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Old 28th December 2008, 09:59 PM   #1 (permalink)
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Breather Cap: One or Two?

<FONT face=border=><B style="mso-bidi-font-weight: normal"><U><FONT size=3>Breather Caps<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com<o:p></o:p>
We have one breather cap on our 302. It is modest engine rated around 375 HP.
<o:p></o:p>
Question: So we need to have two breathers, one on each valve cover, or is one enough?
<o:p></o:p>
I do not plan to use a PCV valve or puke tank.
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Old 28th December 2008, 10:01 PM   #2 (permalink)
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Re: Breather Cap: One or Two?

One or two is OK.
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Old 28th December 2008, 11:07 PM   #3 (permalink)
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Re: Breather Cap: One or Two?

Two & bigger is better, plus take them from the valley side of the covers in between pairs of pushrods if possible. Think about it--- 5 liters/305 cu in @ 5000rpm with 5% leakage = 625 liters of blowby/venting reqd per minute---- thats three 200L / 55 us gal drums per minute. Yeh I know you wont run it that hard etc, but if you dont build it right in the first place you will wonder why it comes back into the pits covered in crap after your first track day.
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Old 29th December 2008, 12:05 AM   #4 (permalink)
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Re: Breather Cap: One or Two?

I agree with Jac, two is the go.
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Old 29th December 2008, 03:47 AM   #5 (permalink)
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Re: Breather Cap: One or Two?

Ditto - one each side and nice big hoses, none of this little -6 stuff..
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Old 29th December 2008, 04:31 AM   #6 (permalink)
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Re: Breather Cap: One or Two?

Agreed, minimum 2 x -10 to a free breathing catch ( "puke") tank.
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Old 29th December 2008, 06:52 AM   #7 (permalink)
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Re: Breather Cap: One or Two?

A question along similar lines, if I may :

For rego, I had to have the (single) breather connected to a carbon cannister (from a V8 Commodore), and have a purge valve to clean out the cannister occasionally (by connecting the purge outlet on the cannister to inlet manifold vacuum).

Unfortunately, I needed the ECU's Aux O/P (used for the purge valve) to operate the rad fan (was on manual for rego). To avoid problems with the cannister filling up (no purging), I connected the breather to the manifold vacuum via 1/8" orifice so that the gases got burnt & the manifold vacuum was maintained.

So the question is - should I :

- leave it as-is, or
- go back to the carbon cannister (with a manual purge switch), or
- change to a free-breathing catch tank

Any opinions would be greatly appreciated - thanks guys.

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Old 29th December 2008, 08:27 AM   #8 (permalink)
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Re: Breather Cap: One or Two?

Thanks everyone. Jac Mac: Good to the point persuasive observations. Two it is.

Sounds like a puke tank may be the better alternative. How many use puke tanks on their '40s?? I see them on Cobras frequently, but not much on GTs.
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Old 29th December 2008, 08:50 AM   #9 (permalink)
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Re: Breather Cap: One or Two?

Just out of curiousity, why are you not using a PCV valve? I've tried both methods and went back to using the PCV valve on one side because of oiling at the breathers. I may have had more blowby than considered acceptable, but never saw it in the exahaust with the valve.
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Old 29th December 2008, 09:01 AM   #10 (permalink)
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Re: Breather Cap: One or Two?

I use a tank. I keeps everything clean and it is another cool piece of aluminum under the bonnet!

The reason there is no PCV is the lack of a good vacuum port on most weber intakes or carbs. (just a guess)
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Old 29th December 2008, 10:44 AM   #11 (permalink)
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Re: Breather Cap: One or Two?

That intake looks like it has a plenum chamber and should have plenty of vacuum to operate a PVC system which will create negative pressure in the crankcase and remove moisture and keep everything cleaner inside and out.
IMHO,
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Old 29th December 2008, 02:47 PM   #12 (permalink)
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Re: Breather Cap: One or Two?

