Sohc+backpressure=?

[jimster502]

Quick question on the exhaust. Would I gain power by down sizing from the 2.25" to a 2" pipe and exhuast on my 97 xlt sohc? I have the stock exhaust system. I remember reading somewhere that the sohc likes back pressure but just wanted to check if this is true..

 

[FIND]

No engine likes backpressure. That is a stupid myth. You will only gain power by going with a more free flowing exhaust system, however, you should not create a system that uses too large of pipe, because this reduces exhaust velocities causing turbulence (backpressure) and diminishes scavenging. Too small of diameter of pipe can restrict flow at higher RPMs, and cools the exhaust charge too quickly (less exhaust gas volume in the pipe per square inch of surface area of the pipe), which results in the exhaust charge shrinking and again, reducing flow velocities which causes turbulence. Car manufacturers build cars with some restriction in flow as a means of reducing emissions and reducing noise, although CO2 emissions are higher due to slightly increased fuel consumption.

For more information about why people who tell you that your engine needs backpressure should be hit in the face with a crowbar until they stop talking about things they don't understand, try google. Backpressure is only necessary in engines that cannot adjust fuel delivery needs, or two stroke engines. Since any engine in an automobile can adjust fuel delivery using vacuum, computers and the other idiosyncrasies of an internal combustion engine, you need not worry about it.

Here is a good article http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm, or you could try wikipedia, or any of a dozen other results that will show up if you search google for "Engine Backpressure". No, the engine in your Explorer is not an exception to this rule, and yes, I have many years of experience as a mechanic, both professionally and as a hobby, as well as experience tuning and modifying cars.

 

[colintrax]

^ thank you for keeping me from having to post a really long post.

To the op, don't mess with the exhaust yet. Start reading until you are ready to kill yourself. Then practice on cheaper engines until you've maxed the mower/rc car/ weed eater/ ect. THEN start messing with the exhaust on the explorer. Although you could always just buy high flow cats and a better muffler if you only want a slight increase.

 

[Sedition]

2.75" Cat Back exhaust system, just cats and pipe. Sounds throaty but doesn't drone on the highway.

 

[num5golden]

I have a 03 sport sport xlt i hacked the exhaust off right before the 2 cats remounted the 2nd O2 sensor, ran a Flowmaster 40 and a down turn rightbefore the rear axle, no tail pipe. The power gain is decent high and low, sound is great. Backpressure is a myth