Hello,

The title pretty much sums up the question.

I straight piped my car from the cats back. Resonator and muffler delete. I was wondering if there is a reduction in HP due to the change in back pressure. I have been running this set up for a while so I cannot tell if there is a difference in power. Sorry if I sound like a noob as I do not know much about this topic.

Thanks

 

You could run straight open headers for more noise and fumes in the cabin. Don't expect anything without a tune.

 

All backpressure is bad. This type of topic has been covered thousands of times.

 

Please quote sources on backpressure? Modern Nissan engines are tuned with a certain amount of backpressure and don't operate as efficiently without it.

 

Wait, what?

I mean, I get what you're saying that in general that back pressure is NOT a good thing. But in and from empirical testing (dynomometer, data acquisition, driveability, etc), back pressure is NOT a bad thing IN THE REAL WORLD.

I've experienced mistakes (not all my own) in exhaust design at several points throughout my life and they were all related to modification of a given engine's torque curve - and how that relates to intended usage. So stating in such general terms that back pressure is bad, well, that causes the left and right hemispheres in my brain to stop firing synapses at each other. Laff...

But I'm open to learn something new, so as dkmura states, please state sources.

 

YES. THANK YOU.

For everyone else. Read up on exhaust scavenging.

 

A while back a user did a before and after dyno and lost 3hp from a muffler delete all else equal, no before after tune.

 

Yes, understand scavenging and because of that, it's a taken point. But where this is probably confusing to most is what the real world effects are on our particular engine and how it fits in with the overall performance of the vehicle GIVEN ITS USE. That is, there is a point of diminished returns when building an exhaust system for the Z33. Too much pipe, scavenging suffers/diminishes and therefore hurts low end performance, where most of our driving occurs on the street.

This is why I question how well some of these huge pipe, dual systems can be any fun in day to day driving when we can't always be pushing 5k+ on the tach.

Back to the original question, I think I'd be a little surprised if the muffler delete would have as dramatic an effect though, being so far down stream. That, as compared to increasing pipe sizes just aft of the downpipes. Given that, I maintain that building or buying a more conservative system for street use is still prudent.

To each his/her own USAGE...

 

No they are tuned with exhaust scavenging in mind, the only backpressure may be caused by restrictions do to emissions items like the cats. Removing bakcpressure is always good.

Use google, or even the search feature on this site, its been covered dozens of times.

 

I would also like someone to explain why a muffler delete is undesirable.

I mean other than being a little ghetto and to some a little too loud what are the disadvantages?

 

There shouldn't be any disadvantage power wise. I remember reading motordyne's R&D on the XYZ pipe and one of the things they found is the most if not all of the scavenging is done at the header to the Y pipe. I think that's why when people on this forum build custom single exhausts, they increase diameter of the exhaust in steps to decrease back pressure. So when you are talking about a muffler delete, being all the way back, there shouldn't be any negative effects.

 

https://my350z.com/forum/autocross-r...er-delete.html

A couple more hp, about 5 less torque. Keep in mind that was with a midpipe delete also, so just a muffler delete will likely have less of an impact on the torque curve. Thank l30thelion also and maybe post questions in his thread since his experience isnt anecdotal.

 

In terms of real-world, first hand experience, an inadvertent muffler delete occurred in 2013 about five laps into a race here in Colorado. While SCCA rules don't allow for a header change, my exhaust was designed to maximize scavaging with non-resonated test pipes, a NISMO Y-pipe and a single outlet Ti muffler. Worked well for several years until the Ti welds started weakening. My T3-spec Z33 was chasing down a pack of BMWs when the Ti muffler literally came apart.

Headed onto the backstraight, the muffler came off in several pieces just as I was drafting a Z4 M-coupe for position. The effect was immediate, the engine note changed and power decreased. I spent the rest of that lap checking the car over to make sure there was not more serious damage. The Z would run, but top speed on the two straights were down by almost 10 mph. My challenge to the BMWs was over, but the car would at least run to the finish (while damaging the rear bumper and LR turn signal). Checking the Z after the race revealed the muffler had come off cleanly, leaving only the front flange in place. In real world terms, I'd estimate the loss of at least 7-10 hp and a corresponding loss in lb/ft of torque when that muffler came apart. By the next race, I had a new steel muffler in place and my race pace was restored.