Supples’ Pub

In the GTO community, and likely all car communities, 2003 Cobra’s are regarded as a real mixed bag if you happen to come across one on the street or at the track. A bone stock Cobra is a decent match for the LS2 GTO, being similar in curb weight and rear wheel horsepower. But how many bone stock Cobra’s are there out there? Very few - it could have 400HP or 600HP with little indication either way until it lets loose.

I’ve always heard that these pony cars are very receptive to mods, gaining a lot of horsepower from relatively simple changes. It wasn’t until yesterday when I came across a YouTube video of HorsepowerTV did I realize just how easy it is.

Background

The well known 4.6L DOHC V8 got treated to an Eaton M112 supercharger, forged internals and a cast iron block. While the factory rates these motors at 390HP/390TQ, the crank horsepower is more likely in the 420-range.

These are respectable numbers for a relatively small displacement engine; at the time GM’s base Corvette featured 350HP from the OHV 5.7L LS1 while the ZO6 supercar was at an incredible 400HP with the same 5.7L displacement, albeit entirely different heads, cam and intake. The F-Body cars, discontinued in 2002, were also available with the 350HP LS1 and were the true target of the Cobra. While the Cobra’s power is great, it weighed several hundred pounds more than the Corvette and was still a bit heavier than an F-Body.

On to the good stuff. HorsepowerTV took a bone stock 2003 Cobra and got some great before & after figures on some VERY easy mods. Modern performance engines can benefit greatly from computer tuning - using either a pre-programmed package to alter the stock computer programming or having an individual custom-tune the computer for maximum performance. The reality is that most factory programming maximizes engine safety (in terms of cylinder detonation), fuel economy and emissions. Tweaking things like the ignition timing and air-to-fuel ratio can result in strong performance increases and even better gas mileage.

Supercharged engines also have an easy avenue for performance increases. There is a pulley on the snout of the supercharger which snakes its way to the crank and thus the supercharger is rotated as the crank rotates. Changing the rotational diameter of this pulley and matching an appropriately shorter belt effectively changes how fast the supercharger itself rotates, allowing it to compress more air in the same amount of time.

Now, if I’m not mistaken, changing pullies will also increase the boost generated and thus put more pressure on the engine internals. Care needs to be taken here to not put too much stress on the internals or serious damage can occur. Disclaimer out of the way, below are HPTV’s results with their 2003 Cobra:

How does 63 RWHP from a computer tune and a very simple pulley replacement sound ? It is pretty impressive to me, making an already potent car downright deadly.

Also note that if you assume even a very optimistic 10% drivetrain loss, we can figure the crank horsepower to be about 400. The parasitic loss is likely in the 15% range putting it in the 420 crank HP arena - so much for truth in advertising.

And finally, I thought I would share some technical specs - as most of you know, I love the hard specs of any machine.

As you can see, the cars are very well matched. The GTO’s slightly lower stock horsepower is likely made up by the slightly shorter gears. If we were comparing off the line performance, the nod would likely go to the Cobra with its 275mm tires and theoretically better traction.

Enough arm-chair-drag-racing, the Cobra looks to be a very potent platform. Today’s prices for a good-condition Cobra seem to range in the $20-30K range, certainly a great HP/$ value. If you can find it at MSRP, the new GT500 offers a 5.4L supercharged motor good for 500 bhp, the newer TR6060 transmission, more advanced safety features and a host of smaller improvements. But at $43K+ MSRP, you get stuck with a plain old live axle instead of an independent rear suspension like the 03 Cobra and a decidedly lower value in performance - not counting the huge markup dealers want to charge for this one-of-a-billion-Mustang-versions that is oh-so-unique.

I’ll leave you with this - the penalty of having all those cams on a V8