HEMI Tech: Vacuum, Breathing and crank case pressure

I was thinking about this topic last night and realized that we don't have much info here on Hemi breathing tech. So let's get it going! Let's talk about...

1) Crank case breathing/vacuum pressure
- Should your valley cover use the stock implementations for filling and breathing
- Should a standard "blank" valley cover be used instead and provisions removed or relocated to elsewhere
- Components for the alterations

2) Head/valve train breathing
- When should breathers be added to valve covers and why
- Pros and cons of doing so
- Components for the conversion

3) Engine Vacuum
- What should be expected for vacuum and from where
- What provisions can be made if any to change vacuum
- Standard or helpful modifications for vacuum
- components for any modifications

4) Any other topics of vacuum or breathing for Hemi's not already mentioned

As always, this if for all early Hemi's. Not just Chrysler, Dodge, Desoto...

Have at it! I'll add this to the HEMI Tech Index in a little while.

 

1) Crank case breathing/vacuum pressure
- Should your valley cover use the stock implementations for filling and breathing
- Should a standard "blank" valley cover be used instead and provisions removed or relocated to elsewhere
- Components for the alterations

In my '56 Desoto 330 I stuck a grommet in the valley cover draft tube hole and added a PCV and a hose going to the back of the carb. It's totally invisible unless I take off the massive oil bath air cleaner. I get around 19 inches of vacuum at the carb base and the brake booster connection to the intake at idle. The only problem I have is that the freshly rebuilt engine is blowing some blue smoke at start up. (every time). This could be a bad valve job or because of a lack of oil seals over the guides, but it could also be due to the oil baffle directly below the PCV. I think the oil might me pooling there when I shut off the motor and then it gets sucked into intake... Any other ideas?

 

There should be seals on the intake valves. How would oil get in position to get sucked up by the PCV valve?

 

There's a baffle plate under the valley cover that the Draft tube used to bolt to. It's really close to the PCV. I'm gonna pull the intake and valve covers off and take a look as soon as I put my Buick back together.

 

I'd think that would prevent oil from splashing up to the PCV. Air sucking in through the oil cap & out the PCV where the draft tube was seems to work, & you don't mess up the valve covers!

 

Theres a big hole in the center of this baffle pan with a foward facing scoop over it. I think the oil travels around the scoop and pools at the rear of the engine. The original draft tube would not have started sucking until the car was moving at speed and the oil would be heated and moved around by then. The PCV starts sucking at idle.

 

Motors can really make impressive crankcase pressure. Sure, while one piston is travelling downward, another piston (at the same moment) displaces the air on the way back up. But, the "accumulator" for all of the positive and negative pressure is the oil pan and it never really runs at atmospheric pressure unless the motor is stopped. (And we aren't even including blowby in any of this) All of this inhaling and exhaling is accomodated on a production motor by a vented oil cap (older motors) or PCV systems (a little bit newer motors). In street use with new seals, this works reasonably well; I find that if I add breathers, my motors stay leak free and the higher you spin it, the bigger the breathers need to be. So, it really won't hurt anything to run a breather/PCV off of both valve covers. Also, gasoline seems to have alot of moisture in it these days, probably from the hydroscopic tendencies of alcohol additives, and I've heard about a few motors found with rusty internals making the breather a good escape route for a steam that is formed
as well.

 

Scooter,
I used a finned aluminum valley cover (hot heads) but added an oil fill tube like the original had and drilled the oil fill plug in the back and added a 90 degree 3/8 hose barb then ran a hose to a horizontal pcv valve and then to the carb.

As for engine vacuum, your cam selection will have a lot to do about how much vacuum you will have at idle. I have 13" of vacuum at idle. If your looking at power brakes the recommended vaccum at idle is 18". You can run a vacuum reservoir to help with the booster or a vacuum pump. I run the reservoir with mine and have power brakes it works fine. Just use the vacuum check valve with either option and it will be OK.

 

Excellent! This is good info! Shoot a pic. if you get a chance. Sounds good.

 

So I see super high HP hemis running two breathers on each valve cover. Seen some just run one. Then there's stock with no breather on the covers. What's really needed and what should be considered?

 

I used two speedway 560-4039 engine breathers on the front sides of my rear sump pan cause i didnt want to cut the dimpled valve covers brazed a L-79 mid year vette closed system oil fill tube in the valley pan ,the tube has a threaded bung in it for a threaded pcv ,hook the hose from the pcv to the carb manifold vac.thats what i just finished doing on my build anyways.

 

Scooter,
I attached a pic as you can see the pcv is clipped to my fuel line and gets it's vacuum source from the rear carb. I welded a 1 1/4 aluminum tube to the valley cove up front and topped it off with a K&N breather.

 

Excellent! Thanks for the effort and thanks for sharing!

 

Here's some stuff that Hot Hemi Heads sells...

http://www.hothemiheads.com/valve_covers/breathers_offy_jr.html
http://www.hothemiheads.com/valve_covers/breathers_offy.html
http://www.hothemiheads.com/valve_covers/breathers_donovan.html
http://www.hothemiheads.com/valve_covers/valve_cover_conversion.html


Breather for valley
http://www.hothemiheads.com/valley_pans_related/breathers_stock_valley.html
http://www.hothemiheads.com/valley_pans_related/pcv_stock_valley.html

Can't forget about Mooneyes:

http://www.mooneyesusa.com/catalog/index.php?cPath=188_191&osCsid=747a3f988cac64bbcd388bdf4db881ef

I would personally really like to hear more about when to use them on Hemi rocker/valve train covers.

 

Cant help ya then.

