Switchable Exhaust vs RPM???
 

What is the story with Switchable exhaust systems? I was just on a boat that said not to run over 2500rpm with the exhaust closed. Is this true of all switchable exhaust systems? Or can you run higher RPM with them closed?

As far as I iknow, any factory set-up is designed to be able to run with the exhaust closed to flow through the drive--no pbroblems with mine. I try to not switch either way once I'm above 3000 rpm just so I don't put high loads on the switching mechanism. Just for reference, I gain about 1-1/2 mph between top speed open (through mufflers) and top speed closed.

I had always heard not to exceed 3000rpm +/- or you risk burning the rubber off the closed flappers. Don't know if this is true.

I was told virtually the same thing at our service center.
Try not to exceed 3000rpm when going through prop and don't switch either way much over fast idle.

Although, just for curiosity I tried running WOT closed...No problems so far. Also, when switching at cruise(3300rpm) it really sounds like the diverters take a beating. They slammed quite audibly. :eek:

i run mine WOT either way with no problems. i just don't switch back and forth over 3000RPM:)

East Coast B,

If you are referring to a system such as Teagues' switchables, then you are correct. When I got mine from them, I was told not to be running at any high r.p.m. with the system running through the mufflers. From what I was told, the baffles in those tips can't take that kind of punishment for too long. I also know it is just not good to run that kind of restriction. In a silent choice (thru prop ) system, the restriction is not as much. You are basically open exhaust in either position, only thru prop quiets it down because the exhaust exits under water. Thats why you don't see any extreme performance gains with a silent choice ( thru prop )system in either silent or open position. When I have my Teague switchables' on muffled, you can hear the engine labor to squeeze all the air out of that little space around that 4" pipe. I wouldn't want to run at speed with the exhaust set to that position.

The fundamental reason you hear about 2500-3000 rpm as the point to switch to straight through exhaust is two fold.

Most engines start into the steepest part of their torque range then backpressure created when going through mufflers or out through an underwater exhaust robs you of power.

The second is that with engines above 425 HP there are no through hub exhaust systems that are large enough (in flow)not to create backpressure. This type of pressure (backpressure) creates heat build up in the combustion chamber and can potentially severly impact your high dollar investments durability and life. If EGT's start to run above 1500 degrees F for a prolonged time something will go!

The new automatic rpm initiated controllers are pretty cool in making this task foolproof and errorproof. They are settable as to initiation rpm and some I believe also have a built in delay to allow you to get the boat on plane and throttle back to a comfortable cruise without going wide open on exhaust.

A good control will also not let it go back to the muffler/hub without going to an rpm (usually 200 rpm) below the initial opening setting. This eliminates system hysteresis .

I had silent choice on my boat, and if you'd try to run at WOT with the exhaust shut (going through the prop) you'd foul out a set of plugs in no time. Open it back up, and they'd clean off.
Plus sounded much better open