trompazo

There are many threads and comments that the Side Mufflers are louder and many comments that they produce drone. This is to be expected at below 4000rpm.

However, in the OEM setup, when the valves open, would the exhaust flow not take the path of least resistance and all go out the center muffler only. IN addition, given the upper inlet on the factory center muffler has more baffling and is smaller in diameter, when the valve is open I would assume that all the flow is out the lower larger inlet that has minimal baffling.

Therefore, it would appear that the Side bypass should only be louder than OEM below 4000rpm, but after that the exhaust flow should be the same (bypassing the side mufflers and out the lower inlet of the Rear center).

Does anyone who has side bypasses notice more sound even at WOT, or just when the valves would normally be closed? Any objective measurements at tracks showing the side bypasses result in higher peak dBA?


Also, in theory, the TPC and Fabspeed valved side deletes should not have peak volumes any louder than stock as there should not be flow through the side mufflers at WOT. But if they are louder, it would imply that the side mufflers still have some flow at WOT.

Would like to get some side deletes but worried about not passing sound on certain tracks.

Tom@TPC Racing

Sorry I haven't measured sound decibels with TPC side muffler bypass pipes. But my subjective feedback is at peak volume its not louder than stock. I do believe that even with the valves open some exhaust gas do flow through the upper(smaller diameter) pipes into the upper chamber of the center muffler for some level of sound suppression.

Here's a video link of a 997.2 RS with 4.0L engine build, Cup 100-cell cats, and TPC side muffler bypass pipes. Its not that loud at all.
https://instagram.com/p/BO3Hc5KhStO/

trompazo

Hi Tom,

Thanks for your reply. On your website it says "Better exhaust flow management allows for increased torque between 2,600 and 5,600 rpm, as well as increased horsepower between 5-8,250 rpm."

Do you have before and after dynos that quantify these gains?

Thanks

OCturbo

Good question. I have always had the same thoughts as you, but have never asked the question!

Tom@TPC Racing

My pleasure to reply. The primary objectives on our design of the TPC side muffler bypass pipes are 1) to reduce static weight over the rear axle of the vehicle, 2) to reduce rotation inertia during corner entry, and 3) significant reduce radiating heat near the tires and the ignition coils. We never expected to have any power gain, in fact we were happy not to noticed a loss. To our pleasant surprise, our 2015 991 GT3 shop car showed a gain in output over stock via the factory Performance calculation function(see image below). We feel that the calculation function is valid for before/after comparison since its based on calculated engine load. We have local customers who reported the same gain. To answer your question, no, we didn't use our DynoJet, but we did use the factory Performance calculation function before/after on the same day, with same weather condition, on the same road, without disconnecting the battery to reset the ECU.