Need more power!!!

[Iceman Yella]

I have a mercruiser 350 or MCM 260 engine in my 1985 well craft scarab 1 and would like to add some mods to get more hp and torque, I was wander what add on such as exhaust, intake manifold, carb upgrade or and thing else that you would suggest to get better preformance. I have an Alpha 1 drive on it also.

 

[6meter]

Re: Need more power!!!

Thats a big 21' that does about 55 mph. With the Alpha I on the back you don't want to push the HP much over what you have, it won't survive. Other than that it takes $$$$. Dual plane intakes help. S/S props help. TRS drives will help. But you still can only turn the RPM of the motor and the outdrive so fast. Good luck.

 

[Iceman Yella]

Re: Need more power!!!

Thanks for the info, I only hit about 4000 rpm at WOT going about 50+ a few, My prop is a quick silver multi pitch which can be adjusted to change the pitch depending on the rpm. I am still playing around with this to see the differences in the preformance but I am having trouble getting on plane. Any other suggestions?

 

[Lyle29464]

Re: Need more power!!!

a little less pitch will help you plane quicker and put your engine into the correct wot rpm range. I would set it so it runs about 4600 but never run it there over a few seconds to test it.

 

[jtmarten]

Re: Need more power!!!

Bad advice here so far.
Lots and lots and lots and lots and more lots of guys running 375-400hp into an alpha. You just have to be careful with your holeshots and getting air.

You can run her at 4600rpm ALL DAY LONG. As long as you don't have a high volume oil pump! If you do, you could pump the pan dry before the oil has a chance to drain back down. The engine will obviously wear faster if you're running her WOT all the time, but, hey, its a Scarab, right??? She's meant to go fast!

Mods: Good dual plane, high-rise manifold; good marine rated 4V carb, Holley or Edelbrock; free-er flowing exhaust manifolds (I'm guessing you have thru-hulls already). If you want to dig deeper, both engine and wallet wise, aftermarket aluminum heads, cam, roller rockers, etc.

I agree you def need a smaller prop, get you into the proper WOT range. Along with a better holeshot, you may even gain a couple mph by utilizing the extra 600rpm.

 

[Iceman Yella]

Re: Need more power!!!

Alright thanks, So if i get a smaller prop this will give me more rpm in the WOT range or are there other adjustments on the engine to give me that? It is through hull and everything seems to be stock on the engine. I was thinking of the mods you posted but was not sure what would give me an increase in mph. I would like it to go faster and be louder...

 

[cooter2506]

Re: Need more power!!!

Before changing prop pitches make sure the engine is healthy. Did it perform better at anytime before? Up in the adult sticky section there is a post on WOT probems. I would go thru that list to make sure engine is healthy first.

 

[Iceman Yella]

Re: Need more power!!!

The engine is fine, I adjusted my 2 speed or multi pitch prop before the last time I went out and took longer to get on plane, probably since I had 6 ppl in it and a full tank of gas, i am not sure if you are fimilar with this type of prop, it cahnges pitch determining on how you set the spring tensioner and the rpm range you want it to change,

 

[45Auto]

Re: Need more power!!!

Changing the point where the prop switches from low pitch to high pitch is only going to affect how quickly the boat will accelerate. It will have no effect on top speed.

The only thing that will affect your top speed is a prop with less pitch that allows the engine to rev higher and get into it's correct WOT range, which would be 4600-4800 RPM.

A 260 makes 240 HP at 4000 RPM, so letting it rev to 4800 RPM will gain you 20 HP. It takes about 10 HP to go 1 MPH faster, so if you're lucky and everything else is equal you MIGHT go 2 MPH faster with a new prop.

 

[achris]

Re: Need more power!!!

If you're looking for red hot acceleration, then throw away that shifting prop. Get a Laser II and leave the vent plugs out. Get a prop that will allow the engine to make 4600-4800 at WOT. (I know the spec is 4400-4800, but the best prop is the one that gets you into the top half of the recommended range).

With the vent plugs out the prop will ventilate until the engine is in the power band, then it will 'lock up' and have you out of the hole like a rocket. (I know, I put one on my boat just to see what it was like). It's like having a high-stall torque converter on an auto tranny....

Chris.......

 

[John_S]

Re: Need more power!!!

What is the starting pitch of the prop? At what rpm is the shift point? and can you adjust the final pitch?

Do you have adjustable tabs to help get on plane?

As far as hp mods, make sure your old motor is in good shape before preceeding. You can get a little over 300hp @ prop for around $1500. After that, it will get expensive, and should compare to BB or 383 upgrades, before sinking more $.

 

[Iceman Yella]

Re: Need more power!!!

I do not know what the starting pitch is but it is stamped on it with 23 p, I am guessing around 19 p. Depending on how tight I set the spring in the prop will determine when it changes, I was told around 3200 rpm it will start to open up to the higher pitch.

I am not so much worried about top speed at the time but would like to get on plane quicker, I will adjust the prop and get back to you all once I do more testing.

Thanks for all the input every one,