Our BMW’s boost leak is back, so we used overkill to fix it

You may recall our BMW sprung a leak recently. A boost leak to be precise.

After several months of trouble-free operation, the silicone coupler between the Evolution Raceworks charge pipe leading from the turbo to the CSF intercooler inlet popped free. We reattached it, adjusting it a bit to better seat it on both tubes, then went on our way.

But after a few hard track laps of full boost, our boost pressure started dropping and our blood pressure started rising. Our coupler had come loose once again, and it was time for some additional investigation and hopefully a more permanent fix.

When we got back to the shop and did some disassembly, we found the silicone coupler between the two pressurized aluminum pipes dislodged again. This time, instead of just reconnecting it, we took it all the way out to do a little more snooping.

What we saw was a fairly large misalignment between the charge pipe and the inlet pipe into the intercooler. The photos make it look slightly worse than it actually was because the charge pipe droops slightly when it’s disconnected, but there was still a misalignment of nearly a quarter of the diameter of the pipes themselves when everything was in its installed position.

This coupled with a fairly short, 3-inch silicone connector allowed for a fairly zero-tolerance installation that could go awry with any engine movement, as we were finding out.

As usual, we got Phil Wurz at BimmerWorld on the phone. Luckily, he’s still taking our calls.

We came up with some ideas for fixing it, but, as Phil says, “We need to figure out whether this is a ‘your car’ thing or installer error or an issue with any of the specific pieces.”

Fortunately, BimmerWorld is also developing a 435i with similar bits and they’re going to do some exploring on their own, measuring some parts on the shelf and talking to their suppliers to see if we can come to a conclusion here. We’ll report back as we figure out what may be actually going on here.

In the meantime, we did the thing you should always do when repairing an issue: engaged overkill.

We first tried a 4-inch coupler to provide more overlap on both pipes, but we still didn’t love the stress that the high offset put it under.

So we trimmed back the CSF intercooler’s inlet pipe to create a larger gap between the two pipes so we could fit a nearly 7-inch-long piece of 2.5-inch ID silicone hose. This, we figured, would bridge the gap and create a lot of overlap on the hard pipes for clamping.

We now have enough hose to nearly reach the joint between the inlet and the intercooler itself. Even without the clamps, the soft hose has no way to come off without someone or something physically lowering the intercooler. In theory, it’s not going anywhere.

Initial tests with this configuration have been favorable. The car is holding its targeted boost and surviving momentary boost spikes with no sign of boost loss. It’s nice being back to full power.