my 42 with 427’s seems to be getting louder. I replaced impellers and belts last winter and I am wondering if maybe they stretched and might be slipping. There is water coming out the back and the temps never exceed 160F. I have no idea what the inside of the muffler looks like but it is a 100% fresh water boat and doesn’t even have surface rust one the outside of the cast rectangle. Is there a baffle inside that might be rotted out and gone? Is there a low margin of water volume between a functional water baffle and basically becoming a straight pipe exhaust? I want that low Chris craft  grumble back, not this brassy harsh sound!!

thx for any advice!

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That was me. I had them made by Kehrig mfg. They have the plans to make copies, I took them the muffler I cut open to duplicate. Mine sound exactly the same as the cast iron I replaced. 

glenn woudenberg said:

In the super disc there is a reference to a guy that makes copies of the original rectangular ones in 3/16” stainless steel for $950 a pair but not sure how old that thread was

Probably has more to do with hose routing, one side probably holds more water than the other.

Alan Waite said:

I have wondered about this as well on my 1974 45'. It has DD's but the starboard side is louder. Water flow seems the same on both sides so i was wondering about these cast iron mufflers as well. Is there another option for these if they need to be replaced or do they have to be custom made?

How was the quality of the copy?

Anyone used parts from another boat manufacturer? Aftermarket? I know you would need to take into account back pressure but surely there are other workable options than having them custom made. I like to keep my boat as original as is feasible but do not care much about whether the mufflers are original. 

I am getting measurements from the existing muffler and it seems the outputs are about 4 1/2” outside diameter. I would prefer not to remove the hose to get a caliper on it. I was under the impression they were 4” hoses. Could someone confirm this measurement for me? I didn’t see the dimension on the  superdisc.


It seems there are different size  outputs as well as the dimensions of the muffler itself? The fabricator has three sets of dimensions and none of them seem to match what I have. He also said the baffle design varies. He said Mike H’s muffler had 3 1/2” outputs. Mike is your boat a 42’ with 427’s?

It’s a high quality piece that will likely outlast the boat. I wanted to retain the sound which these did perfectly. My boat is a 31 with 327’s, they use a 3 1/2” inlet and outlet. As far as I know the 427’s should be 4 1/2”. The design should be scalable. 

glenn woudenberg said:

It seems there are different size  outputs as well as the dimensions of the muffler itself? The fabricator has three sets of dimensions and none of them seem to match what I have. He also said the baffle design varies. He said Mike H’s muffler had 3 1/2” outputs. Mike is your boat a 42’ with 427’s?

I believe Chris-Craft specified the 427 and the 454 with 4.5" hoses when the run was over 10'.   This holds true with my 1981 381 with Chris-Craft Marine Power 454s.   For reference, later on when Chris-Craft switched to MerCruiser 454s (after the sale of the engine division to Bayliner/US Marine) the exhaust size increased to 5".

Thank you for the specs!

Sounds like the baffles are gone. I went with composite mufflers no rust, slight modification of support bracket. That is also on a 31 not 45. I changed them when I did the fuel tanks. Glad I did as there was not much left. It was a wonder they were not leaking. They weigh 40-50 pounds each and the composite ones weighed 11 pounds total.

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