I was looking at a 91 z28 with a 305. it has about 165000 on it with a clean body but when i start it the engine rattles like a knock but then idles fine. If i pull the throttle and it startes to rev there is puffs of white smoke coming from next to the valve covers under the intake manifold tubes on the left back side looking at the car but it only happens when it reved and i took it for a test and it has little power. what i did should have spun the back but it just had no power and the tach says its up past 7000 rpms but its not. can anyone help at all by letting me know what might be wrong or how much it might cost to fix thanks

 

white smoke indicates coolants burning.

most probably its a sign that ur headgasket is either leaking or blown.
u can try engine treatment stuff or thicker oil and
that might seal up the leak for a while.

good luck.. head gasket is very expensive repair.

 

thicker oil wont stop a head gasket leak lol

 

good old bars leak... run it through see what it does... but the permanet fix is to replace your coolant system gaskets... water pump intake and head gaskets... i dont know with that many miles though i would just use bars leak and see if it holds... always worked for me

 

the knock could be a number of things, if it's coming from in front or rear of engine most likely a worn main bearing. you can pull off the oil pan and take a look, but I don't know if you want to.
Were the injectors ever changed? sounds like you have a manifold leak, but hard to say without looking at it.