Chalt

Something I have been wondering about and it is not just 944/951/924/968, but all of Porsche – the sound they make.

I really enjoy the (very loud) sound of race cars, drift cars, drag strip cars, F1, and, well, Ferraris.
Like this Ferrari 812Tunnel Run Video:

(Not to mention Ken Block's Hoonigan cars like that amazing Mustang he built) Loved this video with Ken and Joey in London:

I was recently reading about the sound (philosophy) of Ferrari sound and it was fascinating reading (well, to me).
It was here: https://www.ferrarichat.com/forum/th...errari.371598/
Post #14, in particular, was interesting to me. Anyone else find it interesting?

I do realize 944s are not race cars, but the topic of sound interests me and hopefully I am not wasting anyone's time with my post.

I like the way my 944 NA sounds in the upper RPMs, but it is surely not "loud" and I don't want to modify my exhaust either.
I appreciate that my 944 is not loud at lower RPMs and that it is not loud at cruising speed.

So I guess I have a few thoughts for discussion:

1) For those of you who did modify your 944 exhaust, was it for sound or performance or both?

2) If you did mod your exhaust, is it mild or loud? Or only loud in upper RPMs?

3) Why do you think Porsche in general, opts for quieter cars than say Ferrari? (I'm aware some P-Cars are loud)

walfreyydo

I modified my exhaust for:
-performance
-sound
-a fabrication challenge for myself
-looks (full stainless)

https://rennlist.com/forums/944-and-...y-exhaust.html

In terms of sound, I took it for one drive so far (right before snow hit us) but neglected to record it. Its louder than I want but sounds pretty fantastic. I will likely be adding some baffles which should soften it a tad. I will update the thread (with sound clips before/after baffle) this spring once it warms up and am able to take the car out again. Excited to continue this project!

Ultimately though, a 4 cylinder is going to sound a certain way no matter what you do to the exhaust.

Chalt

Agreed with your last sentence.
Thanks for the link to your thread. I look forward to listening to your sound clips.

orig944

A few thoughts on this. Although manufactures can do several things to tune the cars sound, the primary decision on a V8 engine is... Are you going to use a flat plane crank, or a cross plane crank?

There are advantages and disadvantages to each. A flat plane crank has two advantages. First, distributing the exhaust flow from each bank evenly, resulting in lower peak exhaust pressure and therefore extracting more power. And Second, lower crankshaft weight resulting in less rotating inertia. Lower crank weight results in more power transferred to the wheels instead of spinning up the motor. The cross-plane crankshaft, as developed by Peerless and Cadillac over 100 years ago, results in a much smoother engine, with secondary engine balance issues cancelled out by nature. This is much as the secondary balance issues are cancelled out on our 944s & 968s, by the Mitsubishi developed counter rotating balance shafts. But, due to the nature of a cross-plane crank, there needs to be counterweights on the crankshaft to counter the primary engine balance issues inherent in the design. This means the crankshaft weighs much more, resulting in energy being used to accelerate the rotation speed of the crankshaft, rather than being transferred to the driving wheels.

So, where does this leave us? The 924s, 944, 968 engines are closer to half of a flat plane V8, but are burdened by having to spin up the counter balance shafts for the benefit of cross-plane equivalent smoothness. Some racers will delete the counter-balance shafts to reduce engine rotating mass, at the expense of increased vibration. This is wonderful for racing, where engine RPM changes frequently. But, for normal city and highway driving, engine RPM does not change on that a frequent basis, nor is performance loss so great, therefore the argument for smoothness dominates. Therefore, our engines have counter-balance shafts (thank you Porsche,) and almost every V8's since the patents expired have cross-plane cranks.

Now, back to sound. If our 944's engines are most similar to cross-plane Ferraris, then why don't they sound like it? While our cars have somewhat even pulse characteristic, there are two reasons why not. The Ferrari will have headers with equal exhaust length for each cylinder before combining, tuned for maximum exhaust scavenging for each cylinder. This results in extremely even timing between each exhaust pulse. Our cars have cast exhaust manifolds, which result in uneven lengths in the exhaust path, so the exhaust note is a blend of frequencies. The Ferrari has one primary exhaust note frequency, where our cars have the frequency somewhat distributed. The second reason is that a V8 Ferrari has twice the number of pulses than a 4 cylinder engine for any particular RPM.. The Ferrari will shriek, where the four cylinder only screams.

Finally, a cross-plane crank has, due to the uneven bank exhaust pattern, a sound component that is half the frequency of a flat plane crank engine. This is the "rumble" of a V8, so called because the vast majority of V8s are of cross-plane design.

Obviously, there is much a manufacturer can do to tune, but not eliminate, these basic characteristics. The most egregious of these, IMHO, is adding sound to the stereo systems to make believe your car sounds like something it doesn't. I believe BMW was the first to do this, much to their everlasting shame. Today, I would not be surprised to find a menu in a Tesla allowing you to select the "exhaust" note from a V10 Viper, to the Jetson's space ship, or anything in between.

JC951

Specs:
1986 944 Turbo with 89' M44/52 motor
K26/8
Custom DME chip by Steinel's Autowerks (This was done years ago by previous owners)
Replaced rusted out custom exhaust with Fabspeed cat bypass and Broadfoot Racing catback. 3" all the way.

Love the sound in lower RPMs, typical 944 scream in the higher range. Also have a Broadfoot downpipe to go on whenever the turbo gets some TLC from Evergreen.

Chalt

I think we need a youtube video so we can hear this sound goodness.

V2Rocket

Lots of stuff can affect the overall sound - something that was interesting for me to learn recently was even the arrangement of the pipes and how they meet can influence the sound.

IN my specific example, you've all heard some V6 Mustang or truck or something with a loud exhaust and it can sound sort of weird, or just not good.
In a high percentage of OE RWD V6 vehicles (and most FWD too) there is a long crossover pipe from one bank to the other to meet into a single pipe to go to the back of the car. Often it seems the driver bank gets the longer crossover pipe.
This puts the exhaust pulses out of time with eachother since half of them have to travel so much further. On my V6 swap I made the exhaust manifolds (simple logs) as symmetrical as I could and then made a Y pipe connecting the two banks to a single central exhaust. Both branches of the Y are the same length (or within an inch or two). The result is the pulses are in time with eachother and they sound smooth and nice.

Very interesting stuff.