gone

what is the purpose of back pressure and what would happen if i had gotten just straight pipes after the headers no cats no muffler

enhanced250

i think gibson makes a super truck exhaust with a side exit in front of the wheels

Tony@Performance

iTrader: (16)

Backpressure is needed on NA cars, to help push the piston down after the combustion cycle in the cylinder. If you are an NA car, and run, say straight headers, (open headers), with no exhaust etc... the flow of exhaust is so open, and free that the exhaust will exit better, but the cylinder doesn't have that extra "oomf" to help push it down. The quicker a piston is pushed down in the cylinder, the quicker it can come back up.

FI cars on the other hand usually want to free up backpressure, because the air that is being forced into the engine pushes the pistons down with plenty of force to get the motor spinning well.

Backpressure is needed on any car for the most part, because even turbo cars at idle don't boost, so backpressure is still needed on those cars to prevent the car from stalling etc....
It's all a fine line with tuning....

zzzya

iTrader: (2)

At higher rpms, less backpressure is needed since inertia is helping to keep the crank spinning, thus the reason why a pretty open exhaust setup can result in low end torque loss and higher rpm gain. A good header design can make a world of difference here and if done properly will allow a more open exhaust setup with less low end torque loss. Of course the front end intake also plays its role and in the end it is all a balancing act to get the type of HP/TQ curve that you want to achieve.

Tony@Performance

iTrader: (16)

Very well said. That's correct, with exhaust tuning, it's all a balancing act. With cars that have aftermarket companies that make both headers and exhausts for them, It is often a good idea to use the same company's parts together, since they are often designed for use together. In other cars, hondas especially, (not so much the 350z), mix and matching parts like that can create a different power curve than what the user originally wanted. They try to go for different parts, and in doing so, the flow of the headers in design is negated by the exhaust flow design, etc.... Mitsubishis are another car (like the eclipses and evos) that can hit this tuning "wall." But then again, If you are Turbo, usually the bigger the piping the better up to a point......

You really don't have to worry with the Z which company you use for different parts, the biggest factor is the exhaust. So many companies use different styles to make an exhaust and some are really good and others are just so-so. That's the biggest factor on our cars. THe header, well, I'd say it's more a matter of fitment rather than flow on our cars due to lack of space, that will make the differences between companies noticeable.

PhoenixINX

I tend to disagree here...

Parts are VERY evident here on these cars. Taking headers for example, there has been a recent header design that was sold for a VERY VERY attractive price, and people are making minimal gains at peak, and nothing a redline. Whereas there is a very established name here that is making great gains at peak, and HUGE at redline.

The Z is very **** about the parts that are installed, the only different between us and the Hondas are that we already have a fair bit of torque, which can disillusion someone into thinking they have not lost any power down low, when in fact they may have.

Bringing headers back up, good flow vs. pressure is VERY obvious in Mike Edens (mjedens) car. Where he had Tomei 268 cams installed, along with Nismo headers, test pipes, and a Stillen exhaust... The car lost ALL its bottom end, and was miserable to drive around. As soon as he switched over to another brand of headers, an average of 38 ft-lbs of torque were made down-low. How can one say the 350Z is not impacted by various mods? If anything, this car is more **** then ANY Honda I ever modded.

Hydrazine

iTrader: (53)

Edited for content


No need to be ambiguous or P.C. on brand names here. Just say what you think.

Resolute

iTrader: (2)

Wow, most of this is completely wrong. Run open headers and backpressure increases not the other way around. The air never pushes the piston down in a reciprocating engine, it is pulled in by vacuum. And a car never needs backpressure to run. much less run well. The myth of backpressure being required to make torque or low rpm power is just that- a myth. There are several realy good books on header, exhaust and intake design that cover the value of resonance to achieve higher gas flow at a given rpm range, and that is what makes power in a car. The faster the exhaust can be pushed out by the piston, and the faster the intake charge can fill the cc, both of which are aided by the LEAST restrictive paths possible, the more power an engine will make. In fact, again with resonance, velocity can be increased to actually help pull exhaust out of the cc and intake air into it. For easy reading, Mike Kojima wrote a good article on an online mag several months back. www.Nissanperformancemag.com is the site, and would be worth reading to fully answer your question here, gone.
Will

Michael-Dallas

This is an excellent article written by Mike Kojima on exhausts and backpressure.

