snaik69

sorry if posted in wrong place or repeated but i found this on a 350z forum...thought it would be helpful for anyone looking for info on test pipes:

GENERAL
What are test pipes?
They are metal pipes that replace the OEM catalytic converters. One of the largest restrictions in the exhaust system is typically the catalytic converters, and by replacing them with a straight through pipe, you can free up the exhaust flow dramatically.

What are test pipes made of?
Test pipes are typically made from steel or stainless steel, although there are a few companies offering titanium versions. Stock OEM catalytic converter assembly housings are made from a combination of mild low carbon steel and aluminized sheet steel that is stamped and press bent into the desired shape. The contents of the stock cat contain trace quantities of the exotic metals rhodium and platinum.

Are test pipes illegal?
Yes. That is why they are always labeled "race/track use only". Removing the stock cats is illegal in all 50 states.

What else are they called?
The most common term used in the Z/G community is test pipe. However, there are several equally valid names for these such as, cat delete pipes, down pipes, race pipes, etc..

What are Non-Resonated Pipes?
Non-Resonated test pipes are simply pipes that are of a straight through design and do not incorporate a resonance chamber. Though typically cheaper to manufacture and purchase, non-resonated pipes can produce undesirable sound qualities when mated to certain header/exhaust combinations. The noise is most often described as being "raspy".

What are Resonated Pipes?
Resonated test pipes make use of a resonance chamber in their design. This is most often seen as a bulge or swelling of the test pipe's diameter. The resonance chamber helps to dampen certain undesirable sound frequencies from the exhaust note. Though the use of resonated pipes greatly reduces the likelihood of "raspiness" occurring, it does not eliminate the possibility.

Does installing test pipes produce any unusual odors?
Yes. Since you are no longer converting several of the exhaust byproducts into their more harmless forms, you will notice an increase in the smell generated by your exhaust fumes. The degree of the odor tends to be in direct correlation to the amount of modifications and grade of fuel used. Typically a Z tuned with bolt on parts and running pump premium will notice a mild increase in smell. While a race prepped FI setup on race gas can be overwhelming.




BRANDS AND DIFFERENCES
Who makes them for the 350Z/G35?
See our extensive list here: Test Pipes - Nissan 350Z & 370Z Wiki

Does it matter which brand I buy?
Like any other aftermarket component, brand loyalty and price will typically dictate your final decision. Design, materials and quality of construction should be your primary concern.

Which is the best test pipe?
Again, there are a few factors: diameter, fit and finish, and material. There are always cheap knockoffs that you can find on ebay, but they are always a risk to purchase unless you can find someone that has tried them out before you.

I see that different diameters are available, which should I choose?
You should select the diameter that most closely matches the diameter of the rest of your exhaust components. Abrupt changes in the diameter of any exhaust component can have a detrimental impact on exhaust flow.




PERFORMANCE GAINS
Potential weight savings?
The stock cat core material is fairly dense, contributing to their weight. Generally test pipes tend to be significantly lighter, due mostly to their more simplistic construction. Though the use of thick flanges and and thick stainless steel wall diameters can add up to a weight equaling or exceeding the stock cat.

Is there an alternative to test pipes?
High Flow Cats are also available for the Z/G. Though more expensive, they are emissions legal in most states. Generally HFCs will not produce the same power gains as test pipes (particularly on FI applications). For more information of high flow cats, see the appropriate section.

Test Pipe vs High Flow Cats
For NA (naturally aspirated) engines, this is a wash. With high flow cats (still illegal) you are at least thinking of the environment. Flow test show the test pipes have minimal gains over high flow cats.

For FI (forced induction) and more specifically turbo engines, high flow cats typically cannot stand the flow and heat generated and usually are damaged. For this reason most turn to test pipes when installing a turbo system. As always there are exceptions.




INSTALLATION
How much does it cost to install?
This varies from shop to shop. The job is at least a 1 hour job for someone that has done it before and can be up to 3 hours for someone attempting it for the first time. $100-200 is a fair price to pay to get test pipes installed on your 350Z or G35.

Is it hard to install myself?
Are you good in a garage? It took me 2.5 hours the first time.. now i can do it in about an hour.. There are 4 bolts that are very difficult to remove (upper bolts near engine)

Can I install them with my stock exhaust?
Yes. I have stock exhaust with test pipes.




