I bought my first boat last jan., & it came with a 1972 55HP Chrysler outboard.  I don't think I am getting all 55HP out of even thou the compression levels on both cylinders were great.  It pushes me (by myself) at about 21mph, it is a 16ft fishing bass boat, but if someone else is in the boat it drops down a lot (my guess 10mph so).  So that's why the upgrade.  Just looking to upgrade so I don't lose so much speed when people are with me.

My question is. I was talking to find who has been boating for years, and he said I should look at a new engine (90's) same 40-50HP would be better then a 80's 75-85HP.  He said I would be better to get a newer engine with less HP then a older with more HP.  He said the newer engine may have less HP but it actually perform about the same.  I was thinking about getting a 80's 85HP or so, but now he has me on the fence about if I should stay in the 50HP and get something newer.

I was wondering what your thoughts were?

Your old Chrysler was never regarded as a powerful motor.  Not many people like them, and most hate them.  Getting a late 80s 85, if it is a johnson/evinrude, it will be a V4, and though they are bullet proof motors, they are heavy, and suck gas down like a sumb****.  In a 115, they are a reasonable weight, and reasonable on the fuel intake, but the 75, and the 85 are so close, it isn't worth it, until you get past 100 horses, in my opinion.   The 75 is going to be a three cylinder, and they are good motors.  That is probably on the high side of what you want.  A newer 60 would probably do you fine.  In the mid eighties, the hp ratings started changing from the powerhead, to the prop.  An outboard generally loses 10 % of its crankshaft hp, before reaching the propshaft, so the late 80s motors were 10% stronger than the early ones.  You mentioned going with a 40 to 50, but I personally wouldn't do that, as it doesn't seem justifiable to spend a few bucks on a newer, smaller motor, that doesn't perform any differently from an older, larger one.  I would go ahead, and make the upgrade to a 60 or so.

So the boat in your avatar is only going 10 mph with two people in it.  Your right, that's not fast enough for a 55 hp.  I believe something is wrong even when you take into account the 10% difference between early and late 80's.

For comparison my waterlogged 14 ft fiberglass boat has a 1982 60 hp Johnson and does 31 mph on GPS with just me and about 25 mph with 3 guys in it.  2 cylinder with 160 psi compression each.

Something to investigate.  Do you have a tachometer on the outboard? what RPM does it turn? If it does to turn 5500 RPM at WOT you may need to change the prop to a lower pitch.

Could be his flotation foam is water logged, making the boat super heavy.

I don't have a tach, but when I give it gas it revs up and sounds the same as when I'm by myself, just not moving as fast.  I figured even the same HP but one with the exhaust coming out of the prop, with the bigger prop would make a big difference.  VS my older smaller prop engine.  I'll add a picture (sorry it's not the best) of mine vs the exhaust props.

vs your current style.

The thru-hub, and old style props really shouldn't have much difference.  The old style has the cone to smooth the water flow, and the thru-hub uses the exhaust to achieve the same purpose.  The "newer style" props aren't going to have a different diameter, than the "old style."  Props are made in many diameters.  Your engine is designed for one diameter.  Assuming it has the right diameter, there isn't anything you can do diameter wise.  But, pitch is a totally different thing.  Do you have a tach?  If not, I would look into the TINYTACH.  If you are getting the top RPM, with differing loads, you are under pitched.  That means the prop doesn't have enough pitch to use all the engines power.  The best analogy I can think of, is in a manual shift vehicle.  In first gear, when getting the max RPMs, you really aren't moving all that fast, and the engine is in no way near its max power.  But, in 5th, you are moving at a high speed, and you are using more of the engines total power.  

But, you can't see if you have the right pitch prop, without a tach, so that needs to be your first line of business.

I don't have a tach on my boat, but when I'm by myself the boat shoots to top speed quickly, no planning time just shoots straight to top speed (20-21mph).  So I wouldn't think it would be the prop, I could see when I have other people the in boat it might drop some in speed, maybe even 3mph per person, but not drop in half by one person and still go the same if their is 5 people as if only 2.  

I have heard from another guy that works on boats and he said that the Chrysler engines are actually underpowered engines.  I don't know if this is completely true but he said if you put it on a dyno test a Chrysler 55 hp is 525 and a 60 hp OMC motor is 1275.  Does anyone know if this is true?

I don't know if its true, but what I have seen the chrysler and older force/chrysler motor do not have the power.

An older gentelman that goes to the same camp I do in Canada has a late 80's quantum bass boat, 16 footer with a 75hp force/chrysler, the best speed he could get was about 26-27mph. it would run right at the rpm's it should. just couldn't get any speed out of it and with 2 or more guys in it, it was a dead dog. I hav a 17'6' sea nymph with a  1989 75hp suzuki and I run about 37-38mph on GPS, even with 2-3 guys on it I still run around 37mph. My boat is bigger and heavier and I would still out run him badly. well last year he finaly got rid of that motor. it was costing him to much, it seemed like it needed a few hundred bucks of work every year. He ended up getting a early 90's Merc 60hp. Now it pushed his boat to low 30's on Gps and a few guys don't hurt it that much.

what is the max Hp for your boat? if you get a new motor try to get on as close to the max as you can afford. Motors from the mid 80's on will do, just make sure that its in good running codition even a newer motor can have problems. I would stay away from any more chrysler or force motors. That 85 will work good. is it a Omc? If so its a V4, yes its heavy, but they still made that syle motor untill a few years ago and they are great motors. My grandfather has a 90 hp Omc v4 on his pontoon.  If you look at a 75-90hp Merc or Suzuki, yam they will be 3 cylinders not 4 and weigh less.

How much difference is a 60HP to a 75HP?  I know 15HP, haha, but how much difference does it make with power (when you have other people or equipment) in it or top speed?

Buy a tach first. You will need it to diagnose your existing motor or to dial in a better more powerful HP merc or johnnyrude.

Once you know you WOT (wide open throttle) on the chrysler, then you can make a decision about whether to upgrade your motor.

If you do upgrade you motor, check the manufacturers hull plate to find out your maximum HP for that boat.

Buy the biggest HP motor that will fit on your hull safely.

With the bigger motor, you will have more fun and better fuel economy because you wont need to push it full throttle for cruising.

You will need a new tach, and water temp and water pressure gauges if your boat doesnt already have them. These are must halves.

good luck.

I agree buy the tack, save it for the new motor, chunk the Chrysler cause when brand new they were junk. I'm telling you they were built for trot-line weights at best.