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Discussion Starter · #21 ·
Ah well that makes all the difference. I am going to a 2.5" exhaust from a 3" and will have it back on the dyno next month. Hopefully with negligible power loss between the two.
I'd think you'd lose nothing at all. Every dyno I've seen, even on untuned bone stock cars, shows gains across the power band with no loss of power anywhere when going from a 2.5" straight through exhaust to a 3" straight through exhaust.
 

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K, I think this confirms fitment with a bar...
View attachment 103198
View attachment 103199
View attachment 103200

So that seems like the most "direct fit" possibly. Nice big muffler on the back, hit not so big that it encroaches on suspension. I don't know much about this company, but they do seem to be domestically made by a company in NJ.
Is that the 1320 exhaust ? I had a top mount turbo manifold for b series from them that was very well made. They sell a lot of products alo
I'd think you'd lose nothing at all. Every dyno I've seen, even on untuned bone stock cars, shows gains across the power band with no loss of power anywhere when going from a 2.5" straight through exhaust to a 3" straight through exhaust.
hes going from a 3 back down to 2.5 I believe
 

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hes going from a 3 back down to 2.5 I believe
x2

When I first swapped the motor I had a 2006 K24a2 with bolt ons 3” cold air intake RBC manifold and stock TB with a KTuned 3” muffler connected to KTeller 3” piping and a big tube header (KTuned) which has a 3” exit. The piping has a Vibrant 3” Ultra Quiet resonator as well. I can tell you that the KTuned muffler was loud no matter if you were in VTEC or not. People would roll up their windows when I would be at a light. In a Del Sol, it’s like anything is loud in there from the inside and I still have the full interior.

Right now I have a JDM K24 3 lobe in my Del Sol, 3.5” cold air, ported US manifold, 74mm TB and DC3.2 cams. I swapped out the muffler for an APexi WS2 universal muffler (70mm) and it really made it “quiet”, relative to the KTuned muffler. It took some work to make it fit, but that big ol muffler does fit and has room to fit the 23mm ITR bar I have out back. Now, even when I’m at full throttle in VTEC, you hear the motor much more than the exhaust, and on the highway I can listen to the music in 6th gear (it’s an NSN4 trans with a TSX 6th). I have the idle set pretty low (it’s between 825-875) and if I walk up to the car from the garage while it’s running, you hear the header sound more than you hear the sound from the muffler, if that makes sense. People don’t roll the window up at lights anymore. I have to drive down a residential street about 6 blocks long to get to the garage. With the KTuned muffler, they’d look, with this one, they don’t.

If I didn’t switch to the WS2 muffler, I probably wouldn’t daily drive the car anymore. FWIW, the two guys who have tuned my car asked me what size exhaust I have on my car and I’ve told them it’s 3”. They looked at me puzzled and told me it’s one of the quietest 3” exhausts they’ve heard, and the first tuner had the car with the KTuned muffler. The second one called BS till he raised the car on the dyno and saw for himself.
 

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Discussion Starter · #24 ·
We'll that's a shining review for the WS2 muffler. I wonder if I could fit it in a hatch. The long tip is what worries me there.
 

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Yes, it is a long tip, roughly 7” if I’m not mistaken. I’ve been thinking of changing the tip, but my primary concern was the sound so once it was on and I didn’t get annoyed by the sound anymore, I didn’t pay any mind to what it looked like. I believe, as it sits now when looking down at the top of my rear bumper, the tip sticks out enough for you to see it. If I got a decent tip that’s 3” in length at the most, it would be a little bit behind the bump. But as it is now, it doesn’t stick out ridiculously.

I had an EG hatch years ago but I don’t even remember, between the hatch and Del Sol, which one has the shorter rear end. And a WS2 is roughly $300 shipped at its cheapest so I don’t know if that price point makes it a no-go especially if you aren’t sure of fitment (if you don’t know, it’s entry is not offset like Honda mufflers tend to be, it’s right in the center of the muffler). So that may be a challenge but it worked for me.
 

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Discussion Starter · #26 ·
Whelp, my shop prefers to work with the KTeller kit so I ordered their 3" stainless setup. I guess I'll have to buy stainless flanges and hangers since the ones they provide aren't for some reason.

