[v8Toilet]

Originally Posted by topher1254

Just to ask a question (which I will probably answer myself)...

I currently am running the stock exhaust, except for TRD headers (which luckily came on the truck when I bought it used!!). Should my next change should be (based on v8Toilet's input) replacing the stock muffler with a TRD/Spintech/Magnaflow replacement?

I'd also like to create a more efficient intake system, but it seems there is conflicting advice about the intake kits...any suggestions?

Replace the muffler only is correct Leave the stock pipe in place. The intake system is again hard to improve because often what people here on TS have ended up with is a noisier system that gives you less low end torque in lieu of more top end horsepower. The same principals that apply to the exhaust system also apply to the intake system with the air moving in pulses with the firing rate of the engine. You need a balance of intake velocity (constantly moving air) with good flow in the RPM range that your engine is designed to operate in. Without changing heads, camshafts and intake manifolds you won’t get much benefit from a huge intake system in the RPM range your engine was designed to operate in. I did some testing of an aftermarket clone of the K&N intake system made by SSautochrome and the results where slightly less low end and more noise. My truck ran slower in the quarter mile because it got off the line more slowly. Not a big difference but it was there!

You might think that you can just replace your stock air filter with one of those K&N air filters because the marketing scams from that company have convinced you that it flows more air than the stock filter and They're right some what if you compare them one square inch to one square inch. Hey it sounds good in theory right and remember that flow contraption at the auto parts store that proves it! The K&N and similar TRD air filters do flow more air per square inch of filter area than a stock Toyota air filter but the stock Toyota air filter has 50% more surface area than the K&N filter and because of that the Toyota air filter flows better than the K&N air filter overall when it is new. This is only the case with the Toyota Tundra. I don’t know about other makes because I haven’t tested those and don’t plan on it.

The difference in power between the K&N air filter and stock Toyota air filter is not much of a difference but when I did one of my dyno runs we tested this theory and the Toyota air filter indeed made a little more horsepower to the rear wheels than a similar TRD air filter, which is just a renamed K&N filter. I also tested this at the drag strip and sure enough my average time with the stock filter was slightly better than with the TRD filter or K&N.

The Toyota engineers did a great job of engineering the intake and exhaust systems for the best possible compromise between low end torque and top end power in the Toyota Tundra and left little room for improvement in the intake and exhaust systems without revamping the entire system as a whole. The stock manifolds and muffler are about it for big improvements. The stock manifolds are designed more for cheap manufacture and good fit in close quarters at the expense of flow and the stock muffler is designed for less noise at the expense of some torque and horsepower. The stock exhaust pipe diameter is an engineered diameter designed for just the right amount of exhaust velocity at lower RPM without restricting too much flow at higher RPM. Mess with this and you upset the balance! After all unless you can make an exhaust system that gets bigger as the RPM of the engine climbs it will always be a compromise between low end power and top end power. Too many people are in the bigger is better mindset and just throw these parts on without a clue about what they are doing and upset the balance of the system as a whole.

Unless you’re an automotive engineer and you’ve done your homework than all you’re really doing a guessing and hoping that the $500 dual exhaust system you just bought that would be appropriate on a much larger engine is going to net you 20 horsepower just like the universal claim makes in the literature of the companies that advertisement it. Even if you are an engineer and you do your homework you’re most likely going to find out that the stock system is actually very efficient for the power range that Toyota engineers designed it for. Ever notice that when an aftermarket company claims you get 20 horsepower if you install their part that under that claim is 100 different applications. Do you really think that you are going to get the same results from one make of vehicle to the next?

I hope I have somewhat dispelled the misconceptions here and made some sense. If not than go ahead and put that 2.5” exhaust system on and that huge K&N system on that cost you a grand total of $750 of your hard earned money and you'll gain 20 horsepower at a useless 5200 RPM but don’t look at the toque numbers at 2500 rpm because you won’t believe that you lost 7-15 lb ft of torque and your truck will feel doggie off the line because Torque is what you feel not horsepower. In fact if you don’t already know that horsepower is just a mathematical calculation derived from torque than you don’t already know that torque is what a heavy truck needs to get it’s mass moving quickly and effortlessly. Toque is the actual twisting force produced at the crankshaft and horsepower is just a function of torque * RPM / 5252 or HP = TORQUE * RPM /5252.