Andy's 2003 Cobra

This is the 2nd 2003 cobra I've owned. Look at the story on the first one

Here's a look under the hood. That's the supercharger sitting on top. It's a "roots type" (two counterspinning screw type impellers) made by Eaton. It produces a maximum of 8lbs of boost pressure in the stock setup. This makes the engine put out about 390 horsepower. A simple change of the pulley sizes on the supercharger will increase the boost and horsepower. Other owners have been getting around 450HP at the rear wheels with a few modifications. This engine has a forged crankshaft, forged rods, forged pistons and an iron block (not aluminum as in previous years). This allows the internals of the engine to stand up to the beating of high horsepower production. The engine displacement is 4.6 liters, or about 281 cubic inches (390HP from 281ci, not too shabby!!!!) This engine had dual overhead cams with two intake and two exhaust valves per cylinder. Note the yellow tank at the lower part of the picture. This is the coolant tank for the intercooler. The intercooler is a radiator of sorts that sits under the supercharger and cools down the air before it enters the engine. This lets you get a more air packed in, and therefore it helps make more horsepower. The intercooler has a radiator on the front of the car to dissipate the heat (just like the engine radiator). The intercooler is basically a heat mover. It pulls heat out of the air entering the engine and dumps it to the outside air.

Click for larger image

Here is dyno graph with 10k miles on the completely stock car (including air silencer and paper filter). Best pull was 390.1RWHP/372.8RWTQ. Worst of three consecutive pulls was 381.7RWHP/371.8RWTQ. Average of the three pulls 384.9RWHP/372.3RWTQ. You can see how the HP degrades as the engine and blower get hot. Not bad for a completely stock car that's rated at 390 *flywheel* horsepower.

Notice the Air/Fuel has the characteristic of the stock tune. It's lean at low RPMs (passes emissions tests) and very rich at high RPMs (cautious safe tuning). Looks like the Air/Fuel is spot on 14.7 at low RPMs (optimal for fuel efficiency).

After installing a 6lb lower pulley, Borla Stinger cat-back, and a high flow air filter the car made 429.0RWHP/452.7RWTQ. The tune needs more fuel below 3800 RPM. The torque looks pretty good, but I'm a little disappointed in the HP number. The cats and stock H-pipe need to be replaced. I think the inability to freely flow at high RPM is killing my horsepower

I have since installed long tube headers and an off-road H-pipe. I haven't dyno'ed with this setup yet. I'm hoping the removal of the cats will get my horsepower numbers up with my torque. Somewhere in the 450/450 range. I also changed the cat-back from the Borla stinger to a magnaflow. The Borla stinger was VERY loud with long tubes and no cats. The magnaflows are loud at wide open throttle, but they have a nice growl with normal driving. The Borla was almost unbearable at anything over 20% throttle.
The headers are almost totally hidden when looking from the top of the engine. Also note the moved location of the dipstick. The dipstick tube had to be bent. The headers include a bung for an O2 sensor on each side. The H-pipe also has bungs for an O2 sensor on each side. The front two O2 sensors are much farther back than the stock location. I had to cut the wires on the stock O2 sensor and solder in an extension. If you plan on doing something similar you need to be sure to use heat resistant wire and properly insulate the soldered connections. I used wire with teflon insulation. I think teflon is good up to a temperature of 400F. Teflon also resists rubbing a hole in the insulation. I covered the four wire group with woven metal tubing (aka 'snake skin') and shrink wrapped the end to keep it nice and tidy. You don't want these wires flopping around and touching the exhaust.

The headers and H-pipe from below. The ground clearance is less than with a stock exhaust. I haven't had any problems when driving on the street. I have scraped the exhaust in a friend's driveway with a big drop on the edge of the concrete

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