I want more speed!

[MrPink]

I have a 1996 corwnline 202br with a 5.7L/thunderbolt. The out drive is a merc alpha 1 gen2 with a 1.65 Gear ratio. I have two props, one 21p aluminum and a ss High Five 21p. Yesterday the aluminum was doing 49mph@4600rpms. This is supposed to be the high end of my WOT range(420-4600). I would like to buy a prop that I can get more top speed out of ONLY. If anyone has any ideas let me know.

 

[budsbud66]

Re: I want more speed!

You will get better performance out of a stainless. 3 blade. From my expierence with HI-5's they are very nice for hole shot and handling.. if these are not factors i wouldnt run it. I am no expert, some of the guys on here Definatly can provide more help then i can. Also do you have the specs for the HI-5?

 

[MrPink]

Re: I want more speed!

Your right on about the H5. That's why I want one just for top speed. I don't know the exact specs on the H5 just that it's a 21p

 

[budsbud66]

Re: I want more speed!

My buddy uses his H5 for ruff weather tourneys. the boat sticks to the water alot better, and blows out alot less when powering up and down waves. you definatly dont need a 65mph prop in 5ft waves. I guess in your application it would be good for bringing up water ski'rs. Top speed prop gets used 95% of the time thoe..

 

[MrPink]

Re: I want more speed!

I have the H5 already. I'm looking for a 3B SS prop that will get me about 5-10mph. With the AL 21p 3Blade I was @49mph and 4600RPM with WOT. What props can anyone sugest that will give me that kind of in crease. I know the hole shot will be bad but all I want is top end.

 

[Dhadley]

Re: I want more speed!

I'd try a 23 3 blade in a Turbo or Stiletto but I doubt you'll get anywhere near 10 mph increase unless you're working on the motor too.

 

[Silvertip]

Re: I want more speed!

Your engine is already at its max recommended WOT range. Increasing pitch will very likely pull it below that RPM. Why? Because it takes power to turn the increased pitch. You might find a prop that is more efficient than what you have now but getting a 20% increase in speed with a prop change is wishful thinking unless a boat is terribly under propped to start with which yours is not. You might get 2 or 3 by experimenting with props similar in pitch to what you have now but you will not see the large numbers you are after.

 

[MrPink]

Re: I want more speed!

I thought I might be out of line with that increase but I don't know what I should expect. I'm thinking about putting a 4bl with a new intake that might help.<br />Thanks for getting my feet back in reality.

 

[Dhadley]

Re: I want more speed!

That should help especially if your going to use the cam for the 4 bbl. Looks like some neat testing coming up.

 

[budsbud66]

Re: I want more speed!

Small blocks are the funnest to work on.. you can do alot for reletivly cheap.. there are three main factors in gaining horsepower 1.Cam, 2.Compression, 3.heads... if it were a car i would run a cheap aluminum 4bbl intake, q-jet( the big one, tuned right) and pick up a pair of decent heads.. (vortecs work phenominaly) it is not unrealistic to gain 70-100hp by going 4bbl with good flowing heads. Im not sure how cams differ in marine but im sure a good cam would help.. I like them real lumpy so you can rev the **** out of them. thats on the road thoe. im not sure how marine differs(guessing not lumpy). Just my 2cents

 

[Silvertip]

Re: I want more speed!

Team-Starcraft, remember a boat has no transmission so its always in "high gear" so to speak. A lumpy cam tends to push power and torque up the RPM band. Good for top end but if you can't get out of the hole it's useless power. Marine cams are generally more like truck engine cams. Good grunt low down. You could argue that a prop with less pitch would solve the hole shot problem. Yes -- but then it over revs on the high end. If such changes were really practical, the engine manufacturers would be doing it in a heartbeat.

 

[Dhadley]

Re: I want more speed!

Also cars seldom have wet exhaust systems. You get too wild with the cam and you might pull water back in the cylinder on a boat with wet exhaust. There are dry systems for boats (jacketed rather than water inside) but I think we might be getting a bit crazy in this case.<br /><br />Also remember that a lot of times the drive is the limiting factor rather than the motor. Obviously the sb Chevy can rev a lot but an Alpha drive doesnt like that.

 

[MrPink]

Re: I want more speed!

Love all the suggestions but "let's not get to wild here" I talking about spending 1000-1500 on upgrades over the next year. I wanted to start out with a prop for this summer and I'll worry about the rest when down time is not a issue. As for now the boat engine is STOCK. I would like to hit about 55 with a 3B SS. Back to the first question, What prop will help me?

 

[MrPink]

Re: I want more speed!

PS I don't want to break the outdrive either all I want is a little more speed so I want to limit upgrades to 50hp.

 

[stevens]

Re: I want more speed!

"I would like to hit 55...".<br /><br />You won't.<br /><br />With the figures you quote in the first post above, you're at 11% slip already, which is pretty good. ( http://www.go-fast.com/Prop_Slip_Calculator.htm )<br /><br />Even if you found a prop with slip as low as 7% on your boat, you would still only reach 51 mph.<br /><br />With your current set-up (i.e. engine performance, boat weight and hull shape) that's as good as it will ever get.<br /><br />Dhadley already gave you some good advise above. Probably very few props will be faster than a Turbo or a Stiletto. I wouldn't go too far up in pitch, maybe to 22P, and you may then hit 50...

 

[Tail_Gunner]

Re: I want more speed!

Originally posted by team_starcraft:<br /> Small blocks are the funnest to work on.. you can do alot for reletivly cheap.. there are three main factors in gaining horsepower 1.Cam, 2.Compression, 3.heads... if it were a car i would run a cheap aluminum 4bbl intake, q-jet( the big one, tuned right) and pick up a pair of decent heads.. (vortecs work phenominaly) it is not unrealistic to gain 70-100hp by going 4bbl with good flowing heads. Im not sure how cams differ in marine but im sure a good cam would help.. I like them real lumpy so you can rev the **** out of them. thats on the road thoe. im not sure how marine differs(guessing not lumpy). Just my 2cents

You are absolutely right on that remark, i'm so caught up in into a resoration project i don't have the time to think it through. There is something fundamentally wrong on improving marine engine preformance.For some odd reason i believe it to be a heat realted issue.

 

[Bondo]

Re: I want more speed!

There is something fundamentally wrong on improving marine engine preformance.

Not At All..........<br /><br />As long as you understand the Fundamentals of building Marine HorsePower........

 

[ramster]

Re: I want more speed!

A simple 30 HP is to add 1.6 ratio roller rockers and a four barrel. No need for a racy cam, by adding to much duration you only move the power up in the RPM range, and loose torque. I have a Glastron SX195, 220 HP 5.0. I tried a 14x20 Mich. Vortex 4 blade AL and over-reved at 53MPH. Then a Mich. SS Rapture 14.25x21 and went 55MPH. Then a Solas Amita 14x21 AL 4 blade, that got me 53 MPH but only turned 4200RPM. Now I have a Mich. Apollo SS 14.75x21 and it runs 57MPH at 4600, best prop so far. I will be trying Smart-Tabs next.

 

[Tail_Gunner]

Re: I want more speed!

Originally posted by Bondo:<br />

There is something fundamentally wrong on improving marine engine preformance.

Not At All..........<br /><br />As long as you understand the Fundamentals of building Marine HorsePower........

Perhaps differnt is a far better choice of words.....