Magical sounds: https://www.youtube.com/watch?v=kE1bA4gAFsw

NOT looking for a loud mouthed engine, Don't need it to be obnoxious...

What I hear is every cylinder firing when it is at an idle....

Is it compression ratio that makes the firing of each cylinder more pronounced?

Or is it Dutra Duals type of exhaust manifold?

Or is the only route to that type of idle found through the camshaft? I don't really hear a lumpy idle at the beginning, so I am thinking it is compression and how the exhaust is handled.

Yes this is about emotions. Yes it is about the sound... Not interested in volume, but the character of the sound.

What are your thoughts

I have been around inline 6s a long time. They all have a charecteristic sound to them, similar and definitely different than a V8, with each being distinct between them
I could always tell a UPS truck coming from a mile away, (not so much anymore) a 4.0 Jeep has its own, a slant 6, or even a Cummins diesel especially if the exhaust were even slightly worn out or modified. But among /6's specifically I met member Dad truck in what was the last swap meet before the covid BS started earlier this year and the /6 in his truck has a completely different sound to it than any other /6 that I have heard over the years. It isn't lopey, more the tone of the sound. But yeah to get the lope you want you're most certainly going to have to put a big cam into that engine.
A stock inline is inherently better balanced compared to a v type engine, and smoother, in stock or close to stock form.

I don't think sound is a bad reason to build or change an engine. Just look at the exhaust aftermarket. Heck, Ive been eyeing the Mercedes-Benz M120 V12 engine for just this reason, but will probably settle for a high tech I6.

You mention idle twice. I don't hear anything very distinctive about the idle. Maybe just a little valve train noise. Maybe. What I do hear is pronounced intake roar. The 300SL has a long runner manifold and I think you're hearing intake pulses. I would want to see the intake ahead of the throttle body, but it sounds like is has an un-silenced air cleaner.

That's an awfully expensive car for that kind of work. I'd use a much cheaper, and newer, BMW rather than risk the 300 SL.

Here's a 1953 Hall-Scott 400 series engine of 1091 ci. https://www.youtube.com/watch?v=po_Y7EspkUs

_________________
Joshua

there are three foot long extensions after the Dual Dutra's. That then Y in together.
I have been told the exhaust has a snarl to it. The motor was not built / cam'd for RPM
The exhaust tone comes on in the mid 2000's RPM

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Interested to learn about this exhaust design. I am guessing you built it that way for torque-or low RPM response?

Exactly, for the exhaust I was most interested in scavenging.
The down pipes are not large, 2 1/4 to keep velocity up. After the Y it goes to 2 1/2

I normally have the D150 on the road this time of year, it’s a summer time daily driver. With the stay-at-home this year I have not got it out, or I would get you a sound bite.
I can say it is not nearly as rumbly and as deep as the note in the video. A snarl is a good description, maybe more like a Maserati or a Jaguar.

I have a Flowmaster 60 for a muffler. I had to move up from a FM 40 as it was too loud. If I was to build this today I would likely use a DynoMax muffler.

A portion of the exhaust tone is also due to cam lob timing.
I did something unusual on the cam grind. It was ground with the exhaust center line at 105, that opens the exhaust valve early. Normally exhaust center lines are 110+. Again I was after exhaust velocity and emptying the cylinder to help fill when the intake opens.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

I've seen a cut-away drawing of the 300 SL in the above, it also has a two long down tubes and what I assume is a straight through muffler.

DadTruck, your cam was ground with an early opening exhaust, to help completely empty the cylinder. The desired end result being a cylinder that is devoid of leftover combustion gasses? ( I am guessing it is a nuanced and low RPM variation on the somewhat common idea of having a narrow lobe separation angle for mid range-top end charge) So your intake lobe is of close to normal interms of duration and intake opening/closing, but the Exhaust opens early to give a yank on the intake gasses.

Have I got the general idea?

Would love to hear it, when and if you get the truck out this summer. My Slant 6 is presently stock, and will be until I show myself that I have successfully installed it in the M37.. I've got the motor mounts done, and presently working on the clutch release system.. hopeful to have some workable idea on that front by the end of today.

I distrust any recorded exhaust noise, such as the example in the video. Or when someone posts a video/audio of their new Flowmasters, etc. Too much opportunity for the recording to change the actual sound or pick up/ignore noises you'd hear in real life.

I think that Mercedes sounds the way it does for a variety of reasons...exhaust system/size, intake, cam timing/overlap etc. I have no idea what its engine looks like but I'd also bet it has a crossflow head and multiple carbs.

Mechanical fuel injected, and about 9.0:1 compression if I remember. Although what I am understanding you to be saying is that the microphone can have something to do with how/what we hear in the recored audio.

Jay Leno has a slightly different sounding version, but equally as good, @ 10:50 https://www.youtube.com/watch?time_cont ... e=emb_logo

That Hall-Scott is sitting on an impressive engine stand.

Maybe what I am hearing at idle is the injection pump combined with intake noise..?

What would you be putting the M120 into?

yes the intake is on a 105 centerline, and then I advanced the cam a couple of degrees at the install.

and yes the goal was to clear out the cylinder with a lot of exhaust velocity at low to mid RPM's.

Did it work, well I think so, the truck pulls strong starting in the low 2000 RPMs, but I have no back to back data:
same engine, same vehicle, different cam. I wanted to try an idea and I did.
I picked up a small NOS Mopar Performance slant cam and I plan to install that eventually, just to see, hear the difference.
I may get to that this year,,,,,

I will get you get you a sound clip when I get the D150 out of hibernation.

_________________
Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

Thanks, Ive got plenty to do before I can get too deep into engine work, but the emotive, visceral "aliveness" of an inline 6 at work is now part of the plan, and I have a few leads to follow getting there.

See here (Stepp's dead now and who knows where that car ended up—it had Dutra Duals with no crossover) and the second movie here (with the sound turned up).

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Joshie: Brings me back to Whirlybirds TV show staring a Bell 47 helicopter. At 7:20 minutes in
the 47 takes off.

I got to ride in one of these things a few time back in the early sixties, Whrilybirds was one of my favorite TV shows.

Personally I enjoy the song from 007's DB5 in Goldfinger, and any year Austin Healey 3000. Both of which don't have very high revving engines by today's standards.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC