Bass & Walleye Reviews Engine Louver InstallationReprint of article published in March - May 2003 issues of BASS & WALLEYE BOATS magazine.

"This article on outboard hop up is reprinted with the permission of Bass & Walleye Boats magazine. Click on the link at right to find out about subscribing."



Story and Photos by John Tiger Jr.

Bass & Walleye outboard hop-up with DYNOmiteThese simple,
bolt-on mods yield
extra torque and
speed from a
Evinrude 150

‘Too many Mercs!” is the battle cry of Johnson, Evinrude and Yamaha fans who occasionally write to us commenting on the all-too familiar Mercurys as our subjects for hotrodding projects. Guys, there’s no prejudice — it’s all in the numbers. There are far more Mercs to find and wrench on than Johnnys, ’Rudes and Yammers combined. That said, we’re making an effort to devote more space to building up engines that aren’t painted black, and we’re starting with a hop-up story on a very popular powerplant, the OMC “Eagle” series of V-6s that first hit showrooms in 1991.

Dubbed the Intruder (Evinrude) and FastStrike (Johnson), these compact, lightweight sixes pack a lot of power for stock engines. Offered in 150 and 175 hp versions, they quickly gained a reputation as torquey, dependable performers. Eagle was the internal code name when they were under development at OMC, but the name leaked and became popular among those in the know to describe this engine family.

The moniker designates a 158-cubic-inch, V-6 powerplant with cylinders set at a 60-degree angle. Despite the relatively large displacement, the Eagles were popular due in part to their light weight. OMC listed the dry weight of the 150 and 175 models at 358 pounds. In addition, a unique induction system that utilizes three single-throat carburetors on each side of the crankshaft (unlike conventional intake layouts, which locate the carburetors in front of the crank) shortened the intake tract, giving the engine lightning-quick acceleration and strong low-end torque.


The Intruder and FastStrike 150s and 175s were designated as “high-performance” outboards, and featured louvered cowlings, harder engine mounts, and enhanced tuning compared to OMC’s standard 150/175 models. Aimed squarely at the high-performance bass boat market, the Eagles found a welcome roost.

The downside to this engine series (at least for outboard hotrodders) is that it is a difficult powerhead to modify. For starters, unlike outboards that have removable, bolt-on exhaust manifolds, the Eagles feature cast-in-place manifolds. Lacking a way to remove the manifold, it is both challenging and time-consuming for an engine tuner to access and modify the exhaust ports to extract more power.

Secondly, the ignition system provides a “limiter” of sorts to power production, in that it’s hard for the average tuner to get the stock optical-sensor ignition (OIS) to allow the engine to spin much past 6000 rpm. As outboard hotrodders know, it takes top-end revs to add speed, even if the engine is spinning past its power peak.

Despite these adversities, hop-up artists have found ways to extract more speed from this compact V-6. To learn some of the secrets, we enlisted the help of Evinrude and Johnson outboard drag racer Gordon Montague of Monty Racing, a modification and repair shop in Stuart, Florida. Montague’s pedigree is packed with drag-racing wins and dozens of Monty Racing outboards ply the circuit. They’re always tough to beat, so his shop was a natural for our Eagle project.


As our test specimen, Montague selected a 10-year-old 1993 Evinrude Intruder 150 owned by south Florida tournament fisherman Dan Blankenship. Sporting a custom red and yellow paint job, the ’Rude is bolted to a bright red 1998 Allison XB-2002. While it might seem that Blankenship’s hull is underpowered, he confessed that after a succession of high-powered Merc ’rods, including a 225 Pro Max and a 260 EFI, he opted for the vintage Evinrude after one too many tows back to the ramp. “While the Mercs ran well into the 90 and even 100 mph range, I got sick of the breakdowns,” Blankenship tells Bass & Walleye Boats. “My ’Rude is fast enough, and it always starts and gets me home.”

Well, maybe not quite fast enough. Blankenship released the keys to Montague, saying he wanted to see more speed and better acceleration.


Together with local Allison buff Terry Evans and this writer, Montague brought the rig to the narrow St. Lucie Canal to nail down baseline testing in 95-degree heat with 70 percent humidity. The Allison proved a handful at full throttle, requiring a deft touch combined with massive arm strength to control the horrific torque on the steering wheel. The ’Rude was jacked to the moon on a setback setup consisting of two manual plates — a stock Allison and CMC — bolted together. With a Bob’s Machine Shop noseconed gearcase, low-water pickup and aftermarket torque-tamer screwed to the skeg with too-long sheetmetal screws, our Alli did not have the best setup, as evidenced by its quirky handling and lackluster top end.

Our baseline speed was 70.3 mph at 5350 rpm, as recorded on radar and GPS. Equipped with a 141/2x30-inch Mercury Chopper II propeller, our rig was carrying two 225-pound men and three-quarters of a tank of fuel. Riding solo, Evans reported 74.5 mph at 5400 rpm.

