I am updating 502 MPIs including relocating the stock oil coolers. As the inverted flair hose ends used my Merc are not available I have purchased adaptors and 37 degree flair 90s to make new lines. The merc fittings measured .400" ID and the new fittings measure .340" ID. When I contacted the supplier of the fittings about my concern with the reduced ID I was told that the fittings flowed 18 GPM and my stock oil system would only flow 7 GPM so there would be no issue. All threads on this site suggest bigger is better for oil line size. What is actually required to support oil cooling for a 500 HP 502 with a stock oil pump. I have a concern with reducing the cross sectional area of the cooling lines by @ 28 % over stock but the supplier insists it should not be an issue. Any input would be appreciated.

Thanks.

I use 12AN for my oil lines. Some people use 10AN. I also use a EMI oil/ps cooler, much bigger than stock. I use a aftermarket oil filter relocator. I also opened up and cleaned the restrictions on the oil filter housing.

Should be fine. 6-7 gpm is the norm for that system. If the fittings flowed over twice what the pump does, there should be no issue.

the numbers mentioned above are essentially correct. when using aeroquip type fittings, however, use the 90 deg fitting, with the smooth tube type bend as opposed to the squarish forged type. while the tube type take up more room they do flow substantially better. but either way , -10 will be fine. you might also consider the " pushloc" lines and fittings. aside from the money savings, they won't be stainless and stab you and gnaw thru everything they touch.

The merc fittings are marginal to start with,I wouldn't consider going to .340 in dia, what vsicosity is the fluid medium they are claiming will flow 18 gpm? You will create a flow restriction which in turn will force the relief valve open on the oil pump which will aerate your oil and if still running the factory bypass valves in the block they will open and your oil will bypass the filter and cooler,I have experienced this myself. After relocating my stock cooler and filter housing my boat only had 40-45 psi at its BEST,closer to 38 psi at most wot settings . After getting a bigger oil cooler,full flow-12 fittings,billet full flow block adapter and filter adapter my oil pressure was a consistant 60 psi,Smitty

That is the same thing I did. It works much better than the stock equipment. It does cost money but it is worth it.