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Same engine, completely different sound

Same engine, completely different sound

Same engine, completely different sound

(OP)
I was kind of shocked to hear these two recordings of an LS1, one in a C5 vette, and the other in an LS1 F-body.

The F-body has the typical "muscle car" sound:
http://www.corsaperf.com/cfflash.html

But the C5 has an almost exotic (Ferrari-esque) sound:
http://www.corsaperf.com/flashc5.htm

Amazing, no?

My question is this...  Is it one thing, or a combination of things which cause the difference?

Facts:
The F-body has a Y-pipe which joins both banks to a single muffler, back to 2 rear exits.  Exhaust manifolds are typical stamped and welded steel "clamshell" type.  

The C5 has true dual exhausts, with an H(? possibly x? I couldn't confirm) pipe somewhere upstream of the mufflers.  Exhaust manifolds are similar to "shorty headers", almost a 4-2-1 design:

http://i13.ebayimg.com/04/i/07/7d/51/e7_1.JPG

So is it a combination of the above?  One more than another?  Will true duals on an F-body with an H-pipe give the same sound?  I'm curious as to your thoughts....

RE: Same engine, completely different sound

The classic V8 sound is usually got with two separate exhausts and a cross pipe in the right place. It may be that the F-body's single muffler acts sufficiently like a cross pipe. Unless you know the internal details of the mufflers there isn't much you can tell by eye.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Same engine, completely different sound

most of the noise of an engine comes from the valves. the muffler makes a small difference. how identical are the engines? seems a corvete might have different valve springs and valves and cams.

RE: Same engine, completely different sound

(OP)
I assumed they are the same internally... but to be honest, I don't know for sure.  

RE: Same engine, completely different sound

The quality or character of the exhaust noise (rough, smooth, powerful, etc) is mainly controlled by the firing order, the individual path lengths from valve to tailpipe, plus the degree and location of mixing between the banks.  Mufflers and resonators will attenuate different frequencies different amounts (possibly adding or removing booms) but their effect on the character is less.

Do not underestimate the amount of effort, time and money spent on tuning the sound of a vehicle.  And it's not only the exhaust that gets this treatment.  I heard of a (mentioning no names) German car company that decided to enter the Chelsea Tractor market by transplanting a big V8 from a luxury car into a newly developed 4x4.  It just didn't sound right.  So they deliberately made it sound rougher by messing around with intake runner lengths, spoiling the perfect geometry that was there before.

RE: Same engine, completely different sound

Working with acoustics many years ago, I learned you can do strange things with exhaust systems.  A Tri-Y system sounds totally different then a 4>1 system, as does a 180 system.  Same engine, different exhaust.  Also where the two systems merge will change the tonal quality.  Phasing the exhausts is more than just selecting a convenient place to put in a crossover pipe.  Mickey Thompson experimented with different length runners and collectors in the 60's with interesting results.

Ford spent tons of money on their GT models to get just the right exhaust tone, and its all in the exhaust system, not just the engine.  Take a modern Cadillac STS sedan, add a Magnaflow system and it sounds totally different and feels stronger (my brother-in-law swears by it).  He had another system on first then changed to the one he has now, the difference is unbelievable.

Franz

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Same engine, completely different sound

"I assumed they are the same internally... but to be honest, I don't know for sure. "

Very unlikely.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Same engine, completely different sound

(OP)
I looked up cam specs, and they are identical, or nearly identical through the years.  I don't know which years these two cars are.

Corvette LS1
97-99 Duration 199int/207exh Lift .472int/.479exh Lobe 117
00 Duration 198int/209exh Lift .500int/.500exh Lobe 115.5
01-03 Duration 198int/207exh Lift .467int/.479exh Lobe 116

F-Body
98-00 Duration 198int/209exh Lift .500int/.500exh Lobe 119.5
01-02 Duration 196int/207exh Lift .467int/.479exh Lobe 116

If you think you can tell a difference in exhaust audio between two cars with a couple degrees and 3 hundredths lift difference, you're joking.  blllttt

RE: Same engine, completely different sound

I thought you meant the mufflers.

