Chevy 305 smoking out valve cover breather

Still learning the whole Chevy thing so I'm coming on here for some help. I have a Chevy 305 in the circle track truck I bought. Main seal is leaking so I know I have to pull it and repair that since its a one piece. But while warming up the engine to check that leak the other day, I noticed a steady light stream of white smoke coming out of both valve cover breathers (drivers side). Ran a compression test today and all eight cylinders were anywhere from 150psi to 160psi. Any ideas what might be causing the smoke? Just not real sure what to check next. Old owner doesn't know anything about cars, just had his builder work on things, so he's of no assistance.

What you did was a compression check. A leakdown is different. Likely rings.

Any reason you need to stay w/ a 305? Terrible motors for power.

Not sure why I typed leak down instead of compression. I don't even have a leak down tester. Just trying to make it live long enough to run it a couple times this year. Saving up for the 350 crate motor for next season. May just swap the rear seal and run it till it pops. I thought that a compression test would help diagnose ring issues, but am I reading correctly that I need to run a leak down to check that?

Your correct.
Without knowing the comp ratio of the motor and the valve timing there is no way of knowing what a good compression PSI is. If you did this when the motor was new, you would have a number to reference for times like this. Even then, its still not a good way to check the rings. A compression check will tell you if you have a big hole that results from something like a bent valve or a hole in a piston.

Could be valve seats/seals... compression would be good but might get a little leakby on your exhaust valves... or if it is a new build, the rings might not be seated...

OR... I might be blowing smoke out my A$$... anything is possible..

Ran the leak down test today...... Pooh.:(

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Originally Posted by GlennCMC70

Any reason you need to stay w/ a 305? Terrible motors for power.

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Glen,

Depends on what Ratio he needs to hit. TJ Bain has done pretty well running 305's in his 3rd Gen AI car. We use to get 315-325 rwhp out of ours before we switched to CMC and new donors were easy to get if not free.

Sidney

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Originally Posted by Sidney

Glen,

Depends on what Ratio he needs to hit. TJ Bain has done pretty well running 305's in his 3rd Gen AI car. We use to get 315-325 rwhp out of ours before we switched to CMC and new donors were easy to get if not free.

Sidney

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Hijack: Here is Sidney's old 305. I bought it from him many years back when he switched to a 350, my project floundered, my buddy wanted to build a hot rod, so we built this in my garage and used Sidney's old motor.

Just wanted you to know it went to a good home. :)

https://lh5.googleusercontent.com/-h...0/IMG_3915.JPG

https://lh3.googleusercontent.com/-4...0/IMG_3923.JPG

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Originally Posted by Tobey

Hijack: Here is Sidney's old 305. I bought it from him many years back when he switched to a 350, my project floundered, my buddy wanted to build a hot rod, so we built this in my garage and used Sidney's old motor.

Just wanted you to know it went to a good home. :)

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That motor was sweet. I bought it from Dan Nicoter in Milwaukee where he used it to win the ITGT Championship in '97 and '98 with Midwestern Council. I pulled it when we decided the cheapest way to get closer to AI 9.5 was to build a 350. I think that is the only motor I raced that I pulled before it blew to smitherings.

Sidney