Background

While most automotive research efforts have been aimed at performance improvements, cost reduction, and driver safety/comfort, the issue of emission control, propelled by government regulations, exerts an influence on design and system evolution.

The Clean Air Act of 1970, a strengthening of pollution laws dating back to the mid-1950s, significantly impacted future automotive development, but our 1972 XJ6 was at the threshold of this new world and largely unaffected. In general, emission standards are not retroactive; that is, a 1972 car, even if updated with a new engine, must only meet the standard at the time the model was originally sold (states have different inspection requirements, but this is typically the case everywhere).

Therefore, our 1972 Jaguar is unencumbered by emission requirements which gives us the flexibility to implement various control systems or not, on a case-by-case basis.

Emission controls for E-Rod LS3 crate engine version

As a rule of thumb, emission control does not enhance (and may detract) from performance, increases cost, and has no impact on driver safety or comfort. It does tend to improve gas mileage and certainly reduces various air pollutants.

It is worth noting that even without any emission control, modern engines like the Chevy LS3 are much more efficient and cleaner than the 1972 Jaguar XK engine, so swapping in any new engine is a de facto improvement in air quality.

LS3 crate engine versions

The LS3 crate engine comes in either a 50-state emissions-compliant version, called the “E-Rod”, or one without emission control systems introduced since the early 1970s. This table summarizes the significant differences.

LS3 Crate Engine Emission Verions
Technology E-Rod compliant LS3 no controls
ECM with emissions-legal calibration yes no
Catalytic converters two none
Post-catalyst oxygen sensors two none
Positive crankcase ventilation (PCV) foul and fresh air fresh air only
Fuel tank evaporative (EVAP) emissions canister yes no
EVAP purge solenoid yes no
Fuel tank vapor dome yes no
Harness/fuses for emissions yes no

Non-compliance option

We elected to follow the no-emission-control route that GM provides in its crate engine offerings, but the path is not without some legalistic confusion. To begin with, GM publishes this cryptic notice on the first page of LS3 crate engine documentation:

Crate engine parts, according to GM’s vague disclaimer, are for “vehicles which are used off the public highways” except for certain “pre-emission” cars (like the 1972 Jaguar XJ6). GM also cautions against modifying any existing emission controls. In other words, unless the crate engine goes into a purpose-built track car that never is on public roads, the product should only be installed in models sold before the Clean Act regulations were first enforced. Catalytic converters, for example, began to appear after 1974. So basically, “pre-emission” means pre-1975 model years.

LS3 crate engine modifications

Even with the non-compliant LS3 version, GM still installs the feeder tube and holder for the EVAP purge solenoid. Therefore, this must be removed from the right side of the engine block, and the vent tube end on the left must be sealed off. A compelling reason to remove that EVAP purge solenoid housing is that it conflicts with the A/C compressor pump mount on the Holley front accessories assembly.

EVAP vent must be sealed off

Purge solenoid housing should be removed to enable A/C pump mounting

Fortunately this EVAP component easily unbolts from the right side block face, and the air hose detaches by pressing in on the flat portion of the white plastic clip.

PCV fresh air vent tube

The final adaptation is to hook up the fresh air end of the PCV system by inserting a hose from the right valve cover vent tube into the collar mount that holds the mass airflow (MAF) sensor. This hose must be inserted between the throttle body and the MAF sensor, not upstream of the MAF (this is a source of much confusion on LSX forums). The fresh air inlet is actually a vacuum that draws in outside air. When placed downstream of the sensor, the MAF can will measure the amount of air drawn in by the vacuum suction (this is a little counter-intuitive perhaps).