However, if you seriously think you can't hear the difference in noise that an engine makes when you retune it, please don't get a job as an engine calibration engineer. You can hear changes in spark advance (not pinging) of around 5 degrees, and at part throttle that spark advance is strongly affected by the hardware.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Same engine, completely different sound

Exhaust Valve opening event has the biggest effect on exhaust note. This is why pushrod 2 valve V8 engines sound very different to pent roof 4 valve V8s- as alot of their "energy" is being wasted out of the exhaust during blow down.
The layout of the exhaust system and the types of mufflers used WILL effect it's character.
When I worked on the Aston Martin V8, a priority was to give the engine noise a more sporty note, with perhaps a hint of burble at low speeds.
An NVH characteristic which was rich in 4th order harmonics was required.
BMWs straight sixes tend to accentuate their 3rd, 6th and sometimes 9th order to about 10 db above all the other frequency content, with very little side bands- just to give them their pure and sporty noise/wail.
OEMs will typically set targets on maximum rate of pressure rise within the cylinder for acceptable NVH (2-2.5 bar per degree is common however I know of a boosted German V8 which achieves close to 4 bar per degree!)

A 3 pass exhaust silencer will tend to target low frequencies, while a straight through absorption silencer will tend to target high frequencies. A straight pipe in a muffler with perforations will do something in between- more perfs tending toward a multi-pass silencer. "Metal socks" can be used to vary the amount of open perforations within the pipe of the silencer during NVH development.
It is highley unlikely an OEM would vary primary lengths of either the exhaust or intake system, thus compromising performance and emissions certifiability (uneven air flow distribution). Playing with secondary lengths/geometry is more likely but would STILL most likely involve a totally new vehicale calibration.

RE: Same engine, completely different sound

Quote:

The layout of the exhaust system and the types of mufflers used WILL effect it's character.

Did you mean affect or effect?  Methinks you meant affect although effect is probably more accurate.

Quote:

It is highley unlikely an OEM would vary primary lengths of either the exhaust or intake system, thus compromising performance and emissions certifiability (uneven air flow distribution). Playing with secondary lengths/geometry is more likely but would STILL most likely involve a totally new vehicale calibration.

I've seen it happen.

RE: Same engine, completely different sound

Slightly off topic.. While i was doing my diploma thesis, i had the pleasure to spend alot of time at SAAB and Volvo (engine and earo sections). The aerodynamicists often said that they and the designers had different opinions, and that almost always the designers got it their way.
The cheif aero. eng. at SAAB once told me that they see it like this: The first thing a potentional customer notices is how the car looks, next he notices how the interior are, and finaly he takes a test drive. Therefore we are at the bottom of the foodchain, and the other departments are often more "important" (here he also mentioned Audi TT before they had to add the spoiler, and Audi A8 (rounded back)).

RE: Same engine, completely different sound

(OP)
Marquis - I have to disagree with you on the 4V vs 2V V8 sound differences.  My secret agenda is trying to make a 32 valve V8 sound like the C5 LS1 in the above recording.  Currently, it sounds almost exactly like the F-body above.  The only simularities are the clamshell manifolds.  I am using true dual exhaust with full size "superturbo" mufflers, no crossover pipe.

I'll have to assume "NVH characteristic" = exhaust audio characteristic.

The note on harmonics is interesting.  Those that have heard my car say it sounds like the engine speed is lower than it actually is.  (e.g. 6700 rpm sounds like 5500)  

This is an internal view of a "name brand" superturbo:
http://fle-online.com/images/Pictures/DynomaxSuperTurboCutout.jpg

You will have to fill me on on what a "3 pass exhaust silencer" is.  Something like this (random picture I found on google)?

http://static.howstuffworks.com/gif/muffler-cutopen.jpg

smile

RE: Same engine, completely different sound

"I am using true dual exhaust . . ., no crossover pipe"


I'm pretty sure that's a big part of the reason for the classic muscle-car V8 sound.  Unless you've got a flat crank or a real bundle of snakes exhaust arrangement, sequential cylinders in the V8 firing order dump into the same-side manifolding every so often, and that effect bounces back and forth between the left and right sides.  Once per side per two revolutions vs eight individual exhaust strokes, so it's a low frequency effect.  

Try fully merging the two exhausts into a single (larger) pipe via a "Y" and splitting that back to two after a foot or so.  That should kill off a good bit of the "rumble".

My somewhat non-stock 1979 model year V8 car exhales through a single rather large [aftermarket] converter and a pair of aftermarket mufflers.  It does not sound at all like its 1960's predecessors.

Norm

RE: Same engine, completely different sound

(OP)
I think it is a smaller part of the equation.  The F-body uses a Y pipe.  Although it does go a good 4 feet before being split up again...  Same with this cadillac:

http://www.corsaperf.com/flashcadillac.htm

Which incidentally has my engine... :)

RE: Same engine, completely different sound

(OP)
I did some audio analysis on the two LS1's..  

