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Username Post: crankcase pressure on 350 small block        (Topic#268137)
RICH57TRUCK 
"6th Year" Silver Supporting Member
Posts: 122
RICH57TRUCK
Loc: COLORADO
Reg: 07-28-07
08-23-11 06:23 PM - Post#2129434    

Someone told me the other day if you have oil pan leaks it could be from a high crankcase pressure.
He also said you need to install a vent kit to relieve the pressure.
I thought your PVC valve and oil filler/breather took care of that on a mild build.
Anybody have any thoughts?
Rich
57 CHEVY STEPSIDE
OLD SCHOOL PINSTRIPER


 
Lead sled 
Frequent Contributor
Posts: 1648
Lead sled
Age: 54
Loc: Walton,NY.
Reg: 11-04-09
08-23-11 07:56 PM - Post#2129479    
    In response to RICH57TRUCK

On my basically stock '67 350, I have a pcv,with the hose going to the front of the carb base,the factory vented oil filler tube cap,and just for the hell of it,I added another vent on the opposite rocker cover than the one with the pcv. Works fine for me.
Late yr model (Dec. 51 BelAir/ 52 trim), with a basically stock 67 Camaro SS350/295hp Turbo Fire Edelbrock 1405, Saginaw 4spd/355 geared 55/6 Chevy rear.2,1st place,and 1 top five award trophies so far
http://www.picturetrail.com/bris51deluxe


 
models916 
Valued Contributor
Posts: 2833

Age: 63
Loc: Addison, IL
Reg: 05-28-10
08-24-11 08:15 AM - Post#2129669    
    In response to Lead sled

Poor seal on the rings create more crankcase pressures. Do a leak down test and see if the rings are good.

 
IgnitionMan 
Valued Contributor
Posts: 2639

Reg: 04-15-05
08-24-11 11:07 AM - Post#2129719    
    In response to RICH57TRUCK

Actually, if you could get the engine started with NO RINGS in it, there would still be some moderate engine air area pressure. Leaking rings are a very small contributing factor to engine air pressure buildup.

Example: a 327 Chevy "displaces" 327 cu/in volume moved by the tops of the pistons, and the exact SAME air volume movement BELOW the pistons, 327 cu/in of volume, in the vacuum/pressure air areas of that engine. Add to that, WHATEVER level of piston ring leakage, and managing the air area becomes essential for performance. If an engine could be completely sealed in its air area, it would have a very hard time running, the pressure resistance in that air area volume resistance would work against the piston movement, from their under sides.

That said, a well designed PCV system should take the crankcase pressure out of the engine. The correct spring pressure and volume PC Valve must be used, and, a large air inlet is also required, to allow free air inlet flow into those air areas.

Take a look at stock engines and their PCV systems, the actual PCV vacuum hose is small in comparison to the inlet hose from the air filter into the engine. Shows it doesn't take a lot of vacuum volume to handle the pressures in the air areas, but, a lot of volume must be supplied to the air areas for the PCV system to work correctly.

A lot of people with Pontiac's have pressure problems in their engines, even when a correct PCV system is used, versus Chevrolet's, because the intake manifold area on the Chevy adds air volume area in the whole area size, and the pressures are dampened by the added area. The Pontiac uses a divorced intake manifold, with a valley cover that dips in its center, taking air area volume away from the total area, making it a lot harder to manage the pressures inside the engine.

The Chevy small block engine has roughly 30 percent MORE air area in the combined areas of timing cover, oil pan/crank/cam chamber, valley and valve covers to work with and dampen, over the Pontiac engine.

As we all know, the smaller engine windage/air area we have to manage, the harder it is to manage, especially in larger displacement engines, the higher the potential for rising pressures within that area, the larger that area is, the easier to manage.

Edited by IgnitionMan on 08-24-11 11:09 AM. Reason for edit: No reason given.

 
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