Exhaust (FAQ)
From Nissan 350Z & 370Z Wiki
Contents |
Exhaust Types
What is a Cat Back exhaust?
This is a term used to describe any exhaust system that replaces all of the exhaust components after the catalytic converters.
Is there a difference between dual and true dual?
Generally, when people speak of dual exhaust, true-dual is understood. However, there are many people that think the 2 tips seen on the 350Z and G35 represent dual exhaust, so sometimes the word true-dual is used to clarify. It actually does not. The exhaust is a single pipe system that exits from dual tips.
Dual
This means that it starts at the catalytic-converter spot (regardless of what you have: test pipes, high-flow cats, OEM cats), and has two separate pipes that go back to the muffler(s). If the tubes cross, that is okay, as long as they separate again. Now there are variations on this. It can go into one muffler and have two exhaust outlets (tips) or it can go into one muffler and have one exhaust outlet (tip) or it can go into two mufflers, each with one exhaust outlet (tip). Those with two mufflers are typically "true-true-dual" exhausts (confusing huh?).
Y-pipe-back
This type of aftermarket exhaust replaces only the sections behind the OEM Y-pipe. It can split into two pipes/tubes and go to two mufflers, each with one exhaust outlet (tip) or it can stay with one tube/pipe and go to one muffler that has two exhaust outlets (tips) or go to one muffler that has one exhaust outlet (tip).
Single
These exhausts are best on single turbo kits. They go from the down-pipe on the turbo to the back with a few choices. You can either exit with one muffler or two, it can be one muffler with one exhaust outlet (tip) or one muffler with two exhaust outlets (tips), or you can have two mufflers, each with one exhaust outlet (tip).
What is better, dual or single?
It depends on what you are wanting and what it will be used on. Sound/weight/diameter/material all play factors into the exhaust performance for the application.
OEM Exhaust Info
What is the OEM exhaust setup?
The stock exhaust consists of: 2 headers, 2 catalytic converters, 1 y-pipe, 1 mid-pipe, and one muffler with two tips.
How heavy is the stock exhaust?
The total weight is around 108lbs not including the headers. The break down is:
- Rear Muffler: 34lbs
- Mid Pipe: 12lbs
- Y Pipe: 16lbs
- Catalytic Converters: 2x23lbs = 46lbs
Exhaust Manifold
Catalytic Converter
The catalytic converters (cats) are the most restrictive component in the system. Hard core tuners usually take these out and replace them with test pipes, although this is very much illegal. Another option is to replace the OEM cats with high-flow aftermarket ones. This is actually still illegal in many areas, but is not as harmful to the environment. You can save ~35lbs by replacing the OEM cats with test pipes.
Y-Pipe
The OEM Y-Pipe is the second most restrictive piece in the exhaust system. There are quite a few aftermarket Y-pipes on available, however some have complained that changing out only the Y-pipe produces awkward exhaust sounds. Some aftermarket exhaust systems will replace the Y-pipe, while others replace on aft of it.
Mid Pipe
Muffler
Aftermarket Exhaust Questions
What is the best exhaust?
There isn't. The best exhaust is what you like best. Most of the systems yield approximately the same power gains on an otherwise stock VQ35. However, once you start heavily modding the engine, especially with forced induction, the performance gains start to separate.
Bad smell after installing a new exhaust
This is normal (It does not happen in all Cars). It is not the special coating on your muffler causing this smell. This is the underside of your paint on the floorpan heating up and curing. Paint "cures" at different temperature levels.
The underside of your Cars's paint is cured to withstand the temperature from your stock mufflers (with heat shields). An aftermarket muffler may run hotter than your stock system
("PAINT" - the material used to protect the underside of your car from ojects/rocks tearing the underside of your car - it also helps to reduce road-noise from entering into the passenger cabin. The "PAINT" used under your car feels like tough rubber)
As far as "smell" goes, every time you raise the temperature at the mufflers a few degrees, the paint on the underside of your car will start to smell until it's had a chance to cure at that temperature. This explains why you may not get the smell for a while and then when you drive your car HARD, you'll begin to notice the smell again.
SOLUTION: The way to solve this problem is to drive your car HARD (many 0-60's, long highway trips, etc.) for a long time and really get the mufflers and pipes under your hot HOT. This will cure the paint under your Car at the highest possible temperature and the smell will begin to go away.
Once the paint has cured to this higher temperature under your car, you will have no smell whatsoever. Depending on your driving, this may be several days, to several months! Hard driving will cure your paint faster, everyday normal driving will cure the paint more slowly (several weeks to cure.)
