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Should I Connect Crankcase Breather To Carb?


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#1 Syed Malaysia

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Posted 30 December 2007 - 08:26 AM

Hi

I have a '90 Mainstream Cooper. Im just wondering what's your advice on the breather pipes? Should I connect the two breathers (from the crankcase & the timing chain side) to the carb? I know you do this in "wonderful" UK weather but then I live in Malaysia where it is 30+ degrees all year long ;-)

Should I just buy two K&N crankcase breather filters or connect them to the carb? Thanx

Syed
Malaysia

#2 Guess-Works.com

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Posted 30 December 2007 - 09:18 AM

The crankcase breathers have nothig to do with temperature, they are there to ventalate the crankcase... Ideally they SHOULD be connected to the carb as this prevents ingress of contaminents into the engine, and likewise venting of crankcase fumes into the engine bay...

#3 minimender

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Posted 30 December 2007 - 11:31 AM

Hi

I have a '90 Mainstream Cooper. Im just wondering what's your advice on the breather pipes? Should I connect the two breathers (from the crankcase & the timing chain side) to the carb? I know you do this in "wonderful" UK weather but then I live in Malaysia where it is 30+ degrees all year long ;-)

Should I just buy two K&N crankcase breather filters or connect them to the carb? Thanx

Syed
Malaysia

Stick filters on them.
You don't want oily fumes being sucked in to the carb and affecting performance.
If you are worried about fumes in engine bay then run a couple of pipes out into the under wing area to vent away.
Some people run the pipes into an oil catch tank with a filter.

#4 Dan

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Posted 30 December 2007 - 11:50 AM

You don't want oily fumes being sucked in to the carb and affecting performance.


<sigh> Why do we bother?

#5 Big_Adam

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Posted 30 December 2007 - 11:55 AM

You don't want oily fumes being sucked in to the carb and affecting performance.


<sigh> Why do we bother?


Maybe every little helps is taken too far.

Syed Malaysia, leave the pipes attached. If you got cooling probs then look into a new or extra rad.

#6 THE ANORAK

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Posted 30 December 2007 - 12:02 PM

oh dear, a couple of completely contradicting answers :proud:

guessworks / dan, you have pointed out the bad points of not connecting them but could you be more specific on the benefits of venting them to the carb (if any).

Ive been helping Syed out over on the mainstream site but this area is beyond me, i get the impression that his engine has been messed around with in the past and he's trying to get it back the way it should be. i dont think he has the breathers connected at the moment and he didn't even have the anti run on valve :)

a quick explanation of how and why the breathers work would be helpful all round

thanks ;)

#7 stickycreambun

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Posted 30 December 2007 - 12:20 PM

Id find it good to know the difference between keeping my breather attactched and running a catch tank. :proud:

#8 minimender

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Posted 30 December 2007 - 12:51 PM

I've always thought that the breather pipes were attatched to the induction in an effort to burn any nasty fumes that came out of the crankcase.
I first remember it on the Mk 2 Coopers amd S's and I believe it was done to please the yanks initially.

Could be wrong though.

#9 Dan

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Posted 30 December 2007 - 01:13 PM

could you be more specific on the benefits of venting them to the carb (if any).


If I could still remember how many times I had typed that answer out during this year then I would, but since numbers that high probably don't have names I'll just suggest that you search for threads about engine breathers or positive crankcase ventilation. All I'll say here is that crankcase ventilation is good for the engine of a road car and doesn't harm the performance enough for you to even notice. Race cars aren't road cars.

#10 Ethel

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Posted 30 December 2007 - 01:24 PM

Unless you are running a stupidly high compression and are running the engine within an nth of a degree of detonation there's nothing to be gained from not connecting the pipe. At full throttle the amount of charge being drawn out of the crankcase (1/2" pipe) compared to fresh fuel and air through the inlet (Inch 'n a half plus) won't make much difference.

Might chuck in as logic exercise... a hot climate makes for less of a reason not to connect it to the inlet - as the temperature difference will be less; not running with PCV will be less effective at warding off detonation than it would in a cold climate.

Edited by Ethel, 30 December 2007 - 02:11 PM.


