Generalities: If your engine is bone stock, 260hp small block, 310 hp big block, you probably won’t gain any significant speed. You will benefit from the safety of our manifold (won’t eat your motor when it dies), and light weight; save 70 to 125 pounds over the cast iron stuff. When you step up the performance to the next level, like the 365/385 hp 454 Magnum, or the 385/415 hp 502, for example, the performance gains are significant. We have a boat test elsewhere in the website on a 365 carbureted Magnum Merc in a 22’ Donzi. Hot Boat did a complete test on the boat, including fuel flow and such. After the test, they brought it to the dock and changed the manifolds from the Merc cast iron to our standard Big Block set. No other changes. No prop, no timing, no nothing. Picked up 300 r’s and 6 ½ mph. That is the most optimistic report that we have seen in the 17 years that we have been building this manifold. The least optimistic? “Lost 3 mph!” That is pretty much impossible. Average? Trailer Boat Magazine did a 10 month series on a Sea Ray Pachanga with a 502” Crusader. At the end of the article, they took off the Crusader manifold set and installed our Bravo length set. Picked up 225 rpm’s and 4.5 mph. The headline for that episode is “Of all the changes that we made over the months, the Stainless Marine manifolds made the biggest improvement”. That increase is typical of the reports that we receive from our customers.

Our Gen III Big Block is considered by some top engine builders to be the best choice for an 800 HP and up supercharged engine. This set compares very favorably to the most expensive tubular headers.

When modifying your engine for increased performance, see our web section “What the heck is reversion?” section before choosing a camshaft.

Before assembly, we inspect the cast runner inside and out. It is a simple 2 dimensional shape, like the exhaust manifold on a car or truck. After it passes inspection, we assemble it with the half-shell cooling jackets and water fittings in a fixture, and tack weld it together. We have a 500 degree oven to heat the manifold assembly before welding. When the manifold reaches 500 degrees, the jackets are welded together around the seam. The entire assembly cools together, minimizing stress.

We machine the welded assembly, pneumatically test it, chemically treat it and send it to powdercoat. When it comes back, it is ready for use. What is the difference between our method and everyone elses? Even Superman can’t look into the innards of a 3 dimension cast exhaust manifold, full of lost cores and such. Might be perfect. Might not. Guess who is going to find out. We have the only answer for that problem. We made the inside of the manifold two and one half times as thick as the outside cooling jacket. When it dies, and it will, it promises to tinkle in you bilge, AND NOT IN YOUR ENGINE! We have been using this method for 17 years, and in all that time, we have seen exactly ONE manifold where the inside failed before the cooling jacket.

We were the first company with a five year limited warranty (also the first with 36 and 50 month warranties). The other guys had to follow, but they weren’t happy about it. Another comparison that we face is the occasional ‘new guy’ who gets the great idea of building an all-stainless manifold. Guess what! This company was founded 27 years ago making stainless steel manifolds. One of the great metallurgical lessons of all time! Fabricated stainless steel does not like to see 1400 degree exhaust gasses. Hot-cold-hot-cold-break. Stainless steel is a great material for risers. The aluminum water cooled manifold soaks up some of the 1400 degree heat, and delivers it to the stainless steel riser at a manageable 700-800 degrees F.

Another lesson that we learned the hard way has to do with corrosion. We have very few failures during the warranty period. When a manifold fails, we replace it and cut the old one open for a post-mortem. One thing that confused us was the fact that some of the best cared for, best looking manifolds had the most severe damage. I went to a seminar at the IBEX show in Ft. Lauderdale a couple of years ago, conducted by Ward Eshelman, who is the guru of electrolytic corrosion. After the seminar, I stayed and spoke to Ward about our situation. He explained the following: Standard equipment at that time was sacrificial anode (zinc) for each manifold. A manifold sitting full of salt water with a zinc to protect is a happy situation. If you are a careful owner, or a fresh water boater, or both, and flush the engine after every use, the manifold now sits full of fresh water. The zinc changes its name from anode to cathode, and now the manifold is protecting the zinc! We deleted the zinc and changed the water fittings from hard anodized aluminum to a space age fiberglass reinforced plastic. There is a fair chance that the current Stainless Marine manifolds could outlive your boat!

The boxes are made to mount on either the floor or the side of a stringer.

