[RockyMtnRay]

Originally Posted by Tankerhank

This is where I get a little confused

Don't do the Gibson CAT-BACK exhaust as the 1/8" increase in pipe size will reduce torque by decreasing back pressure too much?

You have it backwards. Increasing the pipe size INCREASES THE BACKPRESSURE (not reduces it) at low to mid RPM. Yes, bigger pipe = MORE backpressure at low RPM. Intuition is wrong at low RPM. The reason is the larger pipe allows more cooling, more loss of exhaust velocity, and the gas has to be pushed out instead of keeping its heat energy and velocity. Pushing the gas out the pipe detracts from the engine torque. This concept that an exhaust pipe is like a garden hose and bigger is better for breathing is correct at high gas velocities (high RPM) but is very, very wrong at low RPMs because the thermodynamic cooling effects are larger than the effects of wall friction on gas flow.

Do headers as the stock exhaust manifold is the most restrictive of the whole exhaust system and headers will open things up (less back pressure)?

Yes, headers do have less backpressure...and backpressure is always bad for torque on the pre-05s. There is no such thing with the pre-05 engine as "needing some backpressure". The '05 and later engine (which do have valve overlap at higher RPM (because of the VVTI design) can be helped by some backpressure.

Do not do K&N cold intake as it will reduce torque, just do the K&N filter?

The K&N is NOT a cold intake. It's a HOT air intake ...it sucks mostly hot engine compartment air (air dam or not). The stock intake IS a cold intake...it pulls air out of the inner fenderwell.

I understand TOO open of an exhaust will not help create low end torque, so you are saying with headers moving to the Gibson CAT-BACK will push the system "over the edge" and start to loose torque instead of improve it? I was reading on the Gibson site where they say the combo of their single side CAT-BACK and headers greatly improves low end torque for towing, is the difference in their headers vs the JBA? What about Hooker headers?

Now help me with the K&N intake too; open up the exhaust but not the breathing? Toyota uses that large "looped" intake manifold to create torque so the gen II K&N intake is a bad thing?

I appreciate all the help I can get.... Thanks

Gibson' marketing has to be taken with a very large grain of salt. They make huge amounts of profit off the 5 feet or so or 2.5 inch tubing in their "system" pricing versus the pricing of just the muffler that's used in that "system". The 2.5 inch pipe in their "system" will undoubtedly help high end horsepower and will also undoubtedly move the peak torque RPM above the stock 3400. It won't help the bottom end torque so necessary for towing. My experience (and others) is that keeping the stock pipe is a key to keeping the peak torque at a low RPM.

I have no first hand knowlege of th Gibson headers...they appear to be a decent mid length design. Hooker headers are notorious for thin metal and shoddy construction...low price but probably won't last more than a year or two (probably less than that in towing). A major advantage of JBA (beside 1st class construction and factory ceramic coatings) is the fire cone collector. Instead of a flat plate, JBAs have conical projection that helps the gasses merge inside the collector, hence causing these "shorty" headers to act like a long tube header. JBAs are much more expensive but are good value for the money.

The stock intake manifold on the pre-05 V8s has extremely long intake runners to maximize low RPM torque (via a ram air effect). The stock intake air box size and ducting is specifically tuned to work with those long intake runners. That air box plays a very key role in the intake tuning through the Hemholz tuning effect. A few (not K&N) aftermarket intake makers (Volant being one) do understand the criticality of including a tuned airbox in their systems.

As for K&N versus stock intakes, the K&N does not flow any better than the stock intake at any RPM. What it does do is introduce a bit of shadowing on the Mass Air Flow sensor at high flow rates that causes that sensor to under report air flow into the engine. The ECU then slightly reduces fuel flow when in open loop conditions and thus slightly leans the mixture. A slightly leaner than stock mixture actually produces somewhat better power than the stock mixture at high power. Hence, the K&N does help top end horsepower but not for the usually mentioned reason of "flowing better". Worse, the K&N sucks in mostly hot engine compartment air; especially at lower speeds and lower engine RPMs (towing conditions). Hot air = less power. Period. If you have to have an aftermarket intake, at least get a decent one such as the Volant that (1) is tuned for low RPM and (2) is actually a true cold air intake. I personally wouldn't mount a K&N intake on my truck if you paid me $10,000 to do it...IMHO, a K&N is truly terrible for towing torque (not to mention the atrociously loud sucking sound they make).