[Cupcar]

This is an interesting discussion.

One data point is a 2.5 liter we built over 10 years ago for vintage racing that has been rebuilt 3 times over that period with about 40 hours on each build cycle.

The car had until its last build a 901 oil pump with the small pressure side, the oil bypass mod, late pressure regulation spring package and the venturi pick up. It also had the Turbo oil restrictors. The idea being that the 901 pump is plenty adequate in a high RPM engine and the relatively larger scavenge side + venturi + restrictors would limit windage losses as Henry points is a good idea.

Cams are GE80 with first Aasco then Eibach springs and Ti retainers. Oil Mobil 1 15-50 which has more ZDDP than the other M1 oils and the engine is set to a 7500 RPM limit.

The cam wear has been acceptable and the cams have never been changed. We were surprised to find one broken Aasco spring at one build though. So to me this shows that oil flow with the restrictors is enough to protect the cams- at least in this engine anyway.

Having said that, I am still a flow freak because I like the idea in my mind of lots of cooling oil going over the parts - hey this is just me, I am not calling it right or wrong - and if an engine has a GT3 or other large oil pump, I would not use restrictors.

With the smaller pumps, I would probably restrict flow to the cams with the restrictor.

Perhaps the most cogent quote from above is "it doesn't make any difference"...