Downpipe fabrication

The straight six original 4.2L Jaguar engine had exhaust manifolds only on the left side of the block.

The V8 LS3 has dual manifolds on opposing sides of the block, so obviously the downpipes coming off of the manifolds must be custom fitted and will hug both sides of the engine block. The fitment, especially on the left side due to the steering column, is very tight.

Left side downpipe welded to the manifold

See the discussion about exhaust manifold fitment. The optimal manifold is a “center dump” configuration but a suitable GM off-the-shelf option isn’t available. Instead, a downpipe must be welded to the 2161 (Corvette 2005) manifold which is reverse installed (left and right sides swapped) to get the best clearance.

Flange ears are ground down with welded center dump pipe

The flange “ears” on the 2161 manifold were ground down with a center dump pipe welded to the modified flange face. Welding saves space and makes it possible to fit the downpipe in past the steering column.

As the pipes run past the transmission oil pan, a Y-connector joins the left and right sides together (this helps balance the exhaust pressures).

Y-connector join on the left side of the transmission oil pan

A single exhaust pipe run along the left side of the propeller shaft until a Y-split mates with the twin rear exhaust components.

Manifold join and rear exhaust split points


Rear components

The XJ6 rear exhaust components remained virtually unchanged between 1968 and 1987 except for minor hanger variations and slip joint versus flange pipe connections.

XJ6 Series 1 original rear exhaust specification

But confusion still reigns due to a proliferation of Jaguar factory part numbers that drifted from model to model. Today none of these part numbers are relevant.

Notes: [1] exits left side, not center [2] requires olive GEX7491

One popular “stock” system is an aftermarket product manufactured by Bell with five different models that reflect the minor variations of the OEM components.

Bell exhaust part numbers

The JR026 system, highlighted in yellow, is the best fit for our Series 1 and also features silencers that exit towards the transmission tunnel (unlike the original Series 1 design that exited on the left side) that will accommodate our dual pipes for the LS3 manifolds.

We use most of the long pipe, cutting it off after it joins into a single pipe (see Bell illustration above) and then fitting in a join for the dual pipes running up to the engine manifolds.

Bell dual mufflers mated to the modified dual LS3 manifolds

Muffler to silencer through-the-cage pass through


Tail pipe

The only esthetic choice in the exhaust system is the tail pipe: straight like American muscle cars or S-shaped, a reflection of traditional Jaguar elegance. There is an argument for both.

Straight pipes on an LS converted Jaguar XJ coupe

Straight pipes are consistent with the powerful 430 HP engine we’re installing. They are blunt and to the point. On the other hand, curved tail pipes underscore the British heritage.

Curved tail pipes on a 1972 Jaguar XJ6

We’re going with curved (it’s very easy to swap out tail pipes).

Chrome curved pipes complete the new look