Unbearable Drone!!!

[christov]

Almost everyone will say 3" is louder, deeper (which may not be the case).
What hasn't been said is that dual 3" catback with stock headers and cats is really not going to sound that good, and the performance benefit is infinitesimal. With proper headers it is retrograde versus 2.5" in terms of velocity due to pressure drop when volumetric flow is less than 310rwkw on a 6.0. It is worth noting you can't get near that volumetric flow without a cam or Clayton's cam (high ratio rockers), full bolt-ons and dyno tune using high octane. The main casualty is torque - exactly what your two tonne tank needs to launch. Common mistake people make is going 4-1 plus big duration which typically exacerbates the situation unless you are circuit racing your Holden.
So on a 6.0 3" is all for show, not go. 6.2 is obviously slightly different.
Problem with most exhaust videos is that the sound is poor, not same car or environment so take a look at a sound comparison with incremental changes to a 2.5" catback. Most of the presence will go unnoticed unless you turn up with headphones or system with sub BtW.
See there's quite a bit to it apart from signing up to less performance coz loud and deep all the time.
Depends what you want in terms of race pitch, idle burble, static rev-up, partial throttle (drone) issues, zero tolerance cabin noise, scare the crows or full bore all the time. Have a listen to this 2.5" burble on idle at the end - deep and horny:

[video=youtube_share;iAqNOVsxzNo]http://youtu.be/iAqNOVsxzNo[/video]

Cue to halfway in this one to realize the difference in-cabin with bi-modal drone control, also puts the slight extractor rasp on static rev-up in perspective:

[video=youtube_share;YfXNfkghTn0]http://youtu.be/YfXNfkghTn0[/video]

PS exhaust cackle / crackle / pop / fart is adjustable in your tune, not the exhaust.

I love your videos! So for what I want, which is more low down oomph than screaming my tits off top end power - I should definately stick to a 2.5"?

 

[PIR4TE]

I love your videos! So for what I want, which is more low down oomph than screaming my tits off top end power - I should definitely stick to a 2.5"?

Yes, particularly if you do not intend opening up the engine and following the dyno queen circus. Definitely sizing of header primaries and collector / secondaries is more important though it doesn't have the same theatrical impact! Most people just don't realise that stock headers are tuned for good torque spread with stock or near stock tune, particularly down low. Most people fall into the trap of measuring performance through chasing top dyno HP, which is purely an exercise in increasing volumetric flow to suit higher RPM. The practical challenge for better 0-100 and in-gear acceleration in our two tonne tank is to maintain exhaust velocity throughout the lower to mid RPM range and reasonable flow for HP screaming its tits off up top on occasion.

Over the years I've said it better in other posts, here is a chart in another post that explains the relationship of velocity to flow given typical header diameters (Cross Sectional Area).. There is some information about 3" to 2.5" there as well.

Taking out restrictors and swapping larger diameter (CSA) bolt-ons to achieve greater HP usually comes at the expense of torque (high velocity of exhaust exit speed). Really the greatest challenge I've found with upgrading the car's output for high output everyday driving is maintaining or increasing low to mid RPM torque (and not wasting petrol).

FWIW the solution I've found the most practical in terms of high output for everyday is mid-20s street cam or high ratio rockers (1.85:1), street headers mated to secondary expansion chamber / cats, slowing down the intake velocity through tumbling the air to get more flow (CFM), and running e85.

Currently in the process of increasing compression (14:1) and capacity (370ci), implementing new valve events via a custom cam with variable cam phasing.

 

[arronm]

I agree with christov. Good videos showing a good range of combinations. And the telemetry and sound quality is good

Lots of crows around there

 

[christov]

Yes, particularly if you do not intend opening up the engine and following the dyno queen circus. Definitely sizing of header primaries and collector / secondaries is more important though it doesn't have the same theatrical impact! Most people just don't realise that stock headers are tuned for good torque spread with stock or near stock tune, particularly down low. Most people fall into the trap of measuring performance through chasing top dyno HP, which is purely an exercise in increasing volumetric flow to suit higher RPM. The practical challenge for better 0-100 and in-gear acceleration in our two tonne tank is to maintain exhaust velocity throughout the lower to mid RPM range and reasonable flow for HP screaming its tits off up top on occasion.

