69 Camaro....383 Stroker, Dyno'd at 503 HP. 750 Holley QF Drag carb.

My question is that due to clearance issues of the hood I cannot run a 1" spacer, which means I cannot run my Power brake booster line to the back of the manifold and the carb is right on top. Seeing that the rear 3/8 vacumn on the Holley is a full vacumn line...could I simply run a breather on the passenger side and use the vacumn line for the Power brakes. Or should I buy the attachment for the Air Cleaner to run the PCV up through the Air Cleaner?

Most of what I read now since making this post is that you have to have a PCV....can you run some sort of a T from the carb Vacumn and run the brakes and the PCV from the same point?

Let me know what you are doing out there under this issue.

Thanks in advance.

Does the manifold have a plug that goes to manifold vacuum that you can put a fitting into?

It's a 1/4" under the Carb and can't use it

Your saying you either can not access the existing Manifold Vacuum location or do not have one. You can drill, tap and install a nipple. I run my Brake Booster, PCV plus a Distributer Vacuum Pod (if using one) from a tapped source on #7 Intake Runner close to the plenum. I use a 4 nipple T in line with the Booster Hose - Works great.

Always run a PCV System.

Looks like a healthy 383- what kind of vacuum at idle? You may want to try a AC746 PCV Valve.

http://www.camaros.net/forums/showthread.php?t=160446

Tom

I'm not famiar with that carb but does the base (throttle plate) interchange with the base of a 4150 carb that has a 3/8 vacuum port. Maybe you could do a swap.

You can run PCV to the header collector tubes like they do on dragsters that don't run a vacuum pump, or if you have the $$$ a vacuum pump would be nice.

PCV should be ran, and you can tap the intake for it in various locations, you have a few options.

No, it's not needed.

But I bet you WON'T get by w/ running a road draft tube like was used before '63 or '64 IF your block is pre-'68 and even still has a place for the oil separator can under the intake and the road draft tube mounting casting boss back next to the dizzy hole!!!

It's now a fed legal SMOG requirement since '64!!!

pdq67

My question is that due to clearance issues of the hood I cannot run a 1" spacer, which means I cannot run my Power brake booster line to the back of the manifold and the carb is right on top. Seeing that the rear 3/8 vacumn on the Holley is a full vacumn line...could I simply run a breather on the passenger side and use the vacumn line for the Power brakes. Or should I buy the attachment for the Air Cleaner to run the PCV up through the Air Cleaner?



Yes, you can run both from the same vacuum port on the back of the carb. Does yours not have another 3/8" port on the front passenger side beside the small one under the edge? Take a look and see...if it's there it's under the edge and pointing toward the battery. If so, that's what Holley calls the PCV port.

The PCV valve itself does not run directly to the air cleaner. The air cleaner attachment is for the fresh air intake for the PCV system. In order to pull vapors out of the engine, there has to be a source of air on the other side or it's like sucking on a straw with one finger over the end. Typically, the PCV is on the driver's side and the fresh air intake is on the passenger side. So, fresh filtered air in on one side, dirty vapors out on the other side. You can also use a breather filter but I like mine running to the actual air filter.

You can put the T in your booster line as it passes by the valve cover and then run a straight hose right to the driver's side PCV.

I run a 736 PCV valve as I pull about 10-12" of vacuum at idle. It is spec'ed for most of the old high hp muscle car motors that had very low vacuum like the 'Vette 375hp 327 and '69 302.

No, you don't 'have to have' crankcase ventilation; if you don't care about engine longevity, blowby control, harmful blowby gases, fouled oil, pressure in the crankcase, and corrosion of components in crankcase.

runnin another breather in place of my PCV valve...as long as the engine can vent...its all good!

Wrong. A pair of breathers won't cut it. You need fresh air circulation through the crankcase to remove the harmful blowby vapors. One of the byproducts of combustion (and blowby) is water which fouls the oil causing sludge, which will reduce your engine's life. Your oil temp needs to be at least 212 degrees to cook out the liquid water then this vapor (steam) is removed by the PCV system. Obviously this water comes from the humidity in the atmosphere. If you own an air compressor, you understand how water is introduced to a crankcase.

Water and acids (another blowby byproduct) are very corrosive to internal engine components, and again, need to be removed/replaced by fresh air.

