Offshoreonly.com - Yeah, we'll pretty much stick almost 1200 hp in anything that floats

Thought I would share some pics of a project that we have been working on. It's a 15' x 8' aluminum airboat from western La. It came to us with a NA 632" carb engine that supposedly made about 800 hp. We pulled that out in favor for one of our 598's with a 4.0L Whipple and custom built Distributor-less ignition system. We originally set it up for a max of 5400-5500 rpm since we were using a 2:1 gear reduction. The prop it had was limited to a max rpm of 2750 rpm. Any higher than that and the tips will go supersonic causing the prop to literally come apart. You don't want to be anywhere near it when that happens. We are now in the process of changing the cam and installing a 2.31:1 reduction so that we can spin the engine up to 6100 rpm or so. After a few months of running and realizing that the cooling system is sufficient and the boat can handle the power, we decided to bump it up a little.

There was a ton of work involved in putting this engine in this boat. Since you can't have a water pickup hanging down, it has to run a closed cooling system. Not only that, but the intercooler needs to be a closed system as well. This was something that we never tackled before, since offshore boats have an unlimited supply of fresh, cold water. The problem was going to be keeping not only the engine coolant cool, but also the intercooler so that the intake air temps stayed within reason. I talked to every radiator company out there. Most either didn't have a clue what would keep it cool or just didn't want to tackle it. We decided to go with Fluidyne and they absolutely knocked it out of the park. Not only did they build a kick ass radiator and heat exchanger, but they did it in 4 days and overnight shipped them to me. The radiator is actually 2 cores that are welded together. The lower core is 36" wide and 16" tall. Since the radiator sits all the way in the rear of the boat on the floor and the lower half is below the transom, they built an aluminum shroud completely surrounding the (2) 14" Spal fans. With the lower half of the radiator so low, the prop won't really pull any air through it. The shroud allows the fans to really pull some air through the lower core. The upper core is 36" wide and 14" tall. Since it's above the transom and in front of the prop, it didn't need a shroud. It has (2) 14" Spal fans that are open. Once the prop really starts spinning, it can pull air through and around the upper fans.

Above the radiator is the heat exchanger. It's 36" wide and 9" tall. It has (3) 8" Spal fans. The rest of the intercooler system consists of an electric Meziere water pump that's connected to a 19 gallon water tank (it's not all the way full). The pump pulls water from the tank, sends it through the heat exchanger, through Whipple's MOAC intercooler in the intake, then back to the tank. Both the radiator and the heat exchanger couldn't have worked out any better. The water temp never exceeded 130* and the intake air temps never exceeded 120*, even with almost 10 psi of boost. Heat was my biggest concern from the minute we started this project. It turned out that it was never an issue.

We also wired in an inline water pump in the cooling system. This pump and the 2 upper radiator fans are hooked to a temp switch in the intake. Most all of the airboats have a problem with heat soaking when they shut them off. There have been several of them that ended up with engine damage because they got so hot after shutting them off. It's not uncommom for the them to see the water temp creep up to 240*, or higher a few minutes after shutting down. The temp switch that we used turns on the upper fans and the water circ pump when the temp reaches 160*. It not only circulates the water through the engine and the radiator, but the fans pull out the heat. Once the temp gets below 140*, the pump and fans shut off. It works like a champ.

Here are a few pics of the engine.. I have a few videos of it running that I will download and post later. Enjoy.
Thanks,
Eddie