IN OR OUT?
Question: I have a 2000 Formula 353 FAS3Tech with Mercury Racing HP500EFIs. I'm spinning 30"-pitch Bravo One four-blade propellers. I plan on swapping props to spin them in. My goal is to improve bowrise and increase performance in terms of throttle response and top-end speed. What do you think I can expect?

Sam Grasso
Mt. Laurel, N.J.

Answer: It is likely that you will gain some top-end speed with your FAS3Tech by turning your propellers inward. However, the gain in speed may not be worth the possible deterioration of handling characteristics that you may experience.

Generally speaking, the boat will come on plane faster with the propellers turning outward. With the propellers turning outward, there is usually more transom lift, which helps to reduce bowrise. This is especially true with side-by-side big-block installations with all the weight aft on boats that are 35 feet or shorter.

If your boat has a slight tendency to chine walk, the additional bowlift realized by turning the propellers inward will probably have an effect on the intensity for better or worse. In some cases, control is improved. But more often the result is a boat that is a little more difficult to drive at top speed.

Another drawback of rotating your propellers inward is the effect that it has on how the boat handles around the docks. If your propellers are rotating in, you may find that you have to steer the boat in addition to shifting, especially if wind or a current are present.

MERCURY 900 SC MOTORS
Question: I have the opportunity to purchase a 2000 Cigarette Tiger that has MerCruiser Hi-Performance HP 900 SC motors with Mercury dry-sump No. 6 drives. My question is: Are the 900s good, reliable motors? I don't know anyone who owns them and have not read much about them.

Any information you can provide would be helpful.

Lance Rue
O'Fallon, Mo.

Answer: During 2000, when your proposed Tiger was built, the 900 SC was the top pleasure-boat engine offering by MerCruiser Hi-Performance (now called Mercury Racing). It was a 542-cubic-inch, custom-built motor put together with some pretty high-end components. The crankshaft was an L.A. Enterprises Kryptonite 4.375 "stroker," and the engine was equipped with Carrillo Rods. The block was a race-prepped GM Bowtie tall deck with billet main caps.

The heads were a hand-ported version of the Brodix BB2 casting. The engine was topped with a Mooneyham 10-71 blower, a Richard Lee intercooler and a pair of Holley 1050 Dominator carburetors. The engines, as provided by Mercury, had a pretty good track record as long as they were maintained well.

In eight years, it is likely that someone has worked on these motors or even totally refreshed them. If that is the case, the engines are only as good as the last guy who built them. I would definitely get all the history you can on the motors.

The 900 SC was equipped with a solid lifter roller cam. This race-bred valvetrain requires more maintenance than hydraulic roller setups. The valve springs and lifters should be replaced at every 100 hours of use.

Mercury Racing no longer offers the ignition system originally provided. The 900 SC used an ignition system that had similar components to the SC1000 and the SuperCat racing engines. Parts can still be found, but are pretty expensive.

You can always replace the ignition system with an MSD system. The Mercury ignition requires the use of special induction pickup tachometers so it is likely that you would also have to replace your tachs to accommodate a more traditional MSD system.

The Lee intercooler does not have a good reliability record. There has been a significant number of core failures. The Lee intercooler used a fabricated aluminum core that proved to not hold up well, especially as a result of being used in saltwater. If the engines are still equipped with the stock Lee intercoolers, I would definitely consider replacing them. Whipple SuperChargers offers a coppernickle replacement core for the Lee housing. Or you can replace the entire intercooler for about the same price with a SuperChiller intercooler. Both the Whipple core and the SuperChiller are reliable alternatives.

If all the original main components are still present in the engines, at least you will have most of the right stuff to build a pair of good quality performance motors.

The No. 6 dry-sump drives are definitely the drives to have on this boat. They have a great reliability record for 900-horsepower engines. Before you buy the boat, have someone drain the drive oil and inspect it for metal and moisture. The oil filters (located in the nose cones) should also be removed and inspected for any debris.

The engine packages were equipped with Huber transmissions. One way to check the condition of the transmissions is to inspect and smell the oil. If the oil is clean and clear red, and does not smell burnt, there is a pretty good chance the transmissions are in good working order.

