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Exhaust Silencer Power Loss - Fact Or Fiction

Debunking Tuning Myths

Luke Munnell
Dec 1, 2009

For as long as enthusiasts have been tinkering with cars, the general public has been upset with it, and therefore, has called upon law enforcement to keep us in check. From ride-height laws to emissions requirements and draconian CARB legislature, every step up we take in enhancing the performance of our cars results in two knocks down by the law. Possibly the biggest attractant of "fix-it" tickets is the aftermarket exhaust. They're legal for street use in some states, provided they accommodate a catalytic converter and remain largely faithful to the factory design. In others, they aren't legal at all. But nearly every jurisdiction in the country enforces the maximum level of sound an exhaust may output for it to be street legal-usually 95dB-and to cope, most aftermarket exhaust manufacturers have adopted a removable silencer in the exhaust's tip that reduces excessive noise.

Impp_0912_03_o+exhaust_silencer_power_loss+miata Photo 2/6   |   Exhaust Silencer Power Loss - Fact Or Fiction

Will Using A Muffler Silencer Always Cost You Power?
The silencer works by restricting exhaust flow, thereby reflecting noise back into the muffler canister where more of it can be absorbed by sound-deadening insulation. Enthusiasts have been loathe to accept the devices, on the grounds that restricting exhaust flow reduces power. But is this always the case? Are there instances in which the added back pressure might actually be beneficial to a street car? To test, we rounded up the usual test subjects-our naturally aspirated Project Miata and turbo-upgraded SR-swapped 240SX-and took them to the Dynojet rollers of Westminster, CA's MD Automotive.

Both cars are equipped with aftermarket GReddy Ti-C cat-back exhaust systems, which utilize muffler silencers to keep sound in check. With the cars strapped to the dyno, we performed three back-to-back runs of each car, both with their muffler silencers installed and with them out. Here's what we found:

Impp_0912_04_o+exhaust_silencer_power_loss+exhaust Photo 3/6   |   Exhaust Silencer Power Loss - Fact Or Fiction

The Verdict:
At low boost, the 240sx lost about 18 whp from mid-rage to redline, and 11 lb-ft of torque. At full boost, the losses were greater and the rush of air funneling through that tiny silencer was actually kind of scary. But power and torque came on earlier in the mid-range, which could be a bonus for daily driving. Overall, the power and torque output of our 114whp Miata didn't budge at all with the addition of the muffler silencer, even though sound output dropped noticeably. Our verdict? It's a five-minute install-keep it in on the street, out at the track.

Sources

MD Automotive
Westminster, CA 92683
714-891-1113
http://www.markdibella.com
GReddy Performance Products
Irvine, CA 92618
949-588-8300
http://www.greddy.com
By Luke Munnell
294 Articles

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