Custom Marine (CMI)

Bridge Spacer Big Tube

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 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

How to measure riser height

Direct Mercruiser replacement for your 496 Mag or 496 HO engine. 10-1/2" Stock Tall Riser Height. Polished. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install our kit, a true plug and play system. Direct Mercruiser replacement for your 496 Mag or 496 HO engine. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install this kit, a true plug and play system.

• 1 7/8" id primary to get peak horse power and torque.
• Mandrel bent and formed from High quality 316L grade material.
• Fully post annealed to reduce stresses built up in the header during the manufacturing process
• Seamless water jacketed header. No welded inner primaries or water jacketed tubes to crack and leak.
• More water jacketed protection than your stock exhaust.
• Approved by Mercruiser to not void warranty on the motor, with the exception of water reversion.
• Same high quality semi automated welding as used on all racing applications
• Cool collar patented flange design to eliminate the risk of getting water in the motor by the head flange
• This kit is price competitive to other aluminum/stainless manifold systems with superior performance and extended life span in harsh marine environments.
• No cast parts to crack, all CMI collectors are forged from American made stainless steel.
• Works on 34.5" drive centers
• Brings a race look to your stock engine.
• Sophisticated engineering leaves your stock oil lines in place and only requires relocating your oil filter with a supplied bracket.
• Step by step, do it yourself instructions using Mercury supplied engine schematics.
• Exhaust Water Temperature Bungs Installed as Standard Equipment.

How to measure riser height

Direct Mercruiser replacement for your 496 Mag or 496 HO engine. 8-1/2" Stock Riser Height. Polished. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install this kit, a true plug and play system. Direct Mercruiser replacement for your 496 Mag or 496 HO engine. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install this kit, a true plug and play system.

• 1 7/8" id primary to get peak horse power and torque.
• Mandrel bent and formed from High quality 316L grade material.
• Fully post annealed to reduce stresses built up in the header during the manufacturing process
• No welded inner primaries or water jacketed tubes to crack and leak.
• More water jacketed protection than your stock exhaust.
• Approved by Mercruiser to not void warranty on the motor, with the exception of water reversion.
• Same high quality semi automated welding as used on all racing applications
• Cool collar patented flange design to eliminate the risk of getting water in the motor by the head flange
• This kit is price competitive to other aluminum/stainless manifold systems with superior performance and extended life span in harsh marine environments.
• No cast parts to crack, all CMI collectors are forged from American made stainless steel.
• Works on 34.5" drive centers
• Brings a race look to your stock engine.
• Sophisticated engineering leaves your stock oil lines in place and only requires relocating your oil filter with a supplied bracket.
• Step by step, do it yourself instructions using Mercury supplied engine schematics.
• Exhaust Water Temperature Bungs Installed as Standard Equipment.

How to measure riser height

Direct Mercruiser replacement for your 496 Mag or 496 HO engine. 10-1/2" Stock Tall Riser Height. Satin. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install our kit, a true plug and play system. Direct Mercruiser replacement for your 496 Mag or 496 HO engine. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install this kit, a true plug and play system.

• 1 7/8" id primary to get peak horse power and torque.
• Mandrel bent and formed from High quality 316L grade material.
• Fully post annealed to reduce stresses built up in the header during the manufacturing process
• Seamless water jacketed header. No welded inner primaries or water jacketed tubes to crack and leak.
• More water jacketed protection than your stock exhaust.
• Approved by Mercruiser to not void warranty on the motor, with the exception of water reversion.
• Same high quality semi automated welding as used on all racing applications
• Cool collar patented flange design to eliminate the risk of getting water in the motor by the head flange
• This kit is price competitive to other aluminum/stainless manifold systems with superior performance and extended life span in harsh marine environments.
• No cast parts to crack, all CMI collectors are forged from American made stainless steel.
• Works on 34.5" drive centers
• Brings a race look to your stock engine.
• Sophisticated engineering leaves your stock oil lines in place and only requires relocating your oil filter with a supplied bracket.
• Step by step, do it yourself instructions using Mercury supplied engine schematics.
• Exhaust Water Temperature Bungs Installed as Standard Equipment.

How to measure riser height

Direct Mercruiser replacement for your 496 Mag or 496 HO engine. 14-1/2" Stock Tall Riser Height. Satin. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install our kit, a true plug and play system. Direct Mercruiser replacement for your 496 Mag or 496 HO engine. No additional custom tails to buy. You don’t need to remove your stock exhaust hose to install this kit, a true plug and play system.

• 1 7/8" id primary to get peak horse power and torque.
• Mandrel bent and formed from High quality 316L grade material.
• Fully post annealed to reduce stresses built up in the header during the manufacturing process
• Seamless water jacketed header. No welded inner primaries or water jacketed tubes to crack and leak.
• More water jacketed protection than your stock exhaust.
• Approved by Mercruiser to not void warranty on the motor, with the exception of water reversion.
• Same high quality semi automated welding as used on all racing applications
• Cool collar patented flange design to eliminate the risk of getting water in the motor by the head flange
• This kit is price competitive to other aluminum/stainless manifold systems with superior performance and extended life span in harsh marine environments.
• No cast parts to crack, all CMI collectors are forged from American made stainless steel.
• Works on 34.5" drive centers
• Brings a race look to your stock engine.
• Sophisticated engineering leaves your stock oil lines in place and only requires relocating your oil filter with a supplied bracket.
• Step by step, do it yourself instructions using Mercury supplied engine schematics.
• Exhaust Water Temperature Bungs Installed as Standard Equipment.

The CMI 496 Sport Tube Performance Package delivers improved performance across the entire operating range of any 496 engine package. When applied to a stock 496 engine, this package will help to increase horsepower, boost mid-range torque, improve fuel economy across the power curve and enhance the engine's overall running quality. The package comes complete with all required mounting hardware plus CMI’s exclusive 496 Relocation Kit, which includes all brackets, tailpipes that accommodate your diverter system, hoses and hardware needed to make relocation of select engine components easier.

Includes Pneumatic Pump Kit for Internal Sound Choice 

ALL CMI HEADERS ARE MADE TO ORDER AND SHIP FROM THE FACTORY IN 3-4 WEEKS

The CMI 496 Sport Tube Performance Package delivers improved performance across the entire operating range of any 496 engine package. When applied to a stock 496 engine, this package will help to increase horsepower, boost mid-range torque, improve fuel economy across the power curve and enhance the engine's overall running quality. The package comes complete with all required mounting hardware plus CMI's exclusive 496 Relocation Kit, which includes all brackets, hoses and hardware needed to make relocation of select engine components easier.

Note: All CMI Systems are sold without Tailpipes
ALL CMI HEADERS ARE MADE TO ORDER AND SHIP FROM THE FACTORY IN 3-4 WEEKS

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

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

• 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 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 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

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″ 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

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 Sport Tube Exhaust System, 2-1/4" Primaries, Polished

These “Big Tubes” offer a large 2.25″ primary, straight back superior long tube header designed for both racing or any high-performance application. These straight, taller headers are commonly used in custom high horsepower builds. These headers feature the CMI Big Tube Flex Flare Tailpipe Connection. For big-block applications, where maximum scavenging and horsepower are required, CMI Big Tubes headers deliver peak performance and power from naturally aspirated engines. The headers can be built to your custom measurements based on your motor.

The all polished Sport Tube system is offered with a range of exhaust tailpipe options, as well as CMI's Sound Choice™ selectable silencing system. Each system includes all header attaching bolts, gaskets and cooling fittings required for installation.

Note: All CMI Systems are sold without Tailpipes