How to upgrade an LFX’s PCV system for track use

Update by Tom Suddard to the Mazda Miata project car
Apr 18, 2023 | Mazda, Miata, Mazda Miata, lfx, Endurance Race Miata, PCV, RX Performance, Catch Can

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Our V6-swapped Miata was rapidly approaching finished, and past experience with modern direct-injected engines taught us to anticipate one problem before it began: the stock LFX PCV system.

We don’t need to take a deep dive into the details, but here’s the basic problem: The crankcase air fills with contaminants and aerosolized oil when running, and especially when racing.

Once upon a time, racers would just vent these fumes to the atmosphere, but a properly functioning positive crankcase ventilation (PCV) system doesn’t just protect the environment: It makes more power by ensuring that the rings stay seated properly, and it makes an engine last longer by removing some combustion byproducts from the oil.

A well-functioning PCV system should also keep our direct-injected engine’s intake valves from being gunked up, as it will keep oil out of the intake tract.

This all sounds great, but didn’t Chevy already attach a PCV system to every LFX? Yes, but it had a few fatal flaws for our use case.

First, it runs on intake vacuum. That’s fine for a street car, but our race car will be at wide-open-throttle–aka no intake vacuum–for much of its time on track. During these times, there’s no source of suction to draw air through the PCV system.

Second, the OEM system has no catch can or filter: Everything drawn through the system is put directly into the intake tract. That’s great on a street car, but we don’t want our race car gulping down oil and contaminants during every session.

Fortunately, we’re not the only ones with these complaints as RX Performance has a very well-developed catch can system for the LFX. It’s dubbed the “Monster.” We ordered one for our Miata and set to work installing it.

The first step? Mount the catch can, a gigantic 32-ounce model designed to hold an entire endurance race’s worth of dirty oil just in case we aren’t able to empty it.

We mounted it on the firewall where we’d be able to easily service it. With a catch can in the system, combustion byproducts and oil vapor will condense into the can instead of going into the car’s intake tract.

Next, we used epoxy to install an RX Performance venturi vacuum generator in the car’s intake. This tube, paired with a check valve connected to the OEM PCV vacuum port, means we’ll have a constant source of vacuum to draw air through the PCV system: At low loads, the factory port will be used, while at wide-open-throttle, the venturi will provide the vacuum needed.

RX Performance says their system provides comparable performance to a belt-driven vacuum pump at a fraction of the price and complexity, so we’re eager to test it out.

After plumbing everything together with the included hose, we crossed “catch can” off the list and called our LFX swap complete.

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GameboyRMH GRM+ Memberand MegaDork
1/5/23 2:18 p.m.

Some kind of grommet needed here (I like to use slit small-diameter fuel hose for odd-shaped holes like this).

Edit: Also here, cable sheathing helps but that edge looks sharp:

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
1/5/23 10:54 p.m.

Yeah, we grabbed the photo before doing some finishing. Rather than split fuel line, I buy real edge protection rubber since it stays put better.

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