"Factory Style"
True Dual Exhaust
For Your 454SS !

By: BlownSS

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

(Illustration courtesy of Dave Desjardins - Thanks Dave!)

Make Your Own 1991-1993 Style True Dual System With Aftermarket Components

This picture shows an example of a custom street system that was hand-built for a very healthy 1991 454SS project, and serves to illustrate some important concepts that you may want to consider in your custom street exhaust.

If emissions regulations prevail in your area, then read on, and then take a second look at this picture.

The headers were built by Belanger’s Custom Exhaust (Irvine, California) from thick wall (.065") tube, and formed into a long runner Tri-Y design for good low to mid range torque. The cross-over pipe sections (2.5"x.065" wall) were mandrel bent and welded by Canadian Pragmatics (Toronto, Ontario). The mixing chamber was fabricated from .065" thick pipe and plate material (by the owner), and includes an oxygen sensor bung. The converters are stock 91-93 SS units. The mufflers are from Flowmaster (Santa Rosa, California) and are positioned side-by-side on edge when installed. The tailpipes are stock 91-93 SS units, and exit in the factory location. The rear hanger assemblies are stock 91-93 SS parts. The front hanger is a slightly modified version of the stock front hanger.

Each joint is free from clamps and gaskets. Instead, two thick ground flanges can be found at every joint. One flange has "through" holes for stainless hex head bolts, while the mating flange has threaded holes to accept the bolts.

After this picture was taken, everything was HPC coated (Manchester, Connecticut) inside & out, end to end, with a thermal barrier protective coating.

The important features to note about this street system are:

• The thick tubes and HPC coatings trap heat, and help the oxygen sensor, and catalytic converters to work as the factory had intended. No need for a heated three wire sensor!


• The AIR pump tube connections are present, and in the factory locations at the exhaust ports.
• The Oxygen Sensor is in the factory location, and it "senses" both of the exhaust streams mixed together at the same point in time. The sensor is also "buried" into the exhaust flow, so as to sense more consistently.


• The Catalytic Converters are in approximately the stock locations.


• The exhaust streams from both sides of the engine are quickly "mixed" and then split in a very smooth "mixing chamber" of minimal volume. This provides two huge benefits. More overall flow potential, and significantly less noise. In fact the harder and faster you drive with this system, the quieter it becomes!

If you are into the factory, or "sleeper" theme,
most people will never know what you have until it is too late!

Installed, the system looked like this:

Blown SS's 454SS

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