Anyone know how you generally deal with the 2.5>3 inch step up? I'm hoping I can find an off-the-shelf 3-bolt 2.5" flange that steps up to 3". We shall see. Tentatively settled on that stainless works muffler for now, and either an 18" or 24" resonator. The Vibrant ultra quiet resonator apparently won't fit comfortably between the rear heat shields since they're only about 6" wide. I see evidence that one might possibly fit in front of the hangers though if needed.

--Matt
 

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Whelp, my shop prefers to work with the KTeller kit so I ordered their 3" stainless setup. I guess I'll have to buy stainless flanges and hangers since the ones they provide aren't for some reason.

Anyone know how you generally deal with the 2.5>3 inch step up? I'm hoping I can find an off-the-shelf 3-bolt 2.5" flange that steps up to 3". We shall see. Tentatively settled on that stainless works muffler for now, and either an 18" or 24" resonator. The Vibrant ultra quiet resonator apparently won't fit comfortably between the rear heat shields since they're only about 6" wide. I see evidence that one might possibly fit in front of the hangers though if needed.

--Matt
I found pieces of pipe that are 2.5”-3” and was going to weld a 2.5” 2 bolt onto the header, and the other end to the 3” flex pipe with a v band to the midpipe.
 

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Discussion Starter · #28 ·
I found pieces of pipe that are 2.5”-3” and was going to weld a 2.5” 2 bolt onto the header, and the other end to the 3” flex pipe with a v band to the midpipe.
Kinda heading the same way. I see plenty of step down flange to pipe setups for header outlets, but not any going up :)
 

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Discussion Starter · #29 ·

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Arouse the DAMPFHAMMER!
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Ah well that makes all the difference. I am going to a 2.5" exhaust from a 3" and will have it back on the dyno next month. Hopefully with negligible power loss between the two.
Would be great if you share a back to back test result. We have at K20a.org some nice back to back tests from 3" and 2.5" CAT-backs. It is very likely to loose about 6-10 whp, depending on VTC curve you already achieved with the 3" setup. My suggestion would be always to use a resonator and a better noise damping muffler as the better compromise. But finally it is a question of application and budget.

2.5" or 3" Exhaust on my K20A2? | Honda / Acura K20a K24a Engine Forum
Is there a power diff between 2.5" and 3" exhaust? | Honda / Acura K20a K24a Engine Forum
Power loss switching back to 2.5" exhaust from 3"? | Honda / Acura K20a K24a Engine Forum
2.5" exhaust vs. 3" exhaust on stock internal K20A2 (Dyno) | Honda / Acura K20a K24a Engine Forum
 

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Discussion Starter · #31 · (Edited)
I managed to find a video of that Stainless Works muffler on a 4-cylinder vehicle. Not a Honda, but at least a 2.0L and 3" without a turbo on the exhaust:

Seems promising.

Here's a better cutaway of the inside. It's the same basic design as the Dynomax setup, or any other traditional turbo muffler, just without the flow directors.

103283


--Matt
 

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Discussion Starter · #32 · (Edited)
Ok, I ended up ordering this stuff...

https://www.summitracing.com/parts/WLK-24248
https://www.summitracing.com/parts/WLK-24241
https://www.summitracing.com/parts/stw-tm5c3c3o

I figured the bullet can go ahead of the hangers in the center of the chassis, and the glasspack can go behind it. Both of those pieces are perforated glass packed tubes, so neither should have much (if any) meaningful impact on flow.

Got these things to mate to the header and step up to 3", and to connect the back section to the front section:
https://www.summitracing.com/parts/VPE-1482S
https://www.summitracing.com/parts/VPE-2630
https://www.summitracing.com/parts/MIO-MMCLAMP-VS-3

🤞

--Matt
 

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Discussion Starter · #33 · (Edited)
I found some numbers comparing this SW muffler to the straight through variety and open pipes here: Stainless Works Exhaust

Their number show virtually no power loss going from straight pipes to their straight through muffler, and about 2.5% power loss moving to the turbo chambered muffler. Dumbed down to cammed NA k20 numbers, that seems like 4-6hp...which I can live with. A younger me would care about that, but me today would rather be able to comfortably carry on a conversation. 😉

