Here’s some exhaust-related advice to keep your engine noise to a minimum.

As Seen In Speed On The Water, Issue 17; January/February 2016

As a way to bring a little more tech to the pages of this digital magazine, I’ve been providing answers to questions about various performance boating topics. In this issue’s column, there are a handful of exhaust-related inquiries. If you have a question you’d like me to answer in a future issue, please submit it.

CAN YOU HEAR ME NOW?
Q: I am considering changing my tailpipes from wet to dry in my single-engine catamaran powered by a 572-cubic-inch, 800-hp EFI engine. My engine builder suggested running dry tailpipes to free up some power that is being lost due to back pressure caused by the water in my exhaust. Will the dry pipes cause a heat problem where the pipes go through the hull?

The headers are similar to the ones from Custom Marine Inc., with wet tailpipes. I understand the fuel mixture will need to be checked and possibly adjusted, which I am capable of doing. Will the decibel level be higher?

A: If your existing headers are similar to CMI’s, they also should be equipped with tailpipes that are water jacketed, which means that there is no water in the exhaust stream until the aft end of the tailpipe. With the CMI-type system, the water entering the exhaust stream at the end of the tail should have very little affect on the performance of your engine.

You could opt to extend water-jacketed tailpipes through the transom instead of
using transom tips that are connected with rubber exhaust hoses. With throughtransom
tips, you will have to use transom rings and seals to keep the water out of the boat. A through-transom tailpipe can either have the water exit at the end of the pipe or a little further forward.

If you want to plumb the exhaust water overboard via a through-hull, you will still have a slight amount of water exiting where the inner pipe is swedged out to the outer pipe. It is not advisable to weld the inner and outer pipe together at the tip because of the temperature differential between the two tubes. The inner pipe gets hotter and expands at a greater rate than the outer pipe. The result will likely be a crack in the inner pipe, which could result in water getting into your engine.

You may gain only a slight amount of performance by using a CMI-style dry tailpipe. I do not believe that having water exiting in your exhaust is robbing your boat of horsepower.

If your headers are the type that a rubber exhaust hose clamps to, it will be next to
impossible to add a dry pipe to them. A water-jacketed tailpipe should not cause a
problem with heat at the transom as long as there is enough water flowing through the
tailpipe jacket.

Here’s the bottom line: Dry tailpipes are loud. Marine-style mufflers are pretty much not designed to work without the presence of water. When it comes to pleasure boating, you
are sure to get tired of the noise and everyone else is likely to get tired of it as well. And in
terms of attention, the focus you get may not be from the folks you want it from, such as
local law enforcement.

OPTION FOR NOISE?
Q: I recently purchased a 24-foot Liberator with the original 454 in it. The boat was used
in a lake, which had a sound ordinance. I am going to be using the boat in the Long Island Sound where there are no noise restrictions. I am thinking about putting through-hull exhaust into the boat (Silent Choice).

I was wondering what I should expect to pay for a system and can you recommend one over another?

A: Two of the more popular switchable systems that divert water through the propeller hub are the CORSA Captain’s Call and the CMI Sound Choice. The price for these kits range from about $1,500 to $2,000.

You also will need to purchase transom exhaust tips, an exhaust hose and clamps to complete the job. I suggest that you purchase tips with internal and external flappers to help protect your engine from water surging or reverting back up the tailpipes.

DON’T DO IT
Q: I need to know if taking the exhaust riser extension off of my exhaust will damage anything. I have a MerCruiser carbureted 454 and I am losing power due to the riser extension.

However, because my exhaust is exiting above the swim platform, if I were to remove the extension, there will be a slight rise from the riser to the exhaust tips.

A: The reason the exhaust riser extensions were installed on your engine is because the tips in the transom would have been higher than the stock riser outlet without the extensions. If you remove the riser extensions, it is very likely that water will be able to run backward into your exhaust manifolds and into your engine.

The water will be able to enter your cylinders through the exhaust ports, which will result in damage and possibly a “hydraulic” lock condition. If you try to crank the engine with water in one or more of the cylinders, you could end up bending a connecting rod or causing other damage.

You are not losing power due to the riser extensions. The installation of the riser extension would not create any flow restriction to an exhaust system that is otherwise not a tuned system. If you want to install an exhaust system that will result in increased power, I suggest the CMI E-Tops or IMCO PowerFlow offerings. Both of these systems are available in “higher rise” configurations. Many other makes of systems are also available.

–Technical editor and offshore racing world champion Bob Teague is the owner of Teague Custom Marine in Valencia, Calif.

This article appears in:
Speed on the Water, Issue 17; January/February 2016