350 w/305 heads?
 

Hello all,
I have an 83 Suburban that I pulled the tired 305 out of, I dropped in a 350 craigslist find. The 350 smokes and incredible amount upon start up. As if oil is leaking past the valve stems into the cylinders as it sits. I am going to a compression test and see if it is a problem with rings, but I dont think it is because the engine is strong and runs great. I am wondering what I need to look for if I swap heads. I have the 305 heads that I could put on if it is possible. I see heads for sale on Craigslist alot also. I am disappointed that the 350 smokes so much, but I think it's going to be a fairly easy fix. I am not looking for a high performance machine, just a reliable driver.
The 350 block has casting numbers 379010, and the 305 numbers are 14010201.
Thanks for your help. Willy in Washington

sounds like stem seals for sure, but comp test will help. 305/350 heads are interchangeable with no mods. the only exception is any motor/head after '87. should be able to swap the 350 heads for the 305's just fine. assuming the 305 heads are good.

Fantastic, Thank you for the quick reply. I think Im gonna do a compression check on it now before bed. Thanks again.
Willy

The 305 heads will bump up your compression a little also because of the smaller combustion chamber

What you gain in compression you lose more by the 305 intake runner being too small.Ideally for a 350 the head intake runner should be 179cc.

Sooo... Are you saying it's not a good idea to run the 305 heads?

That is exactly what I am saying.I know it is a common practice to use 305 heads and it is the wrong choice.Here is a rule of thumb for you to figure out the size of a intake runner for a set of heads.It is .5 times the C.I. size of a engine that runs a compression ratio less than 9.5 and with a increase compression ratio larger than that.For comp engines .55 x's c.i.Racing Head Service has Torquer cast iron heads with a 72cc head and a intake runner that just about right given the compression ratio and is very inexpensive with all the advantages of a much better casting.Thicker decks,better water passages,can be ordered with screw-in rocker studs etc.

The main reason why there are aftermarket head companies is all the short comings the O.E.M. have.By the time you pay to have the 305 usable,you have over paid for a set of heads that don't work nearly as well.

do you have the numbers off the 350 and 305 heads?

I will get those numbers for you in the next week or so. I am busy building an addition on the house. Again, Thanks for your replies.

OK, Heres the latest. I still have the 305 sittin in the garage, I am not going to use any parts off of it, probably haul it off for scrap. The 350 I installed runs fantastic but it smokes a lil bit upon start-up, I can deal with that. It smokes like a steam train when I am coasting down a hill, as soon as I hit level ground and apply throttle the smoke lets up. I am thinking I got some hoses routed wrong, when I pulled out the 305 it had all that smog stuff in it (1983) the 350 is an earlier year without the smog stuff. I don't think it would be bad valves because it smokes out of both tail pipes, what are the chances of having bad valves or broken ring on both side of the engine? It has me baffled why it smokes upon decel. It is very possible that the engine is just worn out, it was a Craigslist purchase. Ya never know what you are getting. But it sure sounds good, and has good power.
Thanks