Custom Marine Inc. - Big Block Chevy Headers

CMI Big Block Chevy E-Top Platinum Exhaust System, Mercury Flat Flange

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. Each header features a permanently attached, non-adjustable exhaust tailpipe configured to meet precise specifications for standard transom layouts and placement of thru-hull exhaust tips. All CMI Elbow Top Systems include rubber water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations. This header comes with the stainless steel distribution tube upgrade. This header has a polished elbow and satin primaries

This Kit includes an upgrade to a Stainless Steel Water Distribution Tree.

Note: All CMI Systems are sold without Tailpipes

CMI 454/502 Direct Mercruiser Replacement E-Top Exhaust System, Satin

The CMI 454/502 E-Top Header Kit is a a true plug and play system. There is no need to purchase additional custom pipes. These are a direct replacement for your stock 454/502 engine. CMI headers offer more water jacketed protection than your stock exhaust can provide. CMI uses the same high quality semi-automated process on these headers as with the entire product line. These headers are fully post annealed to reduce stresses built up in the header during the manufacturing process. Best of all, 454/502 E-Top headers are made to last, they are mandrel bent and formed from hight quality 316L grade material. There are no parts to crack, all CMI collectors are forged from American made Stainless Steel.

Note: All CMI Systems are sold without Talipipes

CMI 454/502 Direct Mercruiser Replacement E-Top Exhaust System, Polished

The CMI 454/502 E-Top Header Kit is a a true plug and play system. There is no need to purchase additional custom pipes. These are a direct replacement for your stock 454/502 engine. CMI headers offer more water jacketed protection than your stock exhaust can provide. CMI uses the same high quality semi-automated process on these headers as with the entire product line. These headers are fully post annealed to reduce stresses built up in the header during the manufacturing process. Best of all, 454/502 E-Top headers are made to last, they are mandrel bent and formed from hight quality 316L grade material. There are no parts to crack, all CMI collectors are forged from American made Stainless Steel.

Note: All CMI Systems are sold without Talipipes

CMI Fusion Integrated Tailpipe Big Block Chevy Exhaust System

This is the all new, salt water rated "Fusion" Performance Header system from CMI. For years Custom Marine has produced custom exhaust systems for just about every Hi-Performance application.  But now CMI has set their sights on offering an affordable Performance Header system for the entry level Hi-Performance market with the new "Fusion" header system. This new header was designed as an affordable upgrade to exhaust manifold systems for engines needing to support upwards of 600 horsepower, while using standard Mercury Bravo exhaust exit locations. These headers are offered in the "Platinum" series finish which features a brushed satin lower section,  then mating it to a highly polished top tailpipe to produce a striking appearance on any engine. By integrating the tailpipe CMI can reduce costs to the user and eliminate costly clamps and gaskets. Premium 316L stainless steel construction, as well as the patented cool collar exhaust flange make for a durable header that will offer years of trouble free service. While the standard version is designed to fit stock Mercruiser Bravo exhaust exit locations, there are also two custom fit tailpipe options available that will allow the header to be assembled at the factory to your boats specifications. Up to a 2" vertical and/or horizontal correction can be made from the stock locations which allows this header to fit a huge range of options. (Additional charges apply)

Note: This system does not have separate tailpipes. It's pipes are set up for standard Bravo hole locations.

CMI Merc 500 EFI Replacement E-Top Exhaust System

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. All CMI Elbow Top Systems include water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations.

Note: All CMI Systems are sold without Tailpipes 

CMI 520 E-Top Satin Exhaust Header System

The satin finished 520 E-top kits offers all the same features as our standard CMI E-Top header. When installed on a Mercury 520 you can expect increases of up to thirty-one horsepower. This are direct replacement headers and will work with the existing exhaust outlets that were installed with your OEM exhaust manifolds. All CMI Elbow Top Systems include rubber water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations. Any Elbow Top System may be purchased with a stainless steel distribution tube upgrade.

• Increases in Horsepower up to 31 HP
• Direct replacement – works with existing exhaust outlets
• Improved mid-range acceleration and torque
• Polished and satin finish available
• Patented “Cool Collar” design
• Mandrel bent and formed from high quality 316L grade stainless steel

CMI 520 E-Top Polished Exhaust Header System

The polished 520 E-top kits offers all the same features as our standard CMI E-Top header. When installed on a Mercury 520 you can expect increases of up to thirty-one horsepower. This are direct replacement headers and will work with the existing exhaust outlets that were installed with your OEM exhaust manifolds. All CMI Elbow Top Systems include rubber water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations. Any Elbow Top System may be purchased with a stainless steel distribution tube upgrade.

• Increases in Horsepower up to 31 HP
• Direct replacement – works with existing exhaust outlets
• Improved mid-range acceleration and torque
• Polished and satin finish available
• Patented “Cool Collar” design
• Mandrel bent and formed from high quality 316L grade stainless steel

• Increases in Horsepower up to 48 HP
• Downturn collector improves water fill
• Improved mid-range acceleration and torque
• Polished finish available
• Equalized primaries for greater performance
• Patented “Cool Collar” design
• Mandrel bent and formed from high quality 316L grade stainless steel

Note: All CMI Systems are sold without Tailpipes

CMI's Gen-X Headers are the true direct factory replacement for Mercury Racing HP525EFI, HP600SCi and HP700SCi engines.

