upgrading from 75HP merc to 90 4 stroke

[Hoffer]

Just throwing a quick question out there.

I have a 2003 Merc 75HP 3 stroke.

Its been bullet proof and I really do love the engine.

Its a little loud and I also wouldnt mind adding some top speed.

I have a 1650 crestliner fish hawrk - and figured I could get 45 to 48 with a 90HP.

I am wondering if its worth upgrading?

Would the 90HP troll down as well as the 75HP 3 stroke?

If I understand things correctly the merc goes from 3 cylinders down to 2 at slow speeds. I get the 75 down to about 2 to 3 mph.

My main reason for upgrading would be the quieter 4 stroke and the higher end top speed.

Is it worth it?

Last, any idea what the approximate cost would be to upgrade?

Thanks!

Hoffer

[delcecchi]

There are sites on the net with prices for various motors. That would give you a cost ballpark, along with looking at what used 75hp are going for on the bay.

I switched from a 115 merc to a 140 suzuki on a 98 1775 provee and wish I had done it sooner. At Idle mine trolls about 2.5 mph, as I recall, and is a real pleasure while doing so, compared to the 115.

A 90 will only be a small amount faster than a 75, maybe 10% at best.

[Hoffer]

Thanks Del

I wouldnt mind an extra 5 to 7. It would get me into the good low 40 range - maybe 45.

That along with the quiet 4 stroke might really make it worth it. However, I am guessing the difference between the 2 with labor and all that is going to be around 5K. So, that is a lot of dough to consider for the change...

[leech~~]

Um, let me know what you want for the 75hp when it's time for the change?

[cere19]

My dad has a 1650 Fish Hawk with a 90 HP Mercury 4 stroke, if my memory serves me correctly we can top out around 42 mph with the prop it came with.

[sheephead2]

Just for reference

I had a 1650 with a Mercury 90 hp 2 stroke It went 40 mph on gps

I now have a 90 4 stroke Mercury Alumacraft Navigator I can get 42 mph with me and 1/4 tank of gas

fully loaded 39.4 mph

I can troll down to 2.7 mph with my 4 stroke Mercury I also bought a troll down switch which lowers down 50 rpm at a time all the way down to 650 rpm which brings my boat to 2.2mph

the older 2+2 would cut down from 4 cylinders to 2 when trolling slow speed and that was I believe the 115 hp

[Hoffer]

I get about 38 on my merc right now.

I think a lot of that speed is prop dependent.

Mine is a 3 stroke that goes down to 2 at slow speeds.

I like how it trolls down - just a little loud as I like to do a lot of fast trolling for long periods.

Thought a 4 stroke would be nice for that.

I am going to make a few calls at some boat places down here and see what they say would say about how much trading up would be.

[sheephead2]

I never heard of a 3 stroke do you mean 3 cylinders

also the 75 and 90 hp has the same gears bore and stroke they just DE tuned the 75hp $5000 just to go 3 to 4 mph faster !!!!!

But a 4 stroke motor is very nice no smoke and starts and idles right away

I sold my fish hawk 1650 90hp for $8500 this spring and then bought new boat

Just a thought

[Hoffer]

Yes! I mean 3 cylinder - sorry!!

So really when it boils down to it - I am upgrading mainly for the 4 stroke - not necessarily for the higher MPH.

Will the 90 4 sttoke have any better MPH?

Thanks again!

Hoffer

[harvey lee]

I was looking at upgrading to a larger hp motor this spring.

I talked to a few dealers and they asked me why I was looking at a 4 stroke and not the newer 2 cycles.

I said for quietness, mileage and trolling speed.

he said you need to come test drive a motor in the same HP range as the new 2 cycles are very quiet, just about as good as a 4 for mileage and has a bit more top end.

After I talked to numerous dealers, I have made the decision that when I upgrade, it will not be a 4 stroke. One dealer told me he seels way less of the 4 strokes now as the others have gotten so much better.

