Motor Sound

[TexasCummins]

Has anyone attempted to quieten the motor down to the level of a 6.7? Is it even possible?

[DoghouseDiesel]

Highly unlikely unless you want to install a VGT turbo. That's the reason 6.7's are so quiet.

I can take a 6.7 and straight pipe it and its still quieter than a stock 5.9 CR.

Now, I have a 6.7 sitting here with a spec'd 66 charger and a Silverline exhaust that sounds viscious.

I was demonstrating sound differences to a customer today. I had 4 trucks; a stock 6.7, one with the dpf/cat removed, the one with the 66, and then my truck. All totally different sounds.

[TexasCummins]

How does the VGT quieten the motor?

[DoghouseDiesel]

The nozzle closes down and basically acts as a muffler.

The 6.7 down pipe is also a catalytic converter, so that quiets it to.

But, if you straight pipe it, from the turbo back, the only extra noise you hear is really just the exhaust brake, you get this a much higher pitched whistling.

[DoghouseDiesel]

The motor itself though is no quieter, until you get to the 2010 - 2011 model year trucks.

They added a lot more insulation and noise and vibration dampening to it for the new trucks.

[olboyowl]

what about timing? rich, i thought u mentioned somewhere that -2 - 0* timing runs pretty smooth from your experience? correct me if im wrong. i have mine at -2 at idle and its pretty quite. if i could quite it more though, i would. interested to hear some comments.

[DoghouseDiesel]

Yeah, you can get it quiet and pretty rattle free with low timing.

Any timing value that is AT or AFTER TDC is pretty quiet.

The thing you have to look at are some of the insulation differences that they did on the 6.7 to quiet it down.

For example, look at the alternator. The alternator has a lot more shielding around it.

The fan. The fan shroud blows the air almost straight down vs into the engine bay.

The motor mounts on the newer 6.7's are a LOT softer than the 5.9's. They are so soft that it actually makes it a pain in the butt to use an optical pickup on the crank damper to dyno it because there is so much flex.

There are quiet a few things they did to quiet it down and reduce the vibration that go beyond what you'll be able to do with just tuning.

[olboyowl]

thanks for that. i'll try uping the timing 2* to get it to tdc

[MQ105]

Also, the 6.7s are 4 (5?? more than 3, though) event-tunes from the factory. That makes a difference. When Chris (Joesixpack on CompD) was tuning his 5.9 with standalone ECU, he made a multiple event tune (5 events, maybe- I don't recall exactly) that was very quiet.