: crankcase evacuation system
Jan 10th, 00, 02:31 PM
can any racers out there tell me the real benefit of a crankcase evacuation system (hose from valve covers to header collectors)? is it for better piston ring seal and reduce blow-by? can it be used on a street/strip car with flowmaster muff's? or can it only be used on cars without mufflers. I have a fresh 355, 12.25:1 comp. i get oil out of the breather, but only when i run the motor hard (5000-7000 rpm)
355, SUPER T10 4 SPD
Jan 11th, 00, 05:35 AM
Positive Crankcase Ventalation, PVC mostly removes heat from the crankcase. If you "seal" a motor, heat expands the air in your engine causing your gaskets to seap oil, or totally blow it out. heat bad, ventalation good. Arggh,
But I have never seen a system that would pump hot exhaust gases back thru the crankcase. I have seen oxygen sensors on HP exhaust systems for super tuning, and I have seen smog systems (EGR systems) that pump small amounts of exhaust gases back through your intake system to burn off excess gasses on stock systems.
67 ss/rs, MODIFIED http://www.geocities.com/motorcity/speedway/6792
IM - sixtsevnss
[This message has been edited by sixtsevnssrs (edited 01-11-2000).]
Jan 11th, 00, 06:49 AM
a cranckcase evacuation sustem will only operate at higher rpms when the speed of the exhaust thru the system creates enough vacuum to pull the air out of the crankcase. For this reason they are generally not recommended for street cars. A good PCV valve will do the trick.
Jan 11th, 00, 10:08 AM
A PCV system works like this. Usually a one way valve in the valve cover with a hose that hooks up to the intake manifold. The valve opens at a given vacumm like 6 inches of vacumm. There is another hose that pulls clean air from inside the air cleaner and hooks up to the other valve cover and basically it recirculates hot gassy air from inside the crankcase into the carb or manifold. This promotes ring seal because it does put some vacumm into the crankcase. Hope this helps. If anyone has objections or additions please feel free to add them.
The night-time is the right time
Cars:'68 Camaro RS, '73 Porsche 914, '69 Datsun 510
Jan 11th, 00, 04:43 PM
I fully understand what a pcv system is and how it works, what i am talking about is a crankcase evacuation system like i have seen on drag cars. a hose runs from the breather on the valve cover down to the header collector. i think "gheatly" is the only one who knows what i am talking about. I really do not think my engine produces enough vacuum to properly operate a pcv valve(256 duration 523 lift)but i am not sure. I had a pcv valve on it and did not think it was helping. I now only have a breather on each valve cover, i would like some more input if anybody can help
355, SUPER T10 4 SPD
Jan 11th, 00, 06:05 PM
I fully understand what you are trying to do. To help you out information wise, the exhaust evacuation system only works at high rpm's. If you have a full exhaust system, you would have to put the nozzles clear to the end of your pipes. I would recomend using 1/2" plastic, aluminum or copper tubing running from each valve cover to each tail pipe. If you don't go as far back as you can, it will not work as well. Do you plan on buying the kit or do you want to make the nozzles yourself? If you do it yourself, install them at a 45deg. angle pointing in the direction of flow and make sure the ends that are in the exhaust pipes have a 45deg. cut on the ends. Also, use anti-reversion valves on each side or you could have exhaust gas trying to get into the crankcase. How well will this system work? I don't know. I do know that it worked great on my modified and I thought about doing it to the sprint car, but I'm not sure of the benefit to a street car. I too have thought about doing this to my car. I'm sure it can't hurt. Isn't it fun tring to create ways to make more power?
Jan 11th, 00, 06:41 PM
I'll throw in my 2 cents,but it might be ideas you have already thought of.I know exactly the kind of system you describe,I myself have never seen it on the street.As you know pcv systems don't operate at full throttle because of a lack of vacume,this is how they are designed,nobody wants crankcase vapors going into the intake under full throttle.Now,in my expierience,I think guys like us run into these problems with blowby because our cars are at full throttle so much more often then the avarage Joe's,pcv systems are designed for street cars,but we drive ours like race cars.I wonder how many of us would have these blowby problems if we rarely drove at full throttle!The problem with the full race set-up,as you know,is that it won't work at lower engine RPM's.So your out of luck either way on a hot street car.Now what can be done?You have done compression checks just to make sure you don't have worn rings,right?I don't know if your cam is to radical for a pcv system or not?Anyway,this idea might sound stupid,but is it possible to run both?I'm no enginier,but what if you ran your tubes to the exhaust,with a check valve, only letting vapors flow from engine to exhaust at WOT,this would prevent exhaust backpressure from reversing the flow,this should handle the muffler question,by the way.Now you would have one breather still,on opposite valve cover from PCV.At WOT would the exhaust scavange the vapors instead of it going out the one open breather?I dont know, the breather opening would be at atmospheric pressure,I guess it depends on if the scavangeing effect overrides the blowby,if it does, fresh air would actully be drawn in the open breather.At idle the PCV system would work as normal,because of the check valve in the tube to the exhaust.Is this to far out there?I don't know if something like this would work or not,I'm just trying to be creative,am I forgetting something?
