I have a 98 f150 with a 4.2L V6. I already have a custom Flo-Pro dual exhaust, but I wanted it louder. A friend of mine with a 95 f150 straight 6 just cut his muffler off. I didn't want to do that so I had a bypass/cutout valve installed. I like the sound of it now but I noticed that my acceleration is not as good as it was before the valve was put in. Is the sudden loss of backpressure bad for my engine?
Thanks,
check out my pictures:

https://www.f150online.com/galleries...y.cfm?gnum=782

 

Also, a friend of mine said that putting new JBA headers on my 4.2 is bad for the engine because I don't have any other significant performance upgrades. Is that true?

 

i don't think headers will create any problems, but theyre more useful with a filter because your pumping in more air, so more air out, make sense? no muffler isn't harmful, but your check engine light may come on, and you lost low end torque because our engines like back pressure to make low end torque. you took out pretty much all back pressure, so have little low end torque.

 

harmful=no
the best performance and torque=no
the best sound=questionable

 

Would reseting the computer help? I read somewhere where you take off the + side at the battery, turn some power stuff on in you vehicle, which drains residule voltage and then reconnect and it will reset setting when you start.
Kinda wondering because I was thinking of doing the same thing on my 4.6.

 

When I did the exhaust on my stang, I researched this a lot. If you take off the mufflers, and therefor have very little back pressure you will lose performance, unless it is a circle track race car that never drops below redline. The way exhaust pulses work, is when the gas is let out of the head, it travels down the pipe. As soon as it meets some sort of change in diameter in the pipe, it sends a wave back towards the head. A perfect exhaust system is designed with the crossover (H part of H-pipe) located at the precise location that causes that pulse to return to the head at the exact moment both intake and exhaust valves are open. This creates a sort of vacuum, as the pulse turns around again, and therefor draws in the intake charge. I don't remember exactly how to determine this location, but it has something to do with coloring the pipe with crayon, running the motor, and looking for the ring formed.

I've never done this or seen its done, just what I've heard from other people who seemed quite educated in the subject.

 

Oh yeah, point behind the above post, incase I wasn't clear, is that with no backpressure, there will be no pulse, or a weak pulse. At high RPM, it doesn't matter so much, but at low rpm, the engine doesn' t make as much vacuum on its own, and so every bit that the exhaust can help with is good.

 

Only to the ears............

Most of them I "hear" around my house sound like "Bubba" coming home late at night...........

But that's just my opinion.

 

I'm with Mitch on this one. I've heard 4.2's that have had their exhaust opened too much and they sound like runaway lawnmowers. Actually my lawnmower sounds more macho than these rides. There is probably a good setup for the 4.2 but losing you muffer won't be it.