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MIGClub Member
14,789 Posts
Discussion Starter · #1 ·
Breather modification for the 20XE/C20XE
(This may also work for other engines)

When modifying the pre Ecotec 2.0 16v engine a common problem is a kangarooing effect when coasting down through the revs at about 2000rpm. This is apparently caused by excess pressure inside the cam cover, due to modifications such as performance exhausts and air filters. To release this pressure you can modify the internals of the cover in order the let pressure escape through the same route as the crank case fumes.

There are two way to do this, depending on what modifications you have done to your engine. One is for systems that route the crank case breather pipes back to the inlet as the standard engine does. The other is for engines running twin carburettors or throttle bodies where the fumes are sent to a catch tank.

In both cases, remove the cam cover. To do this, remove the spark plug cover and remove all bolts and disconnect the three breather pipes. Be careful not to damage the rubber gasket when lifting the cover out of place.

Turn the cover upside down and place it on a workbench. You will see a plate bolted to the top of the cover which channels the fumes coming out of the crank case and into the front of the cam cover, around to the rear two outlets. You need to remove this plate, you will need a Trox socket to do this. You will find that the plate is stuck to the cover with sealant, prise off the plate being careful not to bend it as it is thin. Remove all of the left over sealant, if this gets into the engine, you will get blocked oil ways resulting in engine failure.

The plate that you have removed is the part that needs modifying, but this needs to be done differently depending on your engine configuration.

For standard induction where the fumes are routed back into the inlet, you will need to drill some holes in the plate near the fume inlet side. Do this using a drill of roughly 15-20 5mm holes “pepper pot” style. See the diagram blow.

For those of you who are lucky enough to have twin carburettors or throttle bodies where the crankcase fumes are not sent back to the inlet, you may do the following mod. Cut away the section of plate that fits below the outlet on the cover. Discard all the other plate sections. See the diagram below. The reason this can not be done for an engine with the standard induction is because oil is more likely to splash and get blown out into the breather pipes. The small section that is left in the cover is the shield the breather outlet from direct oil splashes. If this were to be done on a standard induction system, the inlet manifold would get covered in oil and would result in a loss of performance.


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