PCV, advantage or not?

[Bill Harris]

I know of someone who tried the two PCV deal, no breathers, etc on an engine on the dyno and lost serious power. The idea is that the PCV valves would make a poor-man's pan-evac, pulling a vacuum on the crankcase. Problem is that like it has been stated, PCV valve(s) is closed at WOT so the idea falls apart. Pressure builds in the crankcase and you lose power.

I have run with and without a single PCV with a breather on the opposite cover back to back. It made no difference except that I get less oil blowing out the dipstick tube when there are two open breathers than when there is one with the PCV. The pressure has to go somewhere, and no matter how well sealed the motor is, there is going to be blow-by.

[Bub Whitaker]

Originally Posted by Bill Harris

I know of someone who tried the two PCV deal, no breathers, etc on an engine on the dyno and lost serious power. The idea is that the PCV valves would make a poor-man's pan-evac, pulling a vacuum on the crankcase. Problem is that like it has been stated, PCV valve(s) is closed at WOT so the idea falls apart. Pressure builds in the crankcase and you lose power.

I have run with and without a single PCV with a breather on the opposite cover back to back. It made no difference except that I get less oil blowing out the dipstick tube when there are two open breathers than when there is one with the PCV. The pressure has to go somewhere, and no matter how well sealed the motor is, there is going to be blow-by.

Poor-mans pan evac, exactley! If you lost serious power on the dyno, and your blowing oil out the dipstick tube, then you need to work on your ring seal. Serious blowby unloads the top ring and blows oil out the dipstick, causing loss of power. This is one way you guys can check to see if your rings are sealing. A good ring seal will pick up with the "poor mans pan evac"

[Jeff Lee]

Bub's right and you wouldn't believe what I have spent on the dyno with PCV's. The good news is they work. But there's a lot of buts and I'm not going to tell all because my engine builder would kill me!. But I will share that not all PCV's are created equal! That's why there are so many part numbers. I bought from the discount stores and the OEM's. I looked at late model (emphasizing the low drag piston ring models) equipped on small blocks to big blocks to the older stuff. There are more effective ways to find HP, this is just one way to get there.

[junior barns]

what does PCV stand for?

[Bub Whitaker]

Originally Posted by junior barns

what does PCV stand for?

Positive Crankshaft Ventilation, It's a hose from an intake vacume sorce, carb or intake manifold, that draws air thru the engine to remove water and fumes. What they are discussing here is using this vacume source to create a vacume in the pan by sealing off all breathers to aid ring seal, if it's good enough...

[trmnatr]

Originally Posted by Bub Whitaker

Positive Crankshaft Ventilation, It's a hose from an intake vacume sorce, carb or intake manifold, that draws air thru the engine to remove water and fumes. What they are discussing here is using this vacume source to create a vacume in the pan by sealing off all breathers to aid ring seal, if it's good enough...

Bub,

How about running one valve cover with two holes and one with one hole

In the one with one hole you will have a header e-vac, on the cover with 2 holes you will have a header e-vac and a pcv valve + header e-vac through intake valley with baffle so it doesnt suck oil.

Wouldnt this give you good breathing if you couldnt run a vacuum pump as the pcv valve would work great at idle then close WOT BUT @ WOT the header e-vac would be working by pulling vacuum in the heads and lifter valley ??

How much better would a header e-vac work if you had one in the intake too ? With the header e-vac in the valve cover it has to pull from limited area (pushrod holes, drain back holes etc) and as we know oil can get up in the heads and not drain quick so maybe we also cant pull enough vacuum quick enough through drain holes etc. This way with 3 header e-vac's

Any Thoughts ??

[Ian Hill]

...and how about on a stocker. i don't know about NHRA, but in IHRA we can not run header evac, is there anyway of hooking up the carburator metering block tube that creates vacuum throughout the rpm range to the pcv to create vacuum even at WOT.

Ian

[Bub Whitaker]

Originally Posted by trmnatr

Bub,

How about running one valve cover with two holes and one with one hole

In the one with one hole you will have a header e-vac, on the cover with 2 holes you will have a header e-vac and a pcv valve + header e-vac through intake valley with baffle so it doesnt suck oil.

Wouldnt this give you good breathing if you couldnt run a vacuum pump as the pcv valve would work great at idle then close WOT BUT @ WOT the header e-vac would be working by pulling vacuum in the heads and lifter valley ??

How much better would a header e-vac work if you had one in the intake too ? With the header e-vac in the valve cover it has to pull from limited area (pushrod holes, drain back holes etc) and as we know oil can get up in the heads and not drain quick so maybe we also cant pull enough vacuum quick enough through drain holes etc. This way with 3 header e-vac's

Any Thoughts ??

What you want here is what I use on Superstock engines, Delco FB101 breathers that have 5/8 hose nipples and I bore the top 3/4 for a brake booster valve that seals when not being sucked on with hoses T'd to the PCV port on the carb. Don't do this to an intake runner as it will screw up that cylinder. EGR valves on tubes in the collectors at 45 degree cut to draw when exh velocity gets up to take over when intake vacume diminishes. the EGR valves on the collectors also seal the same way as the brake booster valves so there is constant vacume in the crankcase...

[427_ED]

I've seen double PCV setups collapse stamped aluminum valve covers. Definetly a poor mans vaccum pump.

[Buicksstage1]

Originally Posted by junior barns

what does PCV stand for?

Positive Crankcase Ventilation.......Chris