SOUND
Will my stock exhaust be louder?
Yes. If you go with straight pipes, your exhaust will be louder and there will be a strong raspy noise around 3500 RPM. You can go with resonated test pipes and 90% chance will eliminated the raspy noise. I found that different combinations of exhaust react different to test pipes.

Raspiness? What causes it? Will i have rasp if....?
There are a few different reasons for rasp. One of the reasons is proper backpressure (i'll elaborate on that as well). Another reason is the bends and shapes of the part, this contributes to how it will sound. And one more reason is what the material it is made out of is. Yet another reason for the exhaust sounding raspy is how the muffler muffles the exhaust. And of course, all of this together contributes to how it will sound.

Will my (insert brand here) exhaust have rasp with test pipes?
This is not an easy question to answer. The overall setup of an exaust system including: material, material thickness, diameter, bends, and muffler type all play a factor in generating rasp. There is also several types of rasp some of which sound good while others make your 350Z sound broken.




CHECK ENGINE LIGHT / EMISSIONS
Do I need O2 simulators?
Unfortunately, the answer to this one is variable. After replacing the OEM catalytic converter with test pipes, some owners immediately receive an SES/CEL (Service Engine Soon/Check Engine Light). While others may receive it several thousand miles later, and still others never get an SES/CEL. Different combinations of exhaust components, brand of test pipe, and revision of the ECU firmware yield different results.

Will i get a CEL light if i use test pipes? high flow cats?
You may with test pipes, however, there are some options you can use that will trick the ECU into thinking that everything is fine with the O2 sensors. I'll elaborate on what you can use in the next paragraph. High-flow catalytic-converters should not set off a CEL, but if it does, I recommend checking to make sure it is installed properly first, and then try the following if it does not work.

Want to get rid of the SES light after removing your cats?
MIL eliminators or the Help! method here: Stop CEL With Test Pipes - Nissan 350Z & 370Z Wiki

Lean/Rich with test pipes?
Usually the engine will lean out when you modify any part that increases air flow. "Lean" means that there is more air flow at a given load than what the ECU is supplying fuel for, so there is more air than the ECU thinks there is, and the ECU isn't adjusting injector duty cycle (how much fuel is being used), therefore, your combustion chamber and piston cycle is not being as efficient as it could be.

Can I pass emissions with test pipes?
The answer to this is most decidedly NO. Even if a very skilled tuner were to get NOx and CO counts to within legal limits, emissions laws state that all factory installed emissions equipment must be installed and functional to pass emissions testing.

However, car inspection is done different from state to state and even city to city. I believe Florida no longer requires inspection. The part of Texas that I live in only requires an OBD2 scan. So if you are not throwing CEL, then you will pass. No visual inspection needed.

There is smoke coming out of my exhaust now.
This is normal. There will be a coating of oil on the metal from the manufacturing process that needs to be burned away. Expect it to subside after a few short days.

sbmwg37s

iTrader: (1)

Although some downpipes are long enough to replace catalyic converters, they are not the same as testpipes.

JonfromCB

Snaik69, Thanks for providing useful info' on the subject in one place. I know
it took a little time to put that togeather and post it....thanks.

Comment: Under your heading "Performance gains" , you don't really address
the issue of performance. You did address weight comparisons, but that
is not "performance"

It is interesting to note that "performance" has different meanings to
different people....My point is that most modifications to the intake
or exhaust system will actually decrease mileage and engine
response for the average driver. ...AND MAY actually increase
response and power in somevery narrow and specific RPM ranges,
but usually, increases are only realized in combination with
additional intake and tuning (fuel and timing) modifications.

In other words, if the average guy modifies his exhaust, he
can expect decreased across the board response, less power,
and lower mileage unless other tuning modifications are
made.

snaik69

that was a cut and paste i did from another forum....im a novice when it comes to modifications to my car....i have been trying to learn as much as possible and was reading up on test pipes when i came across this....i cant validate whether info is correct or not....just thought it would be helpful having all that info in one spot as oppossed to searching and having to go thru dozens of posts for info.

you bring up a good pt though re the "average guy"....i too am under the assumption that putting in a catback alone would automatically increase whp...i def would not want to see any decreases...esp with torque...like i read happens with CAI...