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  #31  
Old February 6th, 2019, 10:35
Rockwood Rockwood is offline
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Re: Best Sounding Exhaust For The 4.0L?

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Originally Posted by tech1001 View Post
No that's not loud most people can talk at about 50db and they check it 20 inches from the end of the exhaust at 3000 to 5000 rpm . It would be loud if they checked it at 50 yards or so .
You should check out J1169. At one time, it was 75% of rated peak HP RPM, but my understanding is that has since been amended back to idle (or some other relatively low RPM) because many cars did not allow the engine to rev that high when stationary. The test on stationary vehicles is done at 3M, up to 45* offset from the exhaust outlet. Even if you were to still be required to rev to 75% of the HP peak's RPM, that's 3400 on a Jeep, which is about where it shifts when I'm driving around at normal acceleration. Since it's stationary, there is no load on the engine, so 3400rpm during this test will be quieter than when you're driving.

The decibel scale is logarithmic and doubles every 3dB. 95dB has 30 times the sound intensity/energy that a measurement of 50dB does. 95dB has twice the sound intensity my no muffler/no cat/divorced wastegate racecar did at 5000-ish RPM racing at Laguna Seca. 95dB is four times as loud as a lawnmower at full tilt and about the same volume of a leadblower strapped to your back (which requires hearing protection for any operator doing it for work).

Why you'd want to drive around with an exhaust that loud just cruising around is beyond me. No excuse to exceed those sound levels in any vehicle cruising around, let alone on a Jeep 4.0 with it's teensy tiny cam and tractor-like maximum RPM.
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  #32  
Old February 6th, 2019, 14:27
tech1001 tech1001 is offline
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Re: Best Sounding Exhaust For The 4.0L?

I was just saying that you mite want to stay on the quiet side because they are starting to go after loud cars , and some cars with OE exhaust systems that won't pass the test the California bar does , they have there own test that California came up with and most newer cars with a auto trans will not free rev over 2500 to 3000 rpm but that's California .
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  #33  
Old February 7th, 2019, 23:38
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4x4JeePmaNthINg 4x4JeePmaNthINg is offline
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Re: Best Sounding Exhaust For The 4.0L?

Straight pipe, no muffler
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  #34  
Old February 8th, 2019, 08:31
Rockwood Rockwood is offline
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Re: Best Sounding Exhaust For The 4.0L?

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Originally Posted by tech1001 View Post
I was just saying that you mite want to stay on the quiet side because they are starting to go after loud cars , and some cars with OE exhaust systems that won't pass the test the California bar does , they have there own test that California came up with and most newer cars with a auto trans will not free rev over 2500 to 3000 rpm but that's California .
Per the CVC, it's J1169, which has since been modified (but can't confirm since I'm no longer an SAE member) to idle (again, I believe) due to new cars not allowing free-revving to 75% of peak HP.
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  #35  
Old February 9th, 2019, 02:08
tech1001 tech1001 is offline
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Re: Best Sounding Exhaust For The 4.0L?

I don't know how they would be able to test those cars , I was just saying what they are starting to do in California .
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  #36  
Old February 12th, 2019, 07:01
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cherokeecrawler cherokeecrawler is offline
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Re: Best Sounding Exhaust For The 4.0L?

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Originally Posted by Rockwood View Post
Even if you were to still be required to rev to 75% of the HP peak's RPM, that's 3400 on a Jeep, which is about where it shifts when I'm driving around at normal acceleration.
You must get 5mpg! My "driving normal" shifts at about 2200-2300 RPM and i only get around 16 average...
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