As promised, Cheryl and I took both cars to the dyno. It was pretty fun, and we saw some interesting numbers.

Before I get into the meat of the post, I have to apologize. Those of you wanting the actual graphs of the runs, or the run files themselves, will be disappointed. The guy at the garage emailed me, but forgot to attach the run files; they're closed for the evening, so the actual analysis will have to wait until tomorrow.

For my car, we dyno'd in 4th because if we dyno in 5th, the rev limiter will be hit before redline. Also, we monitored temps and waited for coolant to reach 190f and coolant to be +10 ambient before the first run. We did not let the cars do complete cool-downs between runs, and we did not perform ecu resets between sets of runs. These guys at the shop were actually fairly busy today, and frankly, for the agreed upon payment, could not do all the custom stuff we wanted.

I put my car on the dyno first, then had 3 pulls done to establish a baseline. I was somewhat disappointed with the numbers; my peak numbers were down quite a bit from the last dyno performed in November. That dyno was done in 5th gear, but these dynos were in 4th. Also, at the last dyno I had kinetix cats, versus my present crawfords. Conditions were very similar, and the only other difference was the gas from a different vendor.

After the baseline runs, they took off muffler while it was on the dyno. They ran twice before we figured out they had forgotten to insert the a/f pickup, so I got another two runs. Each run began recording at 3k rpms, and I was quite surprised with the results. Zero power loss. Anywhere in the measured rpm range. Actually, the car saw some decent gains.

They took my car off the dyno and put Cheryl's car on for it's baseline runs. Each run was performed in 3rd gear, starting at 2500 rpms. After the baseline, they took off her muffler. She got another 3 runs, and just like my car, she didn't see any loss anywhere in the rpm range.

Next, they put my oem 05 muffler on her car. It didn't bolt right up; hangers are different and the body of the muffler actually rubbed against the left-underside of the car. So I would not recomment a permanent mounting of the 05 muffler on a pre-05. With the oem 05 muffler, she lost just a *bit*, when compared to no muffler at all. But the numbers of the 05 muffler were very close to those of the non-muffler configuration.

I'm sorry I haven't gotten into specifics, or listed absolute numbers. Unfortunately, because I was having the run files emailed to me, I didn't receive any hard-copy printouts. Thus, I'm having to go from memory until I receive the run files. After I get the run files, I will export a few different graphs, and post them tomorrow. After that, we can all analyze the physical data.

One thing that was very interesting was the a/f mixture on both cars. We were running pretty lean on our baselines, and after we took off the mufflers, we both riched out by a significant margin. I'm assuming the ecu's were dumping in more fuel because the 02 sensors were picking up more oxygen in the exhaust. But this is just a guess.

Another thing you guys will notice tomorrow is what I can only describe as Cheryl's ecu adjusting between a few of the runs. She saw some decent gains after taking off the muffler, and the successive runs showed small losses, and adjustments to the a/f. I'm interpreting this behavior as the ecu adjusting.

More to follow...

 

One of the thing I heard/read from multiple people was that I would lose low-end power if I removed the muffler; backpressure and all that. While Cheryl's car was being unlatched, I took my muffler-less car for a multi-block run. I immediately noticed a loss of low-end power; all the way until about 4500 to 5000 rpms, then the car seemed to respond as I was accustomed to.

Now, the dyno showed that there was *zero* loss anywhere across the *measured* rpm range. The runs on my car started recording at 3k, so it is possible that there was indeed a loss below 3k. But in my drive, after I shifted out of first, I never dropped below 3k again. And I still perceived a loss of grunt up until 5k. I find this interesting considering the dyno indicates otherwise.

Now, I gotta saw that removing the muffler just makes the car scream. The sound is unbelievable. I've never heard an aftermarket sedan exhaust in person, but I just hope they sound something close to what this sounded like. In fact, I'm considering forgoing an aftermarket exhaust altogether, and having an exhaust shop put in a straight pipe with inline resonators, just to make it a little less offensive. Unfortunately, Cheryl didn't like the sound, so I've been forbidden from doing the straight pipe thing.

When I was driving around town, and went WOT, it flipped me out. I had my friend who owns an SRT4 ride with me, and he flipped out. He said it was awesome(this coming from a guy whose car came muffler-less from the factory). He said I should keep it that way. I'm inclined to agree.

Now, I've got about 300mb of mp4 video of the dynos, and the short run in my car w/o the muffler. Anyone want to host it?

 

Here are two pictures of the oem 04 and 05 mufflers side-by-side.

The 04 muffler is the smaller of the two. The 05 muffler is longer, and a bit thicker as well. Hence some of the difficulty in mounting(in addition to the hanger changes).

 

What is the one line summary?

