Don Terrill’s Speed-Talk

Now all the components and raw material are catalogued, the fixtures and prints are ready, etc. John Kuhn installed the exhaust, this is the final hookup. After oil cooler and some hoses are done, it’s time for a sound check.

Video of the final install, no sound check yet, though:

https://youtu.be/YM4pdF2HZkQ

I think I found one topic that wasn't debated.Some x pipes are 2 pieces of 90 degree tubing with a section cut out and welded together.That would be a reduction of total volume at the x.Others are formed pieces welded together that increase volume at the x.Does the volume differences change the sound waves?

ptuomov wrote: ↑Sun Jan 07, 2018 7:24 am

naukkis79 wrote: ↑Sun Oct 08, 2017 1:26 pm That infinity pipe probably creates big turbulences and flows very badly, it's shape is extremely anti-flow like.

Look at the poor fools designing F1 exhaust ports and headers. The idiots are using the same “anti-flow” infinity-pipe shape off the head in their exhaust. Fail!

https://youtu.be/Q9X-Xe3ueL0

So you think you know more about their exhaust than they do and you've only seen it in a video while they've tested it and modified and tested, etc?

If you're that good, why don't you model F1 cars over the phone or something? Since you can tell better than they can what their parts do just by looking at them? They would have no need for all those millions of dollars if they'd just hire you. Lol

midnightbluS10 wrote: ↑Fri Feb 16, 2018 11:14 am

ptuomov wrote: ↑Sun Jan 07, 2018 7:24 am

naukkis79 wrote: ↑Sun Oct 08, 2017 1:26 pm That infinity pipe probably creates big turbulences and flows very badly, it's shape is extremely anti-flow like.

Look at the poor fools designing F1 exhaust ports and headers. The idiots are using the same “anti-flow” infinity-pipe shape off the head in their exhaust. Fail!

https://youtu.be/Q9X-Xe3ueL0

So you think you know more about their exhaust than they do and you've only seen it in a video while they've tested it and modified and tested, etc?

If you're that good, why don't you model F1 cars over the phone or something? Since you can tell better than they can what their parts do just by looking at them? They would have no need for all those millions of dollars if they'd just hire you. Lol

Is this in response to me or naukkis79? For what it's worth, I was attempting sarcasm. I think the shape is fine, and the fact that F1 uses it makes me more confident that the shape is fine.

RCJ wrote: ↑Fri Feb 16, 2018 10:46 am I think I found one topic that wasn't debated.Some x pipes are 2 pieces of 90 degree tubing with a section cut out and welded together.That would be a reduction of total volume at the x.Others are formed pieces welded together that increase volume at the x.Does the volume differences change the sound waves?

I don't know, but if I'd have to guess, I'd guess that both reduce noise but the x-pipe that has the smaller minimum cross-sectional area at the merge will reduce the noise more.

This doesn't really tell you much about the sound, but at least there's proof of life now!

https://photos.app.goo.gl/aLw7CcvO2UbR6QZx1

I don't have a high quality audio sample yet, but it's already clear that some thing have changed considerable.

Compared to the old "true dual" no cross-over 3" system with just two mufflers, the new dual 3.5" "infinity pipe" system is
- somewhat quieter
- firing sounds a lot more even at idle
- has none of the high frequency noise of the old system, no snap-crackle-pop
- has much lower and much softer "toned" sound
- sounds like a much larger engine, despite still being only a 5.0L motor

Soon we'll learn what it sounds during part throttle cruise and full throttle, high boost, high rpm acceleration. One of the main goals was to get rid of the low rpm cruise "drone".

Here’s a more informative exhaust sound clip, start at 1:20. It’ll be a little quieter with the intake side fully hooked up. Sounds like a really powerful car, but quite refined. I’m very happy, considering how difficult it is to make a dual 3.5” exhaust quiet.

https://youtu.be/qylNEtqyxHM

ptuomov wrote: ↑Fri Feb 16, 2018 11:31 am

RCJ wrote: ↑Fri Feb 16, 2018 10:46 am I think I found one topic that wasn't debated.Some x pipes are 2 pieces of 90 degree tubing with a section cut out and welded together.That would be a reduction of total volume at the x.Others are formed pieces welded together that increase volume at the x.Does the volume differences change the sound waves?

I don't know, but if I'd have to guess, I'd guess that both reduce noise but the x-pipe that has the smaller minimum cross-sectional area at the merge will reduce the noise more.

A rapid INcrease in cross section can also cut sharp noise. I think the mechanism is, velocity is lost when the flow has to expand into the larger cross section, and then energy is lost when it has to speed up again afterward.

Interesting that OEM X-pipes are generally H stampings with a large cross sectional change.

peejay wrote: ↑Mon Apr 09, 2018 6:40 am

ptuomov wrote: ↑Fri Feb 16, 2018 11:31 am

RCJ wrote: ↑Fri Feb 16, 2018 10:46 am I think I found one topic that wasn't debated.Some x pipes are 2 pieces of 90 degree tubing with a section cut out and welded together.That would be a reduction of total volume at the x.Others are formed pieces welded together that increase volume at the x.Does the volume differences change the sound waves?

I don't know, but if I'd have to guess, I'd guess that both reduce noise but the x-pipe that has the smaller minimum cross-sectional area at the merge will reduce the noise more.

A rapid INcrease in cross section can also cut sharp noise. I think the mechanism is, velocity is lost when the flow has to expand into the larger cross section, and then energy is lost when it has to speed up again afterward.

Interesting that OEM X-pipes are generally H stampings with a large cross sectional change.

The main reason why expansions cut on noise is not so much the mean flow velocity dropping but the expansion chamber muffling from acoustic theory and reflected waves cancelling.

Car factories are working to shave pennies and grams from exhaust systems bolted on cars that retail for $100k while trying to produce a sound that attracts that buyer of $100k cars. I am looking at the exhaust system on my 2018 E63S Wagon and it's not something that can be improved by mere mortals with the factory objective function and constraints.

In any case, what did you think about the twin-turbo 928 exhaust sound on that youtube.com video?

ptuomov wrote: ↑Mon Apr 09, 2018 2:23 pm In any case, what did you think about the twin-turbo 928 exhaust sound on that youtube.com video?

I personally thought it sounded fabulous. Fantastic job.

If my 2.3 turbo can be that quiet, I'll be thrilled.

It does sound good. Well done.

Good to see you keep this thread updated. Sounds really good!

Tantalizing! -So when do we see and hear a WOT launch and some red line up-shifts?