The most common response you’ll hear when you ask experts about marine exhaust systems is, “Well, it depends.” They’re not being evasive and they’re not necessarily guarding any big secrets. They’re just being honest.
Getting the right exhaust system onto an engine can make a huge difference in performance, but the hard part is figuring out what kind of performance the powerboater wants, and matching the systems performance to the powerboaters needs.
There is tremendous variety of options in the marine exhaust offerings, Tubular headers, and complete exhaust Manifold systems available on the market today. Some systems provide a more decorative return—designed to look good and give great exhaust note. But while all exhaust manufactures builders claim performance gains, real-world, side-by-side tests often show the real true benefits.
There are a lot of reasons for that, and most of those reasons are legitimate. But we have to look deep to the core of the true design of the system. There are examples where a high performance exhaust manifold may out perform a tubular header system.
When it comes to the size and design of exhaust headers/, that principle remains true. There’s no point in spending time and money on a big custom header if it’s not going to help. But when the time arrives that a header is required, it can make a significant difference. At that point, you need to know how to make the best possible decision.
Manifold / Header Basics
The most widespread types of performance exhaust systems. The most common are lighter weight aluminum tuned exhaust manifold systems. These systems greatly reduce weight over an OEM cast iron system by as much as 80-100lbs. These systems usually portray a style of separated exhaust runner. Many of the entry level or what we call impostor manifolds systems use a simple separation of the runners for marketing purposes but are not as tuned as they could be
But the best in the business use a varying runner separation designed to maximize exhaust pulses and create a scavenging effect similar to a tubular header. As OEMs realized this benefit they turned to companies that manufactured the GIL/Hardin style of manifold and made these standard equipment all the way up to the 500HP/540HP applications . These systems represents a 38-50HP gain over the OEM cast iron exhaust systems.
When it came to larger horsepower applications the it was deemed to look at tubular stainless steel headers commonly found in racing applications. These use 4-into-1 collectors where the headers gather all four primary pipes together into a single collector; Almost all headers are some variation of this.
Getting It Right
The first step to choosing the exhaust/headers that are right is to ask the right questions to the right people. The industry leaders at giant Marine mail order superstores like CP Performance offer nearly every brand of exhaust on the planet and with highly trained staff they are going to look to ask the right questions. Every engine is different, and the engine builder should be the primary source for exhaust/header specifications to match the engine they created.
“Usually your engine builder is very knowledgeable and particular as to the exhaust system,” said Jeff Stull of Hardin Marine, Palm Coast, Florida. “You need to lean on their knowledge of the engine they created. We have extensive knowledge of OEM applications as well as custom builds but our real specialty and knowledge is how to package headers into a particular style of boat that will live under the constraints being asked of them. You bring us the boat application and specs, and we discuss your needs and come up with a plan.”
Also, both the engine and the exhaust/header must be optimized for the rpm range and the particular type of boating application intended. It’s not that there are special headers just for stock , performance, or racing individually, but exhaust/header design reflects the nature of the power one needs and the space available inside the engine compartment.
Exhaust decisions can usually be well planned out with some research If you know the build specs and details of the engine, you can get pretty close to an optimized design. Hardin Marine offers a detailed online worksheet that takes every engine/boat measurement into account.
“The customer goes onto our website and fills out the form,” Stull explained. “Then we run it through a fitment chart and we get a layout design. Then our engineers go through and make sure we’re taking all the different aspects of the application into account, and we make a recommendation on the exhaust/header design. It has a broad range of applicability as long as you have the data on the engine.”
The diameter and length of every part of the exhaust header makes a difference in the effect on engine power. It’s tempting to think that a bigger exhaust/header like a BIG Tube design will make more power. After all, the objective is to get the exhaust gases out of the boat as efficiently as possible, so why not just use the largest possible pipe in all cases?
“The diameter of the tube matters,” Stull said, “because it establishes the velocity of the gas throughthe port/tube.”
One of the most common mistakes boaters make when choosing a header system, according to Stull, is assuming that any tubular header will do. Of course, this assumption is wrong. He explained that there are many components to consider when choosing an exhaust system or header. “In simple terms,” he said, “the runner/tube size used has mostly to do with exhaust gas speed and pressure. The smaller the tube, the more speed and pressure. The larger the tube, the less speed and pressure.”
He added, “With big-horsepower race boats, the tubes are usually larger to help achieve max horsepower at a desired peak rpm. In general powerboating, the tubes might be a standard size to help achieve max torque for acceleration or planing and such.”
We asked Jeff Stull of Hardin about the choice of materials in manifolds and headers, and were surprised by the variations and why.
“The thing is that materials react differently,” he said. “People sometimes think that making a stainless steel header will be much better because the assumptions is that it is stronger and will last longer than in reality. But sometimes stainless will crystallize under the constant heating and cooling of the material and you’ll develop cracks, specifically due to vibrations on that header.”
This is why performance aluminum exhaust manifolds are so popular. The construction of a 356T cast aluminum manifold that has been heat treated and corrosion coated can vastly outlast the life span of a stainless tubular header system. recognizing the application or style of boating should play a major role in exhaust system selection.