Corvette idle:
1st peak - 453Hz @-20dB
2nd peak - 1336Hz @-32dB

Corvette "WOT" rev:
1st peak - 560Hz @-4dB
2nd peak - 1121Hz @-22dB

Fbody idle:
1st peak - 131Hz @ -13dB
2nd peak - 262Hz @ -12dB

No good analysis of fbody rev...  I think the idle is around 600-800 rpm for each.

RE: Same engine, completely different sound

Come on guys, the days of experimenting with bits of hardware were numbered at least 15 years ago.  OEMs and Tier 1's all use 1D codes for this sort of thing these days.

RE: Same engine, completely different sound

Knowing absolutely nothing about how to change exhaust otes, the cynical side of me thinks that either (or both) recordings may be electronically modified to suit the marketing dept's agenda.

RE: Same engine, completely different sound

"Come on guys, the days of experimenting with bits of hardware were numbered at least 15 years ago.  OEMs and Tier 1's all use 1D codes for this sort of thing these days."

Ahh, a simulation guy, are you working toward a "paper engine"?

Sorry, Ive used 1 D simulation alot and have done NVH simulation. It is a useful tool for general trends and patterns, I also find it useful to place quarter wave/ resonators, however whenever an NVH guy with no performance experience uses 1 D code to predict NVH waterfall plots, either the performance prediction ability/correlation suffers or he can't elaborate or justify/substantiate how he got the simulation to match measurement.

I think the "paper engine" and pure simulation replacing development work is a long way off. It's not only a matter of the simulation itself but the fact that there are too many specialists in One area (say NVH) with little knowledge of calibration or say, performance, undertaking the modelling.

RE: Same engine, completely different sound

|"Marquis - I have to disagree with you on the 4V vs 2V V8 sound differences.  My secret agenda is trying to make a 32 valve V8 sound like the C5 LS1 in the above recording.  Currently, it sounds almost exactly like the F-body above.  The only simularities are the clamshell manifolds.  I am using true dual exhaust with full size "superturbo" mufflers, no crossover pipe."

Exhaust blow down events effect on exhaust note is a documented fact on several SAE papers. I don't have the SAE numbers on me now, but BMW have played with "acoustic cams" that altered the opening flank of the exhaust cam, I also know that Alfa Romeo played around with staggered exhaust opening for one of their pent roof engined 4 valve cars (years ago) to alter the sound characteristic.

There's nothing to stop you from compromising your exhaust valve opening event on your 32 valver to optimise the sound you seek while compromising both performance (the new "NVH" optimum is likely to be much much earlier than even a high rpm "performance" optimum of a 32 valve)and fuel economy (you won't be getting enough work out of the Combustion cycle).

RE: Same engine, completely different sound

gijim, sorry,I almost forgot: a three pass silencer is very similar to the one you posted, but that is a two pass and a three pass has three runs of pipes inside it (not great for back presure!)

And if subjectively you're satisfied that your engine/vehicle set up is similar to your target 16 valve car, then job done and well done- It's good enough to your subjective ear! However if you compared order plots and recorded each engine in a semi anachoic chamber I think the NVH waterfall or order plots may show a different story. In the vehicle other factors come into it which effect the Noise transfer function into the cabin....

RE: Same engine, completely different sound

I was peripherally involved in an active noise cancellation project that added noise back into the cabin to simulate teh sound of a V8.

The lead engineer on this was a very talented NVH engineer, and also a bit of a musician.

He struggled for many weeks trying to match the waterfall plot of the synthesised sound to a V8.

It did not work, subjectively. Finally he ended up tuning it by ear and got a great result.

I'd add, I doubt that any code can really predict enough of the engine sound to give the right answer first time in hardware, certainly 8 years ago a welding torch and a large supply of parts was the quickest way to a good exhaust tune.

Incidentally Goldwave will produce waterfall plots.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Same engine, completely different sound

Last weekend I programmed a software sampler to simulate any engine configuration based on the firing order and exhaust manifold pipe lengths.  The details are boring, but basically for a V8 sound I have 8 single cylinder pulses playing at the same time, but phased 1/8 apart, and each with a resonant filter tuned to a frequency corresponding to the path length  from the cylinder to the outlet of the exhaust manifold.  It's not as accurate as using a true time delay plus manifold resonance, but the sound ends up similar and it's simple.

  I can recreate the sound of the C5 corvette and the Camaro with a nearly identical exhaust system consisting of dual exhaust with a crossover pipe.  If my model is right, the C5 has an extremely symmetrical exhaust system with outlets very close together.  A symmetric system with outlets far apart, or an asymmetric system with outlets close together will still sound like a lumpy muscle car.  The make the symmetric/close outlet system sound like a muscle car in my model, all that has to be done is move the location of one side of the crossover pipe 6" forward or back.  The throbbing muscle car sound is due to a path length difference between the sound from the left and right cylinder banks whether that difference is caused by pipe length difference or geometry from tailpipes to listener.