Enjoy!

Michael.

PhoenixINX

Welcome to the board.

As a representative of a certain brand of product here... I tend NOT to use brands in my suggestions as they tend to carry an opinionated effect.

Middle finger? Happy Holidays to you too pal...

hfm

iTrader: (1)

If you're going to take anyone's advice, my recommendation is to pay attention to what Michael-Dallas says. He doesn't say often, when he does, it's usually pearls of wisdom.

Hydrazine

iTrader: (53)

Whoa hey. No animosity meant. I was just referring to your sig with Z baby giving the bird.

I guessed your affiliation because your reluctance to not say a brand name and your sig says your from Nashville TN. And that little red Crawford address at the bottom. But still I like to hear honest opinions from anyone in a position to know.

Vendor or not, If you know something is great, or trash, and your opinion comes from an objective evaluation, I'm all ears.
If you said the low cost headers were similar in performance to Borla headers or somewhere between Borla and say Crawford headers I would certaintly like to hear the objective "what and why". I'll be putting them in in a couple of days and would like a better understanding of the parts and what direction to take them.

Unless it was a waste of $360 to install them, there will be pre and post dynos to show exactly what the results are. Results will be posted here.


Merry Christmas...... Pal

PhoenixINX

Glad it wasn't anything personal!!!

My word of advice, if it feels good... and you feel what you did was worth the money... then go with it!

I have just spent hundreds of hours at the dyno with various Zs, and have first hand experience as to which things work and which don't. I will tell you now, this car has caused myself tons of others in the group MANY headaches!!!!

Best of luck!

Tony@Performance

iTrader: (16)

If you take a honda and run open headers, the car will more often than not stall, and idle very poorly. THis is due to lack of backpressure. Opening up the headers never creates more backpressure.

Tony@Performance

iTrader: (16)

and also, running bigger exhaust piping (which every company claims is to reduce backpressure) is designed then to increase it?
sorry, bigger piping=less backpressure.
open headers=BIG loss in backpressure

Resolute

iTrader: (2)

Run open headers and you will create more backpressure. Did you read the link Michael posted? I am not sure where your comment on bigger piping being designed to increase backpressure came from, but I don't recall mentioning that. However, since you did mention it, running too large a diameter exhaust pipe will increase backpressure over a properly sized exhaust because you lose the additional velocity of the exhaust gas pulse that the prperly sized pipe makes through resonance. Again, there are lots of well written articles and books to cover more than you may want to know on the principles that aid exhaust flow, and thereby power. For the original poster's benefit though, and for anyone else who might check this out, backpressure is not needed to run well - ever.
Will

zzzya

iTrader: (2)

The thing that people need to focus on is not backpressure, rather exhaust flow. If the piping diameter gets too wide on an N/A car, you can create poor exhaust flow at low engine rpms resulting in less vacuum and less air being pulled into the cylinder while the intake valves are open. However, once the rpms start to climb, the exhaust gases are being pushed through the system with more force. In an N/A car you want a good balance to create decent low end power without sacrificing top end. An FI car has an intake or exhaust that is forcing the air through the system increasing the exhaust flow and increasing the vacuum thus increasing the potential to make more power given proper fuel delivery.

Consider a water hose with the water valve on 30% (N/A) open and a diameter of 1/2". Now consider the hose to be 3/4". Now consider the hose to be 1". The 1/2" hose is somewhat restrictive creating more back pressure at the valve and not allowing as much water out of the valve as the valve can deliver, but the water is still being pumped out the end at a good clip. The 3/4" hose reduces that back pressure at the valve and now the valve is providing max water into and through the hose. The water is not flying out the end of the hose as far as the 1/2" but there is actually more water per second being delivered. The 1" hose is so big the water practically falls out of the valve and into the hose, the valve can not keep up so the water slowly moves into the hose until it starts to fill it. Once enough water has entered the hose, there is enough resistance along the way to start pushing the water out of the hose. Instead of a nice stream however, it is slowly running out. Now open the valve to 100% (FI) There of course are some other things going on with an engine (vacuum and how its applied), but you can start to see why an exhaust needs to be designed given the amount and force of the air being pumped out of the engine to maximize performance.