What´s the best replacement for AQ271C (or 570) 5.7 GM engine, ideally stroker?

[Lou C]

No the vortec engines use the same exhaust, your old exhaust is what allowed water in the engine, corrosion around the sealing surfaces are the usual cause but the parts themselves can rust through and allow water right in a cylinder.
In the USA there are a number of vendors for closed cooling systems, in Europe whoever supplied them to Volvo Penta would be what I'd try to research. Here there is Orca, Mr Cool, and a few others...I think Orca bought out San Juan cooling systems....
The cyl heads I would not worry about. The difference in power is not great.
Personally I would never install a new engine in a boat used in salt water and leave it raw water cooled. 2 must haves for me are closed cooling and a remote oil filter mount. I'm done with pulling seats out and crawling around the bilge to winterize and do an oil change. So when my boat gets repowered those are my 2 'indulgences' because I'm at the age now where I want it to be a bit easier, as long as I have an I/O boat vs an outboard.

So you will need a VP style exhaust for your engine, Barr is a good aftermarket brand here in the USA and if you are in salt water figure on replacing it every 5-7 years if you want the engine to last. I've owned this boat 18 years and its on the 4th exhaust system! Never had water in the engine due to bad exhaust. The only way to reduce the cost for this is to use full closed cooling, which then includes the exhaust manifolds on the cooling circuit but can only be done if the manifolds have a feed port on the bottom and a threaded fitting on the top for an exit port. Most VP manifolds do not, at least the ones that I've seen.
My engine came with the old style OMC one piece manifold/elbow units, I had 3 sets of these over the years, no problems with water ingestion, but they were NLA for a while so I converted it over to the 2 piece system used by both OMC and Volvo on these engines, using V/P hoses and 90* exhaust pipes that mate the 4" elbow exit to the 3.5" Y pipe, and Barr aftermarket manifolds and elbows. It all fit perfect and runs cool.....

 

[Scott Danforth]

you need new exhaust because your were cracked (post #1)

the VP exhaust already flows better than the mercruiser versions. so all you need are BARR or VP replacments

you are over-thinking 906 vs 062 vortec heads

the closed cooling should only be added to freshwater motors or new motors. since your motor was in salt water, no amount of mechanical and thermal cleaning will get all the rust out of the passages. consider your 32 year old salt-water cooled block a casualty of running in salt water.

cost to build a new 377 stroker or a new 350 is within $200 (USD) of each other. its literally just the cost difference of the rotating assembly

a good 5" x 18" shell and tube HX will be required. there are a few aftermarket companies that make complete kits. if you can weld, and have some fab skills, you only need the HX and a gates molded hose catalog.

 

[Scott Danforth]

this is the amount of rust I get every outing plugging up a filter screen I added between my thermostat and heat exchanger. this is only from the cylinder heads which did come off a salt-water cooled motor. to this day, I still kick myself for not spending the extra $5-600 and buying new Merlin heads

 

[Scott Danforth]

No the vortec engines use the same exhaust, your old exhaust is what allowed water in the engine, corrosion around the sealing surfaces are the usual cause but the parts themselves can rust through and allow water right in a cylinder.
In the USA there are a number of vendors for closed cooling systems, in Europe whoever supplied them to Volvo Penta would be what I'd try to research. Here there is Orca, Mr Cool, and a few others...I think Orca bought out San Juan cooling systems....
The cyl heads I would not worry about. The difference in power is not great.
Personally I would never install a new engine in a boat used in salt water and leave it raw water cooled. 2 must haves for me are closed cooling and a remote oil filter mount. I'm done with pulling seats out and crawling around the bilge to winterize and do an oil change. So when my boat gets repowered those are my 2 'indulgences' because I'm at the age now where I want it to be a bit easier, as long as I have an I/O boat vs an outboard.

So you will need a VP style exhaust for your engine, Barr is a good aftermarket brand here in the USA and if you are in salt water figure on replacing it every 5-7 years if you want the engine to last. I've owned this boat 18 years and its on the 4th exhaust system! Never had water in the engine due to bad exhaust. The only way to reduce the cost for this is to use full closed cooling, which then includes the exhaust manifolds on the cooling circuit but can only be done if the manifolds have a feed port on the bottom and a threaded fitting on the top for an exit port. Most VP manifolds do not, at least the ones that I've seen.
My engine came with the old style OMC one piece manifold/elbow units, I had 3 sets of these over the years, no problems with water ingestion, but they were NLA for a while so I converted it over to the 2 piece system used by both OMC and Volvo on these engines, using V/P hoses and 90* exhaust pipes that mate the 4" elbow exit to the 3.5" Y pipe, and Barr aftermarket manifolds and elbows. It all fit perfect and runs cool.....

the HX's for Volvo were obtained thru Champ Products in Sarasota Florida, and sold to Volvo USA for the V6 and V8 GM motors. the volvos using the swede build motors were MOTA heat exchangers

 

[bollerwagon]

Removed the second head today. My engine bay has the size of an average Manhattan midtown appartment (2-bedroom), so I can access everything very easily.


On the first piston was a lot of coal (?), after spraying it with WD40 it coud be scratched off with the finger tip. The other ones were cleaner. I wonder why.


All of the cylinders had these rings from rust and the honing was washed off partially.

And I found sea shells stuck in the smaller water holes between head and block. I wonder if they liked the hot tub style environment, or if the boat was sitting for so long sometimes, that they grew there.


Want to take out the engine next time. How do I unbolt it towards the transom?

 

[Scott Danforth]

you take the drive off
you then unclamp the PDS (6 bolts), and take 3 of the bolts to jack the clamp ring off
you then disconnect everything inside the boat, undo the front mount lag bolts and lift up and pull forward.

your boat can not be in the water to do so

 

[Lou C]

Lol. Just say NO to raw water cooling!
I’ll run my old engine as long as I can but the next engine has to have a heat exchanger and remote oil filter mount!

