What is the purpose besides picking up sand and muck from the bottom? I was under the impression that it keeps the water pick-up in the water during air time, which makes since.
But then there are "Offshore Style" through the transom pick-ups, which would definitely be sucking air during air time.

On stepped twin bottoms that have high drive heights, without them the engine will run hot due to the lack of water getting into the engines. The side pickups will actually get out of the water.

If I am not mistaken Merc now has a kit to plug off the low water pickup for the dual pickup case.

HOOOOOORAAAAAAYYYYY .I have one(2002) on mine and it's a pain in the a$$. My port sides a 1995 with a side pu ....no problem

only reason to use a LWP is if you run a high-enough X dim that the side pickups suck air.

In actuality, the side pickups will still pick up water at ridiculously high X dims, as long as the center of the bullet is still a tiny bit below the hull.

On outboards, we would block the top 2 holes and use a die grinder to make some "water catchers" to "send" water that direction. You could also pop rivet a piece of aluminum sheet stock to the side of the water pickups to "trap" the water that gets up there.

LWP's cost you some speed.

Step bottoms add air to the water coming off the back of the hull, though, and sometimes you just cannot get side pickups to reliably feed the motors at speed.

Friend's boat runs a LWP and STILL runs out of water pressure unless he uses a 1/2" drive spacer.

All boats suck air when they launch. Some of the old Apache clips of Warpath show that he stays in the air so long, that the exhaust appears to go dry before he's back in the water. Cool stuff....

mcollinstn, you have said in the above statement what Hydromotive has been telling me. I called to get a nose cone with a low water pickup and Tom told me you don't need a low water pickup because adding a nose cone(without a lwp) will improve flow around the bullet which will result in the side water pickups receiving enough water. He said some of their race cats run a prop shaft 2 inches above the running surface with side pickups. Now the person doing my motors said he couldn't sleep because that @@@!$# person was telling me #$%^ that wasn't right. He said there's no way. I still admit that I am skeptical, but I can see how this might be true. My builder seems to say not with his motors I am going to have him call Tom and see if they can work something out without the use of firearms. What would you do as I frequently burned impellers with the stock motors and now I will be running 25 mph faster and much more on the surface? Eric