A pair of breathers will only allow the crankcase to 'belch' since blowby creates pressure in the crankcase. There's no circulation of fresh air through the crankcase. With a pair of breathers the crankcase is a constant repository for the harmful blowby vapors.

All engines have some blowby.

An added benfit to a functioning PCV system is, instead a small bit of pressure in the crankcase, you create a bit of vacuum which helps limit oil leaks.

Will one of these help?

http://www.summitracing.com/search/Brand/Edelbrock/Product-Line/Edelbrock-Low-Profile-Vacuum-Fitting-Reducers/?autoview=SKU

While I'm also "for" pvc systems, many do not run one, and while the reason to run one are good, I've never seen an engine rust out from the inside because it was run without a pcv.

a quality breather in each valve cover may work fine.

Something more involved, a hose from each valve cover to a drainable oil separater tank with one or 2 breathers on it is another option.

A quality breather in each valve cover may work fine.

I disagree. Combustion and blowby is nasty business. If you're not worried about water and acids' ability to rust components (as most of us are) then how about your oil's ability to lubricate? How about sludge? There are a half dozen reasons "a pair of breathers" isn't the way to go vs. a PCV system. Again, the key to a PCV system is the 'circulation' of fresh air that displaces the harmful blowby vapors.

But don't take my word for it. Here's some good reading:

http://www.yourautonetwork.com/pcv_valve.html

http://books.google.com/books?id=U4TBoJB2zgsC&pg=PA792&lpg=PA792&dq=performance+blowby+PCV+internal+combustion&source=bl&ots=MUMWXsLIsl&sig=6ap_JSg2W1XkFxHutEMsCMG0buM&hl=en&ei=pWflScWoKIWsnAfwntmqCQ&sa=X&oi=book_result&ct=result&resnum=3#v=onepage&q=performance%20blowby%20PCV%20internal%20combusti on&f=false

http://www.filtercouncil.org/techdata/tsbs/94-2R1.pdf

http://www.106rallye.co.uk/members/dynofiend/breathersystems.pdf

http://www.underhoodservice.com/Article/40258/pcv_service_helping_an_engine_catch_its_breath.asp x

http://www.secondchancegarage.com/public/239.cfm

http://www.aa1car.com/library/pcv.htm

http://autonettv.com/category/auto-tips/pcv-valve

I run one. As you said, there are reasons for that, good ones.

But... pcv's didn't come into play until the mid to late 60's. from 1900 until 1965, npt one single car or truck rid the crankcase of blowby by sucking it into the intake track.

These vehicles ran just fine, for zillions of miles.

The manufacturers did not use positive crankcase ventilation until the federal government required them to do so, and the feds were not thinking about engine longevity when they passed the clean air act.

The engine needs to be ventilated.
There are many ways to do this.
different ways suit different applications.

For example, you do not want to hook a pvc hose above a blower, and you sure as heck don't want to hook one up under it!

Thanks for all the help guys....Yeah my engine builder said if I was only racing, don't worry about the PCV...however if you are on the street, the engine can build an incredible pressure and actually blow oil out of seals.

I had 2 problems...1 the bolt wouldn't come out...2. the carb is way too close to it. less than 1/4". I had said forget it and bought the 1" spacer with a 3/8 vacumn and a 1" lower air cleaner...problem solved.

Prior the closed system which incorporated the PCV valve, cars used a "road draft tube". Same principle; circulate fresh air through the crankase to displace the caustic blowby vapors. This 'open system' used prior 1968, pulled fresh air from the front of the engine (usually through the oil fill cap that also served as a breather) through the crankcase then the blowby exited through the draft tube. A small bit of suction was provided as the car moved down the road.

Here's a schematic of the 'road draft tube' set-up:

http://www.tpub.com/content/armyordnance/OD1001/OD10010120.htm

Obviously, the closed system with the valve is much improved engineering.

But with breathers only, there's no way for fresh air to circulate through the crankcase. A pair of breathers simply allow the crankcase to belch blowby. These emitted vapors (which mess up the engine bay) are replaced in the crankcase by more blowby vapors.

I've presented 6-8 links that explain and detail why the PCV system is needed. I could provide 200 more. I challenge anyone to find one credible recommendation for a pair of breathers as the preferred method for ventilating a crankcase.

