NEW catback systems! BRM Exhaust for 240sx

General discussion forum about the 240sx, and a great place to introduce yourself to the board!
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AZhitman
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Here's the deal - A turbo car is going to be quieter anyway, so I wou;dn't worry about the resonator length. I run a 2.5" system on a built KA-T running 12psi, but certainly 3" would be nice as well.


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slikklogic
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Nice but could u guys make me a muffled side exit?

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AZhitman
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No.

:)

Sil#2
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AZhitman wrote:No.

:)
Hey Hitman, does the aluminized come with chrome tips for the dual setup? Also what's the best price for s14, 3", with resonator, dual tips to 11361? Really want this but funds are unfortunately low. Thanks, Mike.

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AZhitman
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Yes - Polished SS tips come with that system.

If budget is a concern, skip the 3" and go with 2.5". Unless you're running big boost, there's no reason whatsoever to have a 3" system. Period.

An aluminized steel system in 2.5" for the S14 with resonator and dual tips is $475 shipped.

craigyboy
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Hey does anyone have any sound clips of this exhaust on a stock ka24e?

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voiddweller
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Hi Greg. You should have my PM and I left a VM, but for the benefit of other members in the same situation and reading this thread, here's my setup.

I'm running a completely stock exhaust and motor for my S14 KA24DE. The idea is to replace the exhaust with a BRM 2.5" SS w/22" resonator and high flow CAT for a quiet setup during normal cruising. I'm attracted to the BRM due to the good reviews regarding quality and sound. The goal is no drone on the highway and a nice, deep sporty sound during aggressive driving. I also want to reuse the exhaust for a SR swap.

The S13 SR20DET blacktop will be running 15lbs of boost, 810cc injectors, VSPL FMIC, JWT S4 Cams, stock turbo and Enthalpy tuned ECU. The BRM system w/CAT would be attached to a GReddy MX 80mm (3.15") downpipe.

I know you are of the opinion that a 2.5" is perfect for NA (which I totally agree) and also on the SR turbo for anything under 400 whp. The point you made of ground clearance reduction with 3" piping makes sense as well.

You've been doing this a while, so I have three questions:

1. Will there be an issue going from a 80mm to a 2.5" opening for the CAT?

2. What differences did you notice on the DynoJet for SR20DET's running a 2.5" vs 3" exhaust?

3. Does the BRM 2.5 or 3" drone from 60-70mph? I read one post on it and also had an Apexi Hybrid Megaphone exhaust on my S13SR (80mm) that sounded perfect with the exception of a slight drone at the same speeds.

Thank you!

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c29875
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Ordered my exhaust a few days ago can't wait to get it

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AZhitman
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voiddweller wrote: 1. Will there be an issue going from a 80mm to a 2.5" opening for the CAT?

2. What differences did you notice on the DynoJet for SR20DET's running a 2.5" vs 3" exhaust?

3. Does the BRM 2.5 or 3" drone from 60-70mph? I read one post on it and also had an Apexi Hybrid Megaphone exhaust on my S13SR (80mm) that sounded perfect with the exception of a slight drone at the same speeds.
1) No. Remember, the 80mm is an OD measurement. ID is just under 3" for a so-called 80mm downpipe.

2) Too subjective, really. Every engine setup is different. I've always maintained that 3" is a waste of money, a waste of ground clearance (and extra weight) on a 2-liter engine at stock boost (even up into the 12-15 psi range).

3) Again, that's more car-specific than anything, but after over a thousand systems sold, I've never gotten one back with a complaint. The Apexi is a really nice setup, but ALL performance catbacks will have a frequency at which they set up a slight resonance. The resonator we use does away with most, if not all, resonance.

:)

Matina210
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I was looking at the BMR web site and I see there are options for the length of resonator.
I'm interested in an exhaust for my naturally aspirated S13, and I know for sure I want a 2.5" pipe and two straight-through mufflers in series. So, if I get a BMR exhaust, I need a resonator.

Here's my question: Do the different length resonators affect the tone of the exhaust? Or just the volume?
Does the shorter resonator cancel out shorter wavelengths and make the car sound less like a Honda buzz bomb?
Do the resonators affect the power or torque?