SIZES:  Group 24: 7 ¼” W. by 10 ¼” L.
            Group 27: 7 ¼” W. by 12 ¼” L.
            Group 30/31: 7 ¼” W. by 13 ¼” L.

Specify battery brand for height.

Our final version is working perfectly. It has an overboard pressure relief valve which vents at about 7 psi and dumps all the foamy water from the top of the can over the side. Many modern boats have steps in the bottom. These steps tend to aerate the water (make bubbles). Some of these bubbles get sucked up by the water pickup. Unless you have a Stainless Marine Superstrainer, each bubble must travel all the way through the engine and out the exhaust. Every bubble in the cooling system is a place that isn’t cooling the engine. We have had customers report a 30 degree drop in oil temperature after installing our Superstrainer.

Originally, we had a landing (shelf) in the strainer body for the basket to sit on. We received reports of tiny shellfish and turtle grass passing through the strainer and making it into the engine and intercooler. We redesigned for that situation, and now have the basket indexed and held down by neoprene bumpers on the basket handle. All the strainers that we are familiar with use about the same perforated metal basket material. We don’t think that the hole size is small enough to stop the particles which can clog an intercooler. There is a finite relationship of the basket area (number of holes) to the size of the perforated holes. If you count all the little holes, the area of the holes must add up to approximately three times the area of the feed pipe. We don’t think that most manufacturers bother with this sort of thing, but we do.

For the intercooled, supercharged crowd, we made a bag strainer which fits just before the intercooler water inlet. It is fabricated of polished stainless steel and has a volume of about one liter. There are several choices of mounting brackets. It contains a nylon filter bag much like the one in a deluxe vacuum cleaner. With the clear lid, one can observe the amount of trash that DIDN’T go through the intercooler, and dump the bag accordingly.

Today’s marine engines are complex machines. Stock engines can exceed the horsepower output of yesterday’s racing engines. Like everything else in life, it comes with a price. As valve timing changes to increase horsepower, water ingestion problems increase at the same rate.

With watercooled exhaust systems, care must be taken to avoid ingesting the cooling water as it is dumped into the exhaust risers. Standard V8 engines usually have center-rise exhaust manifolds with short risers. The cooling water outlet is usually about even with the end of the exhaust manifold. That is the problem for high performance engines.

V8 engines are not two 4 cylinder engines stuck together. For engine balance and smooth firing considerations, the V8 firing order is arranged so that two of the cylinders on each side fire within 90 degrees of each other. Not a problem on a stock (read; mild cam) engine. When the cam gets more aggressive, it opens sooner, stays open longer, opens wider, etc. This usually results in the two aforementioned cylinders having their exhaust valves open during the intake stroke for about a quarter of a revolution. These cams are meant to perform in a dry environment. I had a 1200 Yamaha motorcycle a couple of years ago. At idle, you could hold a business card against the muffler outlet, and it would stick there because of the apparent suction. Obviously there could not be a real reverse flow there. In fact, the firing pulse was quick, and the intake cycle slooooow. The ratio of bang to suck resulted in much more of the stroke at low pressure. Your car is probably the same way. This situation only occurs at dead idle. When you increase the rpm, the reversion goes away. Many boaters have reversion and never know it. They start the engine and immediately increase the throttle setting. The small amount of reverted water is vaporized immediately. Some reversion can be avoided by increasing the idle speed slightly. This doesn’t work too well on a stern drive.

What is the cure? Make the exhaust riser pipe longer. Dump the cooling water further away from the hole in the manifold. Worst case? Don’t put ANY water in the inside of the pipe. We offer 3 different length risers for a typical Bravo length application: Standard; to the end of the manifold. This length is good for about 224 degrees of duration at .050” lift on the cam. Next is ‘Bravo length’, which is 18” from the hole in the manifold to the end of the pipe. It will stand about 236 degrees of duration at .050” lift. Last is ‘thru-transom’, which offers several choices of water dumps, depending on the cam. There are several other factors influencing reversion, including lobe separation, lift, etc. They are minor players in the reversion game, but they count. Don’t take a chance. Err on the side of safety. If you are not sure, start the engine on the garden hose and let it idle for a few minutes. Lift the riser off and look in the manifold. If reversion is present, it will be obvious. Perfectly healthy exhaust systems can ‘catch’ reversion later in life, via leaky exhaust riser or manifold gaskets, leaky or stuck exhaust valves, degraded manifold flanges, etc.