Is it a good or bad idea to use a high volume oil pump to replace a standard pump in a absolutely stock engine? The application is a 502 Magnum MPI.

I WOULD NOT USE A HIGH VOLUME PUMP UNLESS YOU HAVE A LARGER OIL PAN.

I would save the money and run a stock one on a stock motor

I would recommend using stock volume pump and shimming the spring .125"

There should be no reason to go beyond the stock pump on that motor. Are you having an oil pressure issue?

That stock pump is plenty.

If you are going for more hp you should be concerned about the external oiling system ie:the stock merc oil fittings, lines - size and design.

Take a look at this good thread from Arcticfriends:

http://www.offshoreonly.com/forums/s...ight=oil+lines

I would do what Chris says if you know what he's talking about? He has a lot of knowledge with Steff's oil pans.

I don't but my customer base does. This shimming comes from some of the respected marine engine builders that we deal with on a regular basis.

One of the biggest problems with the Mercruiser oil system is that the oil lines they use are very small. They work okay with stock power, but if you start to modify the engine, you have issues with oil flow.

Shimming the oil pump will get you more pressure, but with stock lines, your volume will not increase, which won't do you a lot of good. If you shim it, AND use larger lines, then you will be on the right track.

Think of it as putting your finger on a water hose. You are still getting the same amount of water, its just coming out harder, because you did not increase the volume

The oiling system is a little different then yourhose/finger example.

The 'finger' is your bearing clearances and other orifices ie: things that will bleed off psi.

Say a pump has no psi regulator for a second.

If your engine needs 75psi for correct protection and your system actually gets to 100psi this means the pump has more volume output then the engine requires. Enter the reason for the psi spring regulator. If this is set for 75psi, in the above engine, then it will open at 75psi to bleed the extra volume of oil away from system to maintain this 75psi.

If you have a 75psi spring bypass setting, but your engine only produces 50psi of oil psi your pump does not create enough volume to reach this point.

So, if you have a 50psi spring setting and your engine maintains this 50psi, then your pump has enough volume.

If you take the same engine and pump but shim (or replace) the spring to 75psi and the engine reaches and maintains this 75psi, then the pump has creates enough volume to keep up - the system is using more oil volume. If it doesn't reach / maintain the 75psi, the pump doesn't have enough volume and a larger volume pump must be installed.

Sorry for rambling - hard to type vs talk .