Silent Choice rpm limit?
 

I was told by one person you can't go from through hull to silent after a cetain rpm. but had to be back at idle. You could be running in silent mode, and open them up to through hull?? Is this true? and if so what is thr RPM that I can't do this past? I ask this because the guy i bought the boat from said you can do it when ever you want.

thought?

boat is a 1999 Baja 252 454 Mag.

No one knows?

On my 382 there are cut outs at around 2500 rpm's that will take it from silent mode to thru hull when getting up to running speed. I have been advised not to ever throw the switch when you are above ideal speed when going from thru hull to silent and there are all kinds of cautions on this from the manuals and directions from the manufacture.
I always throw the switch either way from idle just to be on the safe side. They are a great feature in my book.

Mine would stay close and pop open themselves around 3,000 rpms....now that I have higher compression, bigger C.I. motors they will pop open at idle 1/2 the time....forget getting them to stay closed at any speed above idle.

I think we are talking about differnt things. Mine has electric actuators that open vavles to make it loud. if there is no power going to them then it is silent....coming out under water through the hub. if you send the actuators power they will open and let it go through the hull making it loud. Is this not the same?

Depends on power. Up to 415-425 you can probably run through-hub all the time. Over that, you need to open them at some point. The bigger the power (= more airflow), the sooner you need to go through-hull. CORSA makes a switch that will make sure the valves actuate at a certain speed. The switch can be wired for either normally-open or normally-closed applications.

As far as switching back and forth between through-hub and through-hull, I don't see whay you couldn't do it any time you wanted as long as you are below the critical airflow speed. I do it all the time with my CORSA system.

I'm talking about the same system....electric, but mine must have some type of relief system. I've left it silent a couple times then as I got on plane the boat would get much louder as they popped open.....the new motors pop them open at idle now.

I have the corsa system and they stay closed to wot if I wanted them to. I don't , but have.

Ok well I tried it and they will do it either way, at any speed. I was just told not to go back to quite when above Idle becasue it put to much strees ont he acutators. but i thought it sounded funny...so that why i was asking. I personally only want it quite fo rhte use of talking to another boat or passing the Police or something like that, the rest of the WIDE OPEN..

I have never heard a clear answer on this either. I have Silent choice on a 600sci.

I only leave them on above idle if we are wakesurfing or towing inflatables.

Under normal circumstances(95% of the time), I always open the exhaust before I take off.

They have never popped open on their own.

From all I've gathered and experienced, seems to be fine from idle to 3000 rpm or more....
I figure 3000rpm is moving roughly half the exhaust gas as WOT. (if not less). Above that starts to concern me.

Would be nice to have a clear definitive answer from mercury and corsa though. If there were warranty issues seems like there is a lot of gray area there to get screwed by.

On another note, running all the hot exhaust down thru your outdrive is not doing it any good. You can tell a drive that has all of exhaust going thru it vs one that has not.

I have never heard that before???

Exhaust
 

I have been told there is a back pressure issue and the silent choice system is not designed to remove the volume at RPMs above 2500. I am sure there is a safety factor in the number but I have not tried it.

There we go at least I am not the only one. wel i tried it at 3000 and it worked.

I have heard no more then 3000 with them closed

Oh i did not know there was a problem with runnning them closed at wot, just closing them. I ran mine at wot and they stayed closed

What about at initial start up of the engines? Open/closed or it doesn't matter?

I think it depends on the engines, something small like a 350, you can run them closed, but I am pretty sure anything bigger and you should not run through the hub past 3000. also I heard that it is not good to switch it while running

I am running a 540 with silent choice exhaust. I cant and dont run with mine closed above 3000 rpm. One thing i had to do is add water to the exhaust behind the flaps so the heat from the exhaust that would slip by the flaps wouldnt melt the rubber couplers. Works great, and gets the water police off my arse. Its great to have a big motor and not freak out the kids when i pull them on tubes! The only downside that i have experienced is that my cam couldnt have any more that 230 deration in fear of having water reversion when the exhaust is closed mainly at idle. Gave up some hp but its well worth it.:evilb:

Oh i forgot to mention, I had no less than 1/2 dozzen marine engine people tell me that i could NOT use my silent choice exhaust AT ALL with the 540.

Start up shouldn't matter. That is one of the times you need it most.

Seems like everyone is on par with 3000 or below being safe.

Think of how much air a big block is moving at WOT through twin 4" + exhaust tips. Cut that in half for 2500-3000rpms... and you're pushing it through a single 4" hole out the prop hub. (-a prop shaft etc).
Makes sense that that is a safe limit.

Would still be nice if someone from Corsa chimed in with the official word.

If you are making a ton of horsepower that might be correct....
I've heard CMI's (fairly new?) switchable system is the best or only choice for those setups.