These are sold as a "pair of headers". They have the welded stainless water distribution lines like the factory OEM headers.

The new design increases water fill keeping the headers full at all time, creating cooler temperatures, which leads to improved longevity and a little extra horsepower.

Featuring more equalized primaries for improved performance, the straight-back headers with downturn collectors work with existing tailpipes and are easy to install. Constructed of quality 316L domestic stainless steel makes for one tough header with a sleek stylish look.

CMI's Gen-X Headers are a factory replacement for Mercury Racing HP525EFI, HP600SCi and HP700SCi engines. 

These are sold as a "pair of headers". This model has rubber water distribution trees for a more economical header package.

The new design increases water fill keeping the headers full at all time, creating cooler temperatures, which leads to improved longevity and a little extra horsepower.

Featuring more equalized primaries for improved performance, the straight-back headers with downturn collectors work with existing tailpipes and are easy to install. Constructed of quality 316L domestic stainless steel makes for one tough header with a sleek stylish look.

The all polished, straight back CMI Sweeper style are a superior long tube header designed for both racing and any high-performance application. These leaned, taller headers are commonly used in custom or staggered set up Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sweeper headers deliver peak performance and power from naturally aspirated engines.

The all polished, straight back CMI Sweeper style are a superior long tube header designed for both racing and any high-performance application. These leaned, taller headers are commonly used in custom or staggered set up Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sweeper headers deliver peak performance and power from naturally aspirated engines. This version is leaned for use on staggered engine applications.

A custom straight back taller and/or leaned sport tube header for Mercury HP 525 EFI – 700SCi series motor packages. Used mostly in stagger builds for front motors and occasional rear motors. Exact replacement of existing headers in original builds. Built using the high quality 316L stainless steel that is used in our race systems. Patented “Cool Collar” design provides a short hot section at the flange, which helps minimize the possibility of water ingestion in to the engine. Uses “Flex Flare” technology for tailpipe connection allowing flexibility in the joint. Bolt pattern for the custom Mercury platform.

A custom straight back taller and/or leaned sport tube header for Mercury HP 525 EFI – 700SCi series motor packages. Used mostly in stagger builds for front motors and occasional rear motors. Exact replacement of existing headers in original builds. Built using the high quality 316L stainless steel that is used in our race systems. Patented “Cool Collar” design provides a short hot section at the flange, which helps minimize the possibility of water ingestion in to the engine. Uses “Flex Flare” technology for tailpipe connection allowing flexibility in the joint. Bolt pattern for the custom Mercury platform. Leaned version for use on staggered engine setups.

The all polished, 6” taller, straight back CMI Sweeper style are a superior long tube header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered setup Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sweeper headers deliver peak performance and power from naturally aspirated engines.

The all polished, 6” taller, straight back CMI Sweeper style are a superior long tube header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered setup Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sweeper headers deliver peak performance and power from naturally aspirated engines. Leaned for Staggered Engine Applications.

The all polished, 9” taller, straight back CMI Sweeper style are a superior long tube header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered setup Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sweeper headers deliver peak performance and power from naturally aspirated engines.

The all polished, 9” taller, straight back CMI Sweeper style are a superior long tube header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered setup Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sweeper headers deliver peak performance and power from naturally aspirated engines. Leaned for Staggered Engine Applications.

The all polished, 11” taller, straight back CMI Sweeper style are a superior long tube header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered setup Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sweeper headers deliver peak performance and power from naturally aspirated engines.

The all polished, 11” taller, straight back CMI Sweeper style are a superior long tube header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered setup Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sweeper headers deliver peak performance and power from naturally aspirated engines. Leaned for staggered engine applications.

CMI Big Block Chevy E-Top Platinum Exhaust System

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. Each header features a permanently attached, non-adjustable exhaust tailpipe configured to meet precise specifications for stan¬dard transom layouts and placement of thru-hull exhaust tips. All CMI Elbow Top Systems include rubber water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy E-Top Platinum Exhaust System

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. Each header features a permanently attached, non-adjustable exhaust tailpipe configured to meet precise specifications for stan¬dard transom layouts and placement of thru-hull exhaust tips. All CMI Elbow Top Systems include rubber water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations.

This Kit includes an upgrade to a Stainless Steel Water Distribution Tree.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy E-Top Polished Exhaust System

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. Each header features a permanently attached, non-adjustable exhaust tailpipe configured to meet precise specifications for stan¬dard transom layouts and placement of thru-hull exhaust tips. All CMI Elbow Top Systems include rubber water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations.

Note: All CMI Systems are sold without Tailpipes

The picture for this item is shown with a Stainless distribution tree, but this part includes a rubber distribution tree.

CMI Big Block Chevy E-Top Polished Exhaust System

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. Each header features a permanently attached, non-adjustable exhaust tailpipe configured to meet precise specifications for stan¬dard transom layouts and placement of thru-hull exhaust tips. All CMI Elbow Top Systems include rubber water distribution tubes, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations.

