case and head vents, do I need to run a breather box? Options

[rhcb914]

Well if the oil is staying in the heads for a longer period of time and the heads are the hottest part of the engine it only makes sense that the oil is going to run hotter.

Now with unvented heads will the heads run hotter by not transfering as much heat to the oil?

[ME733]

..........USE THE DAMN HEAD VENTS.....Because, the lowest part of the head,s Is above the crankcase, oil level,...and ANY heat FROM, BY,or TRANSFERED to the head is going to be "captured". THE only way to dissapate this heat is from...air blowing accross the head from the cooling system, BLOWER....But another thing is going on. All the moisture(condension)( from oil above 212-degrees)...and airomatic gasses...fuel and blow-by contaminion is "trapped" in the head......Have you ever disassembled an engine with rusty film on the rockerarm covers?. rocker arms? ....IT,s due to low oil temperature, trapped condensation,and residuals.(airomatics-gas fumes) being trapped in the HEAD. The pushrod tubes equalize pressure in the head and crankcase. Therefore VENTING the heads is equivalant to venting the crankcase-only better as it,s also venting otherwise trapped-HEAT-moisture,and contaminants..............Murray.

[HAM Inc]

Well if the oil is staying in the heads for a longer period of time and the heads are the hottest part of the engine it only makes sense that the oil is going to run hotter.

Bingo! Now put some thought into why the oil spends more time in the rockerchambers on vented heads.

Now with unvented heads will the heads run hotter by not transfering as much heat to the oil?

We have seen no evidence of this. The springs, the rocker arms and the interface between adjuster and valve tip are the only head components that rely on oil cooling. The heads generate way to much heat to rely on oil for cooling. Getting the oil into and out of the rocker chambers quickly benefits this cause.
The more full throttle time your engine sees the more critical this becomes.

[Jake Raby]

Now that the head guy spoke up and said it didn't do jack for the engine , I want to hear more of this new info please, Len ???

It does do something; it slows the return of oil to the crankcase and therefore the pickup and it causes the oil to run a bit hotter.
I'm going to let you guys stew on this one for a while and see if you can figure it out. I'll give you a hint; it has to do with pressure differentials between the crankcase and rocker chambers.

.and it is reality, at least in our application where it has been observed very closely.

When Len made some changes to the engine I was skeptical, but the rule is anytime anyone has an idea that parts of our team we go with it, otherwise we'll never learn and will never benefit from our racing..

It worked and it proved me wrong..

Murray, this isn't a 356, if you want to use that mindset I suggest that you work with those engines. Having an open mind adaptable to the ever changing world of engine dynamics is necessary. Close the mind and you may as well just give up, its the same difference.

If my mind hadn't been open with the experimental approach that Len came up with last season we never would have learned what we have about the dynamics of crankcase pressure.

[Cevan]

I can see why with a vented head, oil in that area would drain back to the crankcase more slowly.

What is the downside to plugging the head vents? The only thing I can think of is there is no controlled excape for excess pressure within the cylinderhead rocker area. But, is this not an issue for a well functioning motor that doesn't see alot of sustained time at high revs?


Now, my L-Jet motor did not have vented heads and didn't leak oil.

[Jake Raby]

With less head breathing from the valve covers the demand for better crankcase ventilation is elevated...

[HAM Inc]

The pressure in the crankcase at large is generated in the bottom end, not the heads. The issue with the T4 is that the drain back passages that are just above the lifters in the crankcase are relatively small. If blowby generated crankcase pressure is moving out toward the heads it does so through these small drain passages, making it more difficult for the oil to drain back into the case.

As a side note we experimented with some jaw dropping big vents (over 1.5")on the chimney to see if this would prevent the pressure differential; it did not. Oil still exited the rocker vents.

By eliminating the rocker vents you ensure that the pressure in the bottom end is the same (or there abouts) as the pressure in the rocker chambers, which allows the oil to return to the bottom end without fighting a pressure differential at the point of entry into the case.

