tunable exhaust?

[Mighty~Mart]

my friend has a tunable exhaust and i was thinking of getting one also.... what is the whole point of being tunable? i don't understand it......

[Razo-E]

the definition of "tune" is "to modify", so it's pretty much anything...


i guess the fact that you can put a slicencer on the muffler to make it quiet or louder is "tuning" the sound...

also, it'll have a few less horses if the cap is on, since the exit is smaller...

[jwa276]

also arospeed makes an insert that goes somewhere in the exhaust pipe that gives the driver an in car valve switch that opens and closes the exhaust pipe. its only use is to be able to be instantly quieter if need be. there might be a difference in performance near the high end of the rpm band.

jon

[rezzle]

'Tuning' in the drag ( and some street race ) circuits refers to accomplishing 2 things.

One, designing a system with the PROPER amount of backpressure. Yes an open exhaust or too large of a diameter can be a bad thing. For example on my GTS the person who did the mods before me thought it cool to install a 2,5" exhaust on a 1.5 Litre this is not a good thing because my car is supercharged not turbocharged, ergo .. no backpressure. There was a loss of low end torque. I was lucky to pull the heads off when I did and check because the exhaust valves showed indications that they had been overheated but they were still usable.

Two, Noise limiting. (Remember racing cars almost always run near full throttle while a street cars don't). So with some fancy engineering the proper amount of backpressure can be custom tuned by either fiddling with the length of pipe or the diameter. In street class drag racing for example there is a noise limit for cars about 92-95DB at 3500 RPM depending on the city.

Here is an example from Race City Speedway (Calgary Alberta)
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Alberta Street Shoot-out Rules & Regs

2002 Race City Motorsport Park
Alberta Street Shoot-out & Alberta's Fastest Street Car
Rules & Regulations
September 1, 2002

CONCEPT
To find the fastest Street Legal cars in Alberta in two categories – Tubbed and Non-Tubbed. The Street Shoot-out will be a heads up elimination program on a 5/10 Pro Tree.

TUBBED
Cars that have had any material removed, cut or added to in the wheel wells or arches.

NON-TUBBED
Cars that have had no material removed, cut or added to in the wheel wells or arches. Running face of all four tires must be within the bodywork of the car when viewed from above.

RULES


Vehicles participating must be ‘Street Legal', properly licensed and insured (see Addendum A), with complete working muffler systems. No open headers will be allowed. The maximum noise level is 95 db as measured on the "A" scale from a distance of 50 feet, at a right angle to the vehicle, with vehicle at a no-load rpm of 3500. Cars may be brought to the track on trailers, but must be street legal. Slicks are allowed. Must follow NHRA 2002 rulebook including driveshaft loops, see NHRA 2002 Rulebook (General Regulation 2:4, page 199).


etc ... etc ...
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Although loud it is easy to exceed this limit if the builder isn't careful. So, to keep the officials (and the cops ) happy Classes other than stock (where the exhaust must exit the rear of the vehicle by a certain number of inches) can fiddle with the pipe length to ensure that no resonance occurs near 3500 RPM and near full throttle ( some tracks, Shannonville?? have a maximum of 103 - 105 no matter what the car RPM may be. )

Achieving both of the criterion above means the exhaust has been 'tuned'