This is a link to a sound file of the same symmetrical dual exhaust with crossover pipe and close outlet, but one side of the crossover pipe is shifted rearward differing amounts compared to the other side.  In the first segment the shift is 2", in the second it is 8", and in the third it is shifted 14".  

http://media.putfile.com/exhaust-sound-V8
 
-Eric

RE: Same engine, completely different sound

Interesting. There's a bit around 39 seconds that seems to have some V8 character, but most of it sounds too even. Also way too much high frequency, sounds like a recording under the hood!

Are you saying that if you are equidistant from each outlet you won't hear the V8 throb? I beg to differ.

  

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Same engine, completely different sound

(OP)
Eric, that's awesome!!

Remember though, the LS1 does not have a 180 degree crank.  There are 2 cylinders firing at the same time.  8-7, 2-6, 5-4, 3-1.  I'm told the "doubling up" on even/odd sides makes the v8 idle.  I'd be interested if you can somehow simulate that...

RE: Same engine, completely different sound

My simulation is of a cross plane V8, and I haven't done a flat crank V8 yet.  In a cross plane V8 no two cylinders fire at the same time, the power strokes are all spaced 90 degrees of crank rotation apart.  However, each bank has an uneven firing order so that it isnt r-l-r-l-r-l-r-l but r-l-l-r-l-r-r-l. The uneven pattern of firing in each bank gives the V8 its rumble.  However, I discovered in my model that the rumble mostly goes away if the exhaust system is symmetric.  The rumble is caused by one cylinder bank dominating the sound of the other either by being louder or getting to the tailpipe first.  

  A certain amount of nonlinear distortion arises in the sound traveling down exhaust pipes and contributes to the sound of engines.  Basically the high pressure part of the wave is hotter and has a higher sound speed, so it catches up with the low pressure part of the wave and distorts the overall sound.  The two sequential pulses on a single bank of a V8 can overlap enough to cause more distortion and a popping sound exiting the tailpipe, making single exhaust and small diameter exhaust V8s sound even more lumpy.  An interesting special case is the peculiar sound of a diesel V8 that I'm sure you've heard.  I can simulate that by using guitar distortion and cranking the low frequencies up.  The distortion from a low quality speaker makes these synthesized engine sounds more realistic.  

Heres a comparison of the synthesized single exhaust, dual exhaust and side pipe V8 sounds.  In the side pipe version you can clearly hear the sound of the left bank of a V8 engine.

http://media.putfile.com/V8comparo

-Eric


  

RE: Same engine, completely different sound

(OP)
Now when you say symmetric, do you mean equal lengths, or equal lengths and muffler in the same place, or all that and same number and location of bends?

I would imagine the muffler location and the length of the pipe is critical, but what about the number of bends and location?

My application is a transverse V8, which automatically makes an equal length system harder but not impossible.  

RE: Same engine, completely different sound

When I say symmetric, I mean the same on both sides in form and function.  However, what is important according to my model is the total time it takes for the sound pulse to get from exhaust port to tailpipe.  I experimented with moving a simulated muffler forward and back on one side of an otherwise symmetric system, and all it did was change the resonance frequencies of the tailpipe on one side without adding or subtracting from the V8 rumble.  Actually the sound was smoother with the muffler located in a different spot.  With regard to bends, I dont know.  From working with brass instruments I can say that bends really dont matter as long as the acoustic length of the tube is right, and you can find that by slapping the end and listening to the resonance frequency.

-Eric

RE: Same engine, completely different sound

(OP)
I'd be interested in hearing a symmetric exhaust with asymmetric muffler location.  smile

RE: Same engine, completely different sound

About 2 years ago i wrote a realtime 0D/1D engine sound simulator. I never finished it but some sounds are quite
interesting.
It runs fine with up to 12 cylinders on an P4 win 3.2GHz.
There are hundreds of parameters, i played some examples with my USB throttle pedal ;)

Example 1:
The very beginning. Switching through engine types. Without room simulation.
Example 1

Example 2:
Supercharged Streetracer ;) (little bit room simulation)
Example 2

Example 3:
Large V8 (perhaps Truck or Diesel Railway Engine, heavy room simulation)
Example 3

greets,
Speedy

RE: Same engine, completely different sound

Nice SpeedyG.

First one sounds like it has bad ignition breakdown about 1/2 way through the file.

Second very V8 like at high revs, down low sound like a 4 stroke single motorbike.  

Last file could be a truck engine, except when it hit those high revs :)

Ken  

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