Oil Catch Can Guide: Why Every HEMI Needs One
An oil catch can is the most overlooked maintenance upgrade on the Challenger. Without one, blow-by gases coat your intake valves with carbon and gradually rob you of power. Here's what it does and why it matters.
# Oil Catch Can Guide: Why Every HEMI Needs One
The oil catch can is the least glamorous performance part you'll ever buy. It has no horsepower number on the box, it doesn't make your car sound different, and it won't turn heads at a car show. But long-time HEMI owners will tell you: it's one of the most important things you can do to protect your engine.
Here's what it does and why you should have one.
What Is Crankcase Blow-By?
Inside your engine, combustion happens in the cylinders. Some of those combustion gases — water vapour, unburned fuel, acidic compounds, and oil mist — slip past the piston rings into the crankcase below. This is called "blow-by," and it happens in every internal combustion engine.
The factory handles blow-by through the Positive Crankcase Ventilation (PCV) system: a hose routes these gases back into the intake manifold, where they get re-burned with the incoming air-fuel mixture. This is an emissions requirement — engines aren't allowed to vent crankcase gases directly to atmosphere.
The problem: that blow-by gas is loaded with oil vapour, water, and acids. When it re-enters the intake, it leaves a coating of oily residue on everything it touches:
- The intake tube
- The throttle body plates
- The intake manifold runners
- Most importantly: the back of the intake valves
Why Intake Valve Deposits Are Serious
Over thousands of miles, that oily mist bakes onto the intake valves into hard carbon deposits. On a port-injected engine like the HEMI (where fuel sprays into the intake port before the valve), the fuel helps wash the valve stems — but not completely. Carbon still builds up.
On direct-injected engines (fuel sprays directly into the cylinder, not the port), there's no washing effect at all — carbon buildup is much faster and more severe. But HEMI owners aren't immune.
What carbon deposits do:
- Disrupt smooth airflow into the cylinder
- Reduce valve sealing — lowering compression slightly
- Create hot spots that can cause pre-ignition
- Force the PCM (powertrain control module) to retard ignition timing to prevent knock
That last point is key: the PCM detects the rough combustion and protects the engine by pulling timing back. You lose power invisibly, gradually, over tens of thousands of miles. The car drives the same — it just makes less power than it should. The only fix is an intake valve cleaning — typically a walnut blasting procedure that costs $300–$600 at a shop.
An oil catch can prevents most of this from happening in the first place.
How a Catch Can Works
A catch can installs inline in the PCV hose — between the crankcase and the intake manifold. The blow-by gases pass through the can, where baffles or steel mesh cause the oil droplets to coalesce (clump together) and fall to the bottom of the reservoir. The cleaner air continues on to the intake as before.
Periodically (usually every oil change), you drain the collected oil out of the catch can. What's in there is a nasty brown sludge — proof of how much oil your engine was about to pour into your intake.
How much collects in a HEMI? Community reports show 1–4 oz of oily sludge per 3,000-mile oil change interval under normal driving. On supercharged cars, where crankcase pressure is higher under boost, significantly more.
Why Supercharged Challengers Need One Even More
Under boost, cylinder pressure forces even more blow-by past the piston rings. Supercharged builds generate far higher crankcase pressure than N/A engines — meaning more oil vapour, more often.
Additionally, oil in the intake charge on a boosted engine lowers the effective octane of the incoming mixture. On a tune already right at the edge of knock resistance, this can cause the PCM to pull timing — exactly when you want it there most.
For any forced induction build, a catch can is essentially mandatory.
What Makes a Good Catch Can
Not all catch cans are equal. The cheap ones are simple chambers with no internal baffling — they capture maybe 30–40% of the oil vapour. Quality units use multi-chamber baffle systems that coalesce oil much more effectively (80–90% separation efficiency).
Signs of a quality catch can:
- Multi-chamber internal baffling (not just a hollow tube)
- Proper inlet/outlet sizing for your engine's PCV flow rate
- Drain valve at the bottom (not just a cap you unscrew)
- Aluminium or stainless construction — holds up to heat
- Direct-fit mounting hardware for the Challenger (no fabrication needed)
Signs of a junk catch can:
- Tiny reservoir that fills up in 1,000 miles
- No internal baffles — just empty space
- Generic fittings that need adapters
- Leaking at the hose connections
Top Catch Cans for the HEMI
J&L Oil Separator (JLT) — Most Popular
The community favourite for HEMI applications. Fits 5.7L, 6.4L, and 6.2L with engine-specific direct-fit mounting kits. Multi-baffle separator design. Passenger-side and driver-side mount options. Very clean installation — looks factory.
Available for: 5.7L R/T, 6.4L Scat Pack, 6.2L Hellcat (each has a dedicated kit)
Price: $130–$180
Billet Technology Signature Series
Premium fully billet aluminium construction. Excellent separation, large reservoir, very clean aesthetic. Popular on show-quality and high-end builds.
Price: $180–$230
Mishimoto Baffled Oil Catch Can
Well-reviewed, compact design. Includes all mounting hardware. Good mid-range option.
Price: $100–$150
BBK Performance Oil Separator
Budget-friendly, OEM-compatible hoses, good quality for the price. Best entry-level option.
Price: $80–$120
Improved Racing (for 6.2L Hellcat/Redeye/Demon)
Dedicated kit for the Hellcat-specific PCV routing, which is different from the N/A HEMI. If you have a Hellcat, get a kit made specifically for it.
Price: $130–$170
Installation: What to Expect
Most direct-fit catch cans for the Challenger are straightforward:
- Time: 30–60 minutes
- Tools: Basic hand tools, hose clamps
- Skill level: Beginner-friendly
- What you do: Locate the PCV hose on your engine, cut or disconnect it, install the catch can in-line between the crankcase and intake, secure all connections
No drilling, no fabrication, no permanent modifications. The can can be removed and the factory PCV line reconnected if needed.
Maintenance: Emptying the Can
Empty the catch can at every oil change. It takes 2 minutes. Unscrew the drain valve (or unscrew the bottom cap on simpler designs) and let the collected oil drain into a rag or drain pan. Reinstall.
If you're seeing the can fill up faster than expected (more than 2–3 oz per 1,000 miles), it may indicate worn piston rings or valve stem seals — worth noting to your mechanic.
Bottom Line
The catch can won't make your car faster today. But it will help your car make the same power five years and 60,000 miles from now that it makes today. Prevention is cheaper than walnut blasting, valve cleaning, or engine rebuilds.
For a $100–$180 investment, this is one of the best decisions you can make for long-term engine health.
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