Diamond Marine Facility Tour
Article by Greg Terzian
Photos by Greg Terzian and Diamond Marine

Engine assembly 'clean room' can handle many builds at once.

Diamond Marine is a very familiar name to most people who are serious about getting the most from their high performance outboard engines. Diamond Marine’s business is strictly Mercury V6 engines, and Diamond is recognized as the platinum standard in Mercury V6 outboard performance modifications.

Joe and Marty Signorelli, Diamond Marine’s founders, have established themselves as two of the top performance boat engine builders and riggers in the country. By performing both routine engine modifications, rebuilds, and supplying custom components, their services are considered essential for top-winning racers. Outboard drag, offshore, and tunnel boats is a steady portion of Diamond’s clientele. Equally important are the weekend river racer and offshore poker runner. Diamond Marine also maintains a strong relationship with Mercury Racing, and they are a Premier Mercury high performance dealer for new engines, parts and service.


Joe and Marty got their start by fabricating race car chassis and components.

While in his teens, Joe started a small welding service specializing in the repair and modification of aluminum big block Chevrolet cylinder heads. Word spread throughout the New York and New Jersey area engine builders, who quickly came to rely on his services. Joe fabricated items which are common today, but were far less available in the mid 70’s, such as scratch built tunnel ram intake manifolds, dry-sump oil tanks, and custom aluminum oil pans with trap doors and windage scrapers. The business grew quickly, so Marty joined Joe forming Diamond Race Cars. Diamond initially built bracket race cars and components. They built and raced a Pro Stock Camaro, which they campaigned on the northeast circuit. Joe, at the time was the youngest NHRA licensed Pro Stock driver at age 22. This trackside experience enabled them to specialize in building the Pro Stock cars only, up until they sold the business, the jigs and fixtures in 1987.


Diamond Marine's first location in Farmingdale, NY in the 1980s.  Diamond's facility is now located in Fort Lauderdale, FL.

Growing up on Long Island, New York, the Signorelli brothers also had another passion – high performance boats. While most performance boat enthusiasts on Long Island were content to overpower their recreational boats, Joe and Marty had different ideas. They started to seriously experiment with Mercury high performance outboards and the then new-to-the-scene STV Mod VP boats during the mid 1980s. A northeast USA dealership territory deal was soon struck with Roark Summerford of S.T.V. Boats. Some people may remember the early Diamond Marine magazine ads showcasing these, which to many, were strange looking little boats. They built winning engines for Champ, SST140, and Mod-VP racers running the I.O.G.P. circuit, and also ran two Mod-VP S.T.V.’s out of their New York shop.

When the Mod-VP class ended, Roark Summerford called upon them to get involved in outboard drag racing which had been growing in the mid-south and Texas. The Yankees soon had an impressive customer list in D.S.R.A., Alabama, and Tennessee Drag boat clubs. These clubs later merged to become the O.D.B.A. that we know today. Diamond Marine was certainly one of the first companies to support the clubs by sponsorship and contingency monies. Today, they still sponsor O.D.B.A. and the re-formed D.S.R.A. Offshore racing played an important roll in those early days at Diamond. The triple engine Pro Stock class (interesting name) which consisted of 32’ Skaters and 35” Motions were devouring up 2.4 EFI Bridgeports at an amazing rate. It was this problem that initiated Diamond’s policy (still in use today) of engine break-ins and dyno testing for new and rebuilt engines before installation. This made the boats race ready and more reliable. A race car team would certainly not consider entering a race without following this same procedure.

Custom in-house aluminum fabrication - in this case, an afterplane for an Allison drag boat. In the late 1980s, Diamond Marine was the first to introduce the programmable ECU for Mercury EFI engines. Diamond Marine's facility includes a CNC and other advanced machining devices. A Predator tunnelboat being rigged.  Note the custom fabricated dash panels.

Inside the dyno testing room.  The control panel is operated from outside protective glass.

