Upgrading Engine on Boat

[tntitans21399]

I bought my first outboard boat last jan. I love it, but the only down side is the outboard. It is a 1972 Chrysler 55HP engine. I pushes my 16 ft Terry Bass around about 21 mph (by myself), which is fine with me, but if one only person (doesn't matter if it's 1 or 4 more) then the boat drops to a slow I'm guessing 10 mph. I checked the compression and both are at 140. A couple of my friends said with the 55HP that it should be going a little faster. I was going to upgrade and get a newer engine 80's model maybe. I'm not looking to be going 80 mph but if I could go about 20 with people would be nice enough. My question is since it's a 72 model it has the small old prop, and I was wondering how much of a difference a newer 55HP, with the bigger typical tradition type prop on most boats now, would make? If the newer type engine would make a big difference then I might stay at the same HP, but I was also thinking about going up to a 75-85HP. What do y'all think?

 

[mrfixitman40]

Re: Upgrading Engine on Boat

whats the horsepower rating for the hull

 

[j442w30]

Re: Upgrading Engine on Boat

My boat is similar to yours and originally came with a 1969 Evinrude 33hp with the smaller prop similar to yours. With 2 or more people it was very slow to plane if at all. The engine ran fine but I never checked compression, in hindsight that engine was probably very tired. I upgraded to a 1992 Evinrude 25hp that has the larger prop and the difference was substantial. Before you go buying a new engine are you sure that yours is propped correctly right now?

 

[Solittle]

Re: Upgrading Engine on Boat

Any idea of what the max rpms are at WOT? Often modest performance is due to set-up, prop and or engine tune. Also Chryslers are not the most popular outboard out there for a lot of reasons.

 

[dimock44]

Re: Upgrading Engine on Boat

If that motor starts and runs ok look in other directions for the problems. Chryslers got a bad rap which was often deserved. but like most outboard problems are self inflicted. 55 hp is 55hp delivered to the drive line start there and move on to other possibilites. boat /motor comb ,check compression, decarb, ect

 

[steelespike]

Re: Upgrading Engine on Boat

Disconnect one plug wire at a time and carefully ground it.See how the motor runs.Obviously if one is dead it won't start.Check that the throttle plates are opening all the way.The antiventilation plate should be about even with the bottom of the boat.As far as props go a larger prop doesn't necessarily improve performance.Prop demensions are given in inches ex.
12"diameter X 12"pitch. Speaking basically the amount of pitch has the main affect on performance.Generally less pitch (lower number).gives more power better hole shot but less top end.more pitch give better top speed but less hole shot.Over propped (high pitch) strains the motor overall poor performance.too little pitch great hole shot poor top end too high rpm.