Loss of torque

[sherv]

I have a 02 GTS. I have Borla Cat Back and Roe Racing Hi-flo cats. I noticed that when i replaces the factory Cats with the high flow cats, I lost some torque. I’ve been told if i upgrade the headers , I’ll gain that torque that I lost. Anyone have any input if this is true? Thanks

[Viper4Christ]

Dyno comparison of before and after exhaust install? Typically on a naturally-aspirated setup, if you remove the muffler's you lose a lot of torque because of not having any back pressure.

The only exception to this is with a turbo setup as the hot side of the turbo acts like a muffler and also determines the torque curve depending on it's A/R size.

[csmwiese]

Maybe it feels like a loss of torque (but not really) because the RPM's are climing faster now with your current set up. I removed my cats on my 2004 and notice any losses in power or torque, different motor I understand. I had a 1997 GTS with no cat with no loss in torque/power in it either.

[sundiego]

You must have a finely calibrated butt dyno.

[b3rndtt0ast]

Originally Posted by Viper4Christ

Dyno comparison of before and after exhaust install? Typically on a naturally-aspirated setup, if you remove the muffler's you lose a lot of torque because of not having any back pressure.

The only exception to this is with a turbo setup as the hot side of the turbo acts like a muffler and also determines the torque curve depending on it's A/R size.

Wrong. Removing back pressure does not hurt engine performance.

[Viper4Christ]

Originally Posted by b3rndtt0ast

Wrong. Removing back pressure does not hurt engine performance.

Removing all back pressure with a full straight pipe setup certainly drops torque down a bit and I've seen it on multiple NA setups over the years regardless of the manufacturer.

Years back, I was helping a buddy with an exhaust system swap and we tested his setup with and without high-flow mufflers. Mid range power fell off completely in the straight-pipe configuration and after reinstalling the mufflers, it came right back.

Engine Masters has a few videos on the subjust and the lowest power output combo always ends up being the zoomie or straight pipe setup.

[Red Snake]

Take a look at dyno runs for Roe cars. Cars with no cats always make more torque than those with high flows or stock cats.









<-------- 660rwhp/710rwtrq with no cats, headers and full 3" track exhaust.





.

[b3rndtt0ast]

Originally Posted by Viper4Christ

Removing all back pressure with a full straight pipe setup certainly drops torque down a bit and I've seen it on multiple NA setups over the years regardless of the manufacturer.

Years back, I was helping a buddy with an exhaust system swap and we tested his setup with and without high-flow mufflers. Mid range power fell off completely in the straight-pipe configuration and after reinstalling the mufflers, it came right back.

Engine Masters has a few videos on the subjust and the lowest power output combo always ends up being the zoomie or straight pipe setup.

Loss of velocity kills torque. Not back pressure.

[dirtbag]

I feel a fluid dynamics discussion will pop up in 3....2....1

[Viper4Christ]

Originally Posted by Red Snake

Take a look at dyno runs for Roe cars. Cars with no cats always make more torque than those with high flows or stock cats.



<-------- 660rwhp/710rwtrq with no cats, headers and full 3" track exhaust.

Right, cat removal opens up exhaust flow to help increase power. I was referring specifically to mufflers and how a quality built high-flow muffler in a S/C or N/A setup helps to maintain mid-range power, excluding turbo setups.