Ok, so you have your quarter-million dollar boat with twin 500 EFI Mercruiser engines for a total horsepower of just under 1000, but that just isn’t enough. What do you do? Well… there is one relatively easy way to dramatically increase horsepower, that’s right—a supercharger. On top of the power increase you get that cool unmistakable whine that will cause any wrench head to notice. This particular install is a stage 3 Whipple supercharger which will add approximately 240 hp per engine; in essence, we are adding a third engine.

Of course there are kits available for many different engines, but since we are installing this on a 500 EFI MerCruiser engine,  I’ll start with a few warnings about this particular engine. Mercury recommends that the top end of these engines be rebuilt every 250 hours. If your engine is due, or close to due for this service, I strongly recommend doing this first. Even if you have 50 hours to go it’s a good idea to get it done since you will have the intake manifold off for the install. The other big concern is the water pressure in the block. Along with the more explosive burn that creates the extra power comes more heat. You will want to install block pressure gauges to keep an eye on this. The reason for wanting to watch block pressure instead of just temperature is that the higher the pressure, the higher the boiling point of the water. If the pressure gets low enough that the water can boil, it will create air pockets in the block.

All right, with all that said, let’s get started. First, it is a good idea to disconnect the batteries. Time for the mass destruction. Now you need to pull the distributor out in preparation for removing the intake. It will help to put the engine at 1 top dead center before doing so. It will be much easier to put it in the new intake if you have that reference.

It’s time for the intake disassembly. Start this by draining all the water out of the engine. You will find blocked drains on either side around the engine mounts. If you do not drain the engine first you will spill water into the lifter valley when you pull the intake. Next you will need to remove the upper plenum which is held on by 12 bolts. A number of connectors and vacuum lines need to be disconnected first.

Once you get the upper plenum off, it’s time to remove the intake. I find it easier on the 500 EFI to remove one of the fuel rails to remove the wiring harness. You will need to remove all injector connectors, engine coolant sensor connectors and anything else that runs across the top of the intake. At this point the harness will push off the back of the engine. Now remove all of the bolts that secure the intake and gently pry the intake free of the silicone.