Bruce L. Hall

This is in the wrong forum. I have a JK, I can't figure out how to delete it... sorry about that guys...

2018 Willys JKU auto

installed cold air intake and freeflow muffler... I feel gains in mid and high RPMs, but lost on the low end.... suggestions?

oh and would I benefit from a shift kit? I do drive a bit aggressively.

karls10jk

You destroyed the back pressure which eliminated your low end. Free flow mufflers are good for HP (@5,250 rpm) but bad for torque.

akguy09

Actually you changed the scavenging effect of your exhaust. Did you change the pipe diameter or just the muffler, I doubt you would see that drastic of a difference from just a muffler

karls10jk

@akguy09- have you actually removed the muffler from your jeep? I speak from experience. Removing just the muffler killed the pressure and low end. Putting the muffler back in and the torque came back....at the expense of the hp (it no longer revs freely to red line).

Take off your muffler and see for yourself.

akguy09

its not really killing the back pressure, but I understand the premise behind exhaust function. I have removed mufflers and messed with exhaust systems on multiple jeeps and diesel trucks through the years.
I'm not trying to piss in anyone's wheaties but the back pressure myth died years ago, its more about pulse energy and scavenging effect of properly designed exhaust