Same engine, completely different sound

[gijim]

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....

 

[GregLocock]

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.

 

[btgeng]

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.

 

[gijim]

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

 

[SomptingGuy]

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.

 

[franzh]

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.

 

[GregLocock]

"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.

 

[gijim]

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.

 

[GregLocock]

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.

 

[Marquis]

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.

 

[SomptingGuy]

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.

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.

 

[xnicke]

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)).

 

[gijim]

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

 

[NormPeterson]

"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

 

[gijim]

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...

 

[gijim]

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.

 

[SomptingGuy]

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.

 

[JDana]

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.

 

[Marquis]

"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.

 

[Marquis]

|"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).