LOVES OUTBOARDS
Question: I have a 1978 Cigarette 35 Mistress hull with no engines or rigging. What is your opinion on instead of installing the customary big-blocks in my boat, adding an outboard engine bracket/swim platform and going with 300-hp, four-stroke outboards?

I realize that I will be making a compromise when it comes to horsepower and speed, but I have better luck with outboards. Do you think this setup will function? What is your opinion on modifying a classic?

Scott Cramer
Tierra Verde, Fla.

Answer: There is no question that the boat will probably work similar to some of the larger nonstepped-bottom center-consoles. A Midnight Express is one of the higher-end outboard-powered center-console boats and has many similar hull characteristics when compared to your Cigarette. One of the main things you need to consider is the cost of your project and how much the boat will ultimately be worth.

If your boat has no engines and drives right now, it is possible that you could put it into nice running condition with some late-model takeout Bravo XR packages with 500EFIs or 525EFIs for between $30,000 to $70,000, depending on what deals are available to you.

A standard inboard/stern drive installation will enable you to use the original engine hatch and cockpit layout.

This type of inboard power is what would normally be expected in your boat. You would never have to explain yourself to potential buyers with the Bravo XR packages and the boat would have reasonable resale value.

If you choose the outboard program, you should plan on installing a minimum of three of them. Some boats in your size and weight range run four big Verados. I think they would install five if they would fit (Midnight Express actually told me that once).

It is easy to see that if you intend to buy three or four of these late-model, four-stroke outboards, your expense will be much higher than keeping the boat as it was originally designed with inboards and stern drives.

You also will have to choose what to do with the large space that is now the engine compartment. It would make sense to move the firewall and rear bench seat back and enlarge the cockpit area. You could leave a small area accessible through redesigned hatches for rigging and batteries.

One thing that I am not sure of is how the balance of the boat will be with all that weight hanging 3 to 4 feet behind the transom. I am guessing that the bow will go into the air easily when hitting waves unless some weight is added up front. If the boat is as heavy as a "tank" now, the weight placement will not be as critical.

Be aware that the big outboards use a fair amount of fuel when installed on heavy boats that are capable of using all of their power.

Depending on how you operate your boat, it is possible to use more fuel at cruising speed with a few big Verados than you would with a pair of fuel-injected 502s.

DOES IT NEED TO BE WARMER?
Question: I installed a thermostat and water crossover on my 502. The first time out the motor started to get hot and I found the problem to be that the thermostat was not opening. It is a 140-degree thermostat with a 3/16-inch hole drilled in it. I removed the thermostat and replaced it with a flow restrictor. Now, the motor will run at about 125 degrees.

Some local mechanics told me to drill more holes in the thermostat and reinstall it, but I need to be careful of the water pressure. Is there a better solution to get my motor to run warmer?

Martin Petermann
Charlotte, Mich.

Answer: If you intend to use a thermostat in conjunction with a crossover, you also need a bypass hose from the crossover to the exhaust water side of the thermostat housing. This ensures that water is always flowing to cool the exhaust system while the engine is running.

The cool bypass water affects how the thermostat functions. This is true even though the "heat sensor" on the thermostat is below the plate in the intake manifold water passage.

If you do not have a bypass line from the crossover to the thermostat housing, it is necessary for you to flow enough water all the time to keep your exhaust cool. If you leave the thermostat in place and drill enough holes in it to flow the required exhaust cooling water, the engine water pressure will drop to a lower point if the thermostat opens.

The proper water pressure in your engine is as important as the correct amount of flow. As the water pressure increases, the boiling point of water increases. In the absence of water pressure, it is likely that steam pockets will occur in your engine.

These pockets are initially created by air bubbles that attach themselves to hot spots in the castings. As they continue to insulate the water from cooling the casting, they grow and a larger area becomes insulated. In order for you to decide the correct orifice size, you will need to install a water-pressure gauge on the engine. I think that if you had 5 psi water pressure at slower cruising speeds and about 15 psi at wide-open throttle, you would be in the ballpark.

A lot of car guys are always trying to get boat guys to run their engines as hot as a car runs. The theory is that a hot engine makes more horsepower. That may be true in the absence of detonation and in lighter load conditions. The additional amount would never be detected in your boat.