Over the years I've said it better in other posts, here is a chart in another post that explains the relationship of velocity to flow given typical header diameters (Cross Sectional Area).. There is some information about 3" to 2.5" there as well.

Taking out restrictors and swapping larger diameter (CSA) bolt-ons to achieve greater HP usually comes at the expense of torque (high velocity of exhaust exit speed). Really the greatest challenge I've found with upgrading the car's output for high output everyday driving is maintaining or increasing low to mid RPM torque (and not wasting petrol).

FWIW the solution I've found the most practical in terms of high output for everyday is mid-20s street cam or high ratio rockers (1.85:1), street headers mated to secondary expansion chamber / cats, slowing down the intake velocity through tumbling the air to get more flow (CFM), and running e85.

Currently in the process of increasing compression (14:1) and capacity (370ci), implementing new valve events via a custom cam with variable cam phasing.

Interesting, hopefully I don't lose any torque down low - that will make me angry. Nonetheless will see tomorrow, not sure what size the headers are but they are he DPE ones and come out of collector at 3" then step down post cats to 2.5". Hopefully the step down doesn't increase flow velocity too much!

 

[PIR4TE]

Interesting, hopefully I don't lose any torque down low - that will make me angry. Nonetheless will see tomorrow, not sure what size the headers are but they are he DPE ones and come out of collector at 3" then step down post cats to 2.5". Hopefully the step down doesn't increase flow velocity too much!

No mate no fear of that, more stepping up tune and other stuff to the required flow of 1 7/8 into 3" because velocity is too slow. This system you mention cleverly offsets pressure drop by the stepdown so should sound great, high velocity high torque More race like.

Once I get the motor rebuilt ima build out my PWTB to x-pipe with 3" sizing to suit exhaust gas temp of ethanol at 14:1. Gives me the chance to get that F1 sound by stepping down into a repositioned X-pipe using same design as below, will sound like this too but I can switch it off with bi-modal (maybe I will stick F1 valvetronic badge on too!):

[video=youtube_share;SbT0IqFIfnc]http://youtu.be/SbT0IqFIfnc[/video]

 

[cgbvfssvute]

Was next to a ve ss ute with 2.5 xforce today and was loud enough for now so will prob just go that in mild and then do every thing else when the full build is done.

 

[christov]

No mate no fear of that, more stepping up tune and other stuff to the required flow of 1 7/8 into 3" because velocity is too slow. This system you mention cleverly offsets pressure drop by the stepdown so should sound great, high velocity high torque More race like.

Once I get the motor rebuilt ima build out my PWTB to x-pipe with 3" sizing to suit exhaust gas temp of ethanol at 14:1. Gives me the chance to get that F1 sound by stepping down into a repositioned X-pipe using same design as below, will sound like this too but I can switch it off with bi-modal (maybe I will stick F1 valvetronic badge on too!):

[video=youtube_share;SbT0IqFIfnc]http://youtu.be/SbT0IqFIfnc[/video]

That is awesome, I'm assuming an IPE X-pipe? Can't wait to see/hear it when you're in Melbourne!

 

[AirStrike]

Each to their own Pirate, but I think your car sounds better now than if you were to try make it sound like the bimmer. I like a nice throaty sounding 8, not some raspy sounding thing.

 

[</3]

Each to their own Pirate, but I think your car sounds better now than if you were to try make it sound like the bimmer. I like a nice throaty sounding 8, not some raspy sounding thing.

Have to agree, honestly dont know what i think about hearing that noise from a commodore!

 

[Hypnerotomachia]

Is yours auto or manual? Any drone?

I suppose drone is subjective, but to me I feel that I can hear the engine when I need to but generally it is quiet enough when cruising around. Sometimes it gets some noise at certain rev ranges/gears (I will take note and get back) and at certain speeds/hills, but it isn't cabin shaking and sh*tty. I'm happy. It's noisy and growly, but not annoying.

Oh, I'm auto (would have got the manual in the wagon if I could)