Thats what I figured and thats why I recommended what I did. Get a good free flowing muffler and keep the pipe size the same as the pipe coming out the rear of the cat. If the pipe reduces in size at that rear flange, cut the flange off. Leave the intake alone, it will flow more air than the engine can use.

 

Already done that heh, just no cats its completely straight with a flowmaster muffler. 2.25 inch all the way. Should I put some cats back on it ??

 

Technically you should have cats on it if you live in the US, but thats up to you. It might gain some bottom end torque in exchange for some top end loss, but it really won't make much of a difference. if you wanted to throw a set of headers that might be a good idea, just get some smog legal ones, they are easier to install, and made with more attention to detail. You should gain some power there and if you ever needed to reinstall smog equipment for any reason, you can.

 

wouldnt the loss of back pressure kill the gas milage?

Matt

 

The loss of air velocity kills gas mileage.

the presence of backpressure will ALWAYS ALWAYS ALWAYS kill gas mileage. Backpressure never has, have, or will help gas mileage.

Air velocity is what keeps gas mileage good and low end torque numbers up.

This is hard to expain, but air has a mass to it, and as it exits the exhaust valve, the moving mass of the air creates a low pressure zone inside the combustion chamber. This low pressure zone happens at the exact same time that valve overlap occures. the exhaust valve is closing, and all the air from the combustion chamber is rushing out, the smaller diameter pipe you have, the faster the air will have to move to leave the combustion chamber, thus increasing air velocity. That mass of air then creates a vacuum in the combustion chamber at the same time the intake valve is opening drawing in the air/fuel mixture, aiding in filling the combustion chamber with the air/fuel mixture.

It drives me insane when someone thinks a little bit of backpressure is good. Backpresure is the devil!

 

then tell me why my ranger runs like dog poo since my muffler fell off, i put it on and it runs great?

Matt

 

Having a longer length of pipe means you have a larger mass of moving air, which increases the scavenging effect in your cylinders. Are you saying that it fell off, so you had just the Y pipe, cat, then exit? Then you put the muffler on and hooked everything back up until the tailpipe?

If so, then yeah, it will run like crap without a muffler. With just a Y pipe and then the cat all of the air exits right away and there is not alot of scavenging going on inside the cylinder.

Just because you have a muffler on doesnt mean you have backpressure. Not if your muffler flows good enough anyway. When you get up into the 4-5k range, you might get some backpressure.

 

The cats don't really introduce back pressure to any real degree, since if they are properly sized, they enhance the low RPM scavenging effect. The effect is kinda hard to explain, but basically, the exhaust gases are incompletely burn, they hit the catalyst and break into many paths forcing the gases to increase in velocity. The gases burn as they pass through the catalyst, resulting in increased volume. Since the gases cannot expand on themselves, they accelerate through the catalyst. This increase in velocity can enhance scavenging, though the effect is very weak. The effect is not strong enough to overcome a slightly restrictive effect at higher rpms, but if the catalyst is properly sized, the slight power loss is a wash and the gains in the bottom end justify them. I have seen many cases where vehicles that had cats produced more torque at low rpms than vehicles that did not, but the difference was very slight. I really don't think it makes much difference. Legally, all vehicles that came with cats in the US should have them, they are very carefully engineered for the factory configuration, and provide a good balance between economy and power. This is not true of all vehicles, but the cats I have seen on most Rangers and Explorers are adequately sized and will often flow more air at 1 psi than some performance mufflers do.

 

Idk if anybody still is using tghis site but if so i could use some help, i have a 1991 explorer 4.0. its obd 1 so idk are there any sort of compter upgrades?? also what would be some non invasive means of gettin some more power outta that 4.0. meaning nothin like cams or engine work. if any body can give me a hand id much appreciate it. Also bigger throtle bodies is that a pretty good power adder?

 

Yes, they can be chipped, talk to the guys at Diablosport on that one.

Yes there are cams and engine work you can do, expensive though. Most are not street friendly.

Forget the larger throttle body. The stock one will flow more air than the engine can use, even at redline. If you make it bigger, all you do is kill intake velocity and create turbulence.

 

i have a 93 ranger 4.0 auto with a small lift,31's,cold air intake,single chamber flowmaster and i am only geting 12mpg what can i do to get good mpg? i have just done a tune up and nothing changed for the mpg. if you have anything to say about it please email me at jamiebius@verivon.net