I'm in the market for a new exhaust but kinda indecisive about weather to go with the single or dual? Is the performance really enough to offset the weight? I'm never going to race the car however I do want something that will be high quality and a great sound. Nothing annoying...

 

I went with the NISMO catback, Borla headers and Crawford cats. Has a nice sound on the street and around the racetrack, friends of mine say it sounds awesome....

 

there is not a huge difference in HP with the NA cat back systems ... if they are dual or single exit...

in PA you may want to get a full stainless steel cat back system since salt on the roads will eat anything else away...

 

Keep in mind that with the NISMO catback, you get larger diameter pipes so the difference between a true dual and it are not that significant.

 

correct...

y-pipe starts 70mm then goes to 80mm at the mid-pipe...

i need to double check the dimensions of the y-pipe off the cats.. but I think thats what it was...

very free flowing system but keeps back pressure which is good on the NA for upper end HP

 

Some of the true duals are heavy.

 

FiarLady Z...

Have I told you how HOT your Z looks!!!!

 

no, but thank you very much!

 

What do you gus know about the Injen dual catback? Seems like a high quality system but coming from german cars I'm not familiar with the brand.

 

Correct me if I'm wrong, but I thought the opposite was true:

>Back pressure = Better low RPM performance
<Back pressure = Better high RPM performance

 

I have the Injen dual. I love it. Great quality and it sounds great too. It also looks pretty nice.

 

correct me if im wrong!

less back pressure = more torque low end / less high end HP
more back pressure = less torque loe end / more high end HP

best is to find a good place in the middle...

 

Sorry Jason, but the first post is correct.

It's more back pressure, more low end torque( to an extent)
less back pressure, more end high end hp.
Which is why turbos love no exhaust.

 

werd

 

So with an N/A car, i should stick with a system that has backpressure...soooooo thats why the magnaflow makes more power that most y-pipe back exhausts? Since it only uses 2.5in piping...am i correct????

 

If more backpressue = more low end tq, and the nismo cat-back has a bigger diameter pipe, doesn't it create less backpressure than an exhaust with a smaller diameter...like say the injen SES?

Or does a true dual create less back pressure because of the dual pipes? anyone know?

 

neither is actually correct. This all goes to the specific VE of the particular motor you are talking about.The only way to measure backpressure is via a gauge....you cannot say a true dual makes more or less backpressure than a single...simply does not work that way.

As for the turbo issue, not every turbo loves no exhaust. Borrow a buddies WRX one time and take the exhaust off - if will run like utter crap as there is no backoressure. There becomes a law of diminishing return when it comes to this stuff and it all comes back to the VE of the engine in question.

That being said, when you compare the true duals to the catback+Y pipe combos you'll see they all produce nearly identical power gains. Difference is in the materials used, sound and of course how it looks.

Adam

 

quote from nissanperfomancemag.com

An old hot rodders tale is that headers produce more power by reducing backpressure and by the long individual runners preventing the exhaust blast from one cylinder from blowing into the next cylinder, contaminating the charge on overlap. While this is partially true it is not the primary reason why headers produce more power than a stock manifold.

Headers make more power by primarily using resonance tuning to create a low-pressure reflected wave rarefaction pulse during the overlap period. The overlap period is in between the end of the exhaust stroke and the beginning of the intake stroke (remember our 4 stroke cycle from part one?) where both the intake and exhaust valves are open at the same time for a few degrees of crankshaft rotation. Engine designers use overlap to help the engine breathe better.

To work right a header must first exploit the inertial force of the out rushing exhaust gas. This rapidly moving, High Mass, high-pressure pulse helps create suction in its wake to pull burnt exhaust gas out of the cylinder. This first negative pressure wave helps evacuate the cylinder of burnt exhaust as the piston nears TDC and slows down.

To get the best breathing and to help pull as much fresh fuel/air mixture into the cylinder as possible during the overlap period, it is best if a low level vacuum or rarefaction can be created and maintained past the initial low pressure wave in the primary pipe. A well-designed header can use acoustic energy to maintain low pressure near the exhaust valve during the overlap period.


this explains it pretty well, its not just about backpressure its more about the velocity of the exhaust gases.

 

^Exactly.
All backpressure is is a force pressing against your engines exhaust. Why would making your engine exert more energy trying to breath -ever- be good?

Backpressure is ALWAYS bad. The less backpressure, the better. It's all about keeping the gases moving quickly and smoothly. Too large a diameter pipe and you have turbulance causing backpressure, and cooler exhaust gases, also causing backpressure (hot gases are lighter and easier to move than cold). Thats why you lose power.

By "tuning" the exhaust flow, you can help suck in the next breath of air for the engine, impoving performance (sort of like a very small mini turbo ).

And of course too small a diameter pipe(s) will cause backpressure as well. Have to find the right balance.

Now turbo's benifit less from "tuning" the exhaust, because the turbines distort the pressure waves, making it very difficult to design a system to take advantage of the scavaging effect. But there still can be some impovement.

Just my .02