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Engine Breathing


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#16 jt19

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Posted 15 April 2019 - 09:31 PM

When I looked into scavenge breather system I understood it that you'd need to have the catch can plumbed in so that it would drain back into the engine. Otherwise you'd fill it up with oil fairly quickly.. not sure I'm right, but just thought I'd leave it as is.

#17 Moke Spider

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Posted 15 April 2019 - 09:45 PM

When I looked into scavenge breather system I understood it that you'd need to have the catch can plumbed in so that it would drain back into the engine. Otherwise you'd fill it up with oil fairly quickly.. not sure I'm right, but just thought I'd leave it as is.

 

You can use a drain back from a catch can, but if you have oil separators, as it standard on the engine and I think you still have on the Timing Chain Cover, then you don't need a catch can or a drain back.

 

If when plumbed up, it is going through oil, then I think you need to look at the rings.



#18 DeadSquare

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Posted 16 April 2019 - 06:29 AM

I'm sorry, but I just can't understand why so many huge vents are advocated.

 

It is not as though the vents are there to relieve pressure, the exhaust ports do that.

 

The vent in the rocker cover was for the carb to remove acidic vapour .


Edited by DeadSquare, 16 April 2019 - 08:08 AM.


#19 Steve220

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Posted 16 April 2019 - 06:53 AM

If your not using the mechanical fuel pump drill the blanking plate and weld in a 1/2" tube


MPi.

#20 mini13

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Posted 16 April 2019 - 07:43 AM

Generally on muy engines I runn all the available breathers onto the rocker cover ( to use it as a kid of catch can/ oil seperator), then have one pipe coming off to either a catch can, or via an oil seperator/ baffle to the manifold, In your case I'd add a PCV valve an port one side tot he manifold, and the other to the Intake pipe with the filter on, basically replicating the metro turbo breathing system.

 

Being an MPI bit trickier as you can do things like use the dizzy hole or fuel pump for breathing, I would like to see at least the transfer case and timing cover vented to the rocker box, even if its with smaller pipes of 10-13mm. really large pipes are only needed with a system breathing to air, if youve got active vacum from the manifold you should be in a much better position.

 

In terms of the exhaust scavenging, Ive not tried this, but am intending to on my next build, Ive added in an extra lambda bung to enable fitting of the "probe" I found some nice stainless angled ones to allow the prove to sit at 45 degress, there seems to be much controversy over what way the probe needs to face for optimum vacum, hence the lambda bung so i can rotate it....

 

https://www.ebay.co....3sAAOSwgspZupOo

 

https://www.theturbo...exhaust.352147/

 

another thougt I had was using an alternator form a deisel car with a vac pump on the back, but I dont  have room for that, maybe i could use on of those electric vac pumps, triggered by a  boost switch, or turned of bu a vac switch.



#21 DeadSquare

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Posted 16 April 2019 - 07:48 AM

The more vacuum you can get in the sump, the less air resistance there is to the crank wizzing round.



#22 unburntfuelinthemorning

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Posted 16 April 2019 - 08:14 AM

Regarding the Vizard "Evacusump" system:

 

The system is said to reduce the amount of oil the oil control rings have to deal with by way of creating a depression in the crankcase of as much as 25 to 30 inches of water.

 

This works when the engine is under high load by the action of the high speed passage of the exhaust in the collector part of the manifold causing suction on the breather pipe.

 

At low load and idle, manifold depression is used instead to draw air from the crankcase via PCV valves.

 

My questions are:

 

1.  With the standard breather setup (breather connected to SU), how does engine load effect what air is drawn into the carburettor through the breather hose?

 

2.  The Evacusump system has no air inlet.  This creates a high depression but does not create a through flow of fresh air.  Does this therefore leave pockets of blowby gas within the engine in a similar way to open breathers?

 

3.  Would a standard breather system with the air inlet blocked off (sealed filler cap) create a depression in the crankcase as the Evacusump system does or would it be less effective under certain load conditions?



#23 Steve220

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Posted 16 April 2019 - 08:16 AM

The more vacuum you can get in the sump, the less air resistance there is to the crank wizzing round.


Difficult on a boosted set up, I think the best way would be for the exhaust scavenge. As my car is neither high revving or a daily, I think my best bet is to vent the transfer case (cleverly) to the rocker cover then a PCV to the inlet manifold.

#24 Kt1966

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Posted 07 July 2019 - 08:42 PM

Apologies for hijacking but I'm very interested in the Evacusump system.
Currently at final stages on a fairly high spec 1400 and only have the transfer case and "fuel pump" breathers - no timing cover one.

Engine builder is recommending an Evacusump type approach but I'm interested in views on this - does it work, is it worth doing and where would I source the various bits.

My understanding is that at all the other breathers would /should be blanked off.

Any thoughts or comments much appreciated.
TIA


Edited by Kt1966, 08 July 2019 - 10:39 AM.


#25 nicklouse

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Posted 07 July 2019 - 09:20 PM

What does he mean by evacusump? We have no idea what he means.

Just plumping it up as standard will be fine. And as you are you are using the vacuum made by the carb out are making a partial vacuum in the engine. Job done at no cost.

#26 Kt1966

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Posted 07 July 2019 - 09:30 PM

Thanks. His plan is to blank off both existing breathers and tap into the exhaust and rocker cover to create the vacuum. There would be a catch tank of sorts and a return oil feed somewhere (not entirely sure where that return line would feed into).

Basically, as per Vizard but it is all new to me and I'm trying to guage whether it does actually work and whether it's worth trying a timing cover breather first/as well/instead of?

Edited by Kt1966, 07 July 2019 - 09:44 PM.


#27 unburntfuelinthemorning

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Posted 08 July 2019 - 06:45 AM

Vizard's system does work but it's value on a road going vehicle is debateable although it's better than open breathers.  Vizard additionally used a PCV system for low speed operation as the Evacusump system only works at high engine speed, people don't seem to read that part.

 

What carburettor are use using?  If it's an SU then the standard breathing system will be sufficient.  You could add a timing case breather into that and delete the fuel pump outlet then the crankcase air would be drawn out of both ends of the engine - as standard. 

 

I'm not sure if you can connect to other carbs - I imagine not in which case you do need a different setup.



#28 Kt1966

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Posted 08 July 2019 - 07:03 AM

That's interesting about the low speed part... What did he use as a PCV ??

 

I have a HiF44 and it would certainly be a lot less faff to just add the timing case breather - I just want something which will work sufficiently well.

 

I'm interested why you would suggest getting rid of the fuel pump one ? - surely more is better ??

 

Many thanks



#29 Ethel

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Posted 08 July 2019 - 07:55 AM

If you're looking to reduce pressure then you really don't need lots of plumbing - look at the vent hole in the bottom of your filler cap, you just have to better that (and suck up piston blow by) enough to create 1 psi of depression. You'd need a very radical engine to get that little manifold depression even at wide open throttle.

 

To justify an "evacusump" you'd have to be chasing the tiniest of power gains by feeding your engine on nothing but fresh air and fuel.



#30 mini13

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Posted 08 July 2019 - 08:32 AM

On my next lump (turbo k1200) I'm planning a three fold approach,

The "evacusump" into the exhaust,
The normal vent to the inlet,
And also an electric vac pump just incase there are any issues with either of the above.

As it's turbod not sure how well the exhaust extractor will work especially at low speeds/ coming on boost hence the pump.




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