This Kit includes an upgrade to a Stainless Steel Water Distribution Tree.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy E-Top Polished Exhaust System, Mercury Flat Flange

CMI Elbow Top headers are designed for direct replacement of most stock cast manifolds. Top engine builders and stern drive manufacturers who want to optimize performance of small- or big-block marinized engines prefer CMI Elbow Top headers for their engines. CMI E-Top systems offer separated exhaust passages with long individual exhaust tube runners to minimize cylinder to cylinder influence and improve exhaust gas scavenging, which allows the engine to breathe freely and deliver peak performance power. Each header features a permanently attached, non-adjustable exhaust tailpipe configured to meet precise specifications for standard transom layouts and placement of thru-hull exhaust tips. This header kit comes complete with our upgraded stainless steel water distribution tube, cooling water bypass couplings installed on the collector elbow, by-pass hose fittings, attaching cap screws, exhaust port gaskets, hose clamps and cooling water inlet fittings needed for most installations. These headers off the Mercury flat flange design.

This Kit includes an upgrade to a Stainless Steel Water Distribution Tree.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy E-Top Platinum Exhaust System - Taller - With Stainless Distribution Tube

These custom size taller, straight back CMI E-Top are a superior long tube header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered setup Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sport Tube headers deliver peak performance and power from naturally aspirated engines. This version has a polished elbow and satin primaries with the rubber distribution tube.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy E-Top Polished Exhaust System - Taller

These custom size taller, straight back CMI E-Top are a superior long tube header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered setup Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sport Tube headers deliver peak performance and power from naturally aspirated engines. This version is polished with the rubber distribution tube.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy E-Top Polished Exhaust System - Taller - With Stainless Distribution Tube

These custom size taller, straight back CMI E-Top are a superior long tube header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered setup Mercury 525-700 series motors. These headers feature the CMI Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Sport Tube headers deliver peak performance and power from naturally aspirated engines. This version is polished with the stainless upgraded distribution tube.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy Big E-Top Polished Exhaust System 1-7/8″ Primaries

These “Big E-top” offer a 1-7/8″ primary, straight back CMI Big E-top E-Top are a header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered set up for your high horsepower builds. These headers feature the CMI Big Tube Flex Flare Tailpipe Connection. For big-block applications. CMI Big E-top headers deliver peak performance and power from Supercharged applications.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy Big E-Top Polished Exhaust System 2 1/4″ Primaries

These “Big E-top” offer a large 2 1/4″ primary, straight back CMI Big E-top E-Top are a header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered set up for your high horsepower builds. These headers feature the CMI Big Tube Flex Flare Tailpipe Connection. For big-block applications. CMI Big E-top headers deliver peak performance and power from Supercharged applications.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy Big E-Top Polished Exhaust System 2 1/4″ Primaries

These “Big E-top” offer a large 2 1/4″ primary, straight back CMI Big E-top E-Top are a header designed for both racing or any high-performance application. They feature a “D” Port flange to match the Brodix heads on Mercury 850-1200 SC motors. These leaned, taller headers are commonly used in custom or staggered set up for your high horsepower builds. These headers feature the CMI Big Tube Flex Flare Tailpipe Connection. For big-block applications. CMI Big E-top headers deliver peak performance and power from Supercharged applications.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy Big E-Top Polished Exhaust System 2-1/4" x 2-1/8" Stepped Primaries

These “Big E-top” offer a large 2-1/4" x 2-1/8" Stepped primary, straight back CMI Big E-top E-Top are a header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered set up for your high horsepower builds. These headers feature the CMI Big Tube Flex Flare Tailpipe Connection. For big-block applications. CMI Big E-top headers deliver peak performance and power from Supercharged applications.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy Big E-Top Polished Exhaust System 2 1/8″ Primaries

These “Big E-top” offer a large 2 1/8″ primary, straight back CMI Big E-top E-Top are a header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered set up for your high horsepower builds. These headers feature the CMI Big Tube Flex Flare Tailpipe Connection. For big-block applications. CMI Big E-top headers deliver peak performance and power from Supercharged applications.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy Big E-Top Polished Exhaust System 1-7/8″ Primaries for Turbo Applications

These “Big E-top” offer a 1-7/8″ primary, straight back CMI Big E-top E-Top are a header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered set up for your high horsepower builds. These headers feature the CMI Big Tube Flex Flare Tailpipe Connection. For big-block applications. This CMI Big E-top headers has a beveled top for easy bolt up of your turbos.

Note: All CMI Systems are sold without Tailpipes

CMI Big Block Chevy Big E-Top Polished Exhaust System 2 1/4″ Primaries for Turbo Applications

These “Big E-top” offer a large 2 1/4″ primary, straight back CMI Big E-top E-Top are a header designed for both racing or any high-performance application. These leaned, taller headers are commonly used in custom or staggered set up for your high horsepower builds. These headers feature the CMI Big Tube Flex Flare Tailpipe Connection. For big-block applications. This CMI Big E-top headers has a beveled top for easy bolt up of your turbos.

Note: All CMI Systems are sold without Tailpipes