I ask because my S13 had an HKS Hi-Power (85mm) exhaust when I bought it, and I'm not happy with the torque or the fart-can sound.
I previously had an S14 with a 2.5" muffler shop exhaust (2x DynoMax UltraFlo in series), and had awesome torque, but still sounded kinda like a fart can from the outside.

Matina210
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Another question for the Hitman;
I saw that some Magnaflow mufflers come with a "sound dampener", just like the A'PEXi "Super Silencer".
But, these dampeners only come on round mufflers.

I see that the BRM exhaust uses an oval muffler on the end, and I like that.
What are the chances you could ship a BRM exhaust with a silencer to go in the oval muffler?

I want it quiet except on race day. :biggrin:

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asoomal
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Longer resonator = Deeper, lower, mellow sound.

Straight through resonators have no impact on performance...it's straight through.

I doubt you would be able to get a silencer for it...

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AZhitman
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Matina210 wrote:Do the different length resonators affect the tone of the exhaust? Or just the volume?
Does the shorter resonator cancel out shorter wavelengths and make the car sound less like a Honda buzz b0mb?
Do the resonators affect the power or torque?
You want a 22" resonator.

http://www.brmexhaust.com/catback-comparison
http://www.brmexhaust.com/f-a-q
Matina210 wrote:I ask because my S13 had an HKS Hi-Power (85mm) exhaust when I bought it, and I'm not happy with the torque or the fart-can sound.
That's because it's way too big, and despite the HKS name, it's a ricer exhaust.
Matina210 wrote:What are the chances you could ship a BRM exhaust with a silencer to go in the oval muffler?

I want it quiet except on race day.
No.

Silencers are garbage.

Think about it: Why would you buy a free-flowing exhaust, then shove something in it to choke it down to a 1" hole?

We've sold over 1,000 systems for S-chassis cars. Not one has come back with complaints of "it's too loud".

You're overthinking it - Let us do the engineering and designing. All you have to do is select what will work best for your application. :)

Matina210
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AZhitman wrote:You're overthinking it - Let us do the engineering and designing. All you have to do is select what will work best for your application. :)
<groan>
I am an engineer...

2FoetySx
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Then engineer an exhaust lol ^^
I will Definitely be buying the dual tip 2.5 with a resonator for my s13. Does the high flow cat really make a difference on the dual cam k?

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AZhitman
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Matina210 wrote:
AZhitman wrote:You're overthinking it - Let us do the engineering and designing. All you have to do is select what will work best for your application. :)
<groan>
I am an engineer...
Hmmm. In that case, you'd know that sticking a potato in your tailpipe is a bad idea, and that it's nearly impossible to increase flow without increasing sound volume (although, we've come damn close).

Silencers are stupid. :)

Thanks Matina!

p.s. Would love to see some pics of the '80!

2FoetySx
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Hitman, weve met before though (i doubt youd remember me) youve always been super helpful. Thanks for that.

I live in arizona, could i buy one of these locally and just pick it up to save on shipping?

could you lead me toward any local 240/nissan/drift/AnythingOtherthanHonda meets?
did you sell that amazing vert project?

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AZhitman
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I remember everyone. :)

Nope - We build in FL and CA. I even paid for shipping my own. :)

Local 240sx board might be helpful - lots of events going on out here.

Vert sold about a month ago.

Thanks much!

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homeslicej2
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You sold the Vert!! :( At least you're still making these awesome exhausts. I need to pic one up, hopefully next summer when I do the turbo upgrade.

craigyboy
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Just got my exhaust in today!!!! cant wait to put it on thanks greg

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AZhitman
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No problem - Enjoy!

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voiddweller
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Hi Greg. Just received the PayPal request. Looking forward to the exhaust!

Matina210
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2FoetySx wrote:Then engineer an exhaust lol ^^
My thoughts, exactly.

Matina210
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AZhitman wrote:
Matina210 wrote: I am an engineer...
In that case, you'd know that sticking a potato in your tailpipe is a bad idea...
I don't know what kind of silencer you're talking about, but the one for my existing muffler fits the inside diameter of the muffler. This is hardly “sticking a potato in your tailpipe.”

