Archive for the ‘Marine Exhaust Systems’ Category

Question: I need to replace my Mercruiser 3.0L marine exhaust manifold but cannot seem to locate the same matching part number. Why can’t I find the same replacement “cast iron” exhaust manifold part number for my Mercruiser 3.0L marine engine?

Response: Mercruiser has made numerous changes to the 3.0L exhaust manifolds over the past 15 years. This has been due to a variety of reasons including GM dropping to large port cylinder head that the 120 Hp marine engines were equipped with. The original 42673 and 99798 series manifolds used back in the 1980’s were replaced by the 806867 series manifolds in the mid 1990’s which has most recently been replaced by the 860235 series manifolds. Today Mercruiser only offers the 860235 series manifolds in two different versions to replace these older manifolds. The new 860235 version manifolds from Mercruiser DO NOT have the removeable end caps with gaskets but they are the correct intended replacement part. Note that these currently available 860235 series manifolds only work for the engines using the large bore Mercarb carburetor. Mercruiser no longer offers a replacement manifold for anything using the small bore “rochester” style carburetors that required different mounting pattern dimensions. Also note that the exhaust manifold ports don’t match perfectly for the older style large port cylinder heads however the manifold/head gasket compensates for this and will seal it properly. Let us know if you need any further assistance we will be glad to assist!

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Have you ever wondered what exhaust risers/spacers were for? Or have you ever wondered why you continue failing marine engines from water ingestion? Here’s the techncial article that addresses this topic in detail and may save you from replacing the engine in your boat yet another time.

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Have you ever wondered if installing a Thru Hull Marine Exhaust system would help your Marine Engine’s performance? Or if you’re the boater that’s always dreamed of having that performance engine “Rumble” when you feel the urge but want it quiet when you want to talk to your passengers then this is the video that explains how easy it really is.

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Warm versus cold manifold refers to the temperature of the cooling water that is introduced into the exhaust manifolds on a marine cooling system. This specific system feature can apply to raw water (also known as open cooling) systems as well as Fresh Water (also known as closed cooling) systems. The benefit of warm manifolds deals with preventing the buildup of condensation from within the marine exhaust manifold which in turn relates to the bigger issue of WATER INGESTION.

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The short answer is yes in most cases reducing engine exhaust back pressure WILL improve the overall level of performance and can also improve the life expectancy of the engine. I’m asked on a regular basis as to what upgrade options are available for 4.3L and 5.0L engines specifically. In most cases the best starting point is always reducing exhaust back pressure. The reason being that most performance options are developed for the 350 and big block engines and therefore there aren’t that many available options for the 4.3L V6 and 5.0L V8 engines. Also keeping in mind that increasing performance comes with the risk of decreasing the longevity of the engine. There are many negative factors that play into increased performance including higher cylinder pressures, inducing water ingestion, etc that boat owners need to truly evaluate the best overall option for their particular case.

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