BTW, engines rarely ran past 100,000 miles in the 50's and 60's. One of the big reasons engines last two or three times longer today, is because the crankcases run much cleaner.

Your engine builder isn't exactly right... Even with breathers in a race engine going down the track they can build up enough vacuum to break parts, my cousins 565reher-morrison did exactly that, I know it was caused from not having proper crank case evacuation and threw a rod or grenaded a piston half way down the track destroying the block and cylinder head, proper PCV or vacuum pump in his case can save you a ton of money in the end.

I often see people puke their dip sticks out at the starting line after a burn out, no pcv (or vac pump), wonder if the build up shoots them out?

A pair of breathers won't cut it.

Very True. I tried it. 2 Big K&N's on each Valve Cover which did nothing but constantly PUKE Stand Oil Vapour over the top of my Engine, caused the Front and Rear Seals to Drip and I believe responsible for fouling Plugs while in stop and go traffic.

Put a PCV in the Dvrs Valve Cover with a Baffle below it. If your running a Girdle close to the top of the cover you will not require the Baffle as the Girdle works like an Oil Separator. Put a Dodge Style Breather on the Psgr Valve Cover and hose it to the Base Plate of your Air Breather (a Plumbers 45 or 90 degree 1/2" Copper elbow works great here). The Air Flown into the Carb will syphon to relieve Crank Case Pressure while the throttle is moving (no engine vacuum) and the PCV is in operative . This hose also supplies the engine with Fresh Air while the PCV is working under vacuum when the throttle is stationary while cruising.

Just "T" the PCV into the Brake Booster Hose if you have no other Vacuum source.

Though the original post concerns street applications, racers understand the value of of vacuum in the crankcase vs. pressure caused by blowby. It's a horsepower thing.

More here:

http://www.jbp-pontiac.com/images/EvacPumpKit/evac.pdf

Again, you'd be very hard pressed to find a credible recommendation for a pair of breathers as the preffered method of crankcase ventilation. The word "Bubba" comes to mind when I see a car or two at shows (usually Fords) with the 'pair of breathers' method.

That article kinda reminds me of the old O2 Pollution Pumps and makes me wonder if one could used as an Evac Pump - LOL

Ok so now I'll ask another question...my motor is a Dyno'd 383, 503. HP at 6300RPM. Flat Tappet cam.

Is there a special PCV valve or does a standard SBC do the trick just fine?

Ok so now I'll ask another question...my motor is a Dyno'd 383, 503. HP at 6300RPM. Flat Tappet cam.

Is there a special PCV valve or does a standard SBC do the trick just fine?

PCV valve ratings usually coincide with the amount of vacuum an engine can pull at idle and several brands use an almost identical numbering system. If you get the wrong one, it will either not open at all or stay open all the time like a straight vacuum leak.

Mine only pulls about 10" at idle so I used a $2 Purolator 736 which is for a '69 302, a very low vacuum motor. The Corvette 327ci 375hp uses the same one. From what I've seen, the higher the vacuum the motor can pull the higher the PCV valve part number. I would imagine that given your hp numbers your cam is pretty large and a 736 would work.

PCV valve ratings usually coincide with the amount of vacuum an engine can pull at idle and several brands use an almost identical numbering system. If you get the wrong one, it will either not open at all or stay open all the time like a straight vacuum leak.

Mine only pulls about 10" at idle so I used a $2 Purolator 736 which is for a '69 302, a very low vacuum motor. The Corvette 327ci 375hp uses the same one. From what I've seen, the higher the vacuum the motor can pull the higher the PCV valve part number. I would imagine that given your hp numbers your cam is pretty large and a 736 would work. Steiner very good point, but how can we check our PCV when its on the motor. Should it be sucking at your finger when idling and should not suck when WOT. Thanks :yes:.

Steiner very good point, but how can we check our PCV when its on the motor. Should it be sucking at your finger when idling and should not suck when WOT. Thanks :yes:.


One of the easiest ways to check it is while the engine is warm, pinch off the hose. Idle should drop by 50-100 RPM when the "metered vacuum leak" is plugged.

One of the easiest ways to check it is while the engine is warm, pinch off the hose. Idle should drop by 50-100 RPM when the "metered vacuum leak" is plugged. Cool thanks :thumbsup:...