Merc 150 4S

[tj309]

Has anyone hopped up a Merc Pro XS 150 4 stroke? It would seem to me that with 3 liters of displacement there's plenty of potential.

[25two.stroke]

Don't have the experience you are looking for, but just want to chime in they run like 180 185 psi of compression...so that and running on 87 octane merc has them tuned pretty good. I'm sure if you ran premium fuel and tuned it you could get somewhere closer to 200 as it is 3.0L like you say. But I would be kinda scared to try adding boost to something that already has that much compression? Or am I wrong about that???

[Tcatrett]

I'm testing one now on my XB02. Just got it broke in. It's impressive stock. Going to test props and engine height first. Then look into tuning.

[25two.stroke]

I'm testing one now on my XB02. Just got it broke in. It's impressive stock. Going to test props and engine height first. Then look into tuning.

Is that a 3.0L 2 stroke sporty adapted to the 4stroke, or is it a higher hp 4 stroke sporty?

[LakeFever]

I know a guy with one on a 15’ runs 72mph at 6200rpm iirc. Goes good but it’s a small light boat. I believe it’s a checkmate splash but I don’t really know

[Tcatrett]

Is that a 3.0L 2 stroke sporty adapted to the 4stroke, or is it a higher hp 4 stroke sporty?

Sporty from a 300XS opti. 1.62 gears with drive shaft mod.

[Glastron1987]

I don't think a 3L 4-stroke has the same potential as a 3L 2-stroke for horsepower. Remember, they only beat every other time.

[LakeFever]

Naturally aspirated four stroke 1.6hp per cubic inch measured at the flywheel is relatively easy, relatively. 3L is 182 cubic inch so there is 283ish hp to be had out of that motor. At bare minimum this would require custom cam shaft/s, head porting/valve job/upsize. Intakes these days have been pretty good since they went dry. Might get lucky there. Then there is tuning which probably is easiest to put a Holley system on from the outset. To reach peak numbers will certainly require raising the rpm limit which strains the oiling system, valve train and rotating assembly. There’s a weak link or two in there somewhere the first guy through the door will discover.

Doable. But sure makes skipping all that work and simply building a 2.5 look awfully attractive

[David]

But can you get 265 HP at high revs and still get on a plane?

[LakeFever]

Can’t say without more data. First thing you need is the factory cam events and some flow numbers from the head and intake. Then start a program to put the torque curve where you want it as best you can and make the sacrifices either way. Meaning if you want max effort the torque curve will move up the rpm scale which will require gearing and prop changes to match. Or try and keep the torque curve lower which will limit the peak hp. Basically there’s no way to make a lot more horsepower out of any motor without radically increasing displacement, or raising the rpm to move the required air. It’s one of those two options or boost it. This finds a whole new area of limits; the first of which will be piston/rod/head clamp strength. Those three things are what will limit how much boost you can throw at it. Quickly followed up by crank and block strength. Again the first guy through the door here is going to need to be super prudent in stepping things up until the first weak link is exposed and with the factory spec engine components we will know what this little merc can withstand.

The only way to properly do this is buy ten motors and add boost til one blows. Repair and upgrade as nec and hit repeat until you get the number you want or figure out the platform is entirely unsuited for this purpose. I can’t really see the market for this for two reasons. The cost mainly just isn’t worth the reward here that I can see. The second being fuel. How many guys want to run on alcohol or c16 type fuels in a boat? Only racers and that ain’t me so if this happens it will be someone else who uncorks the potential from one of these little four strokers.

There is always the super tune approach. Take a stock engine, add a holley engine management and increase compression along with a good valve job and all the “free” intake and exhaust mods. Read that as grinding and porting. See what it has in it. Might find another 25 or so ponies doing this. Without a cam upgrade I don’t see a ton of gains with this method. The cam is what controls all the intake and exhaust events so without matching it to the airflow goals the gains won’t be huge. Probably have to regrind a factory cam. No clue what core the camshaft in this thing is ground from.

At this point im farting in the wind. All blind guesses and just my $0.02 id enjoy being proven wrong here. Heck I’d enjoy that a lot actually

[25two.stroke]

Sporty from a 300XS opti. 1.62 gears with drive shaft mod.

I am surprised Mercury doesn't provide steeper gear ratios for some of their fourstroke Sporties and torquemasters. Its a damn fourstroke, it has the torque to pull a big gearcase on a light boat.

