The Hot Ones

Mercury’s four-stroke outboard stable continues to grow, with new Pro XS and Racing V-8 models.

Last year I wrote about the new series of V-8 outboards Mercury unveiled at Lake X in central Florida, focusing on the FourStroke, Sea Pro and non-supercharged Verado iterations of this 4.6L outboard platform. While their performance was impressive, the Pro XS and Racing versions of the 250 and 300 are even hotter. We’ll likely see these engines on everything from pontoons to offshore fishing boats, but models such as bass boats, flats boats and bay boats will benefit the most, because of the lower water pickups on their available lower units.

The new V-8 family replaces a number of engines, including all supercharged Verado outboards less than 350 hp. The big shock to bass-boat owners is the discontinuation of all two-stroke OptiMax models, and owners of high-performance boats will be equally stunned by the disappearance of the benchmark two-stroke 250XS and 300XS screamers. But a few nuggets of info might help both groups get over their pain. Bassers need not worry about excess weight because the 20-inch-shaft model Pro XS 250 four-stroke weighs the same 505 pounds as the 250 OptiMax it replaces — likely not a coincidence. And don’t worry about a drop in performance, because the V-8 has 40 percent more displacement than the two-stroke’s 3.0L block, which helps it produce up to 44 percent better low-end torque, for vastly improved holeshots.

Mercury still makes the supercharged 2.6L inline six-cylinder Verado 350 and 400R models. Even better for Racing division fans, the 250R and 300R have a full three-year warranty, which is one more year than the two-strokes they replace. And all the new V-8s run on regular gas; there is absolutely no benefit for even the 300R to run high-test fuel.

 

Compare & Contrast

So what’s the difference between a Pro XS and a FourStroke? The first thing I noticed was the satisfyingly deep growl of the Pro XS, an on-purpose design element intended to further reinforce this engine’s attitude. The growl is the result of the Pro XS having only one muffler compared to the FourStroke’s and Verado’s two. Difference number two is the weight. The 20-inch-shaft version of the Pro XS 300 weighs 505 pounds, which is 22 pounds lighter than the 300 FourStroke and a whopping 95 pounds lighter than the Verado 300 with the Advanced Mid-Section (AMS). The reduced weight of the Pro XS and Racing models is largely due to lightweight cowls that are made of low-density sheet molding compound (SMC). The Pro XS 250/300 feature different engine mapping than the FourStrokes, allowing them to achieve 200 more rpm — up to 6200 — for more overall power and higher speed. The 300R is tuned to rev even higher, a peak of 6400 rpm, thanks to shorter intake runners and a custom intake cam. It will outrun even the Pro XS 300. To counter the heat produced by higher revolutions, the 300R has an integrated oil cooler. The 250R has the same power as the Pro XS 250 and they share an identical 6200 rpm redline. Digital Throttle and Shift (DTS) is an option with Pro XS models and the 300R, but the 250R only comes with mechanical controls.

 

Alterations

Higher speeds create more violent outboard movement, so for added control the Pro XS models have harder engine mounts. Unlike the Conventional Mid-Section (CMS) on Pro XS and FourStroke models, the Racing models feature the Tri Ram Racing Mid-Section, which has a harder elastomer upper mount, two solid lower mounts and a forged bracket. The 300R also has an optional Heavy Duty (HD) Mid-Section that features all solid mounts, so it can handle more extreme conditions.

One of the ways to achieve higher speeds is to reduce lower-unit drag, so Mercury Pro XS buyers can upgrade the standard 4.8-inch gearcase to a more robust 5.44- inch gearcase Torque Master lower unit on models with a 20-inch shaft. The 250R and 300R come standard with Torque Master lower units but the 300R also includes two more choices: Sport Master and HD. Which lower unit to choose depends on the boat, how it gets used and its top speed. The major benefit to all of the upgraded lower units is the additional lower water pickups, which allow them to be mounted higher in the water or to be used with a jackplate. This reduces drag and decreases draft, so boats can operate in shallower water.

Performance

During tests at Lake X, a Yellowfin 24 Bay powered by a Mercury Pro XS 300 reached a top speed of 64.2 mph at 6200 rpm but still managed to get 5.1 mpg at 29.1 mph, according to its SmartCraft gauges. The fuel economy is owed to various features, including Advanced Range Optimization (ARO), which uses the onboard computer to sense when the boat is at a steady cruise and then automatically leans out the air/fuel mixture.

I also tested the Mercury 300R on an ES Custom Boats Revolution 25, which is a big Texas-style bay boat with a low gunwale that’s often paired with a Mercury 400R but was really impressive with 100 fewer horsepower. It jumped on plane in 2.8 seconds with little bowrise, furiously accelerated to 30 mph in 5.4 seconds and reached a top speed of 63.3 mph at 6400 rpm.

I just missed the wildest ride of the day: a Bullet SST 21 bass boat rigged with a 300R with a Sport Master lower unit. It reached a blistering 103 mph. By the time I screwed up my courage to ride it, they were pulling it out of the water. I tested the same boat later that fall with a Pro XS 250, and it still hit 84.4 mph. Fast enough for me.