Just something to think about before you purchase a new motor.

[Whoaru99]

Just for reference

I had a 1650 with a Mercury 90 hp 2 stroke It went 40 mph on gps

I now have a 90 4 stroke Mercury Alumacraft Navigator I can get 42 mph with me and 1/4 tank of gas

fully loaded 39.4 mph

I can troll down to 2.7 mph with my 4 stroke Mercury I also bought a troll down switch which lowers down 50 rpm at a time all the way down to 650 rpm which brings my boat to 2.2mph

the older 2+2 would cut down from 4 cylinders to 2 when trolling slow speed and that was I believe the 115 hp

I get 40, give or take, by GPS, out of my Sylvan Pro Select 16 with a 90hp 2-stroke Merc.

[leech~~]

I was looking at upgrading to a larger hp motor this spring.

I talked to a few dealers and they asked me why I was looking at a 4 stroke and not the newer 2 cycles.

I said for quietness, mileage and trolling speed.

he said you need to come test drive a motor in the same HP range as the new 2 cycles are very quiet, just about as good as a 4 for mileage and has a bit more top end.

After I talked to numerous dealers, I have made the decision that when I upgrade, it will not be a 4 stroke. One dealer told me he seels way less of the 4 strokes now as the others have gotten so much better.

Just something to think about before you purchase a new motor.

2 strokes are lighter hanging off the back of the boat as well!

[Hoffer]

Very interesting!

I will check that out!

Thanks.

[clKiekhafer]

From what I've read lately is that some of the new 4-strokes (Yamaha)are competing with the newer 2-strokes (e-Tec and Mercury) for weight. Now I know this was mentioned in a Yamaha ad, but the numbers have to be close or they would be all over that. The ad was specifically for a much larger engine than what the thread is discussing.

[fishadb]

I purchased a new 70 hp Yamaha tiller this summer and love it. When we were shopping some of the dealers tried to talk us into a 2 stroke merc. One guy almost got mad when we told him we wouldn't consider anything but a four stroke. I think maybe they have a lot on hand and want to get rid of them.

[delcecchi]

two strokes are not necessarily lighter. Check the specs.

The rule of thumb is that the top speed of a boat goes up in proportion to the square root of the horse power. Going from a 75 to a 90 is a 15 hp increase or 20%. The square root of 1.2 is 1.095. So you will gain in the range of 3 or 4 MPH at WOT.

But the new 4 stroke motors are much more civilized than the old 2 strokes. The optimax is said to be very good as well. I don't know about etec.

I bought a 4 stroke.

[leech~~]

The rule of thumb is that the top speed of a boat goes up in proportion to the square root of the horse power. Going from a 75 to a 90 is a 15 hp increase or 20%. The square root of 1.2 is 1.095. So you will gain in the range of 3 or 4 MPH at WOT.

Not always. I had a 90HP Force on my boat and when I burnt it out after 15 years I put a 75HP Merc on it and the 75 Merc was about 4 mph faster by GPS.

[delcecchi]

There was a transition from power head HP to propshaft HP, and some manufactureres inflated and some deflated before the standard requiring accurate rating within some small percentage.

Or maybe the force had the wrong prop pitch.

[leech~~]

There was a transition from power head HP to propshaft HP, and some manufactureres inflated and some deflated before the standard requiring accurate rating within some small percentage.

Or maybe the force had the wrong prop pitch.

You are right on the HP rating. The Force was taken off the head where the Merc was taken off the prop. When I was looking for a new motor the guy at the boat shop told me that the 75 Merc would be faster then the 90 Force for that reason and he was right!

[sheephead2]

I purchased a new 70 hp Yamaha tiller this summer and love it. When we were shopping some of the dealers tried to talk us into a 2 stroke merc. One guy almost got mad when we told him we wouldn't consider anything but a four stroke. I think maybe they have a lot on hand and want to get rid of them.

Probably mad because you then would not buy there over price $40 a gallon oil