 

No losses on an 04 5AT below 2500 rpms, and no losses on an 05 6MT below 3k rpms -- that's where the dynos started recording.

 

I feel the need to let any sedan owner that checks out this thread that I have a Stillen Sedan muffler FOR SALE! Okay carry on. Oh and trey good write up.

 

I would like to add quickly in scanning over Trey's posts that there is a chance to mount the 05 muffler onto an 03/04. It comes extremely close to the support bracket area on my nismo kit bumper and it would require some underside modifications. There could also be a heat issue involved but as exhaust items are not my speciality I will not state for certain either way in this case. Spyder took some pics of the 05 muffler mounted on my car and we can post those up soon I would think (Trey's still asleep and he knows where the pics are LOL)

 

Nice info. Question. I read the 05 muffler dyno'd close to the no-muffler. Just a tad below. But how did the 05 muffler do vs the baseline?

 

Sorry it's taken so long to respond Jeff. I didn't want to say anything specific until we got the actual run files. The following posts *should* answer your questions.

 

We *finally* got the run files. So I threw together a few graphs and an excel spreadsheet comparing my information.

Attached are three images:
The set of 3 pulls forming my baseline
The set of 2 pulls forming my run without the muffler(there were actually 4 pulls, but the first two were run without the a/f pickup, so they weren't included)
A graph overlaying the best of the baseline versus the best of the no muffler runs

I could generate a graph with all 5 runs, but because the numbers are *so* close, the lines would just get all jumbled.

 

I exported the runs( best of the baseline runs, and best of the no muffler runs), and imported the data into excel. I compared the numbers in 100 rpm increments starting at 3100 rpms, all the way until 7000 rpms.

There was a gain across the entire rev range. I gained an average of 3.732hp and 3.6865 torque. From 6200 to 6400, I gained over 6hp.

**NOTE** It's attached as a zip file, because we're not allowed to attach excel file apparently. Unzip the file before viewing.

Cheryl's analysis will follow shortly

 

Here are three graphs:

The first is the set of 3 pulls forming Cheryl's baseline.
The next is the set of 3 pulls taken without her muffler.
The last is the set of 3 pulls with the 05 muffler.

 

Attached are 2 more files. The first is a graph of the best of each set of pulls all on the same graph. The second is an excel spreadsheet that breaks-down the data into 100 rpms increments for the best run of each set.

The spreadsheet includes the deltas between baseline and no muffler, the deltas between baseline and the 05 muffler, and the deltas between no muffler and the 05 muffler.

Just like the excel spreadsheet analysis of my runs, this file is attached as a zip.

 

One thing interesting to note on Cheryl's car is the starting point for the runs. Each run started at either 2900 rpms, or 3k rpms. We requested them to start recording at 2500. What confuses me is the fact that we *watched* them start recording at 2500; regardless, the data between 2500 and 3k seems to be missing.

What makes this absense even more interesting is the fact there *is* a documented loss of power on her car, without the muffler, and even with the 05 muffler; this loss only extends to 3200; once that rpm is reached, the dyno reported gains.

Now, this loss of power is open to interpretation. It's all on how the dyno is performed. When the operator is in the car, he presses a button on a wired remote control(wired to the dyno computer), and mashes the accelerator at the same time. There seems to be a "ramp up" between when the operator presses the record button, and when the car actually responds to being put under a load. The point is, that the first 2 or 3 hundred rpms are not necessarily comparable between dyno runs.

As an example, when doing the baseline on my car, the dyno measured 141fl-lbs on the first pull at 3k rpms. On the second pull, it measured 113, and on the last pull, it measured 172. The point is that the first few rpms aren't directly comparable even between dyno pulls performed within minutes of one another. Chalk this one up to operator consistency.

So, did Cheryl's car really experience a loss at or below 3k rpms? Who knows. We didn't have a chance to drive it around.

 

So, there's all the graphs, and even some excel files for every one to pour over. I've even attached the actual run files to this post, for those of you that have winpep7.

Did we prove anything? Well, above 3k rpms there was no loss, on either car, with or without a muffler. Below that, it's anyone's guess.

What's interesting is that the variations were so small that one might consider them to be within tolerances of the dyno itself.

As I mentioned above, on my car it felt like I lost serious power below 5k rpms, but the dyno disproved my own butt-dyno. It's possible I had a loss below 3k(before the dyno started recording), but the only way to check that would be to dyno *again*, or to take the muffler off the next time I go to the track.

This was an interesting, and even entertaining, experiment. We might have raised more questions than we've answered, but the rest is for someone else to figure out. However, I am pretty confident that we debunked the power-loss theory.

Oh, and did I mentioned that running around without a muffler sounded like heaven in my car???