Performance - 1988 60HP vs. 1968 55HP

[atengnr]

OK. This fall, I opted to get rid of my 1988 60HP and re-purchase the 1968 55HP I had previously (lighter motor, matches year of the boat, had put much work in in previously). I had the shop rebuild the 55HP, 0.030 over pistons, rings, pins, rods, several other items (spent way more than is sensible). IE, the motor is now running as new, however, I wont be able to run it on the boat until the spring here in MI.

So, I ran about 33 mph with the 60HP, what do you guess Ill get out of this 55 HP?

Thanks alot.

 

[steelespike]

Re: Performance - 1988 60HP vs. 1968 55HP

What boat are you running?If I have my motors right the 88 60hp is 49 cubes,
the 68 is 45 cubes pretty close 55 is about 40lbs lighter. My guess is you won't be able to tell the diff without a speedo.
Assuming the 60 was just an average setup a careful setup with the 55 will probably be faster.Raise the vertical height to a point just before ventilation becomes a problem.Then get us the max speed and rpm we may be able to suggest a prop for even more performance.Best performance gets best economy.The 68 might go through more fuel than the 88.I know my 65 40hp used more fuel than my 88 50.

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

I have a 1968 safetmate, probably 700 lbs without motor.

Yes, indeed that 68 55hp is much lighter, and the 88 60hp made the stern squat significantly, while the 55hp did not.

Note that this 55 is a 3 cylinder, and I thought they both had the same displacement??

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

I have a 1968 safetmate 15 ft, probably 700 lbs without motor.

Yes, indeed that 68 55hp is much lighter, and the 88 60hp made the stern squat significantly, while the 55hp did not.

Note that this 55 is a 3 cylinder, and I thought they both had the same displacement??

 

[Faztbullet]

Re: Performance - 1988 60HP vs. 1968 55HP

Did your 60 have trim? If so that made engine heavier and it would run faster as you could decrease wetted surface when trimming. The 55 dont have trim unless it was added. Also the 60 was a prop rated motor and the 55 a powerhead rated. Also where did you get .030 pistons as none of my suppliers even offer a piston for a 55. The pistons in a 55 are not a flat top like a 60/65/70 and are domed as the 55 head shape is different. If shop rebuilt with flat tops it will run but wont have any power. I had a customer bring me a engine years ago thats how I know..

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

THe 60 had trim, however, I couldnt use it because if I trimmed it up at WOT, the boat would porpoise almost immediately....

This local boat store has been servicing Johnson/Evinrude since the 1930s and they how to get these parts. If youre looking for such parts (IE pistons for a 68 55hp), call George at 248-356-2477.

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

Any more thoughts on this?

 

[Chinewalker]

Re: Performance - 1988 60HP vs. 1968 55HP

The '88 60 was actually closer to 70hp in 1968 horsepower as it was rated at the propeller, so you're giving up more than 25% on your horsepower... The 1988 is also a 56 cuber, rather than the 49 of the '68 which will give it more low end beef.
- Scott

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

Did your 60 have trim? If so that made engine heavier and it would run faster as you could decrease wetted surface when trimming. The 55 dont have trim unless it was added. Also the 60 was a prop rated motor and the 55 a powerhead rated. Also where did you get .030 pistons as none of my suppliers even offer a piston for a 55. The pistons in a 55 are not a flat top like a 60/65/70 and are domed as the 55 head shape is different. If shop rebuilt with flat tops it will run but wont have any power. I had a customer bring me a engine years ago thats how I know..

This has me worried a bit, because they did say they were going to use newer rods and pistons due to cost of 1968 pistons and improved durability. I did hear it run in test tank to WOT. If they used flat tops, would this be noticeable in the test tank?

I assuming that this shop wouldnt make a major error like this, but now Im a bit worried. What is the compression ratio change in this case? Could the head be milled to get back to correct compression ratio??

Thanks.

 

[Dhadley]

Re: Performance - 1988 60HP vs. 1968 55HP

A 1988 60 hp 3 cylinder is a 49 cid motor rated at the prop. The 68 55 was powerhead rated. There were some design advancements in exhaust, combustion pattern and intake flow. Also some strength improvements in powerhead components which allow some rpm differences. The later gearcase is sleeker too.

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

A 1988 60 hp 3 cylinder is a 49 cid motor rated at the prop. The 68 55 was powerhead rated. There were some design advancements in exhaust, combustion pattern and intake flow. Also some strength improvements in powerhead components which allow some rpm differences. The later gearcase is sleeker too.

DHADLEY - Can you comment on this potential piston issue? If flat tops were used, do you think it would have been noticeable during the tank test? It seemed to run good, started perfectly, seemed to spin up well, though I dont know what load the test wheel puts on the motor.

 

[Dhadley]

Re: Performance - 1988 60HP vs. 1968 55HP

The newer pistons and rods will fit in that motor but I'm not sure what it would do. You'd have to match up the skirt cuts and port timing to see if they're even close. I assume (we all know what that means) that they used one of the heads that go with that piston. I'd guess that the motor would start and run but have no idea about the power. Everyone I know has stayed away from that (68 55) simply because of the ignition. I'd bet the lower unit parts are starting to get hard to come by also.

Fazt - when you saw this before, which head did they use?

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

Well the head that is on mine currently seems to be the original. It is the forest green color of this motor....

I suppose Ill give the shop a call to see what the story is.

 

[Chinewalker]

Re: Performance - 1988 60HP vs. 1968 55HP

I stand corrected - 1988 was the last year of the 49-cuber. 1989 was the first year of the lost-foam cast 56-cube block....
- Scott

 

[Dhadley]

Re: Performance - 1988 60HP vs. 1968 55HP

The first 56 cid was in 86. We had a mixed bag (49 and 56 inch) in the 3 cylinder line for a while.

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

OK, the story is that they did indeed install flat tops, and their reasoning was largely due to benefits of their newer style piston (piston, ring, wrist pin design vs. relatively small change in performance in losing the dome) and the high cost of using the new original-style pistons....

Well, Ill be interested to see how she performs this spring. I ran 27 mph with it back in 2005 (prior to rebuild), so Ill have that as a comparison.

 

[Dhadley]

Re: Performance - 1988 60HP vs. 1968 55HP

OK, they admitted it'll be down on power. And it'll still have the old style battery CD ignition, the hydro-electric gearcase and no power trim. And the 1988 controls won't work.

Did you scrap the 1988 motor or do you still have it?

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

Does anyone know the 1968 piston dome volume and the combustion chamber volume, head gasket thickness on this motor?

Im curious to see how much the static compression ratio dropped.

 

[atengnr]

Re: Performance - 1988 60HP vs. 1968 55HP

Any info here?