ONE-OF-A-KIND 455 OLDS

QUESTION: I’m building a fuel-injected Oldsmobile 455 for my 18-foot Apollo Jet boat. I’m using a MEFI 4 ECU, 1000 CFM four-barrel throttle body, Edelbrock Performer heads and custom-made headers. Could you school me in what makes a good cam for a jet application?

ANSWER: Traditionally, the 455 Oldsmobile engines (especially with the stock bottom-end components and a hydraulic cam) were not considered to be high-revving power plants. They had their heyday in the 1970s as an inexpensive alternative to the high-performance big-block Chevy 454 jet packages.

Selecting the proper cam profile for your engine depends on a few things. It is important to know what your target full-throttle rpm will be, which should probably not exceed the low- to mid-5,000-rpm level. Selecting the cam also will depend partially on what jet pump you have, the impeller, load grate and nozzle, which will dictate how much load it will place on the engine.

Another consideration is if your headers are water-injected. If you have too much valve overlap, the engine is likely to ingest water due to exhaust reversion at idle unless you have a way to minimize or eliminate the injected water at idle. Bassett, one of a few options remaining for water-injected jet-boat headers, offers a spring-loaded check ball assembly that all but eliminates the water flow at idle. As the bowl pressure rises with rpm, the pressure in the engine block also rises slightly to unseat the ball allowing water to flow to the headers. If you opt for a manual water valve located near the driver’s seat, you must remember to open it as you put your boat on plane.

As a side note, the purpose of the water injection is to preserve the chrome plating on headers and to drop the radiant heat so that surrounding components, upholstery and the boat itself are not damaged by heat or fire. Water injection is not designed to cool the headers to the point that they can be touched or accidentally bumped into. If you do, you may leave some skin on them.

I’d definitely choose a hydraulic roller camshaft as part of your Oldsmobile modernizing project. You will realize more power compared to a flat tappet option without sacrificing idle quality. Being that your Performer heads are designed to produce torque (and not necessarily extremely high rpm), combined with the fact that you won’t need to achieve an excess of 5,500 rpm, I would keep the cam profile on the milder side.

Not all cam grinding companies are still supporting the older Oldsmobile engines. Competition Cams is one of the companies that can provide you with what you need. They have one offering that has a lobe duration at .050" of 224 and 230 degrees (intake and exhaust, respectively). The lift at the valve is .505". Their standard lobe separation is 110 degrees. I suggest that the lobe separation be advanced. A split pattern with about 114 degrees of lobe separation will be best for your marine application.

BIG JET BOATS?

QUESTION: Why don't 28- to 50-foot offshore performance boats, such as Fountains and Cigarettes, use water jet drives manufactured by companies like Berkeley, American Turbine or Legend?

ANSWER: Jet drives built by the companies that you mentioned are designed for lighter-weight boats that have less mass and wetted surface. Traditional jet drives are not efficient enough to propel a large heavy boat to a respectable speed. The result would be constant excessive rpm and extreme fuel usage. Propellers on stern drives are much more efficient for larger V-bottom boats.

Some specially built cruisers are equipped with large jet pumps driven by massive diesel or gas turbine engines. Although most of those boats are faster and more efficient when they are equipped with surface-drive propellers.

OIL PANS FOR JET BOATS

QUESTION: I'm upgrading my stock 502 Chevy and installing a M3SC ProCharger. My boat is an Eliminator 21 Daytona jet. My question are, what makes a good marine oil pan? What should I look for in a performance oil pan? Maybe you can help take the mystery out of what goes on in the pan.

ANSWER: The most important features of any wet sump performance oil pan are quality construction, capacity, oil control and windage control. The problem with jet-boat installations is that a shallow pan is generally required. So in order to have a decent oil capacity, the pan should be equipped with kickouts on the sides to increase the capacity.

Your big-block Chevy has the oil pump at the rear. A screened pickup that also is supported by bolts is required. The pickup tube can be supported by a stud from the No. 4 main cap bolt or by a brace held by two of the oil pump housing bolts.

The pan sump should be equipped with baffles with one-way trapdoors that only allow oil to flow toward the oil pump pickup. One of the most important features is windage control. Some pans have a windage tray that is attached to the No. 2 through 4 main cap bolts equipped with extension studs. It is more desirable to have a windage tray that attaches to the rails on the inside of the pan. The windage tray should be the full length of the pan (with exception for where the oil pump is located) for maximum effectiveness.

Oil pans that have the features described previously are available from a few manufacturers. I have had good reliability with pans built by Dan Olson Racing Products and Dooley Enterprises. Later-model Dooley jet pans are available with the windage tray attached to the pan instead of the main cap studs. A pan that has a capacity of 12 to 14 quarts of oil is best. The oil level should always be below the level of the windage tray to prevent the crankshaft rotation from whipping the oil.

—Need some guidance from Bob Teague, Powerboat's lead test driver and owner of Teague Custom Marine? To send him an email click here.

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