1990 25 sport cabin too slow, need ideas

[scrapple]

new member from maryland, looks like a great site. recently purchased 1990 25 sc, just am getting a feel for this boat. problem is the 5.7 I/O will only push the boat 20 mph @ 3500 all trimmed up. I can get 25 @ 4000, but think I blew head gasket last time out. Motor could use rebuild at least. I am considering full repower, or maybe even switching to outboard w/bracket, although this may get deep in my pocket. any ideas, experiences w/this setup? thanks for any suggestions.

 

[pelagic2530]

i would stay away from the outboard. thats a pretty major repower. other than that, i cant help you much. i do know that diesel repowered parkers are praised for their fuel economy, but if speeds your concern thats probably not for you either. im sure other members with inboards can help you out.

 

[ceblizzard]

If it were my boat, I would repower with another 5.7. The newer ones are capable of up to 330 horsepower with the fuel injection versions. You won't be able to beat the fuel efficiency of the new 5.7 versions. It would be much cheaper to go this route than to rig the boat for an outboard.

Charlie,
Eden, Md

 

[HM5]

I work for a tow boat company that has 2520 DVSC that started off in Beaufort with a 5.7 and a Bravo2 and a 19P AL 3 blade prop. The first owner, a TowBoat US operator took it out (blew it up) and put in a hot rod carburated Big Block. It was advertized in the Yellow Sheet (Boats and Harbors) as being able to do 48kts. Well when we got there, the engine was pulled and a carburated 5.0 installed. (Price re-negotiated) Still the Bravo2 but now with a SS 20P 4 blade prop, (probably left over from the 450HP BB). Mercruiser says this 5.0L package should be 220HP The boat runs 26 kts at 3800. Not good, besides the other tow companies can beat me to the scene of a MARB. (Did try different props, got RPM's; speed the same. Bravo 2 props way toooooo expen$ive) So the plan is to install a Cruisader Marine 320 HP this winter. It is a new 5.7L GM engine, big heads, roller cam, Holley carb, for about $4000. We want speed but tow loads, and some fuel economy.

A general rule of thumb that I have lived by: to double speed, you have to quadruple horsepower. Seems simple but it is a round about theory that seems to have worked in my sorted black outboard past. hehe

I agree, stay away with drastic modifications, ie. bracket and big outboard. Stick with the 5.7, or maybe the EFI 6.0L GM Gen III base engine. These can get upwards of 375 HP, then you can have fun figuring out prop you need to be using. Good Luck with your decision. Keep us up to date in the Projects forum.

 

[Hugs Tug]

What brand and model outdrive are you running?
That in itself will help dictate what the best engine combos are available.
Tom

 

[offshoreguy]

Switch over to a volvo package with a duoprop drive I have a 2520 with a 5.7 l throttle body with the duoprop drive (alum wheels prob do even better with stainless) and I top out at like 35kts all loaded up, I cruise at 21-25kts with ease in almost any conditions. I love this power package so happy I went with the I/O

 

[Megabyte]

The least expensive way to go would be with a 5.7L crate motor.
The most economical way to go would be with a diesel...

However, you want speed and towing grunt, and I'm not sure you can get both.
For speed, you want horsepower, and a very efficient prop on the top end.
For towing, you want torque, and a prop with the attributes of a John Deere tractor.

A BBC will give you the tractable torque you want at towing speeds with the proper prop, but so will the diesel.
A SBC will give you the horsepower and speed you want (with the proper prop) at high RPM's.
Unfortunately, you cannot have both.

My guess is that you want something in the middle... and therein lies your dilemma.
Unfortunately, only you can decide which attribute you want more, and which is better for your application. :wink:

 

[ppem45]

Unless you have very deep pockets you will want to stay away from the idea of installing an engine bracket and all the accessories. My boat had an outboard on it so it was not quite as bad as yours would be. The bracket alone is anywhere from $2200. to $3000. I have a friend in the business and he ordered it for me and it was $2218.00 with delivery. Stay with the I/O. Just my opinion!

 

[BlueSky]

Scrapple,

If that speed was 20 Nautical MPH or KTS then I don't think that is too bad.

I would repower with new I/O (engine and outdrive). Mercruiser 5.7 300 HP/Bravo III is about $19k installed with a 3 year warrantee.

You may get another 2-3 KTS cruising speed.

Good luck.

 

[MaxOut]

Stick with the I/O and upgrade to EFI. Like ceblizzard said. Least expensive other than fixing your current engine if possible. You can get a throttle body EFI that is an easy upgrade and may be possible to add to this block. EFI is way more efficient and will give you better idle and better poor fuel tolerance. If you have a reputable engine builder in your area you may want to consider some performance mods as long as you do not exceed the outdrives HP rating. Even if you blew a head gasket the engine may be fine. If the heads got warped then replace them with a complete performance head, EFI throttle body, and even hone/bore if needed. If the bore is good and there is enough clearance you may be able to add a stroker kit and really get some HP. A stroker kit is better than boreing because you do not thin the cylinder walls to the point of not been able to keep it cool. Your performance numbers are not up to par and if the package you have is performing as it should you should see a healthy increase in top end and cruise. You may have compression, fuel issues and or crab issues as well.

I like the Volvo Duo Prop but it is an expensive outdrive and will not fit without major glass work. If you replace the drive consider a complete motor/drive package. Just my two cents.