Exhaust advice - 2.5" down from 3

[dassaur]

I do love my current exhaust but after thoughts on a new one. There a few problems I want to address. the major one is this: it's just too loud for me now.
Medium problem: drone at 1800-2k rpm
Minor problem - hangs too low
Minor problem - stretched it a year ago, requires 3-monthly adjustments to avoid contact with diff

It is a 1 3/4 non long tube 4-1 with 200 cell cats 3" xforce (https://xforce.com.au/products/h2-ve03-98-02kit/). Has centre mufflers and varex rear mufflers (which are pretty much a straight pipe when fully open).
I have the smart box to control the varex at RPM but it requires connection to OBD2 and I am really getting into tuning so always have my scanner connected these days.
Also the variable closing is not all that its cracked up to be - fully closed (0%) is amazingly quiet, but once more than 33% open can't really tell the difference between it and 100%.

I understand that 2.5" is all I need on an NA motor making 350kw (I bought the car with the 3" catback and added headers myself) - at this point it is all about noise & note.

At the moment I have an exhaust from a 2014 senator in the garage with the vacuum bimodals. I am fairly confident it is 2.25" - best I can measure internally with those ball flanges is about 60mm (2.3") Has an x pipe up top then 2 hot dogs - this is more a bonus item as I only really wanted the mufflers - got the whole catback for $200!. Have ordered the NPP in a box to retrofit vacuum operation.

My plan is, I think, to get a 2.5" exhaust made up to mate with the xforce cats, then have the ball ends cut off the mufflers and appropriate flanges put on them.
Logically, it would make sense to get a 2.5" xforce catback and have the senator mufflers modified to mate to it. But I would love to hear opinions.
While I have done my own engine and mechanical work, welding is not something I have ever attempted so anything like that would have to be done at an exhaust shop.

I think the vacuum mufflers should control the drone (closed at that rpm). All contributions welcome. I definitely want something that fits well though and is a littler quieter than a 3" straight pipe!)

 

[Pazzu]

On my VF,
I'm currently running
1 3/4 xforce headers - 100 cel cat
2.5" xforce mid section
and stock VF2 2.25" Bimodals with the baille tip.

I quite like this setup as with the valves closed it does get rid of the drone and sounds decent with it open.
It is definitely a lot milder than the full difillipo system on my VE.

I definitely think modding the mufflers would be the way to go if you can get it done for cheap/ do it yourself.
otherwise my recommendation is to get the VF2 bimodals that already have the flange on them!

https://www.planetparts.com.au/holden-vf-commodore-series-2-sedan-wagon-electric~603

however, given that you are cammed (i assume from 350rwkw) I'm unsure if 2.25" is actually too small for that application. Although i suspect the main issue would be where it steps down in size where the flow would be terrible. if you could make it transition with a reducer, rather than a straight drop it might be better, in which case modifying the your senny mufflers might be the way to go.

2.25" 57MM - 2.5" 63MM MILD STEEL EXHAUST PIPE REDUCER

2.25" 57MM - 2.5" 63MM MILD STEEL EXHAUST PIPE REDUCER

www.performanceexhaust.com.au

 

[Mickcc]

looking to upgrade my VF too
but not too noisy

 

[Ccoastcalais]

I’m running stock manifolds with 100 cell cats, hsv 2.5 mid section, stock vf bimodel rear mufflers.
Really quiet with the valves closed but really loud when you stomp on the accelerator pedal. Best of both worlds really

 

[RevNev]

I understand that 2.5" is all I need on an NA motor making 350kw

A good 2.5" exhaust meaning mandrel bends and genuine 2.5" internal muffler diameter will flow at least 580hp flywheel. To use a 3" exhaust, an NA motor will be pretty radical, mechanical roller cam making power over 7200rpm, not many like that on the road! I think 3" was mostly intended for supercharged engines that can use the volume more so than mildly modified NA engines.

Some have dyno tested 3" exhausts and made more power than a 2.5", but you don't how good the 2.5" system is or whether the 3" had better cats. Most of those tests aren't well documented beyond pipe diameter. What we have dyno tested on 2 different cars and discovered, is that 340 headers catless, are only 3 to 4kw short on 1.75" long tubes with 100 cell cats on a stock LS3.

 

[dassaur]

A good 2.5" exhaust meaning mandrel bends and genuine 2.5" internal muffler diameter will flow at least 580hp flywheel. To use a 3" exhaust, an NA motor will be pretty radical, mechanical roller cam making power over 7200rpm, not many like that on the road! I think 3" was mostly intended for supercharged engines that can use the volume more so than mildly modified NA engines.

Some have dyno tested 3" exhausts and made more power than a 2.5", but you don't how good the 2.5" system is or whether the 3" had better cats. Most of those tests aren't well documented beyond pipe diameter. What we have dyno tested on 2 different cars and discovered, is that 340 headers catless, are only 3 to 4kw short on 1.75" long tubes with 100 cell cats on a stock LS3.

I plan to keep my cats the way they are (4 inch body, 3 inch outlet) and hopefully the shop can mate them to 2.5.
I initially wanted to go 400 cell, but some EOIT tuning has removed the idle smell completely.
At this point its all about the sound anyway (elimination of drone and a decent note and volume), I'm not chasing every last pony.

Do you reckon going 2.25 muffler at rear will impact?

 

[dassaur]

I’m running stock manifolds with 100 cell cats, hsv 2.5 mid section, stock vf bimodel rear mufflers.
Really quiet with the valves closed but really loud when you stomp on the accelerator pedal. Best of both worlds really

My vf1 doesn't have capability for RPM actuated valves. I could build something but I'd need hand holding parsing CAN info with vf2 bimodal. OBD2 port tied up wih scanner.

 

[RevNev]

I plan to keep my cats the way they are (4 inch body, 3 inch outlet) and hopefully the shop can mate them to 2.5.
I initially wanted to go 400 cell, but some EOIT tuning has removed the idle smell completely.
At this point its all about the sound anyway (elimination of drone and a decent note and volume), I'm not chasing every last pony.

Do you reckon going 2.25 muffler at rear will impact?

You can transition the 3" cats down to 2.5" no problems. It's hard to say without dyno testing if 2.25" rear mufflers will reduce power, but as the exhaust gas cools towards the rear of the car, it takes up less pipe volume (contracts), so it has the potential to make no power difference. The smaller pipework leaves more muffler capacity to quieten the exhaust and reduce drone.

I don't like the stock bimodals, I think they're a poor design on the quiet side and open, they have a lousy note. If you go quietish, I'd do a permanent setup to my liking with a VF1 and wouldn't bother with bimodal.

 

[dassaur]

Thanks for the comments so far.
Any thoughts on going with this paired with stock bimodals?

Manta 2.5" Dual Cat Back Exhaust Fits VE V8 Sedan Wagon | Sparesbox

Shop For Manta 2.5" Dual Cat Back Exhaust Fits VE V8 Sedan Wagon at Sparesbox Australia. $9.90 flat shipping Australia wide on all orders.

www.sparesbox.com.au

Except I wont get the mufflers.
H pipe with some small hotdogs, 2.5 inch stainless.
Possibly be quite loud?

 

[daves8]

If you are just getting the front section made up, I would go to Windsor exhaust and have them make the front section, tapering from 3 inch at cats down to 2.5 with H pipe and middle fibreglass resonators and have them add your mufflers