MTI 340X With New Mercury Racing 300R Outboards

We sample the performance potential of the new Mercury Racing V8 outboard.

MTI 340X With New Mercury Racing 300R Outboards
An MTI 340X powered by a pair of new Mercury Racing 300X outboards powers past the famed Lake X observation tower.Courtesy Mercury Racing

A MTI 340X sport cat powered by Mercury Racing 300R outboards was one highlight boats at a recent media day at the Mercury Marine Lake X test facility in Florida. MTI Marketing Manager Tim Gallagher was on hand to supervise demo rides in the beautiful boat, which was decked out in Mercury Racing livery. I was allowed to take the wheel while Gallagher throttled for a blast across Lake X that saw us top out at 109 mph with four people on board. Gallagher told me he's seen 113 mph in this configuration with a lighter load. Some rigging details for those interested: The boat was running Sport Master gearcases with 1.75:1 gear ratio and 15 x 35 inch five-blade Mercury Racing Outboard CNC Cleaver props.

This example of the MTI 340X features an all-carbon lay-up instead of the standard e-glass/epoxy lay-up, a $30,000 option that Gallagher says shaves about 700 pounds off the boat weight. This boat weighs only about 5,300 pounds rigged, according to Gallagher. Boat length is 34 feet over a beam of 10 feet. The boat was rock steady on a stiff lake chop during our short ride, which is the point of a sport cat like this – to deliver 100-mph plus top speed with little or no drama. It makes going fast fun.

This 340X has been used as a test boat by Mercury Racing, and was originally powered by a pair of Mercury Racing 400R outboards. Gallagher told us this is the first example of the 340X he’s rigged with the new 4.6-liter V8 300R motors, so it gave us a chance to get him to compare the proven and very popular Racing 400R outboard to the new Racing 300R motors. The 400R obviously makes more peak horsepower, and can rev to 7000 rpm, compared to 6400 rpm for the 300R, so it’s going to be faster. Gallagher said the speed difference seems to be about 6 to 8 mph, but that because conditions have such a big influence on speed with a boat like the 340X, he’d make his final judgement after a head-to-head run with two boats on the same day.

The 400R has a supercharged 2.6-liter in-line six-cylinder powerhead and weighs as little as 668 pounds. The 300R is a normally aspirated 64-degree 4.6-liter V8 and weighs as little as 512 pounds. That weight difference – 156 pounds per motor – was the first thing Gallagher mentioned. That’s almost like taking two adults out of the boat, and all of that weight is hanging off the transom, so it affects hole shot and the boat’s angle of attack. The 400R and 300R make similar torque, so the 300R has the potential to out-accelerate the 400R, although the 400R will quickly exceed the pace of the smaller motor.

Since the point of a boat like the MTI 340X is going fast, we asked Gallagher if his customers have shown interest in ordering new boats with the 300R instead of the 400R outboards.

“Yes, because there are always customers who are interested in owning the newest design and the latest technology,” said Gallagher, “and maybe just having something different on the transom. The 400R offer more top speed, but the with the 300R you get a lot of new features.”

Those features include Transient Spark Technology that optimizes 300R timing advance for more torque on hole shot. The 300R is offered with a choice of the standard tri-ram midsection with high-durometer upper motor mounts and solid lower mounts or the HD midsection with solid upper and lower mounts, a forged transom bracket and remote trim pump, and an integrated rear tie-bar mounting plate. The 300R also has the nifty Top Cowl Service Door that permits oil checks without removing the cowl plus a quick-release cowl latch system with a built-in carry handle. An 85 amp alternator gives the 300R more charging power than the 70 amp 400R alternator, and the 300R has Idle Change battery management that raises idle rpm and charging power when it senses battery charge is low. Finally, the Racing 300R makes full power on 87-octane fuel while Mercury Racing recommends 91 octane gas for the 400R (although it will survive on 89 octane fuel), plus the 300R has Advanced Range Optimization (ARO) which uses a closed-loop sensor system to lean out the fuel mixture for best-possible efficiency for the given condition. In short, the Racing 300R offers a list of advanced technology – from light-weight die casting to electronic controls – that have been developed since the Verado-based 400R was last updated.

If having the latest-greatest appeals to you the 300R might be your performance outboard of choice. The real question: How much “headroom” has Mercury designed into this new V8, and how much power might the go-fast crew at Mercury Racing extract from 4.6 liters in the future?