Has anyone done an OEM-like QUIET exhaust with catalytic converters on a high HP NA build before? flame suit on i know, but seriously I've been out of the honda game for a while and it seems like the NA numbers out there are astounding, especially on the K-series builds.

I've gotten used to the luxury quiet mufflers of my daily drivers and was wondering if I were to get back into a honda and went for a decent NA build if I could keep it quiet. For what its worth, I think that OEM DC2 ITR/S2000 exhausts were too loud. I'm talking about someone who specifically engineered/rigged a system that made it OEM quiet (without e-cutouts/valves). Even if it sucked up 50whp I would totally go for it. I've never been a fan of excessively loud exhausts on NA builds, I'm just wondering if anyone else has done something similar. There are plenty of OEM 200-300hp cars that are decently quiet.

 

That's true, there are decently quiet cars with 250ish hp, but they have more than 4 cylinders, or a turbo. On my H22A swapped Accord I'm running a 2.5" ceramic core cat, a 2.5" Thrush resonator, and a OBX twin-loop muffler all connected with 2.5" crush-bent piping and its pretty quiet driving around town or on the freeway. It's a very mild build, down on compression, and still spun the rollers to 185whp.

The simple fact is there is no free lunch with this. A quiet exhaust homogenizes the exhaust pulses and the easiest way to do that is backpressure. You can give the gases as much space to expand as possible (two or three actual mufflers) which theoretically would not generate much backpressure, but you get into packaging issues there.

 

It's really not too hard to build a decently flowing exhaust that sounds OEM. We have done this for numerous customers street cars, usually in conjunction with an E cutout for the track, but in your case you would eliminate that. Just get use good 2.5-2.75" mandrel piping and matching OD size cat from a quality company such as Magnaflow, Catco etc. about 12-18 inches from the cat, add a matching OD size "bullet" style muffler, again from a quality manufacturer such as Magnaflow. This will be acting as your resonator. Then continue to run the same size pipe from that back to an OEM muffler (Stock RSX base, Stock 4cyl Camry, Stock 4cyl Accord are all good choices that fit well in most cases) that' inlet is within .25" of the diameter piping you use. This will be a very quiet system that will obviously not flow as good as a full aftermarket but still will flow enough to make power. Using an air box of some sort on the intake will also keep sound levels down. Another benefit to building a system such as this is that it can be done using an aftermarket header and still be very quiet which allows for less power losses than a full OEM exhaust setup but still sound comparable.

 

For a real world example, we recently did a comparable setup on a customers 2.4L RSX. DC header, 2.5" stainless pipe to Magnaflow "Direct Fit" high flow cat, then 2.5" to a Dynomax "Bullet" muffler (16.5" length) then 2.5" back to a Walker QuietFlow OEM style Accord 4 cyl muffler. Sounded like a stock Civic EX. Car made 256/181 with that exhaust, tuned on Kpro and actually had a fairly decent power curve even up top despite the restriction. No internal engine mods, just bolt-ons and tuning but I imagine it would still flow plenty for increased compression and such. Obviously not ideal, but not absolutely killing it either.

 

That is actually pretty darned good. 0_0 Is that whp or corrected-crank?

 

Wheel figures on a DynoJet. Bone stock K24a2 (2006 TSX) shortblock.

 

wow, thanks for the great responses. I think the last time I made a thread about a quiet NA car I got laughed at right away, but times have changed.

Tachi, I see what you meant about more cylinders and turbos, and I gave thought to those as well, but there are still quiet NA OEM 4-6 cylinder cars in the 200-300hp. You're right though, its doable, but you run into packaging issues. I was mainly thinking recent honda v6 accord/acura TL levels of muffling, but those run 2 mufflers. big ones at that. even my old G35 sedan had a sizable muffler setup, but we all know how "loud" OEM VQ35 exhausts are, especially on the FX35 and G35 coupes.

B20vtecvillain, that 2.4 rsx setup sounds inspiring. Thanks for sharing. I will definitely do some research on that setup.

 

Contact LHT performance they builds some real nice custom exhausts! iv seen a few vids of there twin loop mufflers/ex and they make top hp and stay quite! There in florida but they are really helpful and can steer you in the right direction.

 

a buddy of mine dynoed with an rsx-s muffler and the original greddy muffler on his h22a accord a few years ago. the rsx-s muffler was pretty quite, but it also took 20hp off the top.

 

I've got to revisit my exhaust also. When I got my car it had a Greddy muffler on it that was unbearably loud, especially on the highway. I put a twin loop replica on it and it's better, but it's still louder than I'd like, especially eith someone else in the car. I'm going to check into some of the suggestions in this thread and a couple of others.

 

The (OBX) twin loop mufflers I've read break down and get blown out after a year. They might have improved the packing in the 2 years since those reviews/forum posts but its a fancy muffler for $130, my hopes aren't high. did you try adding a resonator in there too? Having a cat also helps.

 

All I did was swap the muffler. I believe the car has a cat, not sure about a resonator. I should have looked when I got the muffler swapped, but I didn't. It's difficult to see underneath without a rack because it's low. I got my twin loop for around $60 from Amazon. Hopefully it will last a while, but if not it didn't break the bank.

 

On my old generic twin loop once the factory cheap packing took a ****.. I cut it open with a dremel and scraped out all the old stuff and bought two packs of this motorcycle repacking material and had it welded back was much quieter than it was with the facotry cheap packing.. I drove around with the new repacking for 4 years before I sold car..

 

I'm running 3" on my B18C without a cat, using two 12" Dynomax bullet's and a VMS Racing muffler (an ebay Magnaflow knockoff). The muffler is the smaller 14" long case oval muffler, but it's near stock at idle, and a bit louder than a stock 8th gen Si under moderate load. With a converter it would be quite nice, but even now it's no rasp and not loud.

My old setup was a 2.5" setup with a large 20" case Magnaflow muffler only, and it was very livable with very minimal rasp and quiet.