67 RS RAGTOP # matching, 4X4 CHEVY TRUCK
Jan 12th, 00, 03:40 AM
These systems keep plugs and valves clean
Jan 12th, 00, 10:02 AM
See if you can find any infomration on PCV valve ratings. If not, buy a couple that were used on factory high performance engines and test the rating with a vacuum pump.
All PCV valves are not rated the same, it depended upon the application. A radical (from a factory standpoint) engine would have a PCV valve with a lower vacuum rating than a milder engine that pulled more vacuum at idle. Maybe try a 69 Z-28 (302 cid) or a 70s LS-6 (450hp 454) valve.
Also, see this month's article in Hot Rod on vacuum pumps. They should be streetable, but the system is complex and takes up a lot of room on the front of the engine. They were pulling 19 inches of vacuum from an 800 hp big block and gained 35 hp just from adding the vacuum system.
Jan 12th, 00, 03:35 PM
Thanks for the input! I think I'll give it a try and see what happens.
355, SUPER T10 4 SPD
Jan 15th, 00, 03:11 AM
if your cam is too radical,try a vacumm pump,test in hot rod ? shown a HP increase in a n/a motor.check it out. http://www.camaros.net/forum/wink.gif
Jan 20th, 00, 12:09 PM
Hey guys, I'm new to the board, but I've been reading for a while. I have personal experience with using a smog pump to pull crankcase vacuum. I put a 406 SBC in a 67 PU and used a smog pump off a 88-92 Camaro to pull the vacuum. The motor is totally sealed, i.e. no PCV or breather tube. It can pull up to 30" Hg vacuum in the crankcase, so much in fact, we had to put a vacuum regulator on it!! The thing runs awesome, and the plugs and oil stay very clean. It has a set of Canfield heads, Crower crank, and a Crower solid roller cam with offset Crower shaft rocker arms. I'm using the same system for my 79 PU, albeit a MUCH milder motor, because I don't like pulling hot, raw crankcase air into my intake (a HUGE vacuum leak if you ask me!!) Stielow has a smog pump on his car, (and he uses the same brackets I am on my 79 PU, off an 88-92 Camaro), and he doesn't have header taps, so I don't know if he is using it for the same reason or not. Just my 2 1/2 cents!!
Jan 21st, 00, 12:56 PM
I run a system like the one you describe on my street 71.
2 AN-12 hoses into the collectors.
One way valves are at the collector ends.
Works well-almost to good.
Have some sort of trap at the valvecover end,or you´ll end up putting a LOT of smoke down the exhaust.Trust me on that.
Then what´s the idea behind it.
Oil control and getting crankcase vaccum-which will deliver power.
Worth the hazzle on the street?
Sure if you´ve reached that level.
You can see my setup at;
482 cubes of fogger injected thunder in a 71 z.
Jan 25th, 00, 09:32 AM
I just bought a used set of headers for my 81 z28, and the guy threw in a set of check valves to put in the collectors. I mostly drive mine on the street, but since I've already got the valves it can't hurt to put them in right?
My question is what kind hose do you run to the valve covers? Will a stainless braided rubber hose melt at the collector? Should I bother installing these since they were basically free, or just sell them off to someone who is going be racing more?
Apr 24th, 00, 09:02 PM
I haven't seen anybody really address the issue properly & I hope to shed some light on the history of PCV systems. 1st of all its not P.V.C. (which is an ackronim for a piece of plastic pipe you plumb your sprinklers with. It's o.k., I deal with hot rodders making this mistake all the time). PCV (positive crankcase ventilation) systems have been around since the 50's, starting with road draft tubes & finally becoming todays type 4 systems. To correct earlier posts. It's true the header check valve system only works when you have enough exhaust flow to produce a negative pressure on the valve therefore sucking the crankcase vapors & pressure out of the engine block. Obviously this is achieved by revving the motor. A type 4 system does the same thing. 1st of all the PCV valve works at idle or whenever there is high vacuum. It doesnt take much (6" or so). The vacuum pulls the crankcase vapors into the manifold (usually from the carb base to one of the valve covers) & burns it. This will not hurt even the highest of horsepower engines. Now the other side of the coin everybody is failing to point out is the breather side. The other side (other valve cover) of your engine should have a 3/4 tube going from a chrysler style closed breather to the bottom of your air cleaner (your should be running an air cleaner!!!). This can be connected to the air cleaner base via a 3/4 aluminum elbow (available at any speed shop for $2-$4). Now this part of the system works like your race/header/check valve system. The air rushing into the air cleaner at wide open throttle produces a negative pressure (or vacuum) on the 3/4 hose going to your chrysler style breather at the valve cover, thus pulling crankcase pressure & vapors into the air filter housing. All cars today use this system & is very effective. I use this system myself on my 8sec. NMCA style outlaw car (a 69 SS/RS Camaro). With a 1000 hp of Nitrous on tap, my valve covers, oil pan, or any other tin doesn't even sweat a drop of oil out of it. So I know the system works. Although others talk of vacuum pumps. This can be good & bad. I had a guy come into the shop with one of those systems. Although they do pull horsepower making vacuum on the engine, his rear main seal was squeeling because of the excessive vacuum that was being pulled on his system. Once we installed a vacuum regulator on his pump, his rear main proceeded to leak like a sieve. Be carefull, a little is good & too much (30" plus)is bad. Hope this helps all.
John Speed & Automotive
10050 Canoga Ave.