Each of the mufflers was tested on F&M Cylinder Heads' Superflo 600 flow bench. Owner Frank Intini made both himself and his equipment available for an hour's intensive work, whipping through the mufflers with the skill of a man who has spent many an hour juggling manometer levels on the 'bench. Each muffler was tested at a pressure differential of 28 inches of water (equivalent to 1.1 psi backpressure), and those mufflers asymmetrical in design were tested for flow in both directions. As is usual with muffler flow bench testing, major variations in flow across the different mufflers were recorded. The flow of a piece of empty tube the same length as a muffler was recorded at 353 cfm. Some of the straight-thru mufflers (probably because of their larger internal diameter) actually exceeded this figure.
However, before the mufflers could be fitted to the bench, an adaptor needed to be made to allow each muffler to be easily and quickly slipped on. It's this sort of time-consuming detail that many people overlook when they consider doing a test like this. But AutoSpeed contributor Graham Pring got his hands dirty and with the help of Exhaust Technology, an adaptor capable of taking 2 inch, 2.5 inch and 3-inch mufflers and cat converters was manufactured.
All of the mufflers were fitted to a Toyota Seca for testing. The standard exhaust of the Seca consists of a cast iron manifold with a single outlet pipe. This leads to a single 44mm internal diameter (ID) pipe that in turn leads to the 50mm cat converter. From the Toyota cat, a 47mm outside diameter (OD) pipe connects to a small Toyota resonator, with a 43mm pipe joining this to the rear-mounted muffler. Exiting the muffler is a 48.5mm OD tip.
After some debate we decided to replace the standard exhaust with a new 51mm (2 inch) pipe from the manifold back. Mark Marchesan of Exhaust Technology fabricated the new system that consisted of a mandrel-formed bend off the manifold, a 2.5 inch cat converter (that we flowed on the test bench at 395 cfm at 28 inches of water), and a 45 degree press bend at the back of the car. The rest of the pipe was straight and - as you've guessed by now - didn't contain a muffler. The tested mufflers were slipped one at a time onto the end of the pipe. We picked an oversize cat (2.5 inch instead of 2 inch) to make sure that the cat could flow at least as much as the best muffler - which it did.
With just the bare pipe and single cat in place, the car was LOUD, LOUD, LOUD. In fact, it was one of the loudest small capacity cars that we have ever heard! Under throttle it roared and shrieked to the tune of 122dB(A), and on the back-off it had a fierce crackle and bark. (We know all about that 'cos we had to drive the car - on the road - from Exhaust Technology to Awesome Automotive, where we did the dyno testing!) In one way the fact that it was so loud was good - all the better to find which muffler worked the best. However, in the real world, most exhaust systems would also run a resonator to try to shut up that over-run bark. However, not having tested all of the available resonators to find the best, we elected to stay with the single cat and single (test) muffler.
Leon Vincenzi of Awesome Automotive donated both dyno time and dyno driving labour to the cause. Leon's the type of guy who likes to see testing done - even if it means giving up an otherwise free Saturday. Thanks, Leon! The Seca was placed on the Dyno Dynamics chassis dyno, FWD 'trainer' wheels in position. The rear wheels were chocked, the large dyno cooling fan located at the front of the car, the intake air temp correction probe stuck near to the engine air pick-up, and testing could begin.
Incidentally, the Seca proved to be an ideal dyno test car. It sat as straight as a die on the dyno, with no torque steer or other poor behaviour visible. The twin cam sang a sweet song - all 52 dyno runs of it! The coolant temp stayed static, and the car didn't even use much fuel. Thanks Mr Budget....
Each dyno run was an averaged ramp up/ramp down, with the mufflers fitted in sequence by the happy AutoSpeed Deputy Editor Michael Knowling. Well, he started happy... after the 20th red-hot muffler changeover, he also started glowing in the face and began to grumble. With each new muffler fitted, Leon did a full power ramp up and then ramp down, the runs averaged for the print-outs.
During this process the peak Sound Pressure Level was measured by Graham Pring using a sound meter, while the dyno PC recorded the power developed at the wheels. Mufflers that were asymmetrical in design (eg offset inlet and central outlet) were tested in both orientations ie they were swapped end to end, with a test performed each way.
During the course of the dyno testing a 'control' muffler (the Genie Turbo) was occasionally re-fitted, so that we could see if the dyno power output was starting to drift. This scenario could be possible if the dyno's reading was susceptible to temperature variations in the eddy current retarder itself, or if the intake air temp correction wasn't accurate. It also tested the consistency of the noise measurements.
Once several hours had elapsed and the dyno testing was completed, the Seca was moved to another location within the workshop (where its tailpipe was directed outside) and further noise testing was carried out. This consisted of two tests:
The car was revved to 4000 rpm in neutral and the noise measured at a 45 degree angle, 500mm from the tailpipe using a Realistic sound pressure level meter. This test is similar (sometimes identical) to the noise tests carried out for legal compliance in many parts of Australia. As with the full-load dyno noise measurements, the meter weighting used the 'A' curve - ie readings were in dB(A).
The car was blipped to 4000 rpm while AutoSpeed Editor Julian Edgar recorded the sound on a Sony TCM-5000EV professional tape recorder. The recording level was adjusted for each muffler so that the magnitude of the sound was similar - the tape recorded sounds were made to assess noise quality, rather than loudness levels. These recorded sounds are the ones available as downloadable files with each muffler's test results in the 'Results' article.
In addition to the testing on the Seca, static (ie the car not under load) noise tests were also performed on Holden V8-powered Cobra replica and 50kW 1989 Suzuki SJ50 4WD. The Cobra has developed a peak power of 195kW at the wheels on the dyno, and is usually fitted with a twin 2.5 inch side-exit exhausts, twin reverse-flow mufflers, and a 2.5 inch crossover pipe. For the noise testing, one pipe was blocked near its muffler, with the remaining single-muffler pipe adapted down to 2 inches and fitted in turn with each test muffler. The engine was held at 3300 rpm (no load) with the meter positioned at a 45 degree angle 500mm from the exhaust. No cat converter or resonator was fitted to the Cobra exhaust while this testing was being completed. The Suzuki exhaust was equipped with the factory cat converter. The Suzuki was revved to 4000 rpm, with the noise meter at the same relative location to the exhaust outlet.
Each muffler was measured for length, width and heights, and was weighed. In addition, its construction was analysed and a description made of its type.
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Morphett Vale Exhausts
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