True Dual Exhaust
Shown below are two different ideas for improving the exhaust of your 454SS truck.
The first deals with the 1991-1993 454SS "True Dual" GM factory exhaust system. This factory system is fabricated from "409 Stainless", and will give you a "Factory" look if you are thinking of upgrading your restrictive 90 SS system. These parts will bolt directly into a 90 SS, and will work nicely with the stock engine & computer calibration. Best of all you can buy all of these parts at your local GM dealership. This system will produce somewhere near 255 Hp, on a stock 90 SS engine, which is roughly what the 91-93 SS trucks came from the factory with. Of course, you should check the emissions legislation of your State/Province to determine whether this type of exhaust swap is legal.
The second deals with how you can reproduce all of the same benefits of the factory system, and more, by using aftermarket components and a little bit of custom fabrication. This could apply to either a 90 SS, or a person interested in improving their 91 – 93 SS. If you don’t plan on leaving your engine stock, then this may be the best option for you in order to meet future horsepower goals. Again, you should check your local emissions legislation.
In either case, if you drive your truck hard or have performed additional engine breathing modifications, you should borrow a Service Scanner (GM Tech I, Snap-On, OTC, etc.) and verify that your TBI fuel system is not leaning out at the top end, once your new exhaust is in place.
Look for a safe Oxygen Sensor value of 800mv, or more, during wide open throttle and high RPM operation. Leanout may also lead to detonation at the top end, so also look for spark retard (ESC Retard = YES). If leanout is suspected, then you will have to buy an adjustable TBI fuel pressure regulator (Hypertech, JET, Turbo City, etc.) and install a fuel pressure gauge that you can read while driving. These "checks" are most easily performed with the help of a co-pilot.
Usually, fuel pressures between 11-13 psig will cover most bolt-on modifications. Never run more than 13-15psig fuel pressure at idle, or around town, or your engine and catalytic converter will load up with excess fuel and carbon.
GM Service Parts For 1991 - 1993 454SS Factory True Dual Exhaust
V8 (L19/7.4N) C1500