#11 THE ANORAK

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Posted 30 December 2007 - 01:38 PM

a few quotes from Dan on the subject (so the poor chap doesn't have to type it all in again :) )

well i guess the quick answer would be.... yes, connect it up to the carb :P


You don't. Positive crankcase ventilation is a good thing on road cars. Without it you are more likely to get oil leaks all over the engine, loose oil faster and get more sludge building up inside the engine. As long as you keep the hoses clean and empty out the cannisters every 80,000 miles or so then the system will work in your favour. Race engines work slightly better without the system but that's mainly because they are after every last horsepower and don't mind a few small leaks and get their motor rebuilt every couple of races too so they can clean it out better and change the leaky gaskets than have blown due to increased crankcase pressure.


Having said that, many people do want to get rid of the system so here's a little rundown. Remove the hose which connects from one cannister to the Y piece, and the sort but to the other cannister. Remove the Tee piece from the end of the short hose connected to the carb emmisions inlet and then you need to connect the hose from the charcoal cannister to this hose so that it will still feed into the carb when the purge opens. Now fit breathers to the two cannisters, you may need to use short lengths of emmisions hose to the filters and use these to slip onto the cannister outlets depending on which make of filter you use.
Now get ready to buy more oil and clean oil vapour off the inside of you bonnet every couple of weeks. :proud:



OK, the air in question is indeed warm! ;)

It's called a positive crankcase ventilation system because the engine is used as a pump to actively draw gasses out of the crankcase. These gasses will not leave on their own, the pressure will build up. It takes a lot of pressure differential to blow all the gasses out and the pressure build up differently in different compartments of the engine. It WILL lead to more oil leaks due to pockets of pressure inside the engine. Oil vapour DOES get out past K&N filters. The sludge that builds up inside the engine due to the water, fuel, oil emulsion inside the crankcase will not leave on it's own and letting more gasses collect there will encourage more varnish to accumulate.

We could just say 'yes it will be OK' and it will in that it won't directly cause the untimely demise of the engine. Or we could give a more complete answer, explaining all the pitfalls of this adaption. I'm certain that's what Joel would prefer, I know I would.



It doesn't go anywhere, it just doesn't form in the first place. The sludge is the result of water oil and fuel collecting as a mix in the crankcase and getting plastered all over the hot metal. The gas does not flow out on it's own. It collects, and while the air does manage to get out the crud that's in it tends to stay behind. The pressure in the crankcase is higher with the system disconnected, mainly because the inside of the engine consists of many different connected chambers. You get different pressures in different regions. If you don't like the thought of it, it's just because you don't really understand what's going on. All it is really is air with some oil, a tiny bit of fuel and an amount of water vapour. It's very similar to exhaust gas. It enters the carb after the jet and just flows through with the mix already travelling through it to get burned off. The rocker cap has a small vent in it which limits the amount of air which can be drawn through the engine, which increases the depression inside the crankcase and limits the amount of gas travelling through the carb. Whether you like the idea of it or not every single road car engine in the world uses the system and it works well. It is technically a requirement of the regs to prevent the C**p inside your engine being released into the atmosphere.



#12 Dan

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Posted 30 December 2007 - 01:43 PM

:proud: ;) :) :P :o

Thankyou Anorak!

The only other thing to say is that the oil will stay cleaner for longer with it connected. Racers change their oil every race or two and even if they keep it for longer in terms of the number of races, they don't do a great many miles. You ideally want it to last at least six months in a road car.

#13 Syed Malaysia

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Posted 30 December 2007 - 02:26 PM

oh dear, a couple of completely contradicting answers :proud:

guessworks / dan, you have pointed out the bad points of not connecting them but could you be more specific on the benefits of venting them to the carb (if any).

Ive been helping Syed out over on the mainstream site but this area is beyond me, i get the impression that his engine has been messed around with in the past and he's trying to get it back the way it should be. i dont think he has the breathers connected at the moment and he didn't even have the anti run on valve :P

a quick explanation of how and why the breathers work would be helpful all round

thanks ;)


Right. After looking at the pictures anorak posted in Mainstream forum, i realised that my breathers are not connected. In fact, the flywheel side has no breather canister at all! Now I just hope that they sell the "Y-piece" or something similar in my area... :)

#14 Syed Malaysia

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Posted 02 January 2008 - 01:24 PM

Hi

I connected the breather pipes to the carb today and the car runs smoother, although I had to adjust the idle speed a lil' as it was below 800 with tbe pipes connected.

Oh I also fitted the anti run-on valve and now the engine dies off right away without sputtering.

Cheers

Syed
Malaysia

#15 Jammy

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Posted 02 January 2008 - 01:59 PM

Good news Syed, glad you got it sorted!

Moved to FAQ, so Dan's answers on the subject are easy to find in future!




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