If you were an engineer, you’d know that engineers don’t settle for answers like “silencers are stupid.”

I went to the nearest shop with a dynamometer to see the effects of the silencer on my HKS exhaust. The only other time I saw a dyno graph with and without a silencer was when Sport Compact Car was testing an A’PEXi N1 Dual exhaust on their Project 240SX. If I recall correctly, they claimed the silencers caused a loss of about 1.5 hp, and a gain of 5 lb-ft of torque. My results from this morning are different: Above 3000rpm, the run without the silencer showed a gain of 2 hp, and 5 lb-ft. This is in addition to the previous 151 hp and 149 lb-ft. Below 3000rpm (the range where I drive on the street) the graph doesn't show a difference with or without the silencer. So, on race day, I would want to run without the silencer…except this exhaust isn’t going to make it to the next race day.

After the test, I drove home without the silencer and remembered why I’ve left it in for the last 3+ years. Without it, the car is LOUD, and sounds even more like a fart can. The silencer is going back in, until this exhaust is replaced.

Thank you for the suggestion of the 22" resonator. Though I know fluid mechanics, my background doesn't cover much in the way of acoustics.

So if you'll excuse me, I'm off to design an exhaust (again). With a diagram and some notes, an exhaust shop in town is going to build what I want.

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voiddweller
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Hi Greg. I just received the exhaust. Wow, talk about fast shipping. It was received in less than 24 hours of placing the order!

I'm going to start a thread with pics and then update it later when I have time to do the install.

Thanks!

Matina210
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2FoetySx wrote:
Matina210 wrote:
<groan>
I am an engineer...
Then engineer an exhaust lol ^^
lol The last time I did that, I had a little bit of difficulty getting the muffler shop to build what I wanted. This time was worse, even though the local muffler shop had an example of an N1-style exhaust. My S13 had an HKS Hi-Power cat-back on it (installed 2 or 3 owners ago). It turned out to have about a 60mm pipe. As bad as the torque felt, I could have sworn it was the 85mm version for a turbo motor.

Hitman, the following info may help your customers decide what they want, as I’m using MagnaFlow mufflers like you.

For my new exhaust, I have two MagnaFlow mufflers in series. There’s a 2.5” (63mm) pipe for coming out of the catalyst housing, a 22” long “resonator” (cylindrical muffler) with a 2.5” core. The resonator is followed by a 2.25” pipe and a 2.25” muffler at the exit. The muffler shop tried to follow the routing of the N1 exhaust.
(parts + labor cost about $431. Kudos to Top Gun Muffler of Fort Walton Beach)

The exhaust sound now has more bass. The sound at idle is less like a buzz and more of a throbbing noise. This might be due to the 22” resonator.

The shop with the dyno can’t fit me in until at least tomorrow, but the “butt dyno” says the torque is better. On the drive home, I was shifting at lower RPM than before. Maybe 300-500rpm lower. I can now cruise around smoothly at 2000rpm (but not anywhere below that). Previously, the engine was really unhappy below about 2500. Since the pipe size is nearly the same as before, the torque might also be due to the length of the resonator. Whatever the reason, I’ll take it.

I think the sound could stand to lose about 5-10 dB. If I was going to do it over, I’d go down at least one pipe size: 2.25” upstream, followed by 2” through the 2nd muffler and the outlet. Or maybe I’d just stick with a 2.0” pipe and mufflers.

Actually, I may do it over. I like the sound better than before, but it’s still loud. It’s almost as loud as the HKS pipe without the silencer. I’ll give myself a couple of weeks to get used to it, but this amount of noise might fail the “girlfriend test”. ...And my experiment may need more test samples before I'm satisfied.

I read somewhere that my DC Sports header has a diameter of 2.1” at the collector.
I’ve also looked for specs for my stock catalytic converter, and it appears to have a 2” diameter at the inlet and outlet.

Knowing this, a KA24DE should run really well if you use a 2” exhaust, and just take the bends out of it. Straight-through mufflers (like MagnaFlow or DynoMax Ultra Flo SS), and routing like an N1 exhaust.

