Max hp or weight on 18
 

Planning a repower this winter after we finish a complete Reno on a Classi 1976 18. Last step is to bring the transom up to 25 inches and paint. As expected My 17 yr old son is itching to put a four stroke 150Hp which weighs around 450. Based on what I’m reading I’m inclined to stay sub 400lbs and go with a 115hp. As always appreciate the feedback.

One of the guys on here has a Suzuki DF 90 that pushes his 18 36 mph and gets 6.6 mpg.

I have a 90 2 stroke on my 75 and it tops out at 32 and gets 3.3 mpg.

I’d be really slow to put a 150 on an 18.

The new Suzuki 20" DF140 is 397 lbs. and I can get 40 mph out of it. Not sure on fuel consumption numbers, but, I can ride quite awhile on a tank. I raised my transom to 23" and have the motor mounted on the 2nd hole from the bottom putting the anti cav plate about 2-3/4" up from the keel. Sometimes I think it might do a pinch better lowered 1 more hole, but, it handles and performs fine. Running a 13-3/4 x 21p prop.

My '87 18' has a 25" transom and my rating decal says max hp is 200 hp.
That said, I have an Etec 90 hp, and I get a WOT speed of 35 mph properly trimmed, and I get 6.8 mpg average, with my cruise speed being about 21-22 mph inshore, and about 18-20 mph offshore. Instead of trim tabs, I run with a Hydro-Shield under my prop.

My ‘87 18SF I bought new in Oct ‘87 has this capacity tag.
I put a Johnson 140 looper on it.

I had a 1975 18' SeaCraft which I repowered with a Suzuki DF90 back in 2015. I think they weigh 342 lbs. I did a lot of research before I made the purchase and was leery it wasn't going to be enough power for the boat. I originally had an old 1987 Evinrude 90 2-stroke on there. I had the original height transom, so I wanted to keep as much weight off the stern as possible. I moved the batteries under my console. I recently sold the boat, but was very very happy with my decision to go with that Suzuki 90. It jumped up on plane quickly and had enough torque to spin a 14x16 prop. I had a great cruise speed in the low 20's and a top end around 35-36 mph. My scuppers were above the water line and the boat self bailed, no problem. I was over 6 mpg at cruise. PM me if you have any specific questions.