Still no links saying back pressure is a good thing?

http://www.uucmotorwerks.com/html_pr...torquemyth.htm

so i reset my ecu and it did help it out have my torque back. and the gas peddle isn't as stiff when i get on the gas. now im just having an idle issue at the lights sometimes.

Every time I hear about an intake system or exhaust system that was "poorly designed" by the OEM, it always originates from somebody selling something that bolts on or replaces the intake or exhaust. 99.99999% of the people selling this stuff could not get a job with the OEM.

If you want more horsepower, all things being equal, you need more displacement, more compression, more cylinders, and more volatile fuel. All of these solutions burn more fuel...lots more...but they do work. On the other hand, nothing you do to the intake and exhaust is going to give you more power. All that happens is you shift the point in the RPM range that the power is delievered OR trade horsepower for torque. Or...you lose some of both, which is usually the case. Where there are gains, it is because you break the law by circumventing the emissions system and, sometimes, break the engine by fooling with something you don't truly understand. There ain't no free lunch.

If you want cheap power, change gearing or add nitrous. With the later, you'll destroy the engine, sometimes very quickly. With gearing, you'll just wear it out a little sooner. Again: No free lunch.

I know I'll hear arguments. There are always true believers that think K&N makes horsepower, money for nothing and chicks for free. But if you truly are not satisfied with the output of a 4.0 liter straight six...buy a V8. Remember: with the Jeep motor, it's just a little bitty thing with 242 cubic inches. It makes outstanding power for that displacement and is reliable to the point of amazing. It's the "deal of the century"...but if you want to mess with excellence, be my guest. I'm sure some dude in Van Nuys has the magic answer.

well im going to be regearing way in the future for when i have a bigger lift. and why would i put nitrous on ?

Oneal. Get under the rig and trace all the o2 wires, make sure they are not chaffed, burnt, cut or missing. Sounds like the PCM is dumping too much fuel because it does not know the air/fuel ratio. Also check the PDC box under the hood, it holds all the engine fuses, for a blown fuse.

Try unplugging the front o2 and take it for a drive. If the idle issue and sputter go away then you know where the problem is.

ok sounds like a plan . thanks for your help

Lol, poor djb, I imagine you're doing something similiar to this everytime you read these posts

I read your link, and I agree. On old carb systems back-pressure was a must because the carb simply couldn't readjust the fuel-air charge when the lack of back-pressure allowed more air to enter the combustion chamber. What noone seems to understand on this thread is that all of us (well most) have systems that have ECU's that constantly watch the air-fuel ratio and what the engine is doing. If I am correct, even Renix systems have this. So, if lean burning is detected, the ECU modifies the fuel input.

Bottom-line: Backpressure isn't as super important as it's made out to be.

Ok so IMHO the stock setup is great but the xj i just bought had went through a series of mods to make it pass emmissions so i have reason to believe that the larger diameter pipe and cat along with a strict muffler would cause me to sacrifice power is this so and will the addition of 2.25 od piping and my thrush turbo muffler from my old xj help me out?

Thank you, well said. I don't really mean to or want to always sound argumentative but facts are always more informative than opinions/myths.

ya you sacrifice a little bit or the low end torque not to much . but give it more top end. but with a throttle body spacer possibly you could gain the low end back but im not there yet into doing a whole engine mods . one thing at a time

Throttle body spacers are essentially junk. Not tryin to sound like an **** here, but they are. A friend of mine had one, so did a relative, and nothing but maybe some whining. Take that money for a TB spacer and save for a bored throttle body.

Dont believe me? Look at this:

Throttle Body Spacer
Myth: Adding a throttle body spacer will increase the intake plenum volume for more air and a higher velocity intake charge. Also, rifling an aluminum spacer helps air flow into cylinder head with less turbulence for more power.
Our Thoughts: Depending on the application, a spacer works wonders on a carbureted or a TBI-injected engine in which the air/fuel mixture atomizes and flows through a wet manifold, but results are less drastic on a MPI engine in which only air flows through the intake.
Claimed Gains: 10-15hp
Actual Gains: 0-3hp
Notes: With our Red and Mileage Master projects, the largest power increase we've seen on the dyno was 1hp.

Sourced from: http://jp.automotive.com/124652/154-...ies/index.html

Hi djb383 I can say that it is nice exhaust.

ya i kinda firgured they arent all that . my buddies dad got one for his ford f150 and was dissapionted for 1-2 hrsp gain he had

A simple K&N drop in air filter isn't going to hurt performance. Its proven that they flow more air, and are reuasble. I've used them on many vehicles.

As for back pressure, it can be useful, but I don't imagine it has as much effect as everyone has been suggesting. Smaller motors, ones below 2 liters of displacement, do benefit from some backpressure. I know this from experience with non-turbo DSMs. I'm not an expert in that area, but I know research has been done with those cars and it has indeed been proven.

Again, these are two very different motors, so I'm pretty sure the backpressurebeing necessary in the Jeep doesn't apply.