VIDEO from Stack Performance Dyno Day and Exhaust Tests

[Super Villain]

Not quite Snakes On A Plane, but how about Vipers On A Dyno? This one has a better ending, I promise.

On April 5th, our SoCal Club had a Dyno Day at Stack Performance in Anaheim. Ryan and his team were very gracious hosts and took good care of us and our cars...not to mention fed us some yummy burgers! A big thank you to them for supporting us! And of course, Dan and Cathy worked their usual magic "herding cats" to organize this event. Hats off and thanks to them!  Of course, after the Western Zone Rendezvous this one must have been a cake walk!

Numbers Game
A quick note about chassis dynos, they basically measure the amount of horsepower and torque your car puts down to the ground (that is a very basic and simple explanation. If you want more details wikipedia is your friend). This number is always lower than what the car is rated for at the engine. For example, Gen 3 Vipers are rated at 510 horsepower according to SAE standards and this is measured at the engine. On a chassis dyno, it would measure about 445 horsepower and this is due to the losses induced from running that engine power through a transmission, rear diff, wheels, etc. So you start with 510 HP, but end up with less by the time it makes it to the ground. Other factors such as different wheel and tire sizes, lower gears, etc. can all affect to give the impression of lower dyno numbers. For example, take two identical Vipers one stock (3.07 gears) and the other with lower gears (3.55) and on the chassis dyno the one with the lower gears will look like it has about 10 less horsepower. But you then take those same cars and drag race them (assuming good traction for both); the Viper with 3.55 gears would destroy the stock one and by a lot!

It is also very easy to get caught up in dyno numbers and then you go running around claiming it is the end all be all of car performance. We have a name for people like that...its "Dyno Queen" and I've got a tiara and pink boa with your name it. Keep it up and I'll start calling you a "waxer" as well. If you really want to know your car's performance then see you at the track!

The fact is, dynos are great tools when approached with the right mindset. The info they provide can help trouble shoot, set a baseline for before and after performance mods, or just testing and data logging. But you cannot really go around comparing dyno numbers unless they were all taken on the same dyno and on the same day. This is because every dyno is different as well as the conditions during which they are run. Even among the same brand, the readings can be different. This one will cook your noodle...at Stack Performance my car dyno'd 489 HP. A week later I dyno'd the car at DC Performance in West LA and it registered 472 HP. Both dynos were the same type- Dyno Jet.  So did I suddenly lose 17 HP?  Nope!  Just proves my point...different dynos read differently.  Dynos are a guide.  Don't get hung up on the numbers unless they're from the same dyno.  Now don't get me wrong, its always fun to see what your car will dyno at and since each dyno is different, it is sort of a guess every time...kinda like Keno, but not as fun.  At least you won't be surrounded by blue haired, chain smoking, old ladies screaming "Keno!"

Exhaust Notes
In addition to just a Dyno Day, I wanted to add a bonus and shoot some video and measure sound levels to help answer the age old performance question about exhaust systems.  We've all seen the posts..."What kind of exhaust should I get?", "Should I get headers?", "What will it sound like?", "How loud will it be?"

I hope that this video will help as an initial reference point for some of those questions.  I kept it focused on just Gen 3 and 4 to make it easy on me and then I tried to avoid duplicates in my editing of the final footage.  For example, there won't be 2 clips of 2004s with stock exhausts.  I wished there was more variety in the setups, but it just means we need more people in the club to MOD!  You know you want to!

Here is the video:
http://www.pod9.com/ant/viper/exhaust_stack_dyno_day.wmv
(I will post this to the big board and the alley later.  I may need to make a youtube version so my server doesn't get hammered)

The sound quality of an exhaust system is subjective and dependant on each individual's tastes.  But to help answer how loud will it be, the sound level meter helps quantify that into terms most everyone can relate to.  In this case, the sound is measured in decibels and it is expressed as a unit of dB or dBA to show the "A" weighting which closely relates to human hearing.  It is also important to note that decibel units are exponential as the numbers go up.  For example, a sound that is 60 dBA is TWICE as loud as a sound that is 50 dBA.

