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I recently spoke with a noted tuner who is prepping my car for an SCCA "stock" catagory.

We were talking about allowed changes to the exhaust system and he related 3 interesing facts to me

1. Some SCCA rules allow "Cat Back" mods however the definition of "Cat Back" varies. Ie. some regard it as immediately behind the Cats where others (the Feds) regard it as the flange just before the over axle tube. I will be inquiring with the SCCA on this.

2. I asked about an after market cross over/ balance pipe and he said they really don't make much difference Horsepower wise over the stock "H" pipe if the stock one is properly massaged. "How so?" I asked.

3. And this was the most startteling thing to me! He said that not all stock "H" pipes are alike. That it is not really an open pipe as one would suspect from the outside and that there is a baffle inside of varying sizes from car to car. Some as small as 1/2"!!!

4. My next question is is this a manufacturing defect or is each "H" pipe tuned to a specific car/engine/exhaust system?

5. Can performance gains be had by reaming out the baffle? The tuner said YES BTW and much cheaper than cutting of the pipes behind the CATS and welding on the aftermarket crossover/balance pipe.

6. Anyone else know of this "H" Pipe Conspiracy?
 

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Very interesting. Kind of like the ported and polished throttle body conspiracy which adds no gains unless a head and cam package is added.
 

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You're guy is looking for a job! Although GM did change the internal size of the factory crossover, any performance changes are miniscule (sp?). I can't prove this, but I bet your tuner can't prove his theory either. I don't know what class you are running in, but in SCCA T1 (club road racing), the fastest drivers with well set up cars win. Some of the "trick" cars are fast, but the best drivers come out on top regardless.

If this is for T1, simply remove the mufflers and run straight pipes out the back. If you must run mufflers, run whater you can afford, as they all perform about the same!


Dave
 

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I have changed my "H" pipe to an "X" pipe but not for performance gain, mostly for sound quality. /phpBB/images/smiles/icon_smile.gif
 

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the smaller the hole size in the H pipe the louder the exhaust. my 99 is much louder than my 97 with the stock exhaust.
 

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I still have my H-pipe that I cut off. Does someone want to cut it and see what's inside. I'm going to "recycle" it. I guess I could cut it but it would be easier with a torch, which I don't have.
 

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Hi there,
As for the different sizes, this is true, although I do not know what the exact size was, there have been changes.
I have seen a few X pipe installs, and while we dont have a dyno here, I suspect that the only thing that changes is the resonance, and tone.
Take care, c4c5
 
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