Did anyone see this in the last issue of Import Tuner? I was reading the Evo Vs. Sti ( which the Evo naturally won of course ) but anyway, flipping through the magazine it had these 3 comparisons.

I don't what car it was tested on and I don't believe it even says... or I don't see it anyway, but the results were :

Stock Cat 104.1 hp 92.63 tq
Hollowed out Cat 103 hp 92.1 tq
Testpipe 105.4 hp 93.9 tq

What do you all think of this? I remember reading that one of the performance places on here made their own downpipe, but wound up picking up no power... I wonder if this could be the case with the Cat?

 

sounds like a civic or some other really low hp car. 99% chance it is N/A, having a turbo would make a larger increase.

 

yeah, I would think it would make a difference with a car with this kind of power and like you said with a turbo.

 

I used to run a "gutted cat" in my Eclipse SDS race car and replaced it with a set of test pipes. I seen a slight hp increase but that might have been due to weather conditions etc...

If its a DD and its a strict state with EPA laws just get a highflow cat and test pipe, if not just get a test pipe would be my thought.

 

i don't understand this statement.. you're replacing your stock cat with EITHER a high flow cat OR a test pipe.. not both together.

 

Lost.....

 

Turbo cars are a lot different. It also depends on the weather and the what kind of dyno.

 

It's one or the other, not both.

EDIT: Whoops, someone beat me to it...

 

n/a cars need back pressure, we got turbos soo thats all the back pressure we need

 

My understanding is that a test pipe is a Cat-Delete pipe. Basically, you have three choices.

1) replace the stock cat with a high flow cat to reduce restriction to exhaust flow, but still be environmentally friendly and be on the right side of the law.

2) replace the stock cat with a test pipe to completely remove any restriction (federally illegal: punishment likely to be severe if caught).

3) replace stock cat with a hollowed cat (a pipe that looks like a cat from the outside, but doesn't really have a cat element inside it) This is illegal too and you will fail emissions with this, just like a test pipe.

Like one of the posters said, it depends on how strict law enforcement is where you live.

 

Correct

Test pipes are for off-road only meaning "race tracks where emissions are not an issue". Most people that get test pipes and live in places with emission laws will keep their stock cats and just swap the OEM parts in when they need to get tested.

 

That's actually incorrect. The theory that NA engines need a certain amount of backpressure is a common myth, and one that was developed by old timers who didn't understand the science behind why exhausts make power. While it is true that NA cars can lose power from large diameter exhausts, it's not because of backpressure, it's because there is a loss in VELOCITY. Here is an excerpt from a great article that was in sport compact car a number of years ago that explains in great detail all things exhaust. This cut and paste is the most relevant section, and will clear a lot of things up. Hope this helps you to better understand the real ins and outs of exhaust design, and why the formula for what works on an NA car is so different from a turbo car.

"Some self-proclaimed engine gurus claim too large of an exhaust tube on a car can cause problems; that engines need a certain amount of backpressure to run correctly. Although the statement about not running too large of a tube is correct, the assumption about engines needing backpressure is NOT. A vehicle needs the lowest backpressure possible to produce the maximum power by keeping pumping losses low. Too big of an exhaust pipe causes power loss, especially in low-end torque, because a big pipe has less exhaust stream velocity than a smaller pipe.

Velocity is essential to get the best scavenging effect from tuned headers. (We will discuss this in more detail later.) In simple terms, if the exhaust gas flow is kept high with good velocity, a vacuum can develop behind the closed exhaust valve allowing even better scavenging when the exhaust valve opens on the next exhaust cycle. Good scavenging is even more critical on valve overlap, the part of the four-stroke cycle where both the intake and exhaust valves are open.

If the exhaust pipe is too large, the flow will be sluggish with low velocity and the scavenging will not be as good. Remember that a good exhaust has low backpressure and high velocity. The only possible exceptions to this rule are for turbocharged or nitrous engines. It is almost impossible to put too big of an exhaust past a turbocharger as a turbo's efficiency depends a lot on the pressure differential across its turbine. A turbocharged engine can have an exhaust gas volume of about 1.5 to 2 times more than an equivalent displacement, naturally aspirated engine. Engines using nitrous oxide also have a pretty high exhaust volume and require a bigger exhaust if they are to be optimized for nitrous operation."

There is a lot of info in the write up, but it's a long read. Here is the link if anyone is interested: http://www.sportcompactcarweb.com/te...ems/index.html

 

BTW, does anyone make a 2.5 in test pipe for those of us that want to retain the stock exhaust? I know that most of the 3 in test pipes on the market will bolt up, but it's more ideal to maintain constant diameter through the whole system rather than going from 2.5 to 3 and then back to 2.5 again (read link above for reasoning behind this if you don't know why this matters). Any vendors want to chime in?

 

If you're running the stock exhaust, keep the stock cat, IMO. You'll still have the restriction of the stock exhaust, so why drive a smelly car that will not likely see much of a HP increase?

 

Uh, because the cat is the most restrictive part of the stock exhaust and a test pipe on it's own has been proven to net 10 whp+ on an otherwise stock exhaust X. It's a worthwhile mod, trust me. And they don't stink that bad man. I've had catless exhausts on almost every car I've ever owned and they are not very noticeable.