1988 88 spl swap fo GT 150

[Colelj]

I have a 1988 laser 1720 with a 1988 88hp spl on it. i can only get 38 mph out of my rig at 4600 rpm with a 19 pitch aluminum prop. the wot rpm for this motor is 5500 rpm. I don't know the compression on the motor because I'm in the middle of redoing the floors and the motor is off the boat. i have a chance to buy a GT150 Johnson but the max recommended hp for my boat is 120. What should I do? btw the weight on my 88 is 300 lbs and the 150 is 386lbs

 

[wired247]

Re: 1988 88 spl swap fo GT 150

#1. If your 88 was in top shape you'd do better than 4600 rpm . Its not in top shape. That boat with a fully functional 88 in good tune should hit 50 MPH with a decent prop. .

2. Don't worry about the nameplate HP unless you state mandates you stay under nameplate HP. The GT 150 isn't a barn burner and 150 HP at the prop is probably optimistic.

 

[emdsapmgr]

Re: 1988 88 spl swap fo GT 150

The GT 150 is the high perf 150(s) version that year. It puts out about 10% more hp than a base 150 model, or close to 165 hp, but keeps the 150 rating. It uses 175 carbs and higher compression heads. If it's made 1986 or later, the hp is rated at the propshaft. I don't think the weight is the issue. The question is whether your insurance company will insure it.

 

[rockyrude]

Re: 1988 88 spl swap fo GT 150

Unless you have assets you don't have any use for(house,cars,etc.) always pay attention to the capacity plate. If you have an accident with an overpowered boat, your insurance won't pay and the "other guy" will most probably own everything you've got.

 

[wired247]

Re: 1988 88 spl swap fo GT 150

Do people have insurance on 25 year old boats?

 

[rockyrude]

Re: 1988 88 spl swap fo GT 150

They had better, liability at least.

 

[wired247]

Re: 1988 88 spl swap fo GT 150

They had better, liability at least.

Is insurance required where you are?

 

[metriccrescentwrench]

Re: 1988 88 spl swap fo GT 150

If you have an accident with an overpowered boat, your insurance won't pay and the "other guy" will most probably own everything you've got.

Do you have any first hand knowledge about this, or are you just repeating what you've heard?




Now then, as for the original posters issues:

I agree, something isn't right with your current setup. Either the engine isn't healthy or you're overpropped. Just as a reference point I have a 15' fiberglass fish-n-ski with a 90 HP Johnson, I get about 42 mph at 5800 rpm with a 17" pitch prop. I'm not familiar with your particular boat, if I'm correct in guessing the "1720" means it's a 17 footer then I'd say you're overpropped.

Start off by checking the compression on your engine, and report back. What do the spark plugs look like?

 

[wired247]

Re: 1988 88 spl swap fo GT 150

Do you have any first hand knowledge about this, or are you just repeating what you've heard?

As for the original posters issues:

I agree, something isn't right with your current setup. Either the engine isn't healthy or you're overpropped. Just as a reference point I have a 15' fiberglass fish-n-ski with a 90 HP Johnson, I get about 42 mph at 5800 rpm with a 17" pitch prop. I'm not familiar with your particular boat, if I'm correct in guessing the "1720" means it's a 17 footer then I'd say you're overpropped.

Start off by checking the compression on your engine, and report back. What do the spark plugs look like?

Until I transplanted a 140 into it I had a 90 in my 17 foot Checkmate Enticer and had no problem topping 50 MPH ( GPS ) with a 19 pitch stainless OMC SST prop. Other than an unregulated stator there is no difference between an 88 and a 90.

 

[rockyrude]

Re: 1988 88 spl swap fo GT 150

Sorry, I don't believe as responsible boaters we should be promoting the overpowering of vessels from all sorts of angles, from the insurance side to the structural side to all of the other things that could go wrong.

 

[Colelj]

Re: 1988 88 spl swap fo GT 150

Thank you fellows for the info. I will report back when I get the compression test done.What would be a good compression for this motor?

 

[wired247]

Re: 1988 88 spl swap fo GT 150

110 psi to 125 would be good. As long as they are within 10 psi and over 110 you should be in for best performance. Less than that or if there is a big difference between cylinders then I'd start looking for problems.

88's also had much smaller carbs than 78-83 90's did . You can pick some top end up in an otherwise healthy motor by using the 1 5/16" '78-'83 90 HP carbs plus picking up a set of the rubber intake stuffers that came in many 90's and 140's. First off check your compression and if its OK do a little more prodding around. A set of 140 heads on that motor will also pick things up quite a bit if your rings are good.