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.

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)!