I just finished my build and i notice when was tuning i was getting some blow by. I know to avoid this you would run a catch can, but my bay looks really stock with all stock parts and i dont want to give a cop a reason to harass me. Is it bad to not run a catch can for an ALL motor build? What are the risk if any? How does blowby affect me?

 

blahhh any help?

its a fresh motor and now i have a small leak... still trying to find out where its coming..

 

i was told if i was to use thicker oil.. it helps avoid blowby? is that true? any help anyone?!

 

blow by causes detonation by lowering effective octane of fuel. I'm sure a ghetto ebay catch can stuffed with steel wool hidden somewhere would be fine.

 

is it bad if i dont use one? and what if i switch to a thicker oil.. 10w50 does that really prevent blowby?

 

im having the same issue is it realy needed?

 

Needed? no. The car will run. What is your definition of needed? Not having one will reduce performance for the reason stated above, as well as an increase in pumping losses.

Think of it this way, the lubrication system is sealed at the valve cover and oil pan. When the engine is rotating, it creates turbulence aka windage. Now, that produces pressure. High crankcase pressures are no good. The stock PCV (positive crankcase ventilation) system, is fine for an n/a car that isn't revved very high and driven normally. It is qualified to handle that. Now, start speaking increased revs and increased displacement, and the stock PCV system struggles. Also, the stock PCV system is operated under very little vaccum. You don't want the oil contaminated air getting into the engine anyway. The stock pcv and breather box (catch can) does a pretty good job, but it's not perfect.

I'd go with an aftermarket breather system. The problem is 96+ B18b/b20 engines don't have said breather system, as the PCV is built into the ls/b20 head. Vtec engines have it built into the block. So if you don't have one, get one.

 

So it is the spinning crank that causes crankcase pressure. I did not know that. I was always told it was compression leakage from rings and non-round (.003 ) cylinder walls and the fact that the piston going down created pressure in the crankcase.
Sounds like improper hone, out of round cylinder, too much PTW cl., LS bearings oiling the cylinder wall above 6700 rpm's,

 

Compression leaking past the rings should be minimal in a healthy motor at <3%.
It could contribute though. And the pistons going up and down does contribute as well. It's everything really, it's having parts moving in a sealed (mostly) environment. The air that is moved around has to go somewhere. And if there is no PCV system, it will usually find it's way out via oil pan gaskets, valve cover gaskets, etc.