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recommendations needed swap out 305 for a 350?

huntmotorsports

huntmotorsports

Member
I have a friend with a 1989 206 Rinker with a 230hp 305, alpha drive, that runs 48mph @ 4800RPM on the 17" hussler prop with 4 adults and a full tank. He asked if changing to a 350 would gain enough for the trouble. He wants to run over 50mph with a prop that will pull a big guy skiing. Right now he changes props to ski or to go fast. I know he has a 19" hussler (50mph @ 4600, but struggles with a skier), and a 20" stainless (that the boat will not pull to RPMs).

The idea is getting a vortec 350 from the junk yard, re-camming it and install a good intake and reinstall all the stuff from the 305.

Since all my boats have been outboards, I do not know about the potential gains with an I/O so I have a few questions.

will it be worth the trouble and $ invested?
will a truck vortec 350 work in a boat?
That is with the proper cam and intake.
will the exhaust manifolds work on the 350?

From what I have read the Alpha drive is rated to 300hp, and was installed with a 260hp 350s in the Rinker line up.

I want to build a 383 stroker and make sure it would be worth it, but the budget is limited and I don't think the drive would handle it.

Thanks for the input.
 
huntmotorsports said:
I have a friend with a 1989 206 Rinker with a 230hp 305, alpha drive, that runs 48mph @ 4800RPM on the 17" hussler prop with 4 adults and a full tank. He asked if changing to a 350 would gain enough for the trouble. He wants to run over 50mph with a prop that will pull a big guy skiing. Right now he changes props to ski or to go fast. I know he has a 19" hussler (50mph @ 4600, but struggles with a skier), and a 20" stainless (that the boat will not pull to RPMs).

The idea is getting a vortec 350 from the junk yard, re-camming it and install a good intake and reinstall all the stuff from the 305.

Since all my boats have been outboards, I do not know about the potential gains with an I/O so I have a few questions.

will it be worth the trouble and $ invested?
will a truck vortec 350 work in a boat?
That is with the proper cam and intake.
will the exhaust manifolds work on the 350?

From what I have read the Alpha drive is rated to 300hp, and was installed with a 260hp 350s in the Rinker line up.

I want to build a 383 stroker and make sure it would be worth it, but the budget is limited and I don't think the drive would handle it.

Thanks for the input.
Click to expand...

I sure wouldnt go over 300 HP with a Alpha. A decent running vortec 350 with restrictive marine manifolds might get in the 250 HP range so you are OK there. Forget about a 383 with an alpha. I'm sure people do it but I wouldnt.
Ive put 350's in front of alphas before just like you are doing. Picked up a few MPH. Still drove like a truck compared to a good outboard.
 
Being that it is a Rinker, he would only probably see 1-2 maybe 3 mph difference between 228 hp and 260 hp. I wouldn't go past 300 hp with an alpha. If he wants a faster boat, buy one. Especially if you aren't already starting out with a performance hull. He is better off just playing with props when he wants to pull skiers.
 
I am afraid the payoff will be small compared to the work and cost involved. Sounds like 3 mph may not be enough. The only reason we even discussed the swap because it is such a nice, clean, and well cared for boat.
 
Realisticaly, you could gain appx. 20-30 hp from the cubic inches, 25 from the better heads, 20 from the cam and intake...you could end up with around a 280-300 HP 350 if done right....but then , alot of times when you do mods like this, they become less reliable, and more tinkering is involved on a more frequent basis. Will it be faster..Yes, will you work on it more, Yes. Will you enjoy it more over all??...that depends on what type of person you are. Just my $.02
 
Oh yea...and remember, just kind of a rule of thumb...it takes appx 15 horsepower to gain about 1 MPH in a boat, in your case, with a small boat, I would guess it would take even a little less, maybe 12 or so to gain each MPH. In the 2 boats that I've really "hopped up" , a 21' Scarab and my current 251 Convincor, I've found that 15 HP per MPH rule is pretty close.
 
Just my opinion prolly get bashed for it but oh well. If the boat is a cared after rig an he likes the hull it is def worth swapping a 350 in place of the 305. It will have more grunt out the hole so he would be able to run more prop then the 305 which also gives more top end speed. It is a simple swap bolts right in all the stuff on the front of the 305 will bolt right to the 350. I would do it, it is easy for guys to say buy a new boat when it isnt there money. The torque curve of the 350 is what will pull it out the hole with more pitch prop the couple extra ponys will keep the rpm up top i def see it running 50-55
 
One thing that you need to keep in mind is that you will always have a "top speed" prop and a "ski" prop regardless of how much HP you are running.

If you find a prop that gives you great out of the hole performance for skiing and gives you your best speed number, you haven't found your "top speed" prop yet. That is when you have found your "all around" prop.

You can buy several props for the cost you will have in switching out a perfectly good small block.

I would say enjoy the boat as is and keep switching props (wish I could follow my own advise sometimes!).

HD
 
thanks for the input and insight. I think he is going to not swap it and just enjoy the boat. I will be pushing him to buy an outboard....because it is the easy way to go fast.
 
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