That being said, I am OK with your engine running at 125 degrees if it is a carbureted, noncomputer-controlled engine that requires a certain "normal" operating temperature. If you are not witnessing any moisture in your oil, and the engine is running well, I would rather see the engine running at 125 degrees with the correct water pressure as opposed to 165 degrees with a higher potential for creating steam pockets, detonation and engine damage. I think it will be easier for you to achieve this goal by removing the thermostat and experimenting with orifice sizes.

UNDERPROPPED
Question: I have an Eliminator 25 Daytona. From the factory, the boat was rigged with a carbureted HP500. The boat is equipped with a Bravo One drive with IMCO Marine full hydraulic steering. An 8-71 Blower Shop blower and dual 750 CFM Holley's were added along with CMI headers. The engine also is equipped with an intercooler, electric fuel pump and an MSD ignition system. Dual sea strainers are installed in the boat for the engine and intercooler.

The boat runs high rpm at relatively slow speeds. For example, at around 5,000 rpm the boat runs about 90 mph.

Why is the engine working so hard to achieve such a slow speed for a catamaran that is only 25 feet long? Is this engine designed to run with a blower at such a high rpm?

Also, what can I do with this current combination to ensure that I don't have an internal engine failure? Finally, the drive is not an XR drive. At what rpm or speed will this Bravo One drive fail?

Steve Marlow
Mission Viejo, Calif.

Answer: Your 25 Daytona is likely equipped with a 1.5:1 drive ratio because of the original stock 500-hp setup. At the time the blower and headers were added, a significant change of propeller pitch or a gear change would have been in order to compensate for the additional 150 to 200 hp. Your HP500 carbureted motor was originally limited to 5,200 rpm.

The stock cam profile and valvetrain are pretty much tapped out at that rpm. The stock GM rods also are known to occasionally spin rod bearings. It is probable that you could add prop pitch and gear ratio to your setup and still be able to attain 5,000 rpm with greater boat speed. This would be the case if you are currently experiencing a valve float condition because of weak valve springs. Accordingly, you should change the gears and/or prop to put a larger load on the motor to keep the rpm lower at top speed.

It is now a good time to go through your heads and upgrade the valve springs. Weak or broken valve springs could be limiting your rpm. If you want to really improve the engine, consider changing the cam to a Crane 139741, which is a good blower cam. This cam is quite a bit larger than your current cam and is about the largest profile you can run that will still result in adequate piston-to-valve clearance with your stock pistons.

A Bravo XR drive has no advantage over the Bravo One drive when it comes to rpm capability. Most Bravo-based drives with good lubrication are capable of running up to 6,000 rpm. The Bravo XR drive is quite a bit stronger than your Bravo One drive when it comes to handling power and torque. You should be concerned about how you bring the boat on plane (gently) and avoid hard acceleration with your current drive. Its days are probably numbered.

OIL COOLER WATER PLUMBING
Question: I just recently purchased a 30-foot Scarab. The boat is set up with twin 502s and TRS drives. I have decided to re-plumb the entire engine compartment. To simplify the plumbing, I am going to mount the oil coolers on plates on the rear of the engines. These plates will also house the sea strainers.

My question is: Would there be any harm in plumbing the oil cooler inline directly after the sea strainer but before the sea pump?

The reason for this is it will keep me from having to run hose from the rear to the front and then back to the rear of the engine again. The sea strainer and cooler on each side will be mounted in the engine compartment below water level so the pump should not have to work any harder to pull the water through the cooler.

Currently, the water is plumbed so that it is pushed through the oil cooler by the raw water pump. What are your thoughts?

Jim Huard
Sandown, N.H.

Answer: There should be no problem with routing your raw water from the sea strainer directly to the oil cooler and then to the raw water pump. The most important thing is that the volume of water cannot be restricted. Make sure that the openings in the sea strainer screen are smaller than the water passages in the oil cooler. This way you can be sure that any debris that gets past the sea strainer is not likely to clog the oil cooler.

You should position the oil cooler and sea strainer so that they are accessible enough to drain. This will be important for your winterizing.