Alright I plan on having a resonator installed but I dont' know which to get. The thing is just too loud on the highway and I commute. Anyways the shop has got an 18in resonator I can get installed now or I can have another size ordered. Whats a good size resonator for our car/my situation? thanks,
Travis

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What else is done to the car? what size exhaust? turbo or n/a?

Bump

I thought resonator where small, like the size of your hand?

I've got SRI, magnaflow SS muffler, 2 1/4 catback, N/A.
I ended up getting the 18in they had with 2 1/4 core. The car's bark was reduced about 50% but I'd say the hum at highway speeds was reduced about 75%. The car also hasnt' made the dragging tin can noise at full throttle since, so i'm very happy.

I think I'm running an 18" as well. Love the sound still, and no more farting/spitting. It won't decrease any gains from the exhaust so don't worry about it.

Keep in mind a resonator and a muffler -- even a round muffler welded into the middle of your exhaust piping -- are not the same.

A resonator is a hollow echo chamber. It cancels out soundwaves by bouncing them into each other, transforming the sonic energy into heat. This is what comes stock on your Celica. Resonators do somewhat reduce the volume, but they more noticably smooth the tone. That idiot with the buzzy 3" exhaust on his Civic is buzzing because he doesn't have a resonator.

Your straight-through muffler (what people sometimes mistake for a resonator) absorbs sound. It's bascially a perforated pipe wrapped with insulation. In the 1950s, it was fibreglass insulation with a louvered pipe (CherryBomb still uses this design, unfortunately). Modern versions use ceramic sponge and stainless steel wool. Either way, the idea is to absorb the vibrations from the exhaust stream. They're great at reducing the volume, but won't particularly smooth the tone. And helpfully, the longer the muffler, the lower the volume.

You can tell the difference by tapping on them. A muffler will absorb the tap, producing a dull thunk. A resonator will ring like a bell.

Both modern straight-through mufflers and resonators have minimal effects on the exhaust flow, even as they get longer. Proper inflation of your tires will have a much greater effect than running without good sound suppression (good meaning not a standard baffled muffler which slows exhaust flow to a crawl).