repowering 2006 Chaparral volvo 5.7 with stroker.

[Scott06]

I found a 6 inch riser adapter. its like 700 . You think that would cure any problem.

the issue with reversion is different from riser height. riser height over the water line is one thing.

reversion from a hotter cam and valve overlap is another. This can pull water in regardless of riser height.

Danforth can walk you through it as you choose a cam. I'm paraphrasing- stock and slightly hotter marine cams keep overlap down and LSA wider to limit reversion.

 

[wellcraftpower]

the small block chevrolet has gone thru 6 minor generation changes in the 70+ years its been around. just the 350 (5.7) has been around for 5 of them. With power from 130hp to 600 hp naturally aspirated....they are not all the same.

building a marine motor is also not the same as a truck or a car or an airboat or a trash pump or a genset or a bus. so you have to first identify what you want to do. very specificially, what you want to do.

because if you said, I want to build a 330hp/410 ft-lb motor for a 24 ft boat is different than a 350hp/450 ft lb motor for a 26 ft pocket cruiser. which is different than a 500hp, 400 ft lb motor for a jet boat

once you pick a direction, do no worry about money..... because building a marine motor costs what it costs. the price of building a small block motor in the past 5 years has doubled.

not sure why you want to be rebuilding such a new low-hour boat motor, however you have your reasons

so, very specifically

what Chap do you have?
what drive? Ratio? prop(s)
what is the true wetted weight?
what is the issue you perceive you have?
what is it that you want to do?
in post #1 you state:

define what you want for a "little more power" and what issues you have had that you think your current motor is not reliable

I just got this boat. It has 700 hours . The boat is known to be under powered with a 350. It did come with a 8.1 but i could not find one that was reasonably priced. It's a salt water boat and just had new manifolds and risers installed. I am very familiar with 350s as i have been messing with them my entire life. 26 ft boat 320 or 330 HP . not sure. stroker would give more bottom end and even a little more top end. If i could get 370 0r 75 horse power without dealing with water reversion that would be good. I know it would probably need to be 425 hp just to see 5 miles faster. I want it to be a 50 mph boat but not sure if that is even feasible. It will be a fresh water boat from here on out. has a dp outdrive.

 

[Scott Danforth]

I just got this boat. It has 700 hours . It's a salt water boat

26 ft

I want it to be a 50 mph boat but not sure if that is even feasible. It will be a fresh water boat from here on out. has a dp outdrive.

Since the salt water motor most likely does not have a heat exhangers, assume you need to start with a new block and heads. Machine shop will advise

What ratio DP? Assume 1.95:1

What props?

What is the wet weight of the boat (actual scaled weight). Dry weight is 5200# for the Chap 256.

330hp out of a stock stroke 350 is doable. 420 out of a 3.75" stroke. However not sure either will have enough torque for that heavy of a boat

To get to 50mph, most likely need a big block or the 430hp LS or a blower on the small block

 

[Scott Danforth]

To echo what @Scott06 mentioned on reversion. I have high speed GoPro videos of the exhaust pulses being sucked back into the exhaust elbows from over a foot past the outlet at certain RPMs

 

[cyclops222]

WE used to do a lot of bench and armchair racing.

 

[wellcraftpower]

Since the salt water motor most likely does not have a heat exhangers, assume you need to start with a new block and heads. Machine shop will advise

What ratio DP? Assume 1.95:1

What props?

What is the wet weight of the boat (actual scaled weight). Dry weight is 5200# for the Chap 256.

330hp out of a stock stroke 350 is doable. 420 out of a 3.75" stroke. However not sure either will have enough torque for that heavy of a boat

To get to 50mph, most likely need a big block or the 430hp LS or a blower on the small block

It has 330 hp now.

 

[Scott Danforth]

Look at the torque curve.

