Silent thunder question

prosno · 08-01-2008, 07:06 AM

I have a 1987 223 LS and the motor was completly rebuilt this winter, risers and manifolds were fairly new and clean, I cleaned them up anyway and we took her out Saturday-Lots of steam comes out the silent thunder exhaust tips.
Engine temp is at 150, riser temp 148.
Also there are no plugs in the bottom holes of the thunder box.
Just seems like alot of steam compared to through hull exhaust which really has almost no steam, Any thoughts on this?
I heard steam is a common trait of these silent thunder platforms but dont know.

jeff32 · 08-01-2008, 07:29 AM

sometimes I have some, sometimes I have less, and sometimes I don't have any.... I think it basicaly depends on the exterior temperature added to some criteria of engines temperature, and maybe silent thunder humidity trapped in the box.

I'm not sure of all this though, but I would not worry about that if your engines are running with no problems...

ThirdBird · 08-01-2008, 12:02 PM

The ST platform does not contribute to steaming. If you're engine is steaming excessively (more than normal compared to others) then there is a problem in the engine. Most likely the heads. You say it was rebuilt, did you get the heads tested (magnafluxed)? Older heads will develop small cracks between the valves. Not enough to really hurt anything but it will produce excessive steam. I've been there. If it gets bad enough, it can cause issues.

Other than heads, it may be leaking risers, very common.

Something is making it steam but it's not neccessarily detrimental.

Monaco20 · 08-01-2008, 04:13 PM

Quote:

Originally Posted by prosno

I have a 1987 223 LS and the motor was completly rebuilt this winter, risers and manifolds were fairly new and clean, I cleaned them up anyway and we took her out Saturday-Lots of steam comes out the silent thunder exhaust tips.
Engine temp is at 150, riser temp 148.
Also there are no plugs in the bottom holes of the thunder box.
Just seems like alot of steam compared to through hull exhaust which really has almost no steam, Any thoughts on this?
I heard steam is a common trait of these silent thunder platforms but dont know.

I also have smoke/steam out of the silent thunder exhoust tips

but only when I driving with speed and when the engine is
having som resistance going to plane or going fast.

My engine seems ok

But maybe there is an issue?

I spoke with a guy who has a 271 1993 with a sound 496
who told me about the same "problem"

On my boat there are more "steam" from the right
exhaust tip

My1stFormula · 08-05-2008, 07:54 AM

Are the holes in the bottom of the thunder box suppose to have plugs?

masi242 · 08-05-2008, 09:44 AM

I have steam coming out and it`s fine most of my water drains out of he platform with the extra holes I put in. I have 200hrs on my rebuilt and it`s ok.

BowenCT · 08-05-2008, 10:07 AM

Quote:

Originally Posted by My1stFormula

Are the holes in the bottom of the thunder box suppose to have plugs?

I believe the plugs help hold water in, keeping things quiet. Removing them allows more water to drain making the exhaust a little louder. Mine has a plug on each side. I don't know if Formula did this, or if the previous owner added them....?

Again, I believe this to be the case. However, I am new to Formula ownership so maybe a veteran can chime in.

ThirdBird · 08-05-2008, 12:08 PM

Quote:

Originally Posted by BowenCT

I believe the plugs help hold water in, keeping things quiet. Removing them allows more water to drain making the exhaust a little louder. Mine has a plug on each side. I don't know if Formula did this, or if the previous owner added them....?

Again, I believe this to be the case. However, I am new to Formula ownership so maybe a veteran can chime in.

The small holes/plugs are factory from Formula. They're really there for draining the platform when the boat is out of the water. Leaving them out won't really make the boat much louder because the amount of exhaust water going into the platform is way more than what can drain from the tiny drain holes. But, it also won't hurt it at all to leave them out all the time.

Keep in mind too that the platform is designed to retain water when going slow, therby muffling the exhaust. When you get up and go, the combination of forward movement and exhaust pressure "blows" most of the water out that's been sitting in there. This lowers back pressure and increases exhaust flow. That's why Formula designed the platforms the way they did.

Mine has large 4" holes in the bottom of each chamber closable by installing deck-plate covers. With these big holes in the bottom, mine never fills with water so it is louder all the time.

My1stFormula · 08-05-2008, 01:22 PM

Thanks for the info ThirdBird appreciate it.

I'm also new to Formula ownership and new to this forum so any and all info is helpful/appreciated.

BowenCT · 08-05-2008, 02:12 PM

Quote:

Originally Posted by ThirdBird

Keep in mind too that the platform is designed to retain water when going slow, therby muffling the exhaust. When you get up and go, the combination of forward movement and exhaust pressure "blows" most of the water out that's been sitting in there. This lowers back pressure and increases exhaust flow. That's why Formula designed the platforms the way they did.

Really? I am a little confused then. My boat at neutral and just over idle sounds absolutely amazing.....deep and loud, but not obnoxious. At speed it emits a nice deep tone, but is almost too quiet for a performance boat.

I had assumed it was loud at idle because the ST was empty of water, and quiet under power because it was full of water muffling things down......????