--Matt
 

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Would be great if you share a back to back test result. We have at K20a.org some nice back to back tests from 3" and 2.5" CAT-backs. It is very likely to loose about 6-10 whp, depending on VTC curve you already achieved with the 3" setup. My suggestion would be always to use a resonator and a better noise damping muffler as the better compromise. But finally it is a question of application and budget.
I am going to try going back to 2.5" for clearance as well as sound. What I'm not seeing is the proof that a very restrictive 3" muffler paired with a resonator(s) will give you better performance or the same sound levels as a more straight through design 2.5" exhaust. Even the ws2, which does sound nice and quiet, is only 70mm. I will definitely update with my results next month. I figured to lose in the 5whp range, however I am no expert and will have a definitive answer next month. The numbers will be a little skewed based on the car was tuned with a 3" exhaust and I am not having it retuned with the 2.5", only ran on the dyno to get numbers for race classing. If I lose in the 10whp range I may have it retuned to see if any of that could be gained back.
 

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Discussion Starter · #35 · (Edited)
I am going to try going back to 2.5" for clearance as well as sound. What I'm not seeing is the proof that a very restrictive 3" muffler paired with a resonator(s) will give you better performance or the same sound levels as a more straight through design 2.5" exhaust. Even the ws2, which does sound nice and quiet, is only 70mm. I will definitely update with my results next month. I figured to lose in the 5whp range, however I am no expert and will have a definitive answer next month. The numbers will be a little skewed based on the car was tuned with a 3" exhaust and I am not having it retuned with the 2.5", only ran on the dyno to get numbers for race classing. If I lose in the 10whp range I may have it retuned to see if any of that could be gained back.
I don't think anyone has such proof (at the moment at least).

The general experience I've had is that restrictions closer to the engine have a more profound impact than those further from it, but they're all on turbo engines that benefit from as little back pressure as possible so they may not be relevant at all here. In that space, switching to a bigger downpipe and leaving the smaller rear of the exhaust often gets you almost all of the power benefits you'd get from a full turbo back exhaust. The theory I've seen on the topic suggests that having an optimally large space for expansion of hot exhaust gasses nearest to their origin is much more important that full end to end flow.

How, or if, any of that relates to Honda k20 engines is unknown to me. In general, NA engines typically see better lower rev power figures with smaller exhausts. Dyno evidence seems to suggest that not to be true for these ones, though, and shows that they thrive with as little exhaust resistance as possible.

My car will go on the dyno for a proper tune after the exhaust is changed, so I won't have a before figure. I'll share the after figure once I have it, though. Until then, it's sitting in storage. My hope is that a 3" exhaust with a turbo style muffler performs at least as well as a 2.5" exhaust with a straight through muffler, but does so more quietly since the straight through 2.5" setup is too loud for my taste.

FWIW, I wouldn't call a turbo style muffler "very restrictive". It's technically still "straight through" in that exhaust gasses are never forced through louvers/perforations/packing to reach the output. It's just 3 passes through straight sections internally, with the obvious flow disruptions you have at each turn-around. These mufflers, and even their chambered and laminar flow cohorts in the "chambered" space are still far less restrictive than your average stock muffler.

--Matt
 

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Discussion Starter · #36 · (Edited)
I'm starting to consider swapping the bullet for a GESI UHO cat when I get this done now. Cat plus glasspack plus chambered muffler aught not be too loud I'd think. Those cats evidently cause less than 1% power loss, even on 500-850hp applications, so it shouldn't cost a lil old k20 much right?

I was thinking of maybe even swapping the chambered muffler for a straight through, but then I came across this post where a person with 2.5" pipes and a twinloop with a GESI cat was reported as a bit too loud so I figured maybe not...

That person's sentiments were:
Exhaust is louder than I would like, but it isn't obnoxious. It has a nice tone when I floor it, but its louder at part throttle than I would like.

Bottom line is that if you want quiet, then you need a resonator and a chambered muffler.
 

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İ m searching for realy stock exhaust sound.
İf i dont find way im going to use dc5 stock full exhaust system.
But if i find a way with skunk2 alpha headers and any stock exhaust im going to change.
İ really want stock exhaust system and lose less hp.
 

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Both of them.
first goverment second comfort no comfort with civic :)
A combination of a resonator and a chamber muffler system my help or like HyTech does it a Twin loop muffler design. I would talk to HyTech, they know exactly what to do.
 
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