A 1 dBA difference is practically imperceptible to human hearing.  In other words, we can't tell the difference between 70 dBA and 71 dBA.  At about a 3 dBA difference, we start to notice a slight change in sound levels.  A 5 dBA difference is definitely noticeable.  A 10 dBA difference is perceived as twice as loud between two sounds.

To help better illustrate this and to provide a reference point here are some sound comparisons:

(The following list taken from a study by Marshall Chasin)
-A Quiet Library  =  30 dB
-People talking in conversation (3' to 5' distance)  =  60-70 dB
-Phone dial tone (held right up to your ear)  =  80 dB
-City Traffic (inside car)  =  85 dB
-Train Whistle at 500'  =  90 dB
-Snowmobile, Motorcycle  =  100 dB
-Power Mower at 3'  =  107 dB
-Power Saw at 3'  =  110 dB
-Sandblasting or Loud Rock Concert  =  115 dB
-Jet Engine at 100' or a Gun Blast  =  140 dB

Sustained exposure to sound levels of 90 to 95 dB without hearing protection can result in hearing loss. 

As for our Vipers, I was able to baseline a stock Gen 3 and a stock Gen 4 and then a couple of different setups for each.  I noted sound levels at cruising, high speed, and then the peak at wide open throttle.  In some cases I had to take a weighted average of the sound.  Here is what I found:

2004 Gen 3 that is totally stock
Cruising = 77 dBA
High Speed = 84 dBA
WOT = 107 dBA

The exhaust temp at the tips after the dyno run was 308 degrees.

05 and 06 Gen 3 with just 3" Corsa Track mufflers
Cruising = 78 dBA
High Speed = 86 dBA
WOT = 107 dBA

Exhaust tip temp after the dyno run was 369 degrees.

My theory as to why the cars with Corsas were hotter at the tip than the Stock one has to do with the long crossover tube in the stock system.  The further the hot exhaust gases have to travel from the engine the more it cools down.  This happens not only due to the length of travel, but also with more metal tubing present more of the heat is absorbed like a heat sink.  Since the Corsas do away with the crossover tube, the exhaust gases go straight out the sides and stays hotter thereby also helping to maintain hot gas velocity.  The stock system retains more of the heat and keeps us nice and toasty inside...if only we lived in Vermont.

Also interesting to note is that the Corsa had the same sound levels as the stock system during cruising and WOT.  And they were just a little bit louder at high speed.  Though one thing the sound level meter can't really measure is tone.  While the sound levels between the two were similar, the Corsa had a deeper tone than the stock system.  The human ear may perceive this as louder even though it really isn't.

06 Gen 3 with American Racing Headers (1-5/8" X 1-3/4" step design with Swain Tech thermal barrier coating) and Classic Chambered Exhaust's 3" Cobrapacks 28" body length with packing.
Cruising = 83 dBA
High Speed = 88 dBA
WOT = 113 dBA

Yes, Virgina, headers do make the car louder and No there is no Santa Clause.  I'll be doing a separate write up of this exhaust system and how it came together at another time (soon, I promise!).

08 Gen 4 with stock exhaust
Cruising = 78 dBA
High Speed = 83 dBA
WOT = 107 dBA

Sound levels were pretty much the same as a Stock Gen 3.

08 Gen 4 with Belanger headers and exhaust
Cruising = 80 dBA
High Speed = 88 dBA
WOT = 112 dBA

At WOT and High Speed, definitely louder than stock and on par with the 06 header/exhaust Viper.  However at cruising it was only a little louder than stock, but still quieter than the Gen 3 header/exhaust car.  Damn VVT!

09 Gen 4 ACR with Belanger headers and stock mufflers
Cruising = 79 dBA
High Speed = 86 dBA
WOT = 112 dBA

This setup is a little quieter at high speed from the Gen 4 with full Belangers.  But again the perception of tone plays in here.  The Belanger with stock mufflers had a more mellow tone than the full Belanger header/exhaust package which had a deeper tone.   

