high rev oil pressure

[speedy]

i am running a t1 2276 turbo motor , i now have an oil light problem, when i hit the gas in third and run up to 7000rpm the oil preasure light comes on, shutting the engine down at over 100mph is not a pleasent experience ,when i looked at the oil preasure guage it looked ok 20psi ,when the engine is ticking over hot oil pressure is about 11psi this is low possibly need the bypass altering but why loose oil pressure on higher revs
any info would be appreciated
cheers jon