The bottom line is that if you have rocker vents the pressure in the crankcase at the drainback point will exceed the pressure in the rocker chambers, thereby inhibiting oil flow back to the bottomend. Period.

The more blowby or full throttle time; the more of an issue this is. Ask yourself why you want your oil to exit the rocker chambers through a hose that then has to run to a vent can and then make its way back to the engine when it could just run back to the case directly through the pushrod tubes.
As Jake said a bit more venting at the chimney is in order, though not a lot more seems to be required. (Brent of Raby Enterprises gets the credit for that observation!)

[Cevan]

I see that the 1.8 L-Jet motor uses a 22mm hose from the oil filler to the intake tube. That's about 4 times the volume as the 11mm hose D-Jet uses. So I'm guessing that part of the demand for better crankcase ventilation is using a larger hose.

[ME733]

............What in the hell...!!!!!("the oil goes through a hose to a breather can and drains back to the crankcase"HAM"). You people must have had a head vent tube kinked, with a down and up loop trapping , and draining oil, through some wierd siphon process. Properly done, and installed , the vent lines from the heads-continiously rise...go up to the catch can, breather box.ANY OIL slung to/into the breather tube will simply drain back to the head.... the hot VAPORS/WATER-IN THE FORM OF STEAM will rise to the catch tank to condense back into what they were...JUST DRAIN... a catch tank and SEE THE WATER, and liquid crud....AND JAKE RABY I was building 914 RACING engines,and 356 RACING ENGINES, and 911 RACING ENGINES, and doing complete turn key race cars........when you were still crapping in your diapers. SO DO NOT tell me what engines to specialize in. I have already gone down the road you are on now, and eventually you will rediscover a very simple yet elusive answer. SO PEOPLE....I still recommend using the STOCK head vents, to the stock location/ filler/location/ routing to the air box, or into the carburators....Unless of course you decide to use a much larger remote catch tank thats well vented. AS we all know the 914 heads are susceptable to cracking, and warping. Anything that can be done to remove heat from them just adds longitivity, and reliability. So VENT the head and help get some of the heat out of them....MURRAY .

[HAM Inc]

I'm not intersted in argueing with anyone, but when someone implies that I'm stupid enough to make judgements based on observations made on a chassis dyno with kinked breather hoses...I have to respond!

You people must have had a head vent tube kinked, with a down and up loop trapping , and draining oil, through some wierd siphon process.

No kinks or wierd process; just good ol' gravity.

the hot VAPORS/WATER-IN THE FORM OF STEAM will rise to the catch tank to condense back into what they were..

Those vapors don't originate from the rocker cavities, they are a by product of blowby. No justification for venting the heads there.

AND JAKE RABY I was building 914 RACING engines,and 356 RACING ENGINES, and 911 RACING ENGINES, and doing complete turn key race cars........when you were still crapping in your diapers. SO DO NOT tell me what engines to specialize in.

Oh Lord, not another one of those! When someone says something like that it is obvious that they feel they know it all and have nothing left to learn. And I suppose you were also reading and writing when Jake was still pooping in his diapers, but it hasn't kept him from doing a better job with his grammer. There's a reason I quit reading Cormac McCarthy! You reminded me of it.

AS we all know the 914 heads are susceptable to cracking, and warping. Anything that can be done to remove heat from them just adds longitivity, and reliability. So VENT the head and help get some of the heat out of them....MURRAY .

Okay now you're just being rediculous. If your implication is that venting the rocker chambers will somehow reduce the propensity to cracks and warpage you need to let to go of the crack pipe and and take a closer look at one of these engines!

I spent a lot of time on this subject. Jake and his team at Aircooled Heaven were involved and Jake conducted the tests (that's tests plural, there were many) while I observed the funtion of the various breathing systems we worked with. The results surprised all of us, including me. But the test were done using a scientific method and then the system was put to the test on the track with a season of racing...hard racing. The results were no leaks, no blowby issues, slightly lower oil temps and superb reliability.
If you have a stock FI engine that uses the vents, keep that system intact. It actually draws air into the rocker chambers and pulls oil toward the bottom end.
If you have a carbed engine breath it from the chimney and if you are concerned about the condensation run the hose into a can about an inch or so above the bottom so you can drain the condensation.