But then again I shouldn't be surprised...cause Mercury is not designing motors or marketing towards "light" boats. If a 1.50 or 1.62 was offered in a torquemaster It would be great on 18-20 ft light boats with a 26 or so pitch prop. Good top end, no lag midrange...all around good combo. I go back and forth in my head about buying one and cutting it up into a 15" dry sump motor and putting a 3.0L 2stroke sporty under it. I love the 150 SeaPro I own. I make it push around THOUSANDS of lbs of fish and slush and it performs no different with the boat loaded or unloaded. Load makes no difference in rpm needed to go any said speed, and hardly any difference in fuel economy. If I get my hands on a blown 20" 150 I will buy a new powerhead on it and cut up the mid. Or in a few years I may cut up my SeaPro and buy a new one...but by that time it will have a few thousand hours, so it may not be a good candidate.

[David - WI]

A 3L 4-stroke outboard has to have way less torque than a 3L 2-stroke?

[tlwjkw]

Can’t say without more data. First thing you need is the factory cam events and some flow numbers from the head and intake. Then start a program to put the torque curve where you want it as best you can and make the sacrifices either way. Meaning if you want max effort the torque curve will move up the rpm scale which will require gearing and prop changes to match. Or try and keep the torque curve lower which will limit the peak hp. Basically there’s no way to make a lot more horsepower out of any motor without radically increasing displacement, or raising the rpm to move the required air. It’s one of those two options or boost it. This finds a whole new area of limits; the first of which will be piston/rod/head clamp strength. Those three things are what will limit how much boost you can throw at it. Quickly followed up by crank and block strength. Again the first guy through the door here is going to need to be super prudent in stepping things up until the first weak link is exposed and with the factory spec engine components we will know what this little merc can withstand.

The only way to properly do this is buy ten motors and add boost til one blows. Repair and upgrade as nec and hit repeat until you get the number you want or figure out the platform is entirely unsuited for this purpose. I can’t really see the market for this for two reasons. The cost mainly just isn’t worth the reward here that I can see. The second being fuel. How many guys want to run on alcohol or c16 type fuels in a boat? Only racers and that ain’t me so if this happens it will be someone else who uncorks the potential from one of these little four strokers.

There is always the super tune approach. Take a stock engine, add a holley engine management and increase compression along with a good valve job and all the “free” intake and exhaust mods. Read that as grinding and porting. See what it has in it. Might find another 25 or so ponies doing this. Without a cam upgrade I don’t see a ton of gains with this method. The cam is what controls all the intake and exhaust events so without matching it to the airflow goals the gains won’t be huge. Probably have to regrind a factory cam. No clue what core the camshaft in this thing is ground from.

At this point im farting in the wind. All blind guesses and just my $0.02 id enjoy being proven wrong here. Heck I’d enjoy that a lot actually

"data, data, data, data".... one of tha best explanation of "how it all works" (R&D for beginners) i've heard in 20 years. ......

brought back a lotta memories... went thru most of this with my son before he was taken.. his specialty was mostly alcohol and/or fuel Brads, AJ's, KB's etc.

thanks for tha post!

[David]

I don't know that the 150 has variable valve timing. That would help widen the torque curve. HP = torque X rpm/5252. As noted above, you get more HP by revs or displacement, assuming a given torque per unit of displacement. A really flexible engine has a flat torque curve over a broad range of revs.

I agree that at equal levels of development and displacement, a 2 stroke will have more torque and therefore more HP than a 4 stroke.

[LakeFever]

Variable valve timing does give a little bump in efficiency but it doesn’t really do much. I built a single cam vvt motor it’s not worth 2% in peak power. Independently variable intake and exhaust events do yield more substantial gains but even the KS free valve or the old desmo stuff didn’t revolutionize ice engines like the sizzle suggested. It doesn’t really matter how much adjustment you have to your valve events at a certain point you just have to fill the jugs and create a column that flows at or near as possible to 100% VE and a good single cam engine can certainly do that with ease, less cost, and improved reliability with less moving parts. The only sacrifice that need be made with a single fixed position can engine is where in the rpm range you want to put the torque curve. Even if you get fancy with variable over head cam multi valve set ups a good single cam motor with more cubic inches is going to be the better performer. Power to weight is always a consideration of course but in package and weight sizes like we are talking here a multi overhead cam engine takes up a lot of room and weighs quite a bit vs a single cam as many cubes displacement as possible would. Dollar for dollar I’d bet the big cube simple mota makes more. That’s the great equalizer it always boils down to cost. How fast do you want to buy?