Based on previous tests (“Still The One,” October 1998), this boat should have been running in the mid-70s with two aboard — which is what we saw with a similar hull powered by a Ficht-injected Evinrude 150 and 29-inch SRX prop during our ’98 session. We suspected that the heat and humidity were probably sapping about 10 percent of the engine’s rated power (compared to the relatively crisp weather during our ’98 test). Drag from the nosecone and poorly installed torque tab also was a limiting factor. At these speeds, the cone and low-water pickup were unnecessary and simply slowed us down.

Acceleration was decent; we clocked 8.3 seconds in our 0-to-30 mph sprints, but 40-to-60 mph trials took an agonizing 9.6 seconds. We hoped to improve on these numbers dramatically.


Although the Eagle series is difficult to modify, Monty Racing produces two upgrade packages. Blankenship chose to start out with the easiest and least expensive “Mod I” package, consisting of a cylinder head upgrade (more on pricing later). Montague swaps the stock heads with his specially machined versions, and re-jets the carburetors to add more fuel. This mod doesn’t require the use of premium fuel, although Monty recommends using mid-grade (89 octane) gasoline.

Back at the shop, Montague used a Land & Sea DynoMite portable engine dynamometer to record baseline horsepower and torque. The key to accurate and repeatable results with this unit, he says, is to continually check for setup accuracy, and provide it with an adequate water supply to properly load the engine. We quickly bolted the unit to the propshaft, and made a couple of “pulls.” According to Montague, the numbers were typical of this engine series: Maximum horsepower was 158 at 5000 rpm, with best torque readings of 200 lb.-ft. at 3200 rpm. Using an automotive compression gauge, cranking compression was 100 to 105 psi per cylinder.

As the engine cooled, Evans and Montague removed the stock heads, cleaned the cylinder surfaces, then mounted the modified heads using a new O-ring gasket and sealer. Next, we installed richer main jets in the carburetors. The entire swap took less than an hour.

With the new heads and re-jetted carburetors, the cranking compression increased to approximately 120 psi. On the dyno, peak power was now 174 hp at 5200 rpm, with a torque reading of 212 lb.-ft. at 3200 rpm. Just as important, horsepower and torque were measurably improved in the lower midrange (see chart). With approximately 16 more ponies and 12 more lb.-ft. of torque to play with, we couldn’t wait to hit the lake.


Out on the water, top speed increased a bit less than 1 mph, to 71.0 at 5500 rpm. When riding solo, however, I saw a constant 76.5 mph at 5600 — a solid 2 mph increase vs. stock. Acceleration improvements were even more impressive. Zero-to-30 mph times dropped 1.3 seconds (to 7.0 seconds flat), and 40-to-60 mph times also dropped by 1.3 seconds (to 8.3 seconds). Both could be felt in the seat. The modified Evinrude literally pushed the boat onto plane, whereas the stock setup labored.

The downside to our project was a little-known phenomenon called deceleration knock, which is a common trait for Eagle engines. Lacking proper carburetor jetting, the outboard will audibly “knock” (similar to a car “pinging”) as the throttle is released, typically when backing off after a high-speed run. This Intruder was no different. The solution is slightly richer high-speed jetting, which Montague provided. After the adjustment, the knock almost disappeared at all throttle settings. This is not something to be overlooked; if ignored, you risk detonation and expensive piston and cylinder damage.

Bass & Walleye outboard hop-up dyno resultsCOST vs. BENEFIT

Although our Eagle project provided only a slight improvement in top speed, we realized substantial gains in torque and low and midrange acceleration. This is a mild, easy-to-perform hop-up that delivers an enticing cost-to-benefit ratio. Best of all, there’s no tradeoff in terms of engine reliability.

For do-it-yourselfers, Monty Racing provides the cut heads, O-rings and carb jets for $250, plus shipping. That’s a mile per hour combined with much better acceleration for a very reasonable price. If you live within driving distance of Montague’s shop in south Florida — or just need an excuse to trailer down for a fishing vacation — he’ll do the job while you wait for an additional $150 in labor. Add $125 for three dyno pulls if you want to see the results on a printout, as well as on the water.

Fishermen who crave even more impressive gains may want to pop for the Mod II package (approximately $2150 including labor). After seeing the results of the basic modification, Blankenship volunteered to put his V-6 block under Montague’s surgical porting knife. This is a more radical hop-up to be sure — and promises equally radical performance improvements. With the port job and new heads, this is one Eagle that should really fly high.


In Part II of our ’93 Evinrude Intruder 150 hop-up, porting adds serious punch in acceleration and top end

John Tiger Jr.
Bass and Walleye Boats
March 1, 2003


As detailed in “Eagle Project” in Bass & Walleye Boats’ March issue, we took a 1993 Evinrude Intruder 150 carbureted two-stroke — a very popular engine family that was codenamed Eagle during its development — and made it faster with some simple head modifications.

Florida basser Dan Blankenship’s Evinrude took on new life after our first hop-up session, gaining some much-needed acceleration and a smidgen of top speed. He liked the value, too. His $525 cash outlay (including parts, labor and dyno testing) for Monty Racing’s “Mod I” cylinder-head upgrade was well worth the 1.3-second gains he saw in holeshot and midrange punch. But as you might expect, the experience left him wanting more (don’t we all?).

