Four exhaust outlets down to two?

1980 Silverton 34C with Chrysler 360s on V-drives. Silverton built these boats with four exhaust outlets through the transom: one for each bank of cylinders on each engine. Each one has a muffler and the hose size on each of 3-inch ID.

What are the consequences of blocking off the inside two holes through the transom and combining the exhausts into one 3-inch muffler and outlet on each engine? Why? The extra exhaust hose and muffler take up a lot of valuable room behind each engine that I could use.

I helped a dockmate replace his exhaust system on a Bayliner 32 last summer and his two 5.0 liter Mercruisers have their exhausts plumbed together as I am proposing.

Later Silvertons had only two exhaust outlets and I don't think any decrease on horsepower is going to be something that an old and fairly slow cruiser like me has to worry about.

Maybe a slight increase in exhaust noise? 2X the cooling water flow through the single muffler, though.

Any reason why a Chrysler 360 can't exhaust through a single 3-inch wet exhaust system?

I'm not doing any modifications until I hear from you guys.

A few years back a dock mate of mine did what you are proposing to an identical boat and saw no difference in performance.

Merc's manual for the 5.7 ( i.e., a 350 cid engine) stipulates dual 3" or a single 4" exhaust. So... if you want to drop down to one exhaust port per engine, increase runs to 4". Undersized exhaust lines lead to increased back pressure which in the mid to long term lead to burnt exhaust valves.

..."Any reason why a Chrysler 360 can't exhaust through a single 3-inch wet exhaust system?"

Mine did and ran fine.

Jeff

PS: This ain't no Go Fast boat, right?

4 cylinders now share one 3" ID exhaust path out through the transom.
IOW, a total of 16 cylinders now share four 3" ID exhaust paths out through the transom.


Physics would dictate that reducing this by 50%, it is going to have an impact on performance.


.

True, but only at high throttle conditions. This is a cruiser, not a Go Fast!

Jeff

At a cruise RPM of 3,600, the 5.7L engine requires approx 309 to 364 CFM of cool combustable air (depending on the % VE used).
On the out side of this, these escaping expanding hot gasses will be larger than 309/364 CFM.


I still maintain that Physics would dictate that reducing the exhaust path by 50%, it is going to have an impact on performance.


.

Thanks, guys. I think I understand the physics.

Jeff is right. I'm just a cruiser. Seeing 3200 on my tach is rare. I'd just like to get rid of all that extra plumbing.

I'll give this more thought before I begin any major disassembly.

..."At a cruise RPM of 3,600"

What! You think he owns a gas station?

Jeff

PS: I've heard people screaming down the river in cruise boats a 4 grand plus lots of times. No way I'd buy THAT boat when they were done with it!

OK..... if you are just cruising around at hull speed...... you would likely not notice much difference.
However, if you operate at/near even 3,200 RPM (I'll retract my earlier 3,600 RPM), aren't you doing over hull speed????
If so...... at 3,200 RPM is this hull up on step????

We have two fuel efficient speeds that we operate our cruiser boats at:
1... Hull Speed.
2... Planing speed and a tad bit more.

If this is not a planing type hull, then I apologize. My info becomes moot!

However, if this is a planing type hull, my question becomes..... at what RPM is this hull fully up on step and a tad bit more. If not up on step and a tad bit more..... you will be wasting fuel and you will most definitely be over-burdening your engines!


Keep in mind your thread title, and the question implied in your paragraph #2.

In your paragraph #1, you mention that; "Silverton built these boats with four exhaust outlets through the transom".
I'd be asking myself; "why did Silverton build these with four outlets?"


If you are after more un-obstructed work space within the engine bay, and if doing this gives you that, and if a performance loss is acceptible....... there ya go!




.

Once again, thanks for the help.

Considering what I've read here, I'm not going to destroy my two Chrysler 360s by combining those exhausts into one outlet. I've started a parts list of the stuff I'll need to do this and I'll post some pics here when I'm finished.

Bill

..."I'm not going to destroy my two Chrysler 360s"

You're kidding, right? (Do you know how many Mopar SB powered boats out there have single exhausts?) And going to 'only' a 3 inch system is only significant at very high throttle settings, like planning off.

Jeff

fastjeff said:

..."I'm not going to destroy my two Chrysler 360s"

You're kidding, right? (Do you know how many Mopar SB powered boats out there have single exhausts?) And going to 'only' a 3 inch system is only significant at very high throttle settings, like planning off.

Jeff

Click to expand...

A single 4" system per engine hedges your bet and gives you the room you need.

My 318s pass through the transom on one 4" run per engine. If you want keep the original performance 4" per engine is what you want. If you don't push the ladies very hard, then one run of 3" with lower performance at top end is what you will get.

The perfect answer!

Jeff