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MG MGB GT V8 Factory Originals Technical - Engine breather

Re. Bob Pulleyblank's comment in bonnet louvre thread about K&N engine breather. It has just occurred to me that I am shoving hot waste gases into my lowrider air cleaner! I wonder how many horsepower that is costing me?? Anyone out there applied some thought to this subject? Danny.
Danny Smith


I don't think it costs you much in the way of HP, and it is one hell of a lot easier on the environment to dump the fumes back into the combustion chambers. That oil vapor that spews out of open breathers is the number one ingredient of smog. Open breathers (by that I simply mean those that don't -- via PCV or air cleaner -- dump fumes back into the motor) are one thing on race cars, where doing so may add just an incremental edge in terms of power), but they are tough to justify on road cars unless you really hate the planet. I read that earlier comment with a shudder because I have some good friends who do pollution engineering work and we have been through this many times.

Can I just give you a heads-up on one thing -- you may want to dump the gases into your inlet manifold via a PCV valve ($2 at the auto parts place) rather than into your air cleaner; provides a little more suction under most conditions and in the Rover V8 prevents, e.g., oil from climbing up the diss shaft etc. (unless you have had that clever mod to the shaft done by RPI Engineering). Remember that on a road car, positive crankcase ventilation (achieved by applying any form of active suction to the crankcase, including your air cleaner setup) is a good thing, because it helps stop oil leaks, which are not really an issue in race engines because they are torn down regularly.

Muchas Gracias Harry. God, hope I haven't started a flame war about contaminating the planet. Naughty, Uncle Bob! Danny.
Danny Smith

I have been dealing with this problem of crankcase ventilation since I installed the Rover V8 in the "B".
First I went with a PCV valve (Auto zone) that piped the gases into the intake manifold but the problem I ran into was the oil dipstick popping out its location due to the pos. pressure build up in the crankcase.This caused some oil to flow out of the dipstick opening fouling the whole engine bay with hot oil! The PCV valve just could not provide a big enough flow to the intake. I had to go with the very earth unfriendly way of dumping the gases into the open air. Until I find a better way to reroute these gases I will have to do it this way.
Any other suggestions?
Werner Van Clapdurp

Werner, something doesn't make sense ... with the PCV plumbed in there correctly (maybe you had it backwards?) there won't be positive pressure in the crankcase; just the opposite.

A much more earth-friendly way to do it in your case, though, would just be to dump into the bottom of the air cleaner ... also good because that will provide a bit of suction and lower your crankcase pressure. Hope you'll consider it and/or give it a whirl.

This thread was discussed between 15/03/2001 and 16/03/2001

MG MGB GT V8 Factory Originals Technical index

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