[vogey]

Just picked up at set of power domes they are for 3000-6000' think i can still run 91 at 1000'?

 

[madcow]

if they are for 3000-6000 feet then you cant run 91 at 1000'.

 

[Student Driver]

^^^
Absolutely correct.
Running those heads at 1,000 feet will require a race fuel mix to bring that octane up to where you are not pinging and pre-detonating.

 

[Ugly_old_Poo_kid]

Correct, the compression is too high, they are intended for use in lower atmospheric pressure.

However, if your engine uses paper/rubber head gaskets, doubling them up will lower the compression. (will it be enough, I dunno)