N20jeep

So after reading many threads with claims of power and mpg increases after certain mods. I've decided to start testing out some of these claims. I will do it as scientifically as possible. This will include fuel cell weighing and dyno runs when needed.

So what are some common myths you'd want to see tested?

On the list so far
-99 intake manifold power gains
-spark plug mpg comparisons

jeepxj19

Throttle body spacers, I have one altho I dont think it does anything besides make a cool noise

alsxj

This thread should be cool. How about the injector swaps?

dshall

X2 on tb spacer. How bout a high flow cat. Ive heard there is no such thing unless you hollow it out. But i noticed a lil gain with my high flow but others have not noticed a gain

FLETCH

K&N cold air intake

greengoblin

x2 on the injector swap

Borego

this

1996XJSport

X3!!!

1996XJSport

-MPG gains with Performance Chips
-Would resetting (learning mode) the PCM really raise your fuel economy?
-Does a free flowing exhaust really increase MPGs and horsepower?
-Does the 97-01 intake swap increase mpg's?

The Black

Borla header? Bored out throttle body 60mm or 62mm?

Andrew89xj

cutting your exhaust off at the cat ex. no muffler.. making better power?? bunch of south dakota people do this i dont believe it

1996XJSport

One time I drove for a weekend with just a cat because I didnt have enough time in shop class. It sounded like complete S***, it was beyond noisy, my gas mileage dropped almost 6 mpg's, my check engine light came on, and worst of all; it didn't have any power at all! In order to even accellerate from a dead stop at a light, I would have to MASH the gas down and it would sluggishly start rolling.

In short: Don't do it, it sounds bad, you'll get a noise ticket, your check engine light will be on, you'll run way too rich, and your XJ will drive like a geo metro; minus the awesome mileage and stupid styling.

Jeep95

X4 try the injector swap!

Tural

you definitely had something else going on. unless it's a 2010 car webbed in computers, i don't see how taking off the muffler can kill that much horsepower, or set off the CEL, or cause a drastic drop in mpg.

HairyPotter

I drove my xj with just a cat for a few weeks, and yeah it was loud (I didn't think it was ticket worthy, but unfortunately an officer disagreed , though I don't think he'd have pulled me over if my registration hadn't been dead), BUT I didn't notice any mpg loss or power loss other than maybe a little low-end torque... maybe. Also no check engine light.

So I guess the effect of the muffler varies from xj to xj.