Y-pipe design effect on exhaust sound

[turbo camino]

Single exhaust LS truck-type deal. Does the unequal length of the y-pipe before the merge contribute to the blub-blub exhaust note at low speed? Would it be smoother with equal length, or is it just inevitable because of the firing order/bank arrangement?

[lefty o]

it's a contributing factor. like the ej subaru's with their unequal length exhaust manifold. it is what makes the "subie rumble".

[turbo camino]

So, another thing, how much of the annoying blub is from the y-pipe and how much from the exhaust manifold layout? What would you call this, a 4-3-1, lol?

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How much of an improvement would there be in just an equal length Y if these manifolds are still there?

[RevTheory]

Interesting thread. I've always wondered what made factory LS engines sound like a V6 under water, lol.

[turbo camino]

With my luck, I would spend 3 days crawling in the dirt under the truck building a spiffy equal length merge and when done it would sound EXACTLY THE SAME. Which is why I bring up the manifold design.

[turbo camino]

No, it doesn't sound like any kind of V6. A 90* V6 sounds like sadness and disappointment.

[ptuomov]

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[turbo camino]

I only notice this at a dead idle, really. At speed it's nice and smooth (unlike the godawful Subies and Buick V6).

Note that the stock y-pipe has the LH bank headpipe something like TWO WHOLE FEET longer before the merge than the RH pipe. The stock pipe is designed to clear both 4WD & 2WD, I'm 2WD so have no transfer case clearance issues to work around, I have more room to put the merge in a more sensible location.

On this truck the fuel tank occupies every last bit of space on the left side of the driveshaft, everything has to go down the right side. So even 'true duals' with a X pipe ends up with the extra length in the LH bank's pipe from crossing over under the trans. Not optimal.

In the middle of writing this I got distracted by looking at some HP Tuners logs. I already raised idle speed by 100 RPM from stock, but this thing is idling with only 12-13* of timing. I bet raising that to 18-20* will clean it up a whole bunch. Either way, easy enough to test and change it back if it doesn't make a difference.

[turbo camino]

This ought to do something, eh? It typically idles hot at 600 RPM & .15-.16g/s.

screenshot.01-11-2020 23.48.51.png

[enigma57]

We have used Randy Brzezinski's 2 into 1 exhaust guidelines on several short track cars and on several road cars as well over the years. Works just as he says in this short narrative......

https://www.castheads.com/2-into-1-exha ... r-systems/

http://www.castheads.com/wp-content/upl ... into-1.pdf

Only thing I would add is to calculate volume of exhaust system downstream of exhaust ports (1/2 engine displacement for each bank on V-type engine) and make sure the shorter of the 2 unequal length primary pipes has at least enough internal volume to equal or exceed the displacement discharged through it priour to joining your 2 primary pipes together.

Best regards,

Harry

[turbo camino]

Unequal Length Primary Pipes are OK — Our dyno tests have concluded that variations in primary length have no adverse effect on power when a collector is used. Primary pipes which are equal in length, or as close as possible, are preferred, but in some applications this is just not possible. So, if your pipes going into the collector are not equal, don’t worry.

No mention of sound, which is the only part I'm interested in. This is a street driven SUV and it already has a 2-into-1 single exhaust so according to that, it's already optimized and sod what it sounds like? I can pick up 20 HP any time I want by pushing a little button on the dash that turns the AC off.

[Truckedup]

I had an 03 truck with a 5 speed,It had an an aftermarket cat back dual exhaust when I bought it. Too much noise so went a stock exhaust. That's when the blub blub noise became very noticeable at idle. like it had a weak cylinder .Didn't the LS powered 2000ish Camaros have a single exhaust? How do they sound?

[turbo camino]

Yeah, the F-bodies have a little bit of unequal length in them but their exhaust runs in the driveshaft tunnel, not waaaaaay out against the rocker panel like on the trucks.

[turbo camino]

This is the TB/Envoy system...

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[Circlotron]

Several other cars I’ve noticed over the years that with stock exhaust have one cylinder sounding louder than all the rest -
English Ford Cortina and Escort with Kent 4 cyl.
Gen 1 VW Beetle.
Australian Chrysler Valiant with Hemi 6.
Whoever did the OEM exhaust systems on those should be put in jail.