blow by
 

i have a sbc 408 with lot of blow back pressure, motor is kind of new just been together for 3 months lot of white smoke coming from breather cap what could this be thanks

Its oil getting past your rings..some HP Race motors are built loose and could possible have some minor blow by....thats why a vaccum pump is highly recommended/required..

if you do not have $600.00 to invest in a vaccum pump..at least install some e-vac tubes in the headers

hard to tell by internet how bad your blow-by is...so i am just making a general statement here..

but its oil getting thru

Brian

White smoke may indicate a water leak, being it's a 400 blk. they are notorious for blown head gaskets. Have you noticed any milking of the oil?

JMO

Zip.

no water in oil thanks

400 blocks if they are not plate honed with the same hardware it will show alot of blow by and if your building a lot of cylinder pressure its even worse.

Do a leak down test.

ok compression check #1-190, #3-135,#5-0, #7-230, #2-220, #4-225, #6-220, #8-230 could it be rings or head problem

You really need to do a leak down test!!!!!!!!

Take the head off on the drivers side, the problem should be quite evident since you have "ZERO" compression on number 5 cylinder.
My money has it that you have a hole in the top of your piston.
Goodluck, Charles

You maybe looking at a bent valve!!!!!!

re; blowby
 

I once forgot to install the #5 piston, but I knew right off, somthing was amiss, rod made a terrible clatter.