[al lkosmal]

Mark,
If your heat exchangers are 74 or earlier, they are pretty much the equivalent, performance wise, to the SSI's, as that is the design the SSI design emulates. The only advantage to the SSI's is they modified the tube length slightly for equal length headers and they are stainless steel. Nice upgrades, but not appreciable performance upgrades over the 74 and earlier design. If, however you have a 75 or later exhaust system, you will notice a power increase.