You can search the web for good reasons for backpressure but it's bunk science.

First, on the loss of power in the stock Z system with resonator removed,
1) Was the loss quantified by dyno testing or just butt dyno?
2) The stock exhaust system is just that, a system, it was tuned by Nissan to work best when it's all there. We don't have the faintest clue how they developed it but I have a good idea they spent a lot more time than most, if not all, of the aftermarket shops to get it to work best in all situations. Taking the resonator out could have upset some balance they designed into it, perhaps by unmasking inefficiencies of the rear muffler. Who knows

The need for backpressure comes from people who have experimented with large pipes, seen low end power losses and incorrectly deduced it must be a lack of back pressure that caused it when it fact it is a loss of gas velocity.

High Velocity, Low Restriction

Chris

 

I have also found another y pipe that is a little cheaper than that at about $125-$150 adn it says it t304 but doesnt look as nuice.

 

This is very interesting. I strongly believe that your original resonator cut was botched somehow, with some obstructions left in the pipe that were fixed by your midpipe installation.

One of the first things I noticed when I took delivery of my 350Z in December, 2002 was that the exhaust was too quiet. In less than a week I had the resonator removed at a custom performance exhaust shop.

Although I get some raspy buzz if I give it too much throttle when the exhaust system is cold, overall I really like the improvement in exhaust note. I'm convinced that I got a horsepower improvement, not only from the butt dyno but also from the real dyno a couple of weeks later when I rang in about 4 HP higher than my buddy who didn't get the cut.

If I had to do it over again I would still have the resonator removed. I have never heard anyone else report negative performance results from this simple mod.

 

Chris, thanks, it is good to have another patriot!


kcobean, I am glad you are not insulted by my post... it was definitely meant in respect but to correct this common misconception.

As Chris pointed out, this myth originated with people trying larger pipe, assuming a backpressure drop and concluding backpressure is needed. The article you reference, although I haven't seen it yet, sounds to me as an attempt (however cleaverly crafted) to explain WHY backpressure would make power when it demonstrably does not.

Let us consider the "fact" used that this backpressure "packs" the cylinder during overlap. Now, in a 2 stroke the situation is MUCH different but in a NA 4 stroke (or as Pat McGivern aka Motoman accurately points out... 8 phase engine) you do not want exhaust port backpressure.

As I pointed out any backpressure while the piston is moving up from BDC will apply its force (pressure x piston area) against crankshaft rotation. In fact, in a highly tuned engine you can actually see vacuum during this phase and that vacuum can assist in "pulling" the piston up... effectively adding "free" horsepower...

Any backpressure during overlap can easily cause reversion in the intake port/manifold. Think about it, what could this pressure be "packing"? There is very little area available when the piston is at TDC and the intake cycle has just barely begun. The critical time when "packing" actually does occur is after BDC on the intake cycle when the intake is still open and the inertia of the intake charge continues to fill even as the piston begins its upstroke. Way before this, during overlap, if there is backpressure during overlap the intake flow is surpressed and the total intake volume is less than it could have been.

As I said, it is during the critical periods of the piston returning from BDC and then again during valve overlap where backpressure is most damaging to the efficiency/power.

Now, the above is still simplified and I have not given some examples of why larger pipes or things like resonators and collector shapes effect velocity and backpressure but again, it is the case.

 

Nope. The removal and replacement of the stock resonator was not botched at all. They used a big turkey carver to cut it out then took the correct length pipe and widened each end so they would slip over the existing pipes, then welded them around. At first when I replaced the pipe this weekend, I expected to see a hole in the weld somewhere, but it is a perfect weld around the entire circumference of the pipe. For some reason having the resonator gone robbed some major torque. I didn't have anything dyno'd, but I'd guess at least 10 to 15 foot pounds!

-Chris

 

I removed my 2 stock resonators and replaced it with a single custom one. I've noticed now my low end torque is i need a lot worse. Would re welding the resonators on be fine to regain that torque?

 

Not bad. A 20 year necrobump but at least a reasonable question.

*2* stock resonators? Where are they located?

I find it interesting that that much loss of low end (as mentioned in this thread) resulted from removal of the stock resonator. Yes, well aware of loss of accelerative feel upon exhaust modifications but as much as these folks described?? Hmmmm.... it's not like they removed the cats, the resonator, rear muff and replaced with 4" straight pipe.

 

VQ straight pipe drag race

 

this thread was last posted in about the same time he was born

 

One was on the floor of his backseat


Either way taking the cat/resonator out is never going to reduce your power. I think there are some dyno charts showing almost 10hp/tq gains from removing both throughout the rpm range

 

i too would love to see what *2* resonators you be talkin about, Willis. 😩😩

 

At first I thought they were my secondary cats, but the guy at the muffler shop told me they were my resonators. they were in between my cats and where the muffler was. I drive a Nissan Fuga 350GT. So I too was confused to here that I had *2* resinators rather than 1.

 

While it shares some similarities, the Fuga (Y51) is a different vehicle than the 350Z (Z33). My wife drives an Infiniti M35 (which would be the US equivalent of the Fuga/Y51). Yes, it does have 2 resonators.

What "custom" resonator did you have installed? It could be more restrictive than OEM.

 

Got it.