[Bill UK]

As you are probably aware any modifications to increase power could result in a premature head gasket failure or worst depending on the condition of your engine. The most common exhaust modification is a front down pipe, which will take out the first cat. Another small length of exhaust pipe will replace the second cat, (often called a test pipe) some manufactures supply this as one complete unit. If you also shim the turbo waste gate with 3 or 4 washers you should be looking at boosting around 14 psi. (Which is fuel cutout) Depending on your location in the US your State may have lower levels of exhaust emissions allowable than the UK, which would restrict the removal of the catalytic converters. When you say 118 mph is this in second gear or with the handbrake on in fifth. Top speed should be around 144 mph or more Link