I have said all I have to say about this.

[bandjoey]

Letter from a getting old fart.
Dear Murray: This is a tough one for a non mechanic minded driver like me. I've absorbed every sports car magazine and book I could find for most of my 60 years and have seen a lot of old ways fall when science is brought into the mix. In the 914 'world' Jake and Ham have spent more money on engine science than I anyone. So I have to respect that. The engines at Daytona from 1980 won't take the punishment the 2010 engines do because someone spent a lot of money figuring out a better way. Now, don't hit me with a wrench. (IMG:style_emoticons/default/beer.gif) You'll always be a better builder in a day than I am in a year.

Thanks for your input. (IMG:style_emoticons/default/smile.gif)

[jaxdream]

Ok , Len , I came out of the rootcellar , don't let one guy dampen this thread , like I said earlier , I have some learnin to do , and having vetrans speak up is what I look for. Not all of us have the experience or the surroundings to garner such. Heck there are probaly 2 dozen on this forum that would give their eye teeth for the opportunity for such experiences everyday , but alas not all of us need to be engine builders, still need Dr.s, plumbers, even lawyers and such.
This thread is getting some hard core info put into it, I for one would like to see more of it , even including what others have to say different . There is usually differing points of view to most every facet of these cars and thier engines.
Please sir , more.

Jack / Jaxdream

[jaxdream]

Mods , don't lock this thread yet ......

Jack / Jaxdream

[bandjoey]

Ditto's. More.
Vent it from the chimney means a hose from the filler neck to a can?

[ME733]

Ditto's. More.
Vent it from the chimney means a hose from the filler neck to a can?

..............I believe that,s the implication....AND. it needs to be REAL BIG ALSO, was it 1.5 inches in diamenter???? If head venting is deleted.....was the mantra. MM

[Cevan]

Ditto's. More.
Vent it from the chimney means a hose from the filler neck to a can?

I think that's the idea. I think I will use an L-Jet oil filler. As I posted above, it's 4 times the cross-sectional area of an 11mm hose.

[bandjoey]

Ditto's. More.
Vent it from the chimney means a hose from the filler neck to a can?

I think that's the idea. I think I will use an L-Jet oil filler. As I posted above, it's 4 times the cross-sectional area of an 11mm hose.

Now the run to classifieds...and who will corner the market on Ljet Chimneys first? (IMG:style_emoticons/default/poke.gif)

[Jake Raby]

AND JAKE RABY I was building 914 RACING engines,and 356 RACING ENGINES, and 911 RACING ENGINES, and doing complete turn key race cars........when you were still crapping in your diapers. SO DO NOT tell me what engines to specialize in.

WOW, another one of those guys that have continued to stagnate development with their 35 years of bullshit doing the same thing over and over again with a closed mind.

You'll not get anywhere with me with that mindset or kind of screwed up outlook on the topic at hand.

I've had more engines wasted by people that called me up saying "I've been doing this for 35 years" than anything else.

Until LAST YEAR my outlook on cylinder head breathing was the same as Murray's. That was proven wrong by studies that we did on my engine and chassis dynos as well as an entire season of SCCA competition.

My Employee, Brent who has been with me since day one gets the credit for the hypothesis that the heads had too much breathing capability... EVERYONE else on our team did not agree with him.

I was wrong and I'll admit it... I was open minded enough to do the exploration and pay attention to the results.



This post has been edited by Jake Raby: Feb 2 2010, 08:47 PM

[Jake Raby]

BTW- Murray which Type 4 engines came from the factory with head vents(VW and Porsche combined)??? Being the all-knowing individual you are I'd expect you to have the case codes of the equipped engines and part numbers of the cylinder heads memorized.

I do.

[johnnie5]

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