A high-flow Cat will flow the same as a straight pipe in that application. My oversized CAT is invisible to the car. It flows BETTER than a 2.5" pipe. I got a cat with 3" inlet and outlet for that reason, and had adapters welded on for it.

why do people buy these if they dont make a difference?
for instance you have plugs and wires??
just asking

Magnusson nose drive is an OEM replacment. He must have fried his.
Gatorback belt prevents slipping with a smaller SC pulley.
Borla tips? Looks and sound.
Plugs and wires are a tuneup item. Ever replaced yours? With hotter coils, a good performance wire CAN be a small power-adder.

my personal opinion is all those small things add up in the end

How is a replacement nosedrive, a pair of Borla tips, and a belt going to 'add up' to horsepower?

I'm not the best on guesstimating HP but I'll try and give you a little food for thought, if its worth anything...

12 things maybe 5 actually make HP. Unless your plug wires are old you won't get a gain from replacing them no matter how big you go. Larger wires are offered to accomidate a hotter ignition system which will allow you to enlarge your plug gap which coupled with more air and fuel will give you power. But wires on their own won't because its part of a whole system. The Magnuson Nose Drive has been looked at before (personally) and it is a stock replacement, it offers a performance gain if you order the optional smaller pulley which it seems as though he has. But thats really just an expensive pulley replacement, unless it was failing him to begin with (somewhat rare) he spent money for nothing. The gator back belts are zilch on the HP gain, not even coupled with the other things. Some may argue that it adds "traction" to the supercharger pulley allowing it to spin better. Something you have to remember is that company estimates on HP gain are not only useless but if they are anywhere near accurate they were done in lab type conditions with every variable taken care of. In other words when they were testing the pulley they would have made sure to use the proper belt size and tension anyway. It would be like claiming a big HP gain (over stock) by replacing your 100,000mile plug wires. You MAY see a gain (0.1-1hp), but you're just getting back what you paid for anyway. Of course the o2 simulator (and pipe) is only so he doesn't get an error message about his cat not being there, another no-hp modification. Platinum plugs are only for durability and offer no HP gain. The only gains possible from plugs are the somewhat controversial plug indexing and making a larger gap coupled with more air and fuel but then most of that gain would be by the added fuel and air anyway, its only common sense that you need to be able to burn it all which our coils don't seem to have a problem with anyway seeing as some are running 11'* down the track with stock ignition. What does he have? A smaller pulley, an exhaust, and a CAI. That ECU makes me wonder but the gains could vary wildly from setup to setup so I can't guesstimate on it. Unless his CAI is insulated from the under hood temps he may very well be negating most of the gains he paid for. You always want a cooler intake charge, common knowledge, and a smaller pulley adds heat because the more you compress the air the hotter it gets. Its been estimated that 1psi adds 10deg to the charge. If he goes from 7-8psi to 10-11psi thats going from winter to summer driving performance. Ever notice you're a little quicker when its cold out? Add to that the hot exhaust air he'* pulling in while he sits there staging for the run or stopped at a red light. Remember, all company estimates are done by taking out all possible variables that would negatively effect the outcome. So I think its safe to assume that the 10-20hp you read about from a CAI is when its actually pulling cold air, same would go for the pulley. So there'* my thoughts on the matter.

Wow that was quite a read Dr. Jay. I will have to agree with most of your points. Only thing would be the CAI. Because he is running a smaller pulley, he needs more air. The supercharger demands it. Therefore I do not believe he is negating very much, even with the air being hotter. Quite a few of us here run open-cone filters, and if it is far enough away, its not much of a problem. But I will agree his air charge will be warmer.

Well, my first question is why does the guy claim 330hp??? Does he have a dyno sheet and he based the number off of the wheel horsepower, or is he just adding everything up and guessing?

And that 330hp may not be as far off as you are thinking. I don't think it is accurate, but it could easily be within 10hp of that.


The K&N filter has virtually no gain. Especially since it is an open cone, meaning it is sucking in hot air from the engine bay. It makes a nice improvement in intake sound though. The snout, like willwren said, probably a replacement. A gatorback belt just helps the belt not slip. The tips, obviously an appearance item. The plugs are probably to help reduce KR. The wires just look good and make plug changes easier.

Now for the mods that probably did something:

-3.25" Supercharger pulley
-TOG Headers
-Borla Cat-bac exhaust
-Catalytic converter removed
-Replaced with a off-road pipe/O2 simulator
-After market ECU

The headers on a completely stock GTP add 18whp & 16wtq. Thats 22.5hp & 20lb.ft at the crank. Bringing our total power at this point up to 262.5hp.

Borla Exhaust, according to borla adds 12hp to a stock GTP. Now we are up to 274.5hp.

The offroad pipe has proven 8whp on a stock GTP. (it gets rid of the u-bend, cat, & downpipe). This is 10hp at the crank. Bringing the total now up to 284.5hp.

Now we have the pulley. Assuming he has all KR problems solved, the 3.25" pulley should add 30+hp or so. This brings our total up to 314.5hp.

If the aftermarket ECU is a DHP, because of the fuel table, timing tables, and KR changes in the PCM, it can add 10hp or MORE in some applications. So lets say it only added 5hp in his application, that still brings him to approx. 320hp.

Wow, this number is suprisingly close to his guess. Now you take all of those exhaust mods and their gain on a stock GTP running 4-5lbs. LESS boost than this guy, and their gains should be higher because of the need for increased exhaust flow.

So really, the guy could be making 330hp. I am just curious as to how he came up with that number.

Shawn