08 Gen 4 with Belanger headers and Corsa Exhaust
Cruising = 79 dBA
High Speed = 87 dBA
WOT = 114 dBA

Sound levels pretty much matched up with the other mod'ed Gen 4's and just a little louder at WOT.  Tone was a little more raspy.  Made the most power of all the Vipers present.

Ford GT
Cruising = 83 dBA
High Speed = 90 dBA
WOT = 111 dBA

Not a Viper, but everybody is going to ask so there are the numbers.  I don't know what the setup of the car was.  Maybe Bruce can chime in with details.  Made some mad power though!  At cruising, sound level on par with the mod'ed 06 Gen 3.  At high speed, louder than most all.  But surprisingly, at WOT about the same as the mod'ed Gen 4s.

Overall it seems that headers have the most effect on the Viper's loudness (especially at WOT).  This does not include heads/cam or supercharger cars.  Muffler changes with factory headers are more about heat reduction and changes in exhaust note/tone with little penalty in overall loudness, at least with the Corsas.  Muffler changes on cars with headers seem to pay more dividends in terms of power.  And between the Corsa, Belanger, and Stock muffler, sound level loudness were close to the same.

Now a very important issue I was not able to test was the one concerning the dreaded drone!  This is best tested from inside the car so maybe at the next dyno day I can run sound tests from inside each car...I'll be sure to be wearing dirty pants with screwdrivers and steak knives in my back pockets. 

[ViperX]

SV,

Great write up as usual.

FYI, I switched to a Corsa cat back after the dyno day.  My impressions are that so far, the Corsa is about as quiet as the stock mufflers inside my 2009 with a bit less drone.  It also seems to make a bit more power.

Dan

[Super Villain]

Thanks Dan!

I knew you couldn't resist moving to the Corsas   Now what about the white car?

Do you have the Mopar ECU in the ACR?  Given that you guys had almost all the same mods I think the ECU accounts for the main power delta between the cars.  Of course gaining a 1/4"-1/2" in pipe diameter doesn't hurt either!  And you were running 18's in the back with 335s so that would explain the rest.

It'll be good to see what Mike dynos when he gets his ECU in.  It would help answer if one is leaving any power on the table by going with the belanger or corsa exhaust.  If its within 3-4 hp then I'd call it a wash since the dyno runs were on different days.  Though I think the Corsas win in the no drone dept.  Will have to ask Mike if his setup has any drone.

[ViperX]

SV,

I've driven Mike's 08 and it does have some drone inside the car.  It's not as bad as in the Gen III cars, but it's still there.

The Belangers with the Corsa's (updated version) has no drone, sounds deeper at idle, is a bit raspy at some part throttle rpms and screams at WOT.

Yes, I do have the Mopar ECU.  It does take a while for the ECU to "learn" if you've got good gas, 95+ octane, or just 91.

I was at Buttonwillow this weekend with Speed Ventures and ran 100 octane mixed with a little bit of 91.  The car was exceptionally strong pulling out of the corners and at top speed in the straights.  In some places I was 5 mph faster than last trip (Viper Days).

Hope you like your Heads / Cam set up.  You'll have to let us know what you're having done and the final results.

Dan  <2

[Super Villain]

So what did Corsa update on the current version vs. the one they had out for the Gen3?  I know one of the things that have turned some people off of Corsas in the past was their lack of bass and low rumble.  Of course, the catch-22 its seems is that the bass and low rumble are contributing factors to drone...sigh never any free lunches

Car is still at DC for the heads / cam work.  I'll do a write up on it later...we'll see how close it gets me to keeping up with the Gen4s

[ViperX]

SV,

Planning to drive the ACR to the Palm Springs event Saturday.  The sound in general from the Belangers and Corsa Track is about the best I've heard from a Viper with side exhaust.  Idle is deep but not too loud, mid range is deep and strong and it sounds really good at WOT.

I still think the rear exhaust on a 3-inch GTS sounds much better.

Let me know what you think when you hear it.

Dan  <2

[Super Villain]

Ah good you're bringing the ACR to Palm Springs...I'll bring my video camera and dBA meter and we can record some tests from inside and outside the car!