MG Sports Cars

I've just been ploughing through the article British PVC in the engine section & I've realised that I don't have a PCV valve in my set up. Do I need one ? The PVC port on the Edelbrock Carby is connected to the RH rocker/valve cover with a 3/8" ID pipe via a flame trap. The LH rocker/valve cover has a small inlet filter. I must confess, the posts on the British PVC article were way over my head, that's why I'm asking this question.. Barrie E

Positive Crankcase Ventilation...PCV

Barry,

If you are using that port on the carb then yes you need to have a PCV valve.

Cheers
Fred

I wish it were just that simple, but if you only add a PCV valve to what you have now you may start blowing oil out the seals. This is because the PCV valve closes down to the metered flow under high vacuum, but can do the same thing under pressure from the crankcase, so at some point blowby can cause it to close down.

What you have now works because it is unrestricted flow to a vacuum, but I imagine your idle is higher than you would like. True? This would be from air being pulled into the engine past the seals.

To use your PCV port at the base of the carb, use a PCV valve to one rocker cover and a 5/8" vent line to the bottom of the air cleaner inside the filter element. That is the most common arrangement.

Jim

Barrie, you have the same set up as mine is now. I originally had the pipe from the LH crankcase piped straight into the base of the air filter, but I changed it to use the PCV valve in the Edelbrock earlier this year and it seems to work perfectly and I have had no problems. The The small mushroomm on the RH crankcase is just a small breather hole.

The PCV in the Edelbrock just sucks out unwanted gases from the crankcase which get produced when the engine is running. You have to have some method of removing the gases else they start to blow out from all over the place which at best smells and worst starts to blow oil out because of the pressure build up.

Thanks to everyone who answered my post. I've fitted a PCV valve & now it all seems to work correctly. I can now control the idle speed (it was a bit high). & my cold start problem has gone. The RH valve cover feeds the PCV port on the carb. via a flame trap & a PCV valve. The LH valve cover is connected to a catch can with an air filter which is also connected to the front timing cover. The catch can was installed a while back to aid the previous engine which had a lots of blow back. I decided to use it's air filter rather than use the one on the carb. Any further comments or criticisms will be warmly welcomed. Barrie E

Quote:

You have to have some method of removing the gases else they start to blow out from all over the place which at best smells and worst starts to blow oil out because of the pressure build up.

Boy, can I relate to that!

That should work just fine Barrie. The only thing running the hose to the air cleaner adds is that the engine ingests any blowby, which often contains oil vapor or droplets, some of which may be able to make it past your vent filter and condense nearby. But then again, maybe it won't.

Jim