So, we tagged along when Blankenship brought his custom-painted ’Rude back to Evinrude guru Gordon Montague for “block surgery.” By the time it left Montague’s Stuart, Florida, shop, his little red ’Rude was packing some serious horsepower.

There’s plenty of these Evinrude and Johnson 60-degree “Eagle” series outboards around, and many owners are probably thinking of trading up to newer models. When performed properly, hop-ups such as our two-part project can give an engine a new lease on life — and keep the sticker shock of a new $15,000 outboard at bay. A side benefit of Monty Racing’s “Mod II” porting package is that for roughly $2900 (including the Mod I heads and dyno time), you not only get a modified outboard that will put the hurt on any stocker, you get a completely rebuilt powerhead. For anyone with a tired Eagle engine, these upgrades only cost about $500 more than it would to perform a stock rebuild.


After installing the Mod I heads and rejetting the carburetors during our first session, we saw the 10-year-old Evinrude jump from 158 hp in its stock state to a healthy 174 hp. Our Part II mods involved tearing down the original powerhead and rebuilding it with fresh parts, including new piston rings, bearings, seals, rod bolts and gaskets. Monty Racing’s policy is that if the original pistons don’t measure up to specifications, they are replaced (at additional cost).

The real magic happens when Montague has the engine torn down to the bare block. At this point, he goes inside with a handheld porting tool and modifies the intake, transfer and exhaust ports to handle a larger charge of air and fuel.

The restricted working area and the Eagle’s cast-in-place exhaust collector make manipulating the porting tool extremely difficult. One wrong cut or grind and the block could be headed for the scrap heap. Montague has perfected his porting schematic from years of dyno testing and racing, and it works. In addition, he modi-fies the cast Evinrude exhaust tuner by welding shut a large hole in the divider plate — a trick he claims adds as much as 5 hp at the top end. Of course, his porting specs remain a secret; he’s spent far too much time on the dyno and in the grinding room to give away the magic.


After the porting work, Montague and local wrench Terry Evans put things back together and reinstalled the powerhead to the midsection. We let it run for a half-hour or so, breaking it in carefully before bringing rpm up to midrange speeds. After about an hour, it was ready for a dyno pull. Montague brought the rpm up to 6000, then gradually loaded the engine with the brake, bringing it down smoothly before allowing it to idle again.

After several pulls and carburetor jet changes, we recorded a whopping 195 hp at 5200 rpm, and maximum torque of 237 lb.-ft. at 3400 rpm. That’s a remarkable improvement. In fact, it’s 21 more ponies than our Mod I upgrade produced — and an incredible 37 hp improvement over stock.

Coincidentally, we also saw a torque gain of 37 lb.-ft. vs. the stock setup. There was a significant jump from the Mod I package, as well, with an additional 25 lb.-ft. measured. Obviously, the porting job’s better airflow turned this Eagle into a raptor to reckon with.

As we fastened the cowl and hooked up the boat to the truck, we fairly vibrated with anticipation to see what effect all this power would have on Blankenship’s Allison.


We weren’t disappointed. With Blankenship and this writer aboard, our top speed was 77.7 mph at 5800 rpm, an improvement of 6.7 mph over the Mod I package and 7.4 mph compared to stock.

Riding solo, Blankenship reported GPS speeds of 81 mph (compared to our best stock solo run of 74.5 mph). In fairness, we point out that Part II testing was conducted in markedly better climactic conditions than our Part I evaluations, where we endured 95 degree temperatures and 70 percent humidity. This time around, we were graced with air temps around 60 degrees and 60 percent humidity. Even so, it’s safe to say that speed and power improvements obtained through porting are nothing less than significant.

As good as our top-end improvements were, acceleration was where the truly incredible gains were seen. In stock form, the Evinrude 150 posted 0-to-30 mph times of 8.3 seconds; with the Mod I heads, it took 7.0 seconds. With the new powerhead, holeshot times dropped to 5.8 seconds — that’s 1.2 seconds faster than the Mod I package and 2.5 seconds quicker than the stock time.

Midrange punch was even more astounding. Our 40-to-60 mph average was now 4.8 seconds — a 3.5-second improvement over our previous Mod I best, and a walloping 4.8 seconds better than stock.

To top off his rig’s improved performance, Blankenship replaced the boat’s dual Ride-Guide steering with a Teleflex SeaStar Pro hydraulic system, and ditched his old manual jackplate in favor of a Bob’s Machine Shop hydraulic unit with 10 inches of setback. Not only is his Allison faster and quicker, it’s now easier and more fun to drive. While he’s elated with the newfound performance, he still loves his trusty Evinrude for its easy starting, reliability and quiet operation. For a decade-old outboard, this ’Rude runs stronger than the day it came off the assembly line. It not only keeps up with newer engines — it makes them eat wake!

Total Improvement: 37 lb.-ft. over stock
Cost per Lb.-Ft.: $78.38

Total Improvement: 37 hp over stock
Cost per HP: $78.38

Monty Racing
Dept. BWB
450 S. E. Monterey Road
Stuart, Florida 34994