Block Venting

496 BB

New member
Obviously with more power there is more compression usually. What I want to know is is there that much pressure below the piston in the crankcase that it puts that much strain on everything else down there such as side cover and turning of crank back up.

I ask because Im wondering if the block needs vented from the crankcase instead of valve cover. I have two in valve cover now both inside reed valve (or whatever it is). I have oil galley drilled out under 1/4" as well.

When is too much pressure relief that your not shooting oil up into the top of the head? Say I add a block vent on top of sidecover like the billet sidecover. And keep two on top. Is that taking away too much?

Is more venting good or bad?
You need too do a leak-down test....there is no-way 'that much' pressure sud be built-up in the bottom-end unless the rings are not sealing. You may consider swapping out the Valve cover also.
I vent from the sidecover with 2 nipples as well as the valve cover.. it helpd my problem of sidecover gaskets and bolts backing out..
If you look carefully at the breather in the clone valves covers you will notice some are not as well made as others.
Often the parts are bent before they are tack welded and sometimes the little disk is not sitting in there correctly.

I take mine a part and adjust them as required.

Next I make sure the venting lines and drain hole are clear.

When you have crank cases pressure issues the first place I would look is the valves cover.
I ran 2 tubes from case to head side of valve cover, then ran an extra vent out of top side of valve cover to catch can... but 2 case vents was too much for my motor 1 did the job in the long run...
I had thought people said you couldnt have too much ventilation?

Though wouldnt it be best to just leave the case alone and vent from the valve cover with a reed/pcv valve?

Isn't it beneficial to have a vacuum behind the piston? Though I see some people run venting without any pcv valves?

Seems to me unless you have excessive blow by, the valve cover should suffice.

Or am I wrong?
when I used 2 block vents I didn't have enough air moving around to run the fuel pump... to me the more you can vent the better... in my mind when you have positive pressure under the piston it will slow the speed of the piston coming down, it has to be able to move that air out of the case to somewhere else as fast as it can...
I have 3 on the valve cover and pulse from the manifold works for me
no blown gaskets or my flat head days I had 3 off the side cover.
and also used the two port breather valve for venting and the
other I used to pulse my pump with.closed off the one in the manifold.
again no blown seals or gaskets.
I'm running 2 off of my valve cover and none from the block on my opens. In my opinion you need to vent from the valve cover to encourage proper lubrication of the valve train components.
Alright I will keep as the same.

I do however want to know if guys running the Arc billet side cover are porting at least one fro that or not???
I had problems with blowing oil out of the seals and side cover gasket. Went to the arc billet side cover. Then had the valve cover bolts come loose in one race with 1 to go with the lead and lost fuel pressure/vacuum. Moved my pulse to the side cover and venting from the valve cover. No more problems. Turning 8500+.