How to Modify a 350, and is it Worth it at 760 hrs?

[greg82255]

Hello,

I have a 1986 Mercruiser 350/Alpha One. I believe it's 260 HP, although who knows how much power its actually putting out now (760 hours). I have it in my Formula 206 Spider and I get about 46-47 mph @45-4600 rpm on a good day with my 19" Ballistic prop, and about 50-51 with my 21" Mirage @ about 4200 rpm. I'd like to see some more speed out of it. After thinking about all the options (383 stroker, free automotive 454 that my dad found, etc.), I think I'd like to modify what I have if possible. So I have a few questions:

1. Is it even worth it to modify an engine with 760 hours? How much longer will it really last?
2. If it's worth it, what could I do to add some noticeable HP?
3. About how much would it cost to do this and how much time/pain will I be put through?
I'm 22, pretty mechanically inclined, have done a 2 to 4bbl carb/intake swap on a merc 898 before, and wouldn't hesitate to do anything as long as I don't have to pull the motor (no access to a hoist, and would rather just leave it in). Any thoughts are appreciated.

 

[RogersJetboat454]

Re: How to Modify a 350, and is it Worth it at 760 hrs?

1. Is it even worth it to modify an engine with 760 hours? How much longer will it really last?

Depends on the health of what you have. Good oil pressure, and compression are a start.

2. If it's worth it, what could I do to add some noticeable HP?

Most popular thing to do is upgrade what you have with Vortec heads, Vortec intake, possibly consider a cam upgrade (would require pulling the engine).

3. About how much would it cost to do this and how much time/pain will I be put through?

Depends on what kind of shape the engine is in, what parts you use, and where you source them. Most things you would be able to do to an engine that's still in the boat will take under a day, and shouldn't be too painful to do (after all, it is a SBC).

wouldn't hesitate to do anything as long as I don't have to pull the motor (no access to a hoist, and would rather just leave it in).

Pulling an engine isn't that big of a deal. Mechanically it's simple. Hoisting it can be a challenge. Large trees, and home-made gantry cranes work well. Or if you really wanted to get technical; jump in your car, head down 114 to Danvers, and visit the new Harbor Freight to pick up one of these;
http://www.harborfreight.com/1-ton-telescoping-gantry-crane-41188.html

 

[greg82255]

Re: How to Modify a 350, and is it Worth it at 760 hrs?

Thanks for the reply. I have good oil pressure and good compression across all cylinders. I bought the boat this year, and was told it was dealer serviced for its entire life, so I think its in pretty good shape. How much power will Vortec heads add? Also is it necessary to upgrade the cam when changing the heads? And would I need a bigger carb to go along with the new heads? Sorry for the long list of questions but I want to be sure before I do anything. I figure I could rent an engine hoist but I don't have a crate or stand to put it on while I work on it, plus I've heard getting alignment right is a real pain.

 

[Bondo]

Re: How to Modify a 350, and is it Worth it at 760 hrs?

How much power will Vortec heads add?

Ayuh,.... 20hp/ 30hp dependin' on the pistons in the block...

No need for cam or carb change, through, I'd go with the Edlebrock carb, 'n ditch the Rochester...
Ya do need the right Intake manifold....

 

[greg82255]

Re: How to Modify a 350, and is it Worth it at 760 hrs?

If they really only add 20-30 HP then I'll probably just stick with what I have until it's time to repower.. That would only give me 2-3 mph, and speed can vary that much on any given day anyways. Is there another way to add more power in combination with vortec heads? Maybe get 50-60 more hp?

 

[John_S]

Re: How to Modify a 350, and is it Worth it at 760 hrs?

If they really only add 20-30 HP then I'll probably just stick with what I have until it's time to repower.. That would only give me 2-3 mph, and speed can vary that much on any given day anyways. Is there another way to add more power in combination with vortec heads? Maybe get 50-60 more hp?

You would need a cam change and aftermarket heads, or modified vortecs. Intake should be a high rise dual plane, such edelbrock rpm. Also, given the year, probably different exhaust manifolds.
Might as well rebuild the bottom end before dumping that kind of money. An once you decide to do that, need to make sure you don't want a 383.

 

[RogersJetboat454]

Re: How to Modify a 350, and is it Worth it at 760 hrs?

If they really only add 20-30 HP then I'll probably just stick with what I have until it's time to repower.. That would only give me 2-3 mph, and speed can vary that much on any given day anyways. Is there another way to add more power in combination with vortec heads? Maybe get 50-60 more hp?

How big is your wallet?

You're not going to be building that sort of power with out pulling the engine. The only exception to that would be bolting a supercharger on which would be; expensive, difficult to tune, may not fit in your engine compartment, and would make the engine a brute to the Alpha drive.