 

[bollerwagon]

you take the drive off

Found this tutorial, will follow that:

you then unclamp the PDS (6 bolts), and take 3 of the bolts to jack the clamp ring off
you then disconnect everything inside the boat, undo the front mount lag bolts and lift up and pull forward.

Can you elborate on this one?
- where are the 6 PDS bolts and what is a PDS?
- where is the clamp ring located?
- front mount lag bolts are where the engine is mounted to the floor, correct?

your boat can not be in the water to do so

I have the boat on a trailer already

 

[Scott Danforth]

once you have the drive off, the clamp ring is around the PDS housing sticking thru the transom.

the front lag bolts should go into a big block of wood and fiberglass mounting to the stringers and the hull.

 

[bollerwagon]

So, aside from the lag bolts, the engine bolts connecting it wiht the boat are only accessible from the outside of the boat?

 

[Lou C]

I think at this point it might be a good idea to pick up a Volvo workshop manual.

 

[Scott Danforth]

you can view it here http://boatinfo.no/lib/volvo/manuals/aq280-dpc_drive.html

 

[Scott Danforth]

So, aside from the lag bolts, the engine bolts connecting it wiht the boat are only accessible from the outside of the boat?

yes. the 6 bolts on the AQ PDS housing clamp are accessible only from the outside, and only when you have the drive off (or at least the upper gear box/transmission off).

the system is sealed with two rubber donuts you will need to buy new.

 

[bollerwagon]

The drive is removed and the engine moves. Didn´t pull too far, since I will have to get the crane first.
There is a thing that´s supposed to prevent water getting in the exhaust, but it was totally bent and the parts don´t move. Also the steering arm was not fixed on the helm-thing, so the helm was too low and rubbing somewhere, quite some material was worn off.

I found a heat exchanger in the garage https://store.danfoss.com/ch/de/Wär...er,-Plattenanzahl:-40,-25-bar,-G-1/p/004B1420. Is there a number or anything that quantifies the percormance, the amount of water that can be cooled per time? Also not sure if it likes salt water.

 

[Scott Danforth]

someone added the flapper from a mercruiser...... throw it away, it doesnt belong on your 271C, its not needed on the AQ series

 

[Scott Danforth]

wrong style heat exchanger.

you need a shell and tube heat exchanger. what you have shown is ok if you have filtered water with filtered oil. however would plug up in a week on a boat.

 

[bollerwagon]

wrong style heat exchanger.

you need a shell and tube heat exchanger. what you have shown is ok if you have filtered water with filtered oil. however would plug up in a week on a boat.

That sounds reasonable. I´ll just put it back where I found it.

Regarding me engine swap. After profound youtubing (I recommend this guy

) I do not feel confident any more to assemble a strokered SBC (not even a normal one!) any more. I need a completed long block at least, ideally including vortecs and intake.
My current favorite is this: http://marineengines4less.com/marin...gine-with-intake-replaces-years-1996-present/
or this (same but new): http://marineengines4less.com/marin...-intake-manifold-replaces-years-1996-present/
Comments?

As an additional challenge literally everyone I ask tells me the opposite of what I´ve heard before. My local boat guy says, vortec and stroker does not really make a difference if I don´t have a new open exhaust system (the pipe that directly blows the noise our of the transom.). And I defenitly should go for a fresh water cooling. Next I talk to a dealer for refurbished engines who says, fresh water cooling is ****, because the engine is supposed to run on the lower temperature (around 60 celsius) to avoid the block of expanding too much and lower gap size of the cylinders of whatsoever.
For someone with little knowledge that makes it hard to set foot on solid ground...

 

[Lou C]

They are ignorant. Vortec gives 30 hp on the V8 and if your in salt water ask that dealer if he’s ever seen the inside of a salt water run raw water cooled motor after 10 years...he does not know what he’s talking about...

 

[Scott Danforth]

if you understand righty-tighty / lefty loosey and can read AND understand instructions, you can assemble a motor.

agree with @Lou C , your local boat guy doesnt know what he is talking about

vortec heads alone on the motor are +30hp, with cam change, more. stroker adds a bunch more to the mix. as I have stated, going from 275hp at the prop to an honest 350hp-400 is very doable with a 377 or 383 if built right from the ground up.

the whole run cooler line is bunk (because I cant say how he sufferes from rectal-cranial inversion in lanquage that strong on a family forum). the reason raw water cooled motors run a 140 degree thermostat is that salt water comes out of suspension about 150 degrees and the salt crystals will wear out the motor - fast.

this is also why a shell and tube heat exchanger will run a row of 90/10 copper-nickle tubes on the glycol side inlet side - to prevent wear.

Heat exchanged motors run between a 160 degree thermostat and a 180 degree thermostat. I personally like about a 175. the larger the temperature differential, the more BTU's transferred.

if you want to build a motor, we will help

if you want to buy a motor, suggest you get one shipped from folks over here that build them all the time. there are a few engine shops I can recommend in the midwest.

on another note, if you buy a HX for a mercruiser 6.2 (864395), I can send you the drawing files of the HX bracket that I made for mine. from there, you need a few gates hoses and an automotive thermostat housing

 

[bollerwagon]

Thanks for the encouraging words and I do not mean the rectal-cranial inversion part of it. I feel good here and you seem to know what you´re doing from your own experience, not from "I heard a rumor..."

What do you think about these two:
refurbished http://marineengines4less.com/marin...gine-with-intake-replaces-years-1996-present/
same but new: http://marineengines4less.com/marin...-intake-manifold-replaces-years-1996-present/
Runnung the numbers you gave me (Scott), building myself will not be cheaper.