I can rationalize using a pipe a little bigger than 2”, because a larger diameter gives you a better ratio of cross section to surface area. The surface of the pipe slows the flow through friction, but too big a cross section (especially if the cross section changes abruptly) slows the engine in other ways.

Matina210
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Some theory that may be helpful:
To paraphrase some good advice from Evolutionm: “The rally people worked out ages ago that exhaust systems starting out large from the turbo [outlet] and gradually reducing on the way to the tail can enhance low- to medium-rpm torque output. This makes sense because it gives the [engine] a large volume to exhale into and the reducing size helps keep the exhaust gas speed up as it cools and contracts along the exhaust system.” This corroborates the law of Conservation of Mass. In other words, your exhaust should act as a funnel, and get smaller toward the exit.

By using a pipe bigger than my catalyst outlet, I know I’m sacrificing some torque. This is why I’m went to a 2.25” muffler at the end of my exhaust, instead of keeping 2.5” for the whole cat-back system like on my S14. Regardless, a 2” pipe would be the best design for ultimate torque.

As for the bends, Conservation of Momentum dictates that it takes momentum for a flowing fluid (like exhaust gasses) to change direction. A bend in an exhaust pipe takes away from momentum in the direction of the flow. In order to maintain the flow, the engine has to work harder. That work could have gone toward making the car accelerate.
That’s why N1-style exhausts come out at an angle. The stock exhaust has two 90-degree bends to make the muffler stick out straight, because that’s what the average car buyer expects. It has nothing to do with performance, efficiency, or even production costs.

Then, the stock muffler makes the exhaust do a U-turn, at least twice. That’s 540 degrees of bends, and every bend hurts the engine’s torque and power.
An N1 fitment, which makes about a 30-degree bend at the differential and goes straight to the cutout in the bumper, loses a lot less momentum from the exhaust flow. To get the full effect, you have to make sure the mufflers are a straight-through type. If you look in one end of your muffler, and can’t see all the way through (like with a “turbo muffler”), you’re giving up torque.

That’s why HKS Hi-Power, A’PEXi N1, etc. are bent the way they are. (The muffler shop in town was able to fit an oval-style muffler at the rear of my S13 without using the two 90-degree bends like a stock exhaust…but it was strange to them.)

Emperical evidence, from my previous experiment:
On my S14 (totaled in 2008), I had a muffler shop make me a 2.5” exhaust with a single DynoMax UltraFlo muffler. It was too loud for me, so I had a DynoMax “bullet” muffler spliced in. Once I had the two mufflers in series, I was impressed with the amount of torque I got from my S14, which was otherwise stock. No header, no intake, no cams…

Another 240SX owner rode with me at an autocross, and thought I had too much midrange power. He thought I might have changed the cams or compression (both illegal for the class I was in). No, I had a stock long-block that had never been opened.

Driving in the mountains of New Mexico, the exhaust made such a difference that I could use 5th gear on slopes where I used to need 4th. This was empirical evidence that taking the bends out of the exhaust path was good for torque.

My S13, regardless of all its bolt-on parts, still needed 4th gear on the same slopes. This was evidence that the HKS exhaust had too little backpressure for a KA24DE.

Matina210
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If you’ll bear with me, I have an explanation for why everyone might be happier with the 22” resonator:

As much as I liked the torque from my S14s muffler shop exhaust, I’m sure I could get more with a smaller-diameter pipe. What I didn’t like about the muffler shop exhaust was that (on the outside) it gave off some "fart can" sound. I really don’t like that sound, and I wanted my S13 to sound better than that.

However, that exhaust sounded bad-a** when I got off the gas and it made this crackling sound. It was a softer version of the sound you hear from a V8 with a dual exhaust and no crossover. It really meant that there was turbulence in the pipe, but I liked the sound as long as it wasn’t too harsh.

For a while, I was actually tempted to put a FlowMaster muffler on the S13, but I’m not sure what sound or performance I’d end up with. FlowMasters are designed around acoustics, not fluid mechanics. I’m going to stick with what I know, which is fluid mechanics.

