[87mk111]

I know that the gte motor can handle between 700 to 800 on stock internals. I wouldnt push that on a ge tho, especially if you dont know how the previous owner treated it. IF you wanted to go turbo, I would suggest buying all the turbo parts you want, and pull the head off have it checked, ad also take a look at the block whilel the head is off. But 400 to 500 should be fine, as long as the engine is in good shape.