Team-BHP - Same issue - opposite effects on low end torque

We have an Accent 1.6 (2003, 26k run) and an Esteem (1998, 95k run) in our family. Both developed holes in their silencers. While the Accent's bottom end grunt dropped, the same on the Esteem improved (neither of these cars has good low end grunt). Any idea why it is so? Ideally, the low end should improve due to lack of back pressure, right? How do free-flow exhaust makers design the exhaust specifically to increase low end/middle rpm grunt? Puzzles me.

As of now:
The Accent's silencer (at the tail end) was repaired and it now gives normal low end torque.

I am driving the Esteem in Bangalore and it helps to have better lower end grunt (the second cog is unreasonably tall, which adds to the problem) and that extra noise especially while driving through busy streets. So keeping it as such until the PUC is due (the engine starts quickly, and the idling rpm has increased as and when the exhaust leak was noticed). Love the exhaust note though wife feels embarrassed when I drop her off at her office gate :)

In most stock cars, the exhaust manifold is designed for a higher revv band. But due to the back pressure caused by the resonators/cat cons/silencers, you end up getting a better low end.

When i first ran my Vtec with just the stock exhaust manifold, i was shocked to find that all the low end torque had just vanished. But beyond 4500-5000 rpm, the acc was amazing.

Shan2nu

Didnt quite get it: how does backpressure help with torque?
Any backpressure just adds to robbing your engine of the torque that could've been delivered to the crank, but since the piston has to overcome the backpressure, it uses that energy to throw the gases out.

Now whether it is low RPM or high RPM, why should it matter?

Are you sure there is a very big difference being felt? Holes in muffler will not really change any power output, apart from sound factor. They cannot be really compared to the free flow exhaust system. Unless the pipe has completely given away from the restricting muffler bits.

@Jaggu: A normal driver will not notice the difference. I do for sure feel it. The Accent's muffler didn't even have 'holes', but some layers had come off due to corrosion.
Not comparing it to the free flow exhaust in terms of the magnitude of difference. My younger bro, who also listens carefully to the car, felt the same in the Accent (he is yet to drive the Esteem in this new state.. not sure how bad the hole is)

I believe the difference is noticeable since both the abovementioned cars in stock condition have pathetic low end grunt.

Quote:

Originally Posted by Jeep (Post 878705)

Wierd.
But the low end grunt dropping is not something that should have happened. If the exhaust gases are allowed to get out freely without coming to catalytic converter, then the grunt should improve.

Its understandable in case of esteem.

Back pressure never helps any grunt in almost all normal road cars.