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O470 / 520 engine shroud wanted

Fastcatak

Active member
Looking for a shroud for my 470 / 520 aircraft engine boat. My aluminum shroud constantly rattles to pieces.
Any ideas where to look?
 

Fastcatak

Active member
What are you running now for a shroud? Anything else on the boat that seems to keep rattling apart?
It’s an aluminum home made shroud bolted onto the engine case through bolts, it shakes and eventually cracks and comes apart, nothing else on my boat falls apart
 

Slidin Gator

Well-known member
Yeah I will as soon as I can.
Is this going to be difficult to find?
I was hopeful that someone in FL produces a nice shroud already

The only one that I know of that is not a custom fab job is the Heat Extractor. But, my experience with 2 of them have been that they fatigue and crack at the mount points and on the bent flaps. But they are not welded, so that helps. Below is an old thread on the subject.

Heat Extractor.
 

John Fenner

Well-known member
A finely tuned engine should not require a cooling shroud, even if you are bulldozing trails or pastures, if you have to work it that hard, then there is 1 or 2 things wrong, the hull and rigging is way too heavy, weight displacement, of the whole rig,,,
Not sure what setup you have, where you run or what terrain.
If it is shaking it apart there is a balance issue, detonation issue "overheat, lean burn, timing too high"
If you are experiencing high oil temps, the ring lands of the pistons are worn allowing combustion gasses to superheat the oil.
High cylinder head temps are from a lean condition, timing or running 93 octane pump gas, there are many narratives unknown here, a shroud on an engine is like a trim tab on a hull that porpoises.
 

Fastcatak

Active member
A finely tuned engine should not require a cooling shroud, even if you are bulldozing trails or pastures, if you have to work it that hard, then there is 1 or 2 things wrong, the hull and rigging is way too heavy, weight displacement, of the whole rig,,,
Not sure what setup you have, where you run or what terrain.
If it is shaking it apart there is a balance issue, detonation issue "overheat, lean burn, timing too high"
If you are experiencing high oil temps, the ring lands of the pistons are worn allowing combustion gasses to superheat the oil.
High cylinder head temps are from a lean condition, timing or running 93 octane pump gas, there are many narratives unknown here, a shroud on an engine is like a trim tab on a hull that porpoises.
Well that’s a few things to check out.
I’m running 100LL fuel, cruising 2200-2300 rpm. It is a fairly heavy 16x7 Alaska boat usually with a load of hunting camp and gear.
2 blade whisper tip 72” prop.
But it never seems like I’m having to run her hard
 

John Fenner

Well-known member
Well that’s a few things to check out.
I’m running 100LL fuel, cruising 2200-2300 rpm. It is a fairly heavy 16x7 Alaska boat usually with a load of hunting camp and gear.
2 blade whisper tip 72” prop.
But it never seems like I’m having to run her hard
Cruising at 22/2300 is take off rpm for a plane, once at cruise altitude it is throttled back, leaned out etc.
16x7, ok, the 7 is likely at the top of transom "beam width" the width of the bottom "running surface" might be much much less, 6'4,6'6,6'8 at the chines, not much displacement to get it on plane quickly and transfer the weight to an easier cruise rpm.
There is a balance between weight and horsepower, you can have a bunch of power on a crappy hull and work the powerplant to its maximum, or a well built and balanced hull with minimal power needs to operate it efficiently even with a load of camping gear.
You are running a great prop.
 

Slidin Gator

Well-known member
Cruising at 22/2300 is take off rpm for a plane, once at cruise altitude it is throttled back, leaned out etc.
16x7, ok, the 7 is likely at the top of transom "beam width" the width of the bottom "running surface" might be much much less, 6'4,6'6,6'8 at the chines, not much displacement to get it on plane quickly and transfer the weight to an easier cruise rpm.
There is a balance between weight and horsepower, you can have a bunch of power on a crappy hull and work the powerplant to its maximum, or a well built and balanced hull with minimal power needs to operate it efficiently even with a load of camping gear.
You are running a great prop.
I'ma gonna have to call you out on this one John. Take off RPM is at max Hp, 2,600-2,750, 22-2300 is aviation cruising. I run 7 foot wide hulls and love them because I can go places with em, probably the reason some folks run em in Ak.

Performance in deepwater vs. dry ground is the tradeoff. Give any airboat 1/4" of water and we are running 20-30 mph at idle. A wide boat will jump up and run water at minimal power for sure in deep water, but put it in the Stick of things and it's running over too much stuff. Bob Stossel learned years ago, you just want to run stuff over once, make the bow wider than the stern, and make them both narrow. Do that, the longer you go, the less Hp to Boat you need (like snow skiing).

I got very limited use for max power, what I need is continuous power. Here is my 13x7 Stossel hull running the sticky, I got about 4-1/2 foot worth of true bottom before it rolls each side, the bow is wider, it runs stuff over and the rest is easy. All systems go, the closer to E the fuel gauge moves, the freer she gets.

All Systems Go.jpg


Looking for a shroud for my 470 / 520 aircraft engine boat. My aluminum shroud constantly rattles to pieces.
Any ideas where to look?
Fastcatak, go through this thread if you want the long story. The short story, run the coolest spark plugs that you can get and will work (see thread), unless it's burning oil. Next, cut off the steel crush washers on your new plugs and run copper aviation spark plug washers. These changes alone are good for over 50 deg F. worth of cylinder temp.

Tuning a Lean Running O-540 & 6AA / M5-4 Carbs
 

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