Question on Headers and Cats..

[VE_CalaisV8]

Hey boys,

I've got a 2.5 cat back system (HM s/s) and now wanting to install some headers and cats. I've done plenty of research and the only two systems that will line up to mine are Xforce 4 into 1's or HM 4 into 1's as they dont have the longer tube. From what i've heard there isnt a huge difference in Mild Steel or Stainless Steel so i'm not overly fussed there.
My concern is the added noise inside the car. I've got a Calais and the car was bought as a family wagon and I want more power without adding a huge amount of noise. Currently the 2.5 system is the perfect noise level in the car. Will the size of the cat effect the noise more then the headers?

Hope that makes sense. Any help will be appreciated.

 

[PIR4TE]

Hey boys,

I've got a 2.5 cat back system (HM s/s) and now wanting to install some headers and cats. I've done plenty of research and the only two systems that will line up to mine are Xforce 4 into 1's or HM 4 into 1's as they dont have the longer tube.

Nah, there are heaps of (better) alternatives for more usable power A-B in a family wagon, and I definitely wouldn't go 4-1. Have you considered HM 4-2-1 stepped headers and this cat:

This very easy, affordable and readily available combo will increase economy, give you a usable, broad torque spread without ridiculous noise of big bore drag race designs, and match your catback perfectly. Plus you won't need to book and pay for a tune just to get rid of CEL in order to realise an immediate mechanical benefit - the seat of your pants will talk that up.
On our car stepped headers will outperform straight headers on every engineering measure except all out top end drag racing (trade usable broad torque for negligible high rpm kw peakiness and shift to the right on dyno chart). Definitely don't put long tube 4-1 big bore drag racing pipes on your family wagon like most Lemmings.

From what i've heard there isnt a huge difference in Mild Steel or Stainless Steel so i'm not overly fussed there.

There is a noticeable raspiness (brightness / clarity) and secondary unwanted engine noises as chrome % gets higher in any exhaust and the resulting cacophony... well, doesn't suit a V8 wagon. Stainless may have better rust resistance so lay down some 'insurance' with mild steel by treating with hi temp paint (easy). Precisely the reason high chrome is used in musical instruments is why mild steel extractors will mask unwanted clarity yet deliver a suitable depth and integrity of sound, particularly with metal hi-flow cats.

My concern is the added noise inside the car.

Changing the cats will move a lot of the noise previously around the gearbox / footwell out the back mufflers, and the combo will increase cabin noise at 50-70hz (which is more growl / imperceptible rumble territory than sound per sé).
In this video the car is already running at the start so turn it up loud to hear, listen to the grumble idle-1500 and around 2000 before the 4500k blips (WOT tip-in sounds at mid-high rpm is heard mostly outside as muffler pass though) and again toward the end. If your speakers are up to the job you can hear the biggest difference extractors and cats make - low frequency "presence" like a bespoke subwoofer.
[video=youtube_share;4r8PPNSS9GU]http://youtu.be/4r8PPNSS9GU[/video]
So yes inside it will waken the beast above 2000 rpm and possibly sound like a V8 sports car overlay from a cartoon, which took me no time getting used to. What you hear inside the cabin is thinner non-cast walls with no ridiculous restrictors. So yeah now you will actually hear efficiency build on mild accel through WOT if you listen. That has trade-offs in driving behaviour (not because extractors = hoon) but eg use less pedal to ride the fatter torque, so it can be just as quiet yet at the same time you get more engagement with our engine's heartbeat.

 

[Turtle2388]

Best thing I ever did power wise was headers and cats 4-1. Huge power improvement and helped with drone. It won't make it noisier in the cabin particularly with Hm stuff.

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[Turtle2388]

Pirate I bet NAAF will disagree with you saying 4-1 isn't worth it.

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[AD07]

Pirate I bet NAAF will disagree with you saying 4-1 isn't worth it.


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But PIR4TE knows all ....HES AN EXPERT !!!!!!!!.

 

[HamaTime™]

Pirate I bet NAAF will disagree with you saying 4-1 isn't worth it.

Agreed.

4-1's are the best option. At the end of the day, going for power = removing restrictions, the restrictions in the exhaust is what keeps it quiet. The best of both worlds is fairly utopian and not achievable IMO. Idling around mine is pretty quiet and it's a very unrestrictive system, sink your boot in and it will sing you the song of V8 harmonies.

More flow = more sound.

Headers = increase in flow and 4-1's are much bigger and flow better than stockies.
200cpi/Less restrictive cats = increase in flow and sound.

 

[Turtle2388]

And more sound from headers and cats does not mean drone by any means! I found they just carried the note better through the rev range as well as power increasing.

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[petern64]

I'm running Genie try Y extractors and Magnaflow cats through a Redback 2 1/2 twin mandrel bent mild steel system with rear resonator, I got 235rwkw's ,615nm torque dyno tuned with Maf and an SS inductions CAI , stock auto and diff (3.07).
there is no exhaust drone and when I give it punch you can hear a good note from exhaust & intake, otherwise cruising is quiet, 4 into 1 extractors will give a little more power but at higher RPM. for every day driving try Y's work well at low to mid range RPM where most people use their daily drive.
I'm sure you will get suggestions from people trying to sell you their products, I would not hesitate using Genie or H&M gear ,they have been around for decades

 

[HamaTime™]

4 into 1 extractors will give a little more power but at higher RPM. for every day driving try Y's work well at low to mid range RPM where most people use their daily drive.

I thought the same thing but after a good discussion with NAAF, he explained that the 6ltr has more than enough torque to cope with 4-1's if your goal is streetable low-mid range power. Tri-y's would sound crap compared to 4-1's and wouldn't yield as good driveability all round as 4-1's.

 

[3onTree]

HI mate I have exactly the same setup as you describe. Mine is a 2.5 inch catback from Walkinshaw. I did some research and if you check out Ozgarage series on exhausts (Oz Garage S02E09 Online - Exhaust Comparo | OzGarage) they do a great comparison of tri-y versus 4 into 1. In short, HP-F did back to back testing of tri-y and 4 into 1 and the biggest rwkw came from the 4 into 1, 7/8 headers. Also there was no difference between the 1, 7/8 on the 2.5 versus the 3 inch catback. Anyway I went for the 4 into 1 (1 7/8) HM Stainless and these come with the high flow Outlaw cats. They bolted up perfectly to the HM catback system (not surprisingly). I got the guys from APS in Frankston to fit up and do a proper custom tune (not the generic tune from Walkinshaw) and the result was magnificent (260kw at the wheels and 785Nm of torque). Which is higher than stock HSV VE - I think.

I too drive a wagon which I use for family and business duties (with occasional track circuit time). There is a change in the noise type. I found that the note got deeper and the 6th gear drone reduced (less raspy overall). Is it louder? yeah a bit but not much. It is subjective - I did not get a sound level meter and take readings. I think if you go for 4 into 1 from HM with the metal cats (go stainless) 1, 3/4 you'll be very happy. It is a worthwhile upgrade and the car will be fine for general family duties. The power gain was huge in my experience. Get a good shop to fit up and tune. Getting a good tune is worthwhile irrespective. I can say from experience with 4 into 1 headers that are big bore, do not turn your car into a drag racing headache. My car produces over 700 Nm of torque at 60km/h so the theoretical lack of torque using 4 into 1 headers is just that, theoretical. In practice I have a great deal of torque and great top end which I enjoy using to surprise 'sports cars' at track days - wagons are not the conservative older brother to the sedan. Oh and I looked over my shoulder and am pretty sure I am not a lemming ( I might be the last one