Per my previous inquiry regarding exhaust fumes in the cockpit of my Typhoon Senior, I found two exhaust holes on the shaft housing just below the power head. This Mariner 8hp motor is supposed to have through the prop exhaust so I was surprised to see the holes just below the power head. I did get an initial answer back from another CD owner who had the same problem and he indicated that he fashioned an upper exhaust and vented it by installing a through the hull fitting. As I would prefer not to put holes in the hull, I would appreciate comments to two questions.
1) What might/would be the consequences of closing off the two exhaust ports under the power head, hopefully, forcing all the exhaust out through the prop?
2) How might the motor work if I fashioned a manifold to direct the exhaust gas from the two small holes under the power head and vented the gas through the bottom of the motor well and into the water?
Kehann@servtech.com
Exhaust fumes in cockpit
Moderator: Jim Walsh
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JimL
Re: Exhaust fumes in cockpit
The ports under the power head are well above waterline because the engine is a very poor pump when the throttle is nearly closed. For example, one of the tests I often use (on cars, etc.) is an "active compression test). I install a compression gauge in one cylinder, then start the engine at idle. People think this will blow up the gauge, but are shocked to see a cylinder that reads 180 psi cranking only has about 50-60 psi at idle. Why? Because the cylinders are sharing their air source from a pretty tiny hole. There just isn't enough air to compress. Likewise on the outboard. It doesn't make enough exhaust pressure, at idle, to push it through the prop.
You can probably tap into the holes, and fit stainless pipe and EGR (exhuast gas recirculation) hose. This would give you a method to get outside the boat with this low pressure exhaust. The EGR hose can be purchased through good automotive parts suppliers. It is designed to live at 300-316 degrees F., continuously.
Be sure to use standoffs to keep the pipe or tubing from touching anything, on it's way out of the boat (don't try to put the end under water). Use the water relief port, under the back of the power head, for additional cooling for this pipe. TIP: You'll have to clean/replace the pipe and/or tubing on a regular basis (for 2-strokes). Excessive cooling of the exhaust, at low pressure, results in carbon and coke deposits. If the engine gets too rough at idle, check for plugging in your low pressure exhaust (this can happen to the orginal port, also.....seen a few carbs replaced for no idle....when the relief port was plugged).
You can probably tap into the holes, and fit stainless pipe and EGR (exhuast gas recirculation) hose. This would give you a method to get outside the boat with this low pressure exhaust. The EGR hose can be purchased through good automotive parts suppliers. It is designed to live at 300-316 degrees F., continuously.
Be sure to use standoffs to keep the pipe or tubing from touching anything, on it's way out of the boat (don't try to put the end under water). Use the water relief port, under the back of the power head, for additional cooling for this pipe. TIP: You'll have to clean/replace the pipe and/or tubing on a regular basis (for 2-strokes). Excessive cooling of the exhaust, at low pressure, results in carbon and coke deposits. If the engine gets too rough at idle, check for plugging in your low pressure exhaust (this can happen to the orginal port, also.....seen a few carbs replaced for no idle....when the relief port was plugged).