 

[wellcraftpower]

the small block chevrolet has gone thru 6 minor generation changes in the 70+ years its been around. just the 350 (5.7) has been around for 5 of them. With power from 130hp to 600 hp naturally aspirated....they are not all the same.

building a marine motor is also not the same as a truck or a car or an airboat or a trash pump or a genset or a bus. so you have to first identify what you want to do. very specificially, what you want to do.

because if you said, I want to build a 330hp/410 ft-lb motor for a 24 ft boat is different than a 350hp/450 ft lb motor for a 26 ft pocket cruiser. which is different than a 500hp, 400 ft lb motor for a jet boat

once you pick a direction, do no worry about money..... because building a marine motor costs what it costs. the price of building a small block motor in the past 5 years has doubled.

not sure why you want to be rebuilding such a new low-hour boat motor, however you have your reasons

so, very specifically

what Chap do you have?
what drive? Ratio? prop(s)
what is the true wetted weight?
what is the issue you perceive you have?
what is it that you want to do?
in post #1 you state:

define what you want for a "little more power" and what issues you have had that you think your current motor is not reliable

Rebuilding a small block is peanuts to me. When i said reliable. what i meant was not building a motor that is like a racing motor. The boat came with 330 hp. i just want to increase it to about 370. i want a new engine , not one with 700 hours on it that lived in the ocean. I have been doing show car paint jobs for 40 years so i am OCD with my stuff. i want only new. just like all my show cars. My boat will look like it just came in from the factory when i get done with it., But it won't have a underpowered motor in it. I talked with this guy from raptor engines who has a 370 hp stroker that he says is a direct replacement for my boat for 3800 to the door. i want to build my own motor. I have a a few good machine shops i work with for my cars . i have 2 small block dart 350s in a box brand new and i also have 2 dart chevy big blocks in boxes brand new. Blocks only .

 

[alldodge]

Note on HP ratings
HP rating of a motor I stalled in a boat is listed as less HP then one in a crate. Reason is the boat has the reduce power because of the drive

So a 370 HP crate motor is closer to a 350 HP one in a boat. Main reason is the cylinders have been bored

Look at a 377 cu in Virginia bore 6.2 to a actual 383 6.2

 

[wellcraftpower]

My drive is dps-A 1.95 26 ft boat. dry weight of boat is 4950 What ever the speed is after putting in a new motor is what is. Im not looking for a racer just a little more than stock.

 

[alldodge]

My drive is dps-A 1.95 26 ft boat. dry weight of boat is 4950 What ever the speed is after putting in a new motor is what is. Im not looking for a racer just a little more than stock.

Sorry my bad, the above had nothing to do with what i just said. I was talking about listed HP and actual HP at the prop.

I'll back out

 

[Scott Danforth]

If you can get a new 377 marine motor for $3800. Buy hundreds of them. The going rate is $10,000 for a 6.2 SBC long block

 

[wellcraftpower]

If you can get a new 377 marine motor for $3800. Buy hundreds of them. The going rate is $10,000 for a 6.2 SBC long block

Thats crazy. my machinist quoted 1700 to prep the block. clearance it for stroker if thats what i want. 500 for refreshing the vortec heads, and 1200 for a scat stroker kit. Pistons , crank , rings , bearings, rods. deck block ,bore magnaflux block. cop Cam, roller rockers and roller lifters and springs will probably set me back 1200 maybe a little more.

 

[Scott Danforth]

You still need to get the block and heads

 

[wellcraftpower]

If you can get a new 377 marine motor for $3800. Buy hundreds of them. The going rate is $10,000 for a 6.2 SBC long block

Look at that website for raptor engines. I did talk to him , seem like a nice guy says he has been in business for 30 years. Reviews are not good though. I wouldn't trust him but some guys swear by him. I have to many connections to not do it myself. because everyone wants a car painted. 40 years of doing this payed off. I only do my own cars and occasional customer. i do not do it for a living.

 

[wellcraftpower]

You still need to get the block and heads

Scott . I have never dealt with salt parts. Lets just say the previous owner used salt away on the motor every time out. Would 700 hours in salt water still destroy the motor.

 

[wellcraftpower]

michigan motors looks like they have good motors pretty reasonable. stock motors. 5 grand. I guess trying to go a little over stock is not doable without tearing everything out and starting over.

 

[Lou C]

No in salt that won’t destroy the motor unless you neglected the manifolds/elbows. We routinely get 1500 hrs or more here in the salt

 

[wellcraftpower]

No in salt that won’t destroy the motor unless you neglected the manifolds/elbows. We routinely get 1500 hrs or more here in the salt

That's pretty good. The manifolds and elbows were just changed.

 

[Scott Danforth]

You can't get the salt out of the motor.

Even baking the block and heads.

Good news is the 1996 and later L31 V8 was in tens of millions of 1/2 and 3/4 ton trucks. So for about $350 (was $150 pre COVID) you can get a running core at a pick a part yard