Crankcase breather return to airbox - needed?

Topics relating to the Lotus Exige S1 (series 1)
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Evoman
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So I have a question on this because I have a new airbox in carbon fibre that I plan to fit. However currently the crankcase breather return location needs drilling if I am indeed to set it up as factory. That said I understand technically part of the 190 upgrade (perhaps for the 340r only) included the addition of a catch can system for this rocker cover breather hose.

I can see the topic has been discussed on here over the years with various set-up installations for catch cans and rerouting the breather hoses. Is this an advisable step to take from experience? From what I understand the removal of those recirculated oily mist vapours from entering the inducted air stream has benefits in maintaining octane rating of the fuel? The oily mist vapours can reduce this?

Having a catch can set up I guess could introduce oily odours into the engine bay if it isn't set up well though I assume if it is contained it may also have a vent so odours will be noticeable?

But ultimately is it recommended for a road car? Is it beneficial or detrimental to the engine?

And finally if the original set up is recommended what diameter hole is required in the airbox for the breather hose?!

I am leaning to the latter set up but convince me otherwise if the other option is best!
tlracer
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The point of returning the crankcase breather to the airbox is twofold:

a) To avoid crankcase gases escaping into the engine compartment and, potentially, into the cabin;
b) For environmental/overall emissions control, as any combustible vapours are burned and then the resultant gases dealt with through the cat

It's common to vent the crankcase on race engines to a catch tank as it's a standard job to check/empty as necessary; however it's basically pointless on a road car and simply makes 'another job to do'.
winthattt
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I run a catch can on my VHPD for the odd track day I do with the car. At high rpm you want the air fuel mixture to be right, running lean is hotter and not good. Off the track I remove it and fit the breather pipes. It takes about 5 minutes to swap, as you suggest, it’s less smelly and slightly less polluting.

I’d pick the hole in the air box to take a suitable grommet to get a good seal on the breather hose.
Evoman
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Thanks guys, helpful as ever.

That's an interesting set up to install for just track use.

Wnthattt - would you mind sharing any photos you have of the installation? I'll go for OE set up just now and drill that hole in the cf airbox but would be interesting to see the set up for 'track use'. Cheers!
gonein60seconds
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winthattt wrote: Wed Aug 26, 2020 9:45 pm I run a catch can on my VHPD for the odd track day I do with the car. At high rpm you want the air fuel mixture to be right, running lean is hotter and not good. Off the track I remove it and fit the breather pipes. It takes about 5 minutes to swap, as you suggest, it’s less smelly and slightly less polluting.

I’d pick the hole in the air box to take a suitable grommet to get a good seal on the breather hose.
I don’t suppose you can share a picture of your “on track” set up, just for my education/understanding? Found detail in thread pretty informative as not very mechanically savvy.
tlracer
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winthattt wrote: Wed Aug 26, 2020 9:45 pm At high rpm you want the air fuel mixture to be right, running lean is hotter and not good.
Other than air, crankcase gases are predominantly unburnt hydrocarbons and combustion products from blowby, plus the more volatile oil fractions, so the Lambda sensor should adjust within acceptable limits to prevent excessively lean conditions.
winthattt
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tlracer wrote: Thu Aug 27, 2020 10:54 am
winthattt wrote: Wed Aug 26, 2020 9:45 pm At high rpm you want the air fuel mixture to be right, running lean is hotter and not good.
Other than air, crankcase gases are predominantly unburnt hydrocarbons and combustion products from blowby, plus the more volatile oil fractions, so the Lambda sensor should adjust within acceptable limits to prevent excessively lean conditions.
Quite right, the blow by will be CO2, NOx hydrocarbons, water and will not be a big percentage of the induction gases. Lambda will adjust but it’s very slow moving compared to the changes in rpm and is really a trim. As was said, for a road car, catch cans are not worth it and they are smelly.
FlyingDutchman
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I swapped by hose for a small filter. Have a K20 engine. So far I'm happy with that.
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