The Signorellis capitalized on their race car knowledge and master-class metal fabrication skills to modify the Mercury V6 platform for increased performance and race durability. Further experiments led to modifications that produced impressive results, and their scientific approach to engine modifications started catching the attention of performance-minded boaters and racers. Before long, the two young brothers decided to leave the race car world and switched gears to focus solely on expanding the Mercury V6 platform.

Diamond Marine was established in Long Island, New York in 1987, at a time when electronic fuel injection was a new phenomenon, and the 200 horsepower V6 was still considered a very large outboard. The new business quickly and aggressively separated itself from other performance shops with its ‘anything can be improved’ philosophy. In these early years, Joe and Marty were already finalizing what would become possibly the world’s first programmable fuel injection electronic control unit (ECU) for Mercury motors – the Diamond Marine Digital Fuel Injection. This ECU was fitted to Mercury Bridgeport engines, which were the pinnacle of Mercury performance at that time, and some of these rare units are still in use today on 2.5 liter EFI engines. In March of 2005, Dennis Vitolo ran 141 MPH in his STV River Rocket with the same Diamond ECU that he has had since 1989 (Re-programmed of course)!

One of Diamond Marine's first magazine ads, circa 1992.  Note the introduction of the 2.5 EFI Mariner.

In 1996, Diamond Marine relocated to Fort Lauderdale, Florida.  The 8,000 square foot facility is one of the most comprehensive and advanced in the world, with the ability to perform any modification or custom fabrication in-house.  The facility can accommodate numerous boats at the same time, with hull sizes of up to 40 feet. 

But it’s not only the size of the facility that sets Diamond Marine apart – it’s the comprehensive set of state-of-the-art equipment.  The equipment at Diamond Marine includes a custom computerized powerhead dynamometer, a crankshaft balAancer, a Sunnen CV616 cylinder king hone, custom fabricated boring bar, T.I.G. welders, 18” and 36” vertical band saws, steel shot-peening equipment, manual vertical milling machine, manual lathes, surface grinder, two 10” X 72” belt sanders, pedestal and bench grinders, two ultrasonic cleaning tanks, a Kasto 30” power hack saw, crankshaft polisher, sheet metal brake, rollers , tubing bender, two drill presses, automatic  tapping machine, high pressure detergent block washer, and practically everything else imaginable. In addition to the air-conditioned machine shop alone comprising of 2,200 square feet, the shop has a dedicated grinding room for block porting, a paint spray booth, gearcase department, disassembly and cleaning area, a custom eight-station clean and parts room for final assembly, show room, conference room, and shipping office and rigging / service area.


Joe Signorelli designs Diamond Marine's products in-house.  All design and production takes place at Diamond's facility.

The Diamond Marine facility also features an EDM which is used to make their lightweight crankshafts and other specialty products. One of the most impressive pieces of equipment on their site is their 44” travel 50 taper Kuraki CNC vertical mill. A few years back they added a 25 H.P. slant bed CNC lathe to their arsenal. Some of you may be familiar with how a CNC works, and you’ve probably seen one in action on television shows such as American Hot Rod. These huge machines require detailed programming and absolute precision, since mistakes can be very costly in both materials and time. For this task, Joe uses the latest Mastercam software to run his CNC machines, producing works of high performance art from solid blocks of metal.


Diamond Marine STV at a St. Louis race in 1991.  This boat led the race until a cracked fuel rail resulted in a second-place finish.

Diamond Marine’s “mail order “parts sales is also an important facet of the business. Customers have long come to rely on their experience to advise them on the parts they need and as important, the parts that they do not need. With the popularity with the internet, there are more places to buy parts than ever, however in the performance world accurate advice cannot be read in a parts breakdown. These parts include OEM Mercury engine parts as well as quality aftermarket accessories.

If Joe and Marty need it, or if you can think of it, Diamond Marine can make it.  New products are always under development, and the two brothers often can be found testing on the clear waters of Florida’s Atlantic Ocean, rivers and lakes.

This year marks the brothers' 30th year in business together and they still look forward to helping the racer as much as ever.