Tuning the C20LET - Crank Ventilation

The LET cam cover has three pipe connections.

The large one upfront connects to the crankcase. At the back, the thicker one connects to the vacuum side of the turbo, drawing a strong, healthy vacuum and burning any excess rubbish. It also tees-off for supplying vacuum to the amal valve. The smaller pipe has the one-way valve to ensure that the camcover doesn't get pressurised under boost.

If it's suspected that too much oily mist finds it's way to the compressor from the camcover, a DIY catch tank can be made to verify this.

Here's one I made earlier out of kitchenware. Just a plastic bottle with a removable (but airtight and secure) lid. Two pipe connectors like this should do the trick. For experimental purposes, the connectors aren't even needed, just holes in the plastic would do, as long as the rubber pipes seal around them.

Inside there is some scourer. This will help separate the oil mist into air and oil at the bottom of the bottle.

No stock pipes need to be cut. Check the contents after a few hundred miles. If there's nothing there, then there is no need for a catch tank and put the pipes back to their original places. Job done.

This is an aluminium catch tank, commercially available from some tuning shops. It's got a 'viewer' so you know when it's full. It's squeezed next to the airbox. Note that the cap is sealed with ducktape to keep it airtight. That's because these are sold with breatheable caps, which is not what we want on a LET setup (that connects to the turbo intake)

 

 

Cam breather mod

The need for this mod arises when older engines start to smoke, and we've verified that smoke is not from the turbo, neither the valve stem seals. A quick test is to temporarily block the breather inlet on the turbo and see if the exhaust smoke goes away. If it does, then there is excessive blowby from the pistons perhaps compounded by high boost pressures.

The result is that the breather tract within the camcover cannot cope with these quantities of oil mist, and a lot of it is sucked in by the turbo. The right way to tackle this is changing piston rings, or even the pistons. But this might be messy and expensive (head needs to come off, as well as the sump for starters). So the next best thing is to modify the camcover to handle the extra traffic.

Below is a view of the camcover upside down. The thick crank ventilation pipe is at the top right corner - the gasses have to go across the cover to the left, then make a 90 degree turn, then another one, and enter the inlet stream via the pipes at the bottom left corner (not visible from this angle)

Right after the crank ventilation pipe, there is a series of vertical walls, seen at the bottom right of this shot. They are meant to provide a 'torturous path' for the agitated oil mist, forcing the liquid oil from the splashing to separate and drain through a tiny drain pipe (seen at the further end of the bottom right end):

Below is the same part upside down. The drain pipe can be seen on the left:

This is the camcover without the tract 'floor'. The crankcase side is at the top right, the series of separator 'walls' would be a bit to the left of it, and from then on it's just a journey to the camcover pipes (seen at the lower left). It begs the question of why there is no oil drainage during or after the 'walls'. Surely if they were to do their job, there would be liquefied oil all over the place, with no way to drain back into the head. In fact it would be sucked in to the inlet by the turbo vacuum (or the inlet manifold vacuum in the case of the smaller pipe). The whole contraption is sealed from the factory with copious amounts of thick black sealant - so the suction would be most effective.

Why separate the oil from the gasses, when the whole lot is going to be ingested by the engine anyway? We're asking too many questions now, are we?

Here the 'floor' is right-side up. The separators can be seen on the right. The middle section looks like a natural drain section. Drilling a few holes will actually let it drain!

Here is the series of holes. No need to go crazy, this thing is there for a purpose, we don't need to waste it, we want to help it do it's job properly. Two-three holes in the 'vertical wall' section are not a bad idea either.

Putting the thing back together:

There is no need to use sealant again (obviously!) Drilling creates swarf - this has to be carefully filed and evened out. All traces of the old sealant have to be carefully scraped away and removed. Cleaning everything meticulously is extremely important, as any leftovers will end up in the tiny oil passages in the head.

 

 

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