J's Racing 4-2 exhaust manifold and 2-1 decat

The J's Racing 4-2 manifold is made of SUS304 stainless steel with a 1.2mm to 1.5mm thickness. It's a beautiful piece of engineering with a number of key design features:

• Reduced weight of 4kg Vs OEM (7.2kg)
• Simliar design to Spoon with an increased bore size and runner length

The 2-1 decat section is made of the same material and offers advantages (aside from decatting) in both bore size and weight reduction (forgot to get this weighed before fitting!). One point to note which many people are unaware of is that the design has been improved from the first iteration (still shown on the J's website) to increase durability:

• The 4-2 has a small strengthening plate welded between the two middle runners
• The 2-1 has a new flexi section

I have not seen (outside of Japan) any dyno figures of a DC5 with the J's manifold. However people have always said they would expect to see good gains from this system, primarily based on the technical, visual comparison with the Spoon manifold. Based on my dyno figure of 216 wheel HP. at Surrey Rolling Road (known for not showing 'generous' figures), it's definitely an impressive piece of engineering.



OEM on left, J's on the right. Notice the strengthening plate welded between the central runners



J's 4-2 and 2-1. See new flexi section