The crankcase ventilation (CCV) system on the 6.7L Cummins plays a vital role in managing blow-by gases and maintaining proper crankcase pressure. However, the factory design often results in excessive pressure build-up, oil consumption and turbo contamination. This article details actual pressure testing of a stock CCV system, identifies key restriction points, and explains why CCV redirection or PCV redirection is often necessary for optimal engine performance and longevity.
Why Test CCV System Pressure?
Excessive crankcase pressure can cause:
· Oil leaks (seals, gaskets, turbo feed lines)
· Increased oil consumption (blow-by carrying oil into intake)
· Turbocharger contamination (oil coking on compressor wheel)
· Reduced engine efficiency (higher crankcase pressure = more parasitic loss)
By measuring pressure at different points in the system, we can pinpoint where restrictions occur and determine the best solution—whether that’s a CCV reroute kit, a catch can, or a complete redesign.
Testing Methodology
We conducted pressure tests on a stock 6.7L Cummins using:
· Digital manometer (measuring in inches of water column, "H₂O)
· Pressure taps at critical locations:
o Valve cover outlet (pre-CCV restriction)
o Post-CCV hose (before turbo inlet)
o Crankcase dipstick tube (baseline pressure)
Tests were performed at:✔ Idle (700 RPM)✔ Mid-load (2,000 RPM, light throttle)✔ High-load (WOT, 3,000+ RPM)
Key Findings: Where the Stock CCV System Fails
1. Excessive Crankcase Pressure at Higher RPM
· Idle: ~1.5" H₂O (acceptable)
· 2,000 RPM: ~4.2" H₂O (approaching problematic)
· WOT: 8-10" H₂O (far beyond ideal)
Why It Matters:
· Pressures above 4-5" H₂O can force oil past seals and into the intake.
· At WOT, the stock system cannot evacuate blow-by efficiently.
2. Major Restriction: Factory CCV "Rooster Comb" Baffle
The stock Cummins CCV system uses a "rooster comb" baffle inside the valve cover to separate oil from blow-by gases. Testing revealed:
· Pressure drop across baffle: ~3.5" H₂O at high RPM
· Oil carryover: Significant mist still reaches the turbo inlet
Problem: The factory baffle is too restrictive and doesn’t separate oil effectively.
3. Turbo Inlet Contamination Risk
· Post-CCV testing showed oil mist accumulation in the intake piping.
· Over time, this leads to turbo coking and intercooler clogging.
The Solution: CCV Reroute or Performance Baffle Upgrade
Since the stock system is restrictive and inefficient, there are two proven fixes:
Option 1: Full CCV Reroute (Vented or Catch Can)
· Eliminates intake contamination by venting to atmosphere or a catch can.
· Reduces crankcase pressure to safe levels (<3" H₂O at all RPMs).
· Best for modified/high-performance engines where blow-by is increased.
Option 2: High-Flow Baffle Upgrade
· Replaces restrictive "rooster comb" with a better-flowing design.
· Improves oil separation while maintaining emissions compliance.
· Good for stock/near-stock trucks where rerouting isn’t desired.
Performance Gains from a Proper CCV Solution
✔ Reduced oil consumption (less blow-by oil loss)✔ Cleaner turbo & intercooler (no more oil coking)✔ Longer engine life (less pressure on seals/gaskets)✔ Better throttle response (reduced crankcase pumping losses)
Upgrade Your CCV System Today
If your 6.7L Cummins is suffering from excessive crankcase pressure or oil consumption, a CCV reroute kit is the proven solution. Check out our high-performance CCV/PCV Reroute Kits to optimize your engine’s breathing and reliability.