Chuck,
I am a big fan of the PCV system. I personally would not run an engine without one. The PCV evacuates all the nasty combustion byproducts and moisture from the crankcase replacing it with filtered fresh air. Kind of an "out with the bad, in with the good" on a continuous basis.
I grew up in northern Minnesota where the old road draft tubes would collect moisture and freeze up causing oil to be blown all over the engine compartment, valve covers and oil pans would rust from the inside........a real mess. When the PCV systems came out in the mid-60's it fixed all those problems and more.
Just my two cents, but I know I want to protect the money I have invested in my engine with a PCV system by getting the moisture and corrosive vapors out of the engine.
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Old 29th December 2008, 03:54 PM   #13 (permalink)
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Re: Breather Cap: One or Two?

If your running Webers or FI on an IR manifold th PCV wont function correctly, However on Carb systems or common plenum FI it will. What lets PCV down is the absolute junk baffle systems on most aftermart Rocker Covers, these are the cause of many oil consumption/smoke problems on cars simply because the PCV is too close to splashed oil & pulls it into the intake under high manifold vac conditions. Nothing wrong with the PCV, just the manner in which its fitted--- take your cover lines to a puke tank & fit both the breather & PCV to the puke tank ( suitably baffled of course.).
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Old 29th December 2008, 04:21 PM   #14 (permalink)
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Re: Breather Cap: One or Two?

Quote:
Originally Posted by CESLAW View Post
Thanks everyone. Jac Mac: Good to the point persuasive observations. Two it is.

Sounds like a puke tank may be the better alternative. How many use puke tanks on their '40s?? I see them on Cobras frequently, but not much on GTs.
In the UK, anyone competing with breathers has catch/puke tanks as it's an MSA requirement that any breathers fitted do not dump any fluids off vehicle. Also - if you were to drop fluids on a trackday from an exposed breather, you'd at best be unpopular and quite possibly picking up a bill.. (read smallprint carefully)

I'd have figured something similar would be in place in the US??
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Old 29th December 2008, 04:35 PM   #15 (permalink)
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Re: Breather Cap: One or Two?

Good points. Now perhaps a little info on puke tanks for the uninformed:

1. Should both valve covers be hosed to a tank or is one sufficient? I suspect both, based on Jac Macs prior observation

2. Are there any issues regarding the level of the puke tank? In otherwords should it be about even with the valve covers or lower?

3. Dean: what tank did you use and where did you find room for it?
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Old 31st December 2008, 08:15 PM   #16 (permalink)
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Re: Breather Cap: One or Two?

Here's how I did mine. The fitings are AN8. I did this because I knew I would need to vent to a tank if I ran it on track.

It does seam to work. I find it interesting that Jac thinks two AN10's are the way to go. I have noted the AN10 point and as it is said by Jac it shall be done on the SC-C 350 chevy now in progress.
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Old 1st January 2009, 10:41 PM   #17 (permalink)
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Re: Breather Cap: One or Two?

The 351 Windsors have a big vent opening. Mine took a 12 hose. Only running one line to the catch can. I originally wanted to mount the can up front of the engine on the left side, but there was no room for it with the main fuse box and the roll cage. Also the line was so short that I was afraid the rocking of the engine would put a strain on the line, so I went to the right side and ran it to the back. The engines will rock toward the right side so there won't be a strain. Still thinking about adding a stabilizer bar off the right head to the frame. Will decide after the fire up of the engine.

Bill
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Old 2nd January 2009, 10:36 PM   #18 (permalink)
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Re: Breather Cap: One or Two?

Thanks for the info. Looks like plumbing both valve covers to a collection tank is the way to go. I note that both Moroso and Canton make nice aluminum tanks with a filtered vent on top and a drain spigot on the bottom.
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Old 6th January 2009, 02:36 AM   #19 (permalink)
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Re: Breather Cap: One or Two?

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Old 6th January 2009, 08:24 AM   #20 (permalink)
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Re: Breather Cap: One or Two?

Rick: that is a gorgeous looking set up. Very original looking.
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