As seen in Speedboat Magazine’s
AUGUST 2022 Issue.
BBC Gen V & VI
Q. I have a question regarding the GM Gen V 454 block oil bypass when running an adapter on the oil filter mounting pad for a remote oil cooler and filter. There are 2 oil bypass valves in the engine block. Does either one of these valves need to be removed when running an adapter plate in the original oil filter location? Does either one of these valves need to be changed to a higher pressure valve? It is so confusing on the internet regarding information on this subject. I don’t want to make a mistake that will damage the engines that I am putting in my boat. I am restoring an older Scarab which originally had Mark IV engines, so I don’t have the original marine engines to compare them to. Thank you.
Kansas City, KS
If you’re installing an adapter in the stock oil filter location, both bypass valves should be removed. Then, the port that is in the face of the area where the adapter goes should be plugged to prevent dirty oil from bypassing the cooler and filter. We make a small aluminum plug that presses into that port. The bypass valves are used for automotive applications where the remote oil cooler is connected to the two 3/8″ pipe ports on the flange just forward of the oil filter mounting location. The purpose of the bypass valves is to allow oil to bypass the filter in case the filter is plugged or restricted for some reason. But the result is that un-filtered oil would be going back to the engine bearings and components.
In the past, we have tapped the port in the filter mounting face to 1/2″ NPT and put an Allen pipe plug there. Now we sim-ply press in the aluminum plug. Mercury Racing uses a plug similar to what we make on their 8.2L based engine offerings.
The plug is made so that it has about a .002” interference fit. We usually install it with a little Permatex Right Stuff, or you could use Loctite 680.
The two 3/8” NPT ports that are in the block next to the pain rail can now be used as a location for an oil pressure sender. It is not the best place for an oil temperature sender because the location is a little remote for normal oil flow. The 3/8” NPT port just above the filter mounting pad on the side of the block is the best place to measure oil temperature as it returns to the engine after the cooler and filter.
Exhaust Muffler Options
Q. I have a twin engine boat with motors that are 461 cubic inch with side mount Whipple superchargers. The motors make 720 horsepower each with 5 pounds of boost. I added a larger oil cooler on the back of the motors which required me to remove my Y-pipes for the Captain’s Call switch-able exhaust system. After using the boat last summer, I realized how much I miss the option of switchable exhaust, especially idling down the river and docking. At idle the decibel level is 110. I’m looking at the TCM ST-450 switchable exhaust system, or the CMI Sound Elimination exhaust tips. I don’t mind the loud exhaust sound when on plane. I just want to make it quieter at idle. Any help would be greatly appreciated. Are these items readily available?
There’s a difference between the CMI Sound Elimination muffler tips and the TCM ST-450 switchable system. The CMI Sound Elimination Tips are “spring loaded” mechani-cally operated tips that open more as exhaust pressure increases. They are not switchable. The CMI tips are available in various clamp on sizes and transom mounted offerings.
The TCM ST-450s are replacement tips that are 4½” in diameter. They use electri-cally operated actuators to close the but-terflies which routes the exhaust through a muffler section in the tips. With your engines, you could run them closed up to 3500 or 4,000 rpm without excessive back pressure. When the tips are open, they do not create any back pressure.
If your boat was equipped with Captain’s Call, you already have the switch neces-sary to operate the ST-450s. The kit comes with a “slave solenoid” that is connected to the helm switch that in turn operates the actuators. The tips are installed from the inside of the boat with all mechanisms pro-tected from water. External transom rings are provided and external 4½” flappers are included. Options are available for various tailpipes and exhaust hose sizes.
The price of the CMI Sound Elimination Tips is about $2300 per pair. The TCM ST450’s are priced at about $1550 per pair.
Other popular full time mufflers include those made by Gibson and IMCO.
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