Exhaust modification

[prattvan]

OK. Please educate me.
I did a google search on modifying an exhaust system on an 4 stroke outboard. I found alot of info stating not to do it, that you would burn your pistons.
So.........I'm kind of new to outboard engines, but have worked on automobiles and go-karts for about 20 years (not professionally, just as a hobby).
For as long as time is, people have modified combustion engines in search of more power. If you buy a new car or truck, one of the first things some people do is change the exhaust system (because most stock exhaust systems are restrictive). And also change the intake system (such as adding K&N products). Therefore, making the engine breathe better creating more power.
So I'm kind of confused on this. If someone puts headers on a 4 cylinder or V-6 engine in a car, you get more power. But, if you open up the exhaust on a 4 stroke outboard, it will burn the pistons ??

I'm open to all comments.

 

[steelespike]

It has been many years but I believe any carbed 2 stroke or 4 stroke you need to enrich jets.
We're talking headers, fully rtelieved exhaust.If your going to a glass pack or low restriction muffler not likely to be a problem.

 

[Tnstratofam]

Similar to any 2 stroke or 4 stroke motorcycle engine. If you modify the exhaust you should change or modify the jets to allow for correct mixture. The risk of running to lean or to rich is more important as damage can be done faster on an outboard. That's all an uneducated guess by the way. Just 20 + years of tinkering with motorcycles. I'm also not sure how much aftermarket support there is for modifying most outboards.

 

[GA_Boater]

The problem is unlike a car, bike or go-kart, the exhaust ports are buried under a water cooling system. So you can't just pull off a set of pipes or exhaust manifold and bolt on a tuned pipe or headers. Everything has to be custom and parts of the motor redesigned. If you hit the lottery, go for it. Until then, tuning with the prop or safely lightening a boat will pay bigger dividends. IMHO

 

[Frank Acampora]

Outboards are way different than automobile engines. In most cases they are small displacement engines with intake--either carb or fuel injection-- and exhaust optimized for best performance. Yes, racers do modify them for higher performance but the trade-off is a much shorter service life. Yes, you can modify them to make more horsepower BUT you must study what you are doing. Most mods done without extensive research will result in a lower horsepower production.

It CAN be correct that intake and exhaust modifications CAN result in burned pistons. Remember that these modifications are meant to increase airflow thus resulting in a need for more fuel. Failure to provide this additional fuel will or can result in melted pistons. This is much like adding nitrous to a car. You must also install additional fuel jets to deliver enough fuel for the added oxygen that nitrous supplies.

Want to go faster? The easiest way is to buy a bigger engine.

 

[ondarvr]

You can get many high performance parts for big 2 stroke Mercs and a few for others, not so much for newer 4 strokes.

There isn't much of a market for after market performance parts on outboards, mainly because most parts aren't that easy to replace. You can change the pipe on a shifter cart easily, it would be a major project on an outboard to make more than a minor modification to the exhaust. Same with porting, pistons, carbs etc. it's just easier to buy a higher HP motor than do it yourself. The Merc crowd likes to do these things though, and Merc supported them for years.

 

[ondarvr]

And yes, you can destroy any motor by modifying it and not making sure you compensated for any changes you made in air or fuel flow.

 

[Chris1956]

Dry stack that Bi$%&? Pop on over to the scream and fly forum and see what they recommend. They dry stack the 2 cycle Merc V6 motors all the time.

 

[nwcove]

Dry stack that Bi$%&? Pop on over to the scream and fly forum and see what they recommend. They dry stack the 2 cycle Merc V6 motors all the time.

......that poor lil 5hp tohatsu wont know what happened when it grenades .