i have seen the kits to swap from the road tube to the pcv fitting on my 354 hemi from hot heads. so i want to know what is the difference and why do it ? do you need to ? is it for power brakes?
Ummm...stops oil spewing out under the car? Just going out on a limb here. I'm pretty sure that's why they changed over in the first place. PCV has nothing to do with power brakes.
The PCV stands for Positive Crankcase Ventilation. Meaning, venting the crankcase from blowby. Every engine has it and more of it as it wears. Pressure in the crankcase causes leaks and it also impedes the piston travel. Containing and controlling this was what the OEM determined as a best case scenario. Emissions later had something to do with it if not also the driving ideal.
It performs the same function as a road draft tube system. Is it better than a road draft? Probably but it's not a necessary upgrade. A road draft system will have oil fumes coming out of the breather when it is idling in gear but not in motion. Your engine will stay cleaner both inside and out with one. They did not want those oil vapors to escape into the air like they do on a road draft system. The vacuum pulls them into the intake where they are burned. If you care about the looks of your engine, it's a good idea to add one. Road drafts worked fine for many years when nobody cared if their daily driver got a little greasy. For our show cars it's a nice advantage not to have to wipe down the engine at the show.
PCV valve is the first emission control device. I laughed at my boss when he said they were the beginning of the end back in the early 70's. Larry T
I consider it a performance downgrade; 1st - Oil vapors degrade the fuel when mixed and can cause pinging. 2nd - Also, those oily vapors that are now ****ed in by the engine will deposit and cause major build up on the intake valves. I've seen this in a couple of seasoned engines where all the intake valves had a serious hard tar-like goo build up on the back of the valves around the stems. Needless to say this hinders airflow greatly. 3rd - The PCValve is actually a controlled vacuum leak, which has to be compensated by the carb again. No, a PCV system certainly not a performance upgrade in my book.
So, a billion cars built with PCV valves have all had pinging, build-up, and carb problems? Really...? You know the PCV valve only works at idle and very low throttle, right? It's only a vacuum leak issue when it's stuck open. I've seen more than a couple of seasoned engines with hard tar-like goo all over the outside...from the breathers. No thanks. I'll give you that 2hp any day.
Actually they make this really cool stuff called sea foam you put a can in your tank once a year if your car is a true dailey driver and your goo is eliminated. The PCV works on the principal that you have pressure in your crank case which causes ring flutter and can be eliminated but useing vacuum to draw that pressure out. A road draft tube will accomplish the same thing using air p***ing by the end of the tube to cause a vacuum. Real race cars use a vacuum pump to clean the crank case an old air pump from a '70s Ford can be used for a low bucks vacuum system. Yea the PCV was used for a form of emissions control but it has become the excepted way to control blowby (caused by hot oil in your crank case) on a non dedicated race engine. I run 'em and don't make any bones about it. I probably wouldn't run one with a road draft tube any more but I don't see that one is measureably any better than the other.
One of the big advantages of a PCV system is that it removes the water vapor that is a byproduct of the combustion. When we did tune ups we always checked the PCV valve. If it had any signs of the chocolate milkshake ****, it was a sure sign that the PCV system was not working and the water vapor was condensing inside the engine mixing with the oil to make the chocolate milkshake substance. I don't want that moisture or the milkshake oil residue in my engine. The old road draft did the same thing.
ex, I'm talking about older used engines here. I agree on a fresh/new engine a pcv system is good. But once the rings & cylinders are getting worn, the pvc system can cause more harm than good. Pork, a pcv system does not create a vacuum in a motor because there's a breather-cap in the opposite valvecover. It's just for ventilation, therefore ring-flutter has nothing to do with this system. I do agree a proper vacuumpump 'gives back' horsepower by holding the rings teasyt at the pistons. But the crankcase will need to be closed off to outside air. I've seen gunk build up on intake valves of old engines that no amount of fuelsystem cleaner can handle anymore. Only lye or a powerful sandblaster was able to get it off.
1. You are incorrect about what he said. It most certainly does introduce a vacuum in the crankcase. The breather is a there to filter the air that is being drawn into the crankcase. Ever replace that little filter in the stock air filter housing of GM product? You know, the one that is connected to the tube that is on the opposite valve cover or end of the valve cover from the PCV. It's got that funny "c" clip that hold the hose barbed end of the FILTER to the air filter housing base outside of the carbs air filter element. 2. That gunk you are referring to is oil burned from bad guides....it's on the intake side because that's the one thats open on the intake stroke. The valve is closed with fresh oil on the back side of it that gets baked on during combustion due to the heat. Like fry oil in a pan gets sludgy. The exhaust valves don't get it cause nothing gets pulled on to them during the intake stroke and what little could from overlap gets blown out with the exhaust.
I disagree about pulling a vacuum. They knew back in the early 40s that they need air to p*** through an engine to remove fumes and water vapor to prevent sludge build up. The purpose of these systems is to pull air through the engine. This old diagram shows the path of the air as it p***es through a 48-53 Ford flathead. They found out that even the early PCV systems couldn't keep up with the g***es under heavy loads. So they changed to a "closed system" with that tube from the valve cover to the air cleaner housing. Normally that is where the air enters the crankcase but under heavy loads the vapors build up in the crankcase and back up into the air cleaner through that tube and is ****ed down the carb. and not released to the atmosphere. If you've ever replaced one of those breather elements on an old worn car you will notice how oily and gunky they can get. That is the oil fumes that back up and are pulled into the air cleaner under load. You can not pull a vacuum on any vessel that is open to the atmosphere. ****ing air out of a vessel and replacing it through a filter somewhere else is very different from pulling a vacuum. IMHO
lot of opinions on road draft vs pcv, neither has anything to do with manifold vacuum for power brakes.
PCV is a good thing for engine longevity. Most any carb from the mid-60s on is already set up to compensate for the small amount of air the PCV valve byp***es. Drag racers use a system similar to the road draft tube in the headers to pull fumes out. F1 (Honda) found HP using a vacuum pump on their engines, but again, that is Vacuum in the crankcase. They were not concerned with longevity and fumes. If you wait a while between oil changes, there are enough fuel fumes in the crankcase to actually richen the mixture. I've had many cars where they responded to idle mix adjustment after an oil change.
Not sure how that would work, tinman. Vacuum at the top of the oil and at the crank throws should even out. http://www.enginebuildermag.com/Article/4123/stroker_tips_from_the_pros.aspx Parting Shots We asked our panel if they had any other advice about stroker engines. The following are some of their parting thoughts on the subject. Jon Kaase volunteered some information on crankcase vacuum. He said that in his wet sump motors he likes to see at least 10˝ of crankcase vacuum, and for his dry sump engines he looks for 20˝. Jon left off with, “When the pistons are going up and down, there’s a lot of air trying to swap places at 8,000rpm!” also this one mentions the relief valve (15" of vacuum is pretty high) http://www.dragstuff.com/techarticles/vacuum-pumps.html
oil is under pressure from the pump. crankcase is full of vaccuum. its easier for the oil to flow to the low pressure than to stay in place on the unloaded side of the bearing. If it wasnt a big deal why would the engine builder specify what vaccuum levels to run with each type of oiling system?
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