Love Machine

I learned the hard way. I have 454 Mag MPIs with silent choice. I forgot to turn off silent choice one day before cruising at 3600 rpm. I ended up blowing a hole in the exhaust y-pipe. Water ended up pouring into the bilge and getting everything wet. Really sucked.

By the way, JB Weld and a stainless screw got me through the rest of the season.

PhantomChaos

I know that Formula's have a built in sensor that automatically opens the silent choice above about 2500 RPM......so I would figure that it would be bad to run it anything above that. Otherwise, why would they engineer some nifty thing like that???

rush

Thanks for the replys.

Downtown42

I agree.

Reckless32

This is how I've always played it, and it sounds like from the uncertainty above it's the safest bet. I'd hate to replace these things for using them wrong. But I only use them for when in no-wake zones; docking up at a restaurant where it could be obnoxious to patrons dockside; engines running while doing maintenance etc; well you get the gist. If you tend to use them at 25-3000 rpm chances are at some point in time you're gonna slip and run them above those marks several times over the course of your ownership. Odds are they'll fail on the next guy buying the boat too....

NetGain

I have the Corsa and here's what I was told. Don't run it over 2500 RPM's. On the other end, under 2500 RPM's, I was told you can have vivration which could lead to reversion? It doesn't sound as good around the Gas Dock, but I am not going for a rebuild either.

Oh yeah, they guy who did the rebuild on the top end told me this. I have a 99 454 MPI and the metal gaskets rotted out. He would say the Corsa caused it, but he strongly recommended it go through the hub under 2500 RPM's

grimmy

i had it on the 502 in my cheetah, used it whenever i wanted, hi-low whatever, run it.

FOUNTAINATLAST

I honestly can't see any reason you can't run it either way. How many boats are there out there that have just through the prop exhaust, are you telling me they could have problems running over 3000RPM??? I can understand not switching at RPM but other then that the only abuse I would see is the stress on the solenoids under load..

offshoredrillin

I'm tellin ya you can run wide open with it on, my donzi used to only have the exhaust through the drive, I added it to go through hull. Why would some one say you cant run it through the exhaust? Does that mean that any boat that doesnt have thru hulls cant run wide open?

SteveO

RUN SILENT
Question: I have what I hope will be a simple question for you. I have a new 496 Mag HO with Corsa Captain's Call/Silent choice through-hull exhaust. I am wondering if there is a limit on how much rpm you can run with the exhaust "closed" before you should open it to the full through-hull position. Are there back-pressure concerns? What I have been doing so far is opening it when I hit 1,500 rpm.

In all the literature I've read, nothing has referred to a limit or suggestion regarding the rpm you should open the exhaust. I'm guessing this may be something I don't need to worry about, but I wanted your opinion.

Mike Shaver
Canton, Mich.


Answer: I think that you are being more conservative than you need to be. I would be more concerned if your engine were supercharged, or made 500 horsepower or more. I would say that you can run constantly at 3,500 rpm, which would allow you to cruise in the quiet mode. If you inadvertently run full throttle for a short burst, it probably won't hurt anything either. The system does create a little more back pressure. If you try a comparison at full throttle between open and closed, you will probably notice that it takes longer to get to full speed with the exhaust closed, and that the rpm is a couple of hundred less than when the exhaust is open.

Powerboat Magazine, Teague on Tech, Sept. '03