The other answer is to re-paint the underside of your car with high temperature paint that has a "fast cure" this paint will cure faster than your stock paint and won't smell for that long. This paint smell is not an exhaust leak, you'd need a terrible exhaust leak to produce a smell inside the cab with the windows down and you would hear it as well.
Also, newer cars ('96 - newer) have a greater chance of getting this smell problem because the paint on the underside floorpan is still new.+
Other Info
Will the back pressure myth ever die?
If you have ever watched a leaf floating down a stream, you will remember that in the narrow sections of the stream, the leaf moves quickly and in the wider sections the water slows and so does the leaf. Sometimes the leaf gets into a turbulent spot and just spins in circles, or has difficulty going around obstacles. The same thing happens in your exhaust system.
A short time after your ignition systems lights on your fuel charge your piston is already near the end of its exhaust stroke. At this point the exhaust valves open and the pressurized gasses attempt to escape as best they can through a somewhat convoluted path. Keep in mind it is not leaving through an open round hole; the diameter of a hole with the valve head under an inch from its seat. Not exactly what I would call streamlined but the hot gasses have great motivation to get out of it’s cramped confinement as the piston comes up to squeeze the remaining portion out of the cylinder. I will mention now that the intake valve will open before the piston gets to top dead center and the exhaust will hang open a short time after the piston begins its intake stroke. This time is called valve overlap and its reasons will become clear further along in this discussion.
So the exhaust is moving through the exhaust port like a cleared Drano clog, a big slug. This slug has a beginning and an end and the goal is to keep it moving as smoothly and as quickly as possible without introducing congestion or unneeded restrictions. If we were only running one cylinder at one speed, exhaust tuning would be easy, find the tubing size that aids in the best salvaging at our target rpm and call it a day. What we need is a balance at both ends of the spectrum; keeping low rpm slugs and high rpm slugs moving without interruption. If we can time the slugs as they reach the collector so they don’t crash but instead zipper together, they will help scavenge each other through the pipe.
On an even fire V6, 3 pipes per side, headers with equal length tubing will help but attention needs to be paid to the distance the slug travels before the collector or you may have unnecessary collisions are maximum rpm. On single exit systems the Y pipe is also a concern. All of this is also dependant on tubing size. Like I said before the bigger pipe the slower the gasses move. First you need to find the optimum size for one cylinder and calculate how long it will take the slug to travel down the pipe.
Equal length tubing will give your slugs the best chance of missing each other as they meet at the collector. A smooth transition to the header is what is most important here, you want the ports to maintain or increase their size from the valve at all times.
The reason bigger pipes make less torque is because the low rpm exhaust slug looses velocity once in the larger pipe. If velocity remains high during valve overlap the last remaining exhaust, and some fresh air, are drawn out of the cylinders by the vacuum created by the slug moving down the exhaust system. This is one of the reasons equal length headers are important, so the slug from the previous cylinder has a vacuum effect on the next one. This is also why single pipe systems tend to get better low end numbers, because all 6 cylinders are pulling on each other.
When top end HP is the goal, the pipe that was sized just right before is now getting a bit overfilled. It still has good velocity but it can only take so much at a time, this is back pressure. Going to freer flowing pipe will stall the slug out at lower rpm but optimize its travel at higher RPMs, so you get more HP. Typically these systems claim higher torque numbers too, but usually higher in the rev band.
It all comes down to balance. Street cars feel better with torque, having to rev the motor up just to pull away from a light is annoying. Race cars and track cars are better with top end because they spend their time with the pedal mashed. I guess what I am saying is "how are you going to use the car?" granted, an exhaust system alone is not going to free fall your low end grunt, but throw in some other high HP modifications (F/I not included) and they whittle away at it.
The term "backpressure" is a misnomer. All exhaust systems are pressurized to some degree because you are restricting the flow of a gas. That pressure can be measured. For normally aspirated engines "street" type engines an exhaust system pressure (measured at the collector or "Y" pipe merge) of 1.5 psi is a good target. For normally aspirated "race" type engines an exhaust system pressure of .5 psi is a good target.
|
|
This page is part of the Exhaust category. To learn more about related items click the links below. Components: Exhaust Systems (Dual Tip only) • Exhaust Systems (Single Pipe) • Exhaust Systems (True Dual) • Exhaust Systems (need categorized) • Headers • High Flow Catalytic Converters • Test Pipes • Y Pipes FAQs: Catalytic Converters (FAQ) • Exhaust system overview • Headers (FAQ) • Test Pipes (FAQ) • Y Pipe (FAQ) Tutorials: Exhaust System Installation (Borla) • Exhaust System Installation (Invidia G200) • Header Installation • Making custom O2 simulators • Stop CEL With Test Pipes |
Categories: Exhaust | FAQ | Engine