Lotus Elan

Oil breather

PostPost by: HCA » Mon May 25, 2020 2:32 pm

There is another thread on catch cans not so far back where I asked what everyone is using. Might be worth having a look.

Why a catch can?

Problem with older engines where a pipe connects rocker cover to airbox is that if there is a lot of oil mist/vapour, it is sucked into the engine and with individual ports, the port nearest the intake has to burn the stuff that often fouls the spark plug.

Problem with even older engines that vented to atmosphere is that wherever the mist/vapour exits - usually under the car - gets messy with a build up of oil mist. Then there is the environmental damage.

So a catch can will get rid of both these issues.

A neat but expensive can is a Mishimoto. https://www.mishimoto.eu/?gclid=EAIaIQo ... gKNp_D_BwE It has a baffle mechanism inside that goes a long way to separate the oil mist into air and oil, retaining the oil and allowing the air to leave through a small airfilter.

Better still, vent the catch can outlet into the exhaust pipe where the exhaust will pull the air out of the tank and burn it. Described above by using a disused O2 sensor, but better still use an agled entry into the exhaust where the capillary pull will be greater: https://www.ebay.co.uk/itm/Universal-St ... SwgPVcljXW.

Do note though if you do vent into the exhaust you must fit a one way check valve as close as possible to the point you enter the exhaust pipe. It must be a valve suitable for the job and not a high spring fuel delivery type valve: https://www.mishimoto.eu/performance-ch ... e-3-4.html This prevents any back pressure from the exhaust getting back into the rocker chamber and acts as a flame arrestor. Finally you should have some stainless gauze stuffed into the pipe as well.

If your engine bay is tidy and the car belly is clean, then a catch can is a must...
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PostPost by: 1969Plus2 » Mon May 25, 2020 2:51 pm

One last comment on the topic for consideration.

Most engines vent somewhere that has some modicum of vacuum. I'd ask why you want to vent to catch can if you could vent to a place that will create just a bit of vacuum, as originally designed.
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PostPost by: nmauduit » Mon May 25, 2020 3:19 pm

fwiw there is one such tube for sale on auction in the UK (no affiliation)

early elan breather dump tube.jpg and
early elan breather dump tube

https://www.ebay.co.uk/itm/Lotus-Cortina-Mk1-2-Elan-S1-S2-S3-Super-7-Metal-Breather-Tube-NEW-1962-19/193477662091?hash=item2d0c2ad58b:g:~VIAAOSwlj9eUaH4
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PostPost by: HCA » Mon May 25, 2020 4:08 pm

1969Plus2 wrote:One last comment on the topic for consideration.

Most engines vent somewhere that has some modicum of vacuum. I'd ask why you want to vent to catch can if you could vent to a place that will create just a bit of vacuum, as originally designed.


Correct, and is good for an engine in good nick with normal backpressure and minimal oil vapour.

However more modern engines with turbos and/or injection do not like oil vapour.

Race regulations often insist that engines have catch cans.

As engines get older, they get more sloppy and puff out a lot of vapour from the crankcase and when sucked in through an airbox/filter, it all gets a bit mucky - especially with the likes of our engines where No4 intake takes the full brunt unlike, say, and MGB where the cylinders can share the job.

Plumbing the catch can outlet into an exhaust does create the bit of suck you are looking for.
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PostPost by: 1969Plus2 » Mon May 25, 2020 8:11 pm

All good points and a good reminder that there is always more than one way to skin a cat.
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PostPost by: My72Sprint » Mon May 25, 2020 8:18 pm

I'm going to vented from the front of the cam cover > AN10 fitting> AN hose > to a small billet tank I purchaed @ Amazon, $37 ,The tank exit hose to Weber carb Intake port. Should work ok, If not I'm only out a few $'s
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PostPost by: Andy8421 » Tue May 26, 2020 11:49 am

HCA wrote:However more modern engines with turbos and/or injection do not like oil vapour.


I cant see why a turbo or fuel injected engine would care about a bit of oil mist getting burned, but I can easily imagine that there would be problems meeting emission standards, and I am sure the catalytic converter would be unhappy if this were the case.

HCA wrote:Plumbing the catch can outlet into an exhaust does create the bit of suck you are looking for.


I could well be wrong, but I find it hard to believe that a pipe of whatever shape stuck into an exhaust pipe will generate sufficient venturi effect to overcome the back pressure in an exhaust to the point that it achieves a pressure below atmospheric and 'sucks'. Does anyone have experience of this happening?
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PostPost by: HCA » Wed May 27, 2020 7:00 pm

On the part about [modern] turbo and injected engines not liking oil vapour, the fact is well recorded and accepted and is the reason for very elaborate PCV systems. I have a 500bhp Audi that has an MTM conversion where there is an oil catch can inserted in the PCV where MTM tell owners that various regulations stipulate it vents into the intake and explain how doing this coats the turbo vanes etc - in other words, vent it outside! Much is written on the subject. Here is one that I think is quite readable:
https://www.enginebasics.com/Engine%20B ... h_Can.html

On the part re venting into exhaust, you are right, I should not have mentioned it without all sorts of caveats, although I did go to pains to stipulate a proper check valve in place. Venting into exhaust is only good at near or at wot. But I have found - on MGBs mind you - that inserting the vent further down the pipe away from bad pressure areas does appear to work, assuming that you are not piddling around town all the time and have a chance to open the throttle a fair bit.

I was trying another more radical method with me last B and will continue on the Elan - fitting a small 12V vac pump such as the little ones fitted to some Fords that pull maybe 7 inches that would put the crankcase into a permanent vacuum. However, I was warned off this by a chap well respected in preparing Formula Ford cars, that this method might upset gudgeon pins. My B had a new 5L V8 where I could not afford this to happen, but as I intend to go to town on the Elan engine next year, might try this pump again and see if anything dries out.
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PostPost by: mbell » Wed May 27, 2020 7:38 pm

My idea is to re-route the breather to near the front of the airbox. Just in the area where it expands from the round inlet to the square section.

If I understand things correctly the increase in cross section in this region should create a low pressure area that will help the efficiency of the standard breather. It will also distribute the vapors between the cylinders more evenly.

I've got as far as buying vacuum gauge to try and measure the vacuum level in the various positions to see if there is any significant difference. Give it another 5 years and I might have got around to measuring it...
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