The Selin is going to be more stable and would offer more consistent A/F, especially with just chip tunes. The Idle and low speed would also be better as the JWT design was at best, less than perfect. The only difference in power with a custom tune would be from the Selin Elbows offering less restriction. The JWT elbows are cast aluminum and crazy thick. The reduced side is a bit smaller inside than the stock pipe they connect to. The outside diameter of the cast elbows on the reduced side is 2.5" as they use a 2.5" coupler to connect to the thin wall tube that is in the car stock. The cast elbows are about a 1/8" thick or more making the inside diameter about 2.25". The Selin Elbows are Silicone and they are a full 2.5" at the smaller end as they go over the stock thin wall pipe. It all adds up........
