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There are a number of mods and quite a bit of debate about their value on the FE forum. I believe a there is one that should be done on all FE engines. In addition you should use the '68 amd later oil filter adapter bracket as is has much bigger passages. This adapter is often referred to as the CJ oil filter adapter. However it was used on all FEs starting in '68.
I think additional mods are necessary only on high RPM engines but this is not agreed upon by everyone.
The oil mod I that I always do is:
Open up the oil pump to oil filter adapter pad gallery from 3/8 to 7/16 inch and smooth and round the opening on the pump end and both holes on the adapter pad end. All of the main galleries except this one between the pump and the filter adapter pad are 7/16. Leaving this one at 3/8 of an inch is a mistake. You have a 1/2 pump outlet going into the 3/8 gallery to the filter. This 3/8 inch gallery restricts the total flow and until it is opened up neither the stock pump nor a high volume one can deliver the pumps full capacity to the engine. It is like having a set of headers feeding a 2 inch pipe into the mufflers and 3 inch tail pipes. The restrictive 2 inch pipe into the mullers limits flow and must be enlarged.
I sometimes also restrict the flow of oil to the rocker arms using #80 Holley jets under the stands.
The mods reserved for racing engines are: opening the the oil holes in the main bearing saddles so they are as large as the hole in the bearings, drilling and tapping all oil gallery plugs for screw in plugs, and changing the jet size from #60 under the rocker stands. The reason for the jet size change is less oil is needed to cool the valve springs at the track; on the freeway they can get very hot during expended driving. I only recommend the use a high volume pump if the oil pan has a cpacity of 7 or more quarts. The use of the windage tray is highly recommended.
Something I encountered recently was an oil pump with an output passage of less than 7/16 of an inch. Checked a couple of others and found they varied from 7/16 on a TRW to 15/32 on a Melling High Volume one. Thus the stock oil gallery size should be 7/16 inch and there is nothing to be gained by going larger unless you pump's output passage is at least that large. I see no reason why the pump's output passage could not be increased in size however.
You should read these as well.
This is how I drill out the passage from the pump to the oil filter adapter pad.
Note I drill the hole 1/64 inch larger in successive passes using 25/64, 13/32, 27/64 and 7/16 inch bits. This allows better control of the drill and allows me to center the bit easier.
1. First I open up the hole in the oil filter adapter pad using a small grinding stone. This allows the drill to easily be centered on the original 3/8 inch hole.
2. Using a 25/64 inch drill bit I start drilling the hole, stopping after the bit is about 1/8 inch deep. I check the hole to see if the bit is centered and if so proceed to drill the hole. If not I use the grinding stone to center the starting hole and try again.
3. I repeat steps 1 and 2 for each drill bit.
While I have opened this oil passage up to 1/2 inch in the past, the next gallery is only 7/16 inch so its really not useful to go over 7/16 unless you are opening that one also.