 

Scooter,
You need to vent the engine and how you do it is your preferrence. The orginal worked and the breathers that moon and hothead sell work also it is just a matter of the look you want. Hotheads has the moon type breathers with one of them that has a pcv valve in it so keeps the performance look but gets the benefit of a pcv valve.

 

I was thinking I would run a right angle breather on the front of each valve cover. Should that be enough to get the job done? Do I need to run those AND a PCV adapter in the valley cover?

 

I'd run the breathers & the PCV in the valley cover. Get some suction working for you!

 

The aluminum breathers were designed for race applications where you're not running a lot of miles between teardowns and oil changes. If I was running on the street and with normal oil change intervals, I'd rather pull filtered air through my motor if I was running a PCV valve.

 

Yeah, I'll just be running around the streets and oil changes will be at regular intervals. So you're sayng just run the PCV with maybe a filter on the PCV then? Sorry if that's a stupid question...

 

Scooter,
When you use a pcv valve you need a filter as far from the valve as possible to draw in fresh air as the pcv draws out the oil fumes. You want to draw from one side of the motor to the other, that is why you see a breather on one valve cover and a pcv on the other. A breather on the front of the valley cover and a pcv on the back will work also. One other thing make sure the pcv valve can flow the air for you size engine and is it made to operate horizontal or verticle depending where you are mounting it.

 

Scooter I've been thinking about the very same problem on my Hemi. I've got the Hotheads alum valley cover with pvc. I'm running stock steel industrial covers and I'm thinking about the small moon breathers on the front of each cover. Thats what I ran on my 55 gasser with the 406 (.030 over 400) small block and it worked well. With just breathers there was always oil around them due to the high RPM blasts down the strip and I don't think a PCV would keep up by itself due to the low vac condition under full throtle. Besides nothing looks more "retro" than those moon breathers and the PCV is outa sight in the valley pan.

 

This is the setup I had invisioned also. A breather at front on both valve covers and a PCV at rear using HHH little kit they offer. Anyone see a problem with this setup?

 

I replaced the steel wool (or what ever it was) in the oil fill cap with a cut down lawn mower green foam filter. Don't know if that would stay in a breather.

 

I am looking for a good solution. I don't want to cut into my indy covers for breathers. I am running a Cragar 4x2, with limited access up front for a breather/filler in the valley cover. I don't care for the shiney HHH or Moon breathers. What is the best location for a vacuum sorce on a multi-2 induction? Thinking about taking stock valley cover, adding PCV to road draft tube hole, and making my own breather for the front that will sit just under the front of the intake. This leaves me with still needing a place for oil fill. Ideas? Pictures? Here is a picture of the orignal crankcase system that came on this airport tug indy.

http://www.directimagehost.com/is.php?i=146550&img=100_0716.JPG

The big glass jar was the oil seperator...sorry, not a great picture.

Kurt

 

With the original vally cover you could do some cutting & welding on the OEM oil fill tube to get it in the right place. Then use the OEM oil fill cap/breather. I have a valley cover from a 331 that had the 2X1 set up on it, the fill tube is "swan necked" to go around the intake. You should be able to do the same thing to get around the Cragar.

 

With using a stock valley cover, you also get the benefits of the baffle built into it...for whatever that is worth. I am using 3 inch risers between each carb and manifild. I was thinking that maybe I would plumb a fitting into the rear carb riser which is a secondary carb for my vacuum sorce. Does HHH have a suggestion for the size of breather that is needed with their PCV conversion?

 

Hot Heads valley cover with rear PCV plugged in.
Aluminum intake with a medium size Holley bolted to the top
all buttoned up with breathers.

I dont do allot of miles. Usually it is a friday night thing which involves about 15 miles and 6-7 street races.

 

I've had two similar PCV setups on my hemi for just over 30 years now.

The first utilized the original draft tube. I took the canister/breather off the end then plugged the tube with a rubber (expandable) core plug. I then put a 90 degree elbow where the pipe plug was screwed in just above the canister. I ran 5/16 steel line up to the back of the manifold and used a slant six PCV valve plugged into the back of my R-3310.

I had a pair of Offenhauser 4" breathers on the front of my chromed "Imperial" valve covers to let the air in. I stuffed a rag down the filler tube to keep the timing chain from slinging oil up the tube AND to prevent air from being drawn into the valley as opposed ti into the valve covers.

Later on, I swapped on a set of Donovan valve covers with twin breathers.

I ran that setup for years and when I switched to the Weiand 4 carb setup I had to relocate the vacuum source to the intake manifold runner.

I put on a set of Dennis O'Brien's valve covers and his valley cover in '95 but notbefore I installed a set of Offy 4" breathers on the front (Birthday present from Mr. O'Brien, thank you)

I sectioned the factory valley cover baffle to clear the flatter O'Brien aluminum cover and installed an elbow in the back of his valley cover and ran a hods off to the PCV valve.

I've put nearly a quarter of a million miles on the car and I don't get any moisture build-up in the heads and, until this year, I never had an oil consumption problem.

This year's eight gallons of oil was due to my machinist handing off the head work to someone else.

You can't do up a set of hemi valve guides like a Chevy. You'll go through oil like it's going out of style every time you go down a long hill, especially with an aluminum flywheel. Sloppy valve guides (over-reamed) and manual transmissions spell disaster.

 

Aren't PCV valves and breathers mutually exclusive? I always thought if you ran a PCV there should be no breathers, otherwise you're setting up a path for constant airflow, and the result is a leaner mixture since you're now pulling air through the crankcase and into the manifold. If you look at any modern engine designed with a PCV, there is no breather, the oil filler tube is sealed, and there is no way for air to get into the engine except from blow-by, or leaks. The point is to run a vacuum in the crankcase, isn't it?