What I did differently this time is to try MagnaFlow mufflers where I previously had DynoMax UltraFlo SS. Either way, you can look in one side of the muffler and see all the way through it. Compared to what I remember of the S14s exhaust, I think the S13 sounds deeper. Since the muffler design is so similar, I think it might be due to the longer resonator. I think my S13s exhaust is louder than my S14s. This may be because the S13 has a header and intake.

http://en.wikipedia.org/wiki/Helmholtz_resonance

^ I found the equation for Helmholtz resonance on the internet (easier than digging old textbooks out of storage). This equation calculates the resonant frequency of a body of air, such as the column of air in a muffler. I made a chart in MS Excel where I plugged in different exhaust diameters and lengths. I used the dimensions of different MagnaFlow resonators, and found that the output frequency varied by the length of the resonator, and the diameter didn’t matter.

This was because I filled in “Area” in the formula with the cross-sectional area of the resonator core. There were dimensions elsewhere in the formula that made up an Area (Volume = Area x Length), and the Areas cancelled each other out. The resonant frequency was then a function of the speed of sound, divided by the square of the resonators length. Longer lengths resulted in lower frequencies: Less buzz, more bass.

(Note that the speed of sound is the speed of sound waves in your exhaust, not at all related to the velocity of exhaust flow.)

I still don't know how to make my KA24DE sound like a V8, but using the longest possible resonator is a step in the right direction. :biggrin:

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AZhitman
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Matina210 wrote:I don't know what kind of silencer you're talking about, but the one for my existing muffler fits the inside diameter of the muffler. This is hardly “sticking a potato in your tailpipe.”

If you were an engineer, you’d know that engineers don’t settle for answers like “silencers are stupid.”
I'm not interested in arguing - The point is, this is a typical silencer:

Image

Putting that in an exhaust system is simply a band-aid for poor design. You CAN have a free-flowing system that makes good power and sounds great. We've proven it. :dblthumb:
Matina210 wrote:this crackling sound... It really meant that there was turbulence in the pipe, but I liked the sound as long as it wasn’t too harsh.
That is, in a word, incorrect. (Notice I didn't make a wisecrack about engineers? :nono: ) It's not "turbulence".

That crackling / popping is caused by the lean condition brought on by deceleration. When you lift, the throttle plate closes off incoming air and your ECU returns to a leaner mixture. However, you're still moving, which keeps the engine spinning, at an rpm that normally would want more air (and fuel) than your closed throttle plate (and turned-almost-off injectors) can provide. The popping occurs when sufficient fuel builds up in the chamber to "fire" that cylinder on the exhaust stroke of the engine.

Easier to show on a carb'ed car. Not harmful, and I agree - sounds way cool. Has ZERO to do with "turbulence".

Wanna confirm? Next time you're driving, press the clutch in on decel - It won't pop / crackle like it does with the clutch disengaged.
Matina210 wrote:...showed a gain of 2 hp, and 5 lb-ft.
...all well within the variability of a dyno. One pull means nothing.
Matina210 wrote:After the test, I drove home without the silencer and remembered why I’ve left it in for the last 3+ years. Without it, the car is LOUD, and sounds even more like a fart can.
Correct. It's a poorly-engineered system, which you already knew.
Matina210 wrote:Thank you for the suggestion of the 22" resonator. Though I know fluid mechanics, my background doesn't cover much in the way of acoustics.
No problemo. We've been building these for 10 years, going all the way back to Dave Coleman's rally B14 Spec-V and one of the first turbo KA S13's... We've learned a lot.

Believe it or not, the "acoustics" part tells you a lot about what's going on with the exhaust. That raspy "fartcan" sound is a symptom of restriction, believe it or not. The Honda guys will argue until VTEC kicks in, and they're still wrong. :)
Matina210 wrote:So if you'll excuse me, I'm off to design an exhaust (again). With a diagram and some notes, an exhaust shop in town is going to build what I want.
Cool. Not sure why you felt the need to share that tidbit in my thread, but go get 'em, tiger. :)

fastma11
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Nice, thinking bout getting something like this


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