The Mercury Racing 525 EFI is one of the most popular OEM engine packages for adding forced induction. As almost all of these engines are now out of warranty, we are seeing a lot of interests in refresh projects and supercharger installs. A Conquest TopCat II recently came in looking for more power, and we are going to serve it up with a Stage 2 Whipple 3.3L kit. A lot of prospective owners of the Whipple kit are sometimes surprised by the overall cost of an installation as compared with just buying the kit from Whipple. Read more to see the extent of a proper installation in a very common single engine deck boat application. We go way above and beyond what the kit instructions specify for almost every system in the boat and on the engine.

First things first, we run the engine in stock configuration in the boat and give it a general evaluation. We leak the engine down, scan the ECU, assess plumbing and determine where things will get installed in the bilge before the engine comes out. Then the engine is removed and worked on separately. On the boat side of things, every system is modified to handle the increased power and demand. We add an additional through hull water pickup to use in conjunction with the existing stern drive pickup. They are both plumbed to a TCM 10" Sea Strainer that also features pressure relief and flush fittings. Custom SS through hulls are installed for the intercooler, pressure relief, and flush hookup. The fuel pickups are checked for proper material and size, and the entire fuel system is replumbed with at least -8 USCG line and aircraft fittings. On the dash, we add mechanical water pressure, fuel pressure, and boost gauges. Dual ram hydraulic assist steering is a necessity for installing a supercharger for control and safety. Full hydraulic is not mandatory, but recommended (once you have it you will never go back).



Back to the engine. If the engine has only moderate time on it, leaks down well, and has the later model MLS head gaskets, we will leave the heads on. If any of those conditions are not met, we recommend at least pulling the heads for a top end job and valvetrain refresh. This engine checked out, so we pulled the intake and left the heads on.

As a side note, if your 525 has high hours or needs a rebuild anyways, we can go through this same Whipple kit process in conjunction with a full rebuild to turn the engine into a TCM 825EFI, which will result in 70 more horsepower and a 6200 RPM rev limit (instead of 5750). To accomplish this, we CNC port the heads and run our 825 cam, along with the suitable ECU calibration. Those are really the only extra expenses beyond a typical full rebuild and Whipple kit. As is the case with all TCM engines, it would come with a full one year warranty.

The new style Whipple kit reuses the Motorola PCM555 computer and wiring harness, so we install the intake and then modify and relength certain connectors according to the instructions. Then the intercooler, supercharger, and fuel system are installed. Here are some things that set our installs apart:

We use a custom configured Latham 2 Stage SS water pump that is a complete and direct replacement for the OEM assembly to add durability and pump feed the intercooler on its own impeller. Since the pump is fed from two pickups supplying one big strainer, both systems have debris and pressure spike protection. We plumb the intercooler with custom -12 polished SS 90 deg adapters. This kit features the dual core MOAC intercooler upgrade, which we usually don?t opt for, but it was the customers call. We usually plumb the MOAC with SS inlet and outlet rails so we only have to run one line to and from the intercooler, but the 525 heat exchanger prevents us from using a bottom rail, so we custom made a pair of shorty -10 90 deg inlets and plumbed two hoses from the intercooler stage outlet on the Latham pump. The kit includes aluminum fittings to plumb the intercooler which will rot out in about 5 years, and are hard to plumb clean with 4 lines running everywhere.




We integrate the entire fuel system onto the engine with USCG line and anodized aircraft fittings. The Aeromotive pump and high pressure filter are installed onto the Cool Fuel bracket beneath the crank pulley. The fuel cooler is also plumbed next to the pump. The cooler can be eliminated if fuel is returned to the tank instead of the filter head, which is more practical on twin engine boats or singles with one tank. All lines are supported with SS Adel clamps and ran low and hidden on the engine. Fuel pressure and boost line hookups for the dash gauges are at a custom -4 SS dual bulkhead we mount to the ECU bracket.



Now for the most challenging part of most 525 Whipple installs: The engine hatch (no I'm not kidding). The overall height of the engine is very similar to stock, but the rear throttle body on the blower usually causes some issues at the back of the hatch. These Conquests are some of the hardest to make a clean hatch modification because there is only a fiberglass shell before the foam and vinyl cover. Sometimes there is an inch or so of wood you can notch into for some room. This time, we cut out a box of hatch over the engine and then raise up the rear of the hatch top about two inches before reglassing it in place. The hatch is finished with more foam to contour it much like it was originally. Last time we were very satisfied with this method, as it kept the boat looking factory and retained the hatch space for people to lay on.


John Teague
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