This idea comes from my own head. Am I ridiculously stupid?

What if I had a `Y' splitter installed somewhere after the CAT and before the first muffler. One half would continue the exhaust and the other would just have a screw plate covering the end. For autocross (or track, if I do any more) race-day I can take off the plate for reduced back-pressure and quicker turbo-spool. And hopefully generate more torque, or at least a broader torque-band. This mod is allowable, as long as it is behind the seated position of the driver and the car does not create over 102 db noise under full acceleration.

Any thoughts?

Will the exhaust back pressure differential alter computer thinking? Sounds like it would work pretty good otherwise if routing allows exhaust gas to clear out.

Can't do that according to my regions autocross rules. Otherwise, good idea.

Stock class, at least in my region, allows replacement of parts that commonly wear out (ie brake pads). Upgrades are allowed with these items. This includes exhaust. However, the OEM cat must be retained. So, any 'cat-back' exhaust is an allowable mod.

Showing my age here, but for a long time the hot rodders have had these on their street n' strip cars. Instead of unbolting the mufflers at the strip, they would simply open up the cutout. Just be careful, some locales do not allow them on street driven vehicles anymore.

See the link below for a ready made cutout from JC Witless.

-Steve Jensen
87 5kcstq<ul><li><a href="http://www.jcwhitney.com/catsubpic.jhtml?CATID=3166&BQ=jcw2">http://www.jcwhitney.com/catsubpic.jhtml?CATID=3166&BQ=jcw2</a</li></ul>

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As quattro5 mentioned, these were known as "lake pipes" in the 60's (after the salt lakes used for speed runs). Although the lake pipe connected to the exhaust pipe by the front wheel, it terminated just ahead of the rear wheel. I believe that Whitney still sells the "stubby" variety for which there is also a name, but I forget it. They used to sell a cable controlled valve so that the pipe could be opened from inside the car. My '67 Dodge has them, but not with the cable control. I have period headers and they are built into them. I believe the comments on varying back pressure are correct, at least as far as carburetored cars are concerned, I am not sure whether the compurter can correct for it. I have flowmasters so that back pressure is not substantially reduced by opening the pipes. An interesting side effect, aside from the sound of "American thunder", is that they will shoot flames. It is an interesting car, but I prefer my Audis for day to day.

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Try this one, the crankshaft in the Dodge pictured in my post above is from a "Six Pack" 440. Remember when Chrysler cars came with "three deuces",which MOPAR called a "six pack" these required an opening in the top of the hood. I just transferred this motor from my Charger, that had the "power bulge" hood.

Funny, I always thought it was Leg Pipes.

'52 Merc 2 dr hrd tp. Lake pipes with cut outs. Wonder if that's what's wrong with my ears and memory?

OK boys and girls. I ordered a cutout from JC Whitney. I'll let you all know how it goes after I get it installed.

Should work well enough, although I don't know if it will be measureable. Normally aspirated cars benefit from some backpressure. This aids in proper 'cylinder scavanging". As I assume your Audi has forced induction this is probaly not an issue. I think that in general all turbo cars improve from increased flow