i just bought a 85 z28 with a 305, its got the stock bore with flat tops but it burns oil, theres blue smoke on startup so i know the valve guides are bad, theres a little but of blue smoke when it idles too, it has roughly 150PSI on each cylinder, do you think my rings are not properly seated and thats burning oil or do you think its just the valve guids?

 

Guides/stem seals.

 

Engine has been running for more than 10 minutes, the rings are seated.

Start with new valve seals. If that doesn't stop the smoke then guides would be the next step.

 

150 psi is fairly low. If you give it hard throttle after it's warmed up, and it blows blue out the tailpipe - then you've got a ring problem (cracked, etc etc). Sounds like it based on 150 psi.

Do the seals though, that's cheap and easy and can reduce your oil consumption.

 

To properly seat the rings you need to build cyl. pressure, this is done by low rpm high gear pulls to about 3500-4000K and engine braking (not so easy on auto but w/ stick it's very doable)

Just running an engine for 10 mins will not seat the rings. You need to do the pulls, don't baby it but there's no need to rev the snot out of it either

 

sorry to go off topic, but SONIX. How are those ported 416's? I've got a 355 with stock 416's. Was wondering how much better they are? Did you put bigger valves in em too? What size if you did?

 

Cylinder cranking pressure also depends on the cam grind.

 

I am having the same problem, I replaced the heads and the intake on my 305. The intake was not sealed and oil was getting dumped into the cylinders, for how long I dont know, it came that way when I got it. And it still burns oil, I know that when the heads came off there was oil caked up thick in the exhaust manifolds. I havent realy run it much so I dont know if it is just the oil burning off and out of the exhaust. I am thinking thats what it is because it doesnt smell like fresh burning oil. It has a woody / carbon smell to it as well as fuel. Also the smoke color isnt blue but more of a white and it is not steam. So I dont know what it is yet. I am going to do a compression test to it and see what I get. But just in case I have started on the 350 build. I hope it isnt the rings but I just dont know at this stage.
BTW, what should I be running in each cylinder? I was thinking somewere around 160-170lbs. In my old 350 a few years ago it was 185 per.