I am thinkin about doin the exhaust on my 1988 f150 351W will I get more low end torque by keepn a Y pipe set up or runig true duels

 

Y/H/X pipe will be best for low end torque. X pipe is best for both horsepower and torque

 

Flow master makes a American thunder series that's a cat back set-up that works great all around performance

 

A larger single or smaller dual pipes will both reduce back pressure and give the same performance. Some kind of crossover increases scavenging for better power and mpg as well as canceling exhaust pulse which makes that putting noise you hear on Hondas. The main difference is in sound preference.

 

How much back pressure can you lose before you lose torque?

 

It's not so much loosing back pressure as loosing velocity. if the pipe gets too big the gasses move more slowly and decrease scavenging. Scavenging pulls exhaust out of the cylinder leaving a vacuum which draws fresh fuel into the cylinder and increases torque. The rule of thumb I have seen is to use one 3" pipe or twin 2 1/4" pipe on a 302 motor. Some vehicles have egr systems powered by back pressure ( 80's jeep Cherokee for example ) and changing the stock exhaust caused driveability and emissions problems.

 

Any ROT for a 5.8?