Exhaust Batching

[Administrator]

Do you see engine cooling water batching out of your exhaust while at your favorite cruising power setting, and is there a relationship between that condition and sooty plugs?

[YOUTUBE]vU8mZgTkARI[/YOUTUBE]

[Dave Neptune]

Yep!

Yep mine batches no matter how hard I run. I have approximately 25 feet of exhaust with 2 risers and a long run to the transom from them. When I replaced my entire exhaust I reduced the diameter to 1 1/2" for the last 15 feet and it still batches. My engine runs very good although I do have reduced compression in #'s 3&4 and the STOCK J8 plugs are nice and clean just a bit of greyish tan and #'s 1&2 are a bit "lighter" in color. I cruise at !800~2100 RPM's with my Indigo prop at betweem 8~10 inches of manifold.

Dave Neptune

[Don Moyer]

Thanks (as usual) for your thorough report, Dave. We've known for quite some time of your clean running engine even in the face of batching engine cooling water. Depending on the outcome of our survey, I'd like to get you back into the conversation to see what we can learn from your system.

[Bold Rascal]

Water Batching?

Geeze O-man, yet another term. What is water batching?

[chiron]

My exhaust water batches throughout all RPMs, however while cruising the transom is lower and the exhaust port is underwater so I am not sure if it batches while under load. My plugs are slightly sooty.

I am curious as to the possible connection between sooty plugs and water batching, would it be a slight back pressure.

[dvd]

I am assuming that the question is does the water from your exhaust at high cruising rpms come out in a steady stream or does it batch? (kind of a intermittent and uneven force of water every few seconds like it does at idle)

At crusing rpm my exhaust water comes out of the exhaust in a more even or steady fashion. No soot on the plugs.

dvd

[ILikeRust]

Geeze O-man, yet another term. What is water batching?

Splash. Pause. Splash. Pause. Splash. Pause.

Rather than a steady stream.

The engine of course will be running continuously, so you've always got exhaust spitting out - the question is whether you also have water continuously coming out, or is it blblblbl-plop-blblblblbl-plop-blblblblblb-plop, with the "plop" being a glob ("batch") of water coming out.

[dvd]

Rust,

Exactly. Good definition.

[Don Moyer]

Chiron, you have the correct understanding. We think the batching is caused by the inflow of engine cooling water getting ahead of the engine's ability to keep it moving continuously through the exhaust system with the exhaust. In this scenario, the buildup of water sequentially builds up a small amount of additional head which the engine sees as a slight net increase in total exhaust back pressure as it "batches" the water out of the back of the boat.

[Dave Neptune]

Fyi

Don, an old friend and A-4 mechanic who does work primarily on diesel instalations told me this a long time ago when I asked him about the "batching" in my case. He said~~~"In many cases the batching can be problimatic, however in many long eshaust runs what you are seeing is the water batching because it is the water not ejected that sloshes back down the exhaust to be combined with what is heading out thus the batching. But if it is the inability of the water to be forced up&out until adequate preassure is achieved that will cause the engine to see "elivated back preasseres" and a smaller exhaust volume is my recomendation."
That is the reason I reduced the diameter of my exhaust just beyond my homemade muffler/riser. The exhaust still batches however not as much as before and the new run added about 8 feet to the system. I noticed absolutely no differance in performance and a few of the little gains I have made have been since I installed the reduced diameter exhaust system. When I changed it out it was because I wanted more room in my lazerett and storage areas not because I was loosing power.

Dave Neptune

[Don Moyer]

dvd, did you post your exhaust data on our survey as well as in your posting?

Also, for all, please note that the Administrator has just posted a short video of what we take to be classic "batching" of water out of an exhaust system. Notice what appears to be large spikes of discharging water as the exhaust sequentially builds up sufficient pressure behind each slug of water to blow it out the back of the boat.

[TomG]

Since I have the MMI SS standpipe, I don't have water batching...just a nice steady stream and the melodious purr of my A-4. Also, since I changed to the standpipe, I don't worry about flooding the exhaust manifold during hard starting. If your boat's layout is agreeable, I highly recommend the standpipe upgrade. My J12 spark plugs are not sooty.

I know this post isn't really helpful to the thread, but I do feel a debt of gratitude to Don for putting the standpipe in the catalog. It is superbly engineered and remarkably trouble-free. Thanks Don!

[ndutton]

Batching is directly related to waterlift muffler capacity and exhaust system size (other factors too). The smaller each is, the steadier the stream.

[Ball Racing]

Even though it's not a A-4, and not in a sail boat,
the Majority of the large chesapeake bay deadrise workboats with their diesels "batch" water like crazy.
it gives them a sound that is true music to my ears, the engine sound gets a rythm and pauses, and water bursts that is unlike anything else.
Especially on a old 2 stroke detriot diesel.
These guys regularly race at events and this has not seen as a disadvantage.
They run the exhaust hose basically on the bottom of the boat, in the deep vee, then in the back of the boat where the horn timber rises up, and at the stern the exhaust exit is higher than the hose from the engine, so the water backs up until forced out.

Most of the maryland boats are dry exhaust.
but I am a true sucker for the sound of the wet, a pulseing wet,

Daniel

[sastanley]

Daniel, You are right...big old work boats batch exhaust similar to an A4, but in the diesel, you hear the exhaust sound muffled for a brief moment and that sound is not as pronounced in the little A4, but the actual batching effect is very similar.

My boat has always "batched"..even when I was a kid and spent hours on end staring out the transom.