quite a bit. 5300-5500 would be alot better for it. And if you're after performance, ditch teh aluminum prop, and go with a stainless. I would reccomened a 17 pitch stainless 3 blade prop.

[smokeonthewater]

I can say this, when merc went prop rated the 140 became a 115... That's a 21% reduction.

[THEFERMANATOR]

Originally Posted by smokeonthewater

I can say this, when merc went prop rated the 140 became a 115... That's a 21% reduction.

johnson/evinrude did the same in 85 when they started propshaft rating. yamahas 220 excell became there 175. also keep in mind they could be +/- 10% of the rated hp and still be legal. like how yamahas 200 and 225 4 strokes were the same exact engines except for decals when they 1st came out. they didnt get in trouble because they both made roughly 205-210 hp which was within the 10% hp allowance, but it was frowned upon when it was discovered they were charging $1000 more for different decals.

[jamesbalog]

the johnson was an 88 so it was prop rated

thanks for the explanation

[THEFERMANATOR]

Originally Posted by jamesbalog

the johnson was an 88 so it was prop rated

thanks for the explanation

Yep, you swapped from a 175 to a 175, so performance will be about the same. But like you found out, the 2.4L MERCURY is ALOT better on fuel than the old OMC crossflow was. Reprop to a stainless prop, and let it turn up to at least 5300 and it should do a bit better performance wise. And take care of that 2.4L MERC as it is a good engine.

[RidgeRunner]

Most folks don't know it but the old 2.4L 200's and 175's were chrome bore motors.. The chrome isn't the same chrome as what is on your bumper of your pick-up truck. This chrome is a chemical process essentially making the bore very hard. One thing that the chrome bore 200 did not like was being lugged around. Lugging the motor, ie. tuning the setup so that the motor is not in the recommended WOT rpm range, generates additional heat and could lead to pre-detonation. Translation- Certain death to an old carbed 2-stroke.. They didn't like heat because heat could cause the chrome to start to give up and flake off the bore.
Keep the carbs clean too, it should last a while if you follow the rules. LOL! Performance isn't bad for such a load, your using it to its potential..

[draglink]

you might need to re-prop. I have about the same motor. '80s 2.4 200. I turn it 6100-6300 WOT depending on the chop. Motor wants to turn more! I bump 50mph, fastest I have seen on GPS is 53