Teague On Tech: Q & A with Bob Teague September 2019

Speedboat Magazine Cover

As seen in Speedboat Magazine’s September 2019 Issue.

Props for Formula

Dear Bob:

I have a 2006 Formula 382 FasTech running twin Mercury Racing 600SCis with Bravo XR drives. The current propellers are 30-pitch lab finished Mercury Racing Bravo One 4-blades. I am looking for a mid-range cruise performance increase with a prop change. The boat currently runs 60 mph at 4000 rpm. WOT is 5,100 to 5,200 rpm at 82-84 mph. What diameter and pitch would you recommend in a Mercury Racing lab finished Maximus 5-blade propeller? Is there a long wait for a set of Maximus lab finished propellers?

I am looking to purchase immediately because my boating season is somewhat short.

Thanks for your time!

Patrick Owen, Henderson, NY

Your slip numbers are very high, above 20 percent a 60 mph, and not any bet­ter at WOT. Usually, lab finished 4-blade propellers are better on lighter boats at top end speed but always result in a slight decrease in mid-range efficiency. Stock Bravo One four-blade propellers are actu­ally more efficient in the mid-range but may result in a little lower top-end speed.

The Maximus propellers were originally designed to be used with the NXT drives on the

Mercury Racing Propellers

Mercury Racing Propellers include a lab-­finished Bravo One (upper right), Max-5 (left) and Maximus (lower right).

700SCI engine packages but most of those ended up using racing cleavers. The standard Maximus propeller is 15 5/8 inches in diameter. Most of the lab finished versions are cut down to either 15 or 15¼”. It is also common practice to remove about 5/8″ off the diffuser to reduce stern lift. The Maximus propeller is probably the best if your only con­cern is mid-range efficiency. It is hard to compare the Maximus to other Mercury offerings because of the large blade sur­face area. It is not uncommon for the slip percentage to drop to about 10 percent on a twin-engine boat like yours. I would recommend going back to a 28″-pitch Maximus in a 15″ diameter with the dif­fuser trimmed for your boat. The reason I suggest going down to the 15-inch diam­eter is because of the increased blade area surface of the Maximus propeller. These propellers should result in about a 4 to 5 mph speed increase at 4,000 rpm. But you may not be able to get to the previous top speed of 82-84 mph.

More recently, Mercury Racing devel­oped the Max-5 which is made from the same casting as the Maximus, but the blade shape more closely resembles that of the Bravo One four-blade. The intent was to provide a five-blade propeller for the 400R outboards. We started experimenting with this propeller on stern drive applications with surprisingly good results. Originally it was only offered in a 15″ diameter and we requested to have some special ones built in a 15¼” diameter to increase the efficiency and trim control. Ultimately, the 15¼” inch diameter became more popular. I would select the Max-5 propellers for your boat because they will result in nearly the same increase in mid-range efficiency as the Maximus props but will also result in the same or better top-end performance as you have now with lab finished four-blades. For your boat, I would select either a 151/4″ x29″ or 30″-pitch in the Max-5 propeller.

These propellers are pretty much readily available with shipments arriving daily.

525EFI Valve Spring Replacement

Dear Bob:

525EFI Valve spring setup. I want to change the valve springs on my valve guides. Mercury Racing 525 EFI engine with low hours (150) and low rpm history. It is a 2003 model. I feel it is better to be safe than sorry.

I need advice on which valve springs, retainers and valve locks to choose, there are a bunch of different ones available out there.

Thank you!

Andy Preuninger, Miami, FL

The cylinder head used on the Mercury Racing 525EFI is the same as what is used on the 600SCI and 700SCI. They use a stock length Manley 3/8-inch stem diameter valve. What is unique about the set up is the very short installed height of the valve springs which is 1.800″ on your motor. There are limited options for springs suitable for hydraulic roller lifter set ups with such a short-installed height.

The correct spring to use is a PAC 1VS1631. It is designed for an installed height of 1.800″ and will accommodate the higher lift with adequate “over the nose” spring pressure required with the hydraulic roller camshaft. The stock retainer works well which is a Manley part number 2399M3T. The valve locks are a 7-degree type also made by Manley. The part number for the locks is 1299M3T.

If you need to remove the valve seals to modify the shim height, they are tough to get off. We Bob TEague Photohave found that heat­ing them with a propane torch makes it easier. For a replacement, we use a Viton seal that is .375″ for the .530″ diameter

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