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Un-blocking the blocked off pipe on a AU XR6 VCT exhaust

5K views 21 replies 8 participants last post by  BLACK XR6-VCT 
#1 ·
I have read somewhere previously that if you un block the exhaust pipe which has been blocked off on a AU XR6-VCT then you will have a louder exhaust, but you will also lose power due to less back pressure.

Now I have spoken about this to an engineer at the FPV open day, and he reckons that this mod will have no effect on power - it will just make the exhaust louder. This was also confirmed by the local Midas bloke, who said that the twin mufflers themselves would provide adequate back pressure.

Basically I like my exhaust note a bit louder, so I reckon I should go for it.


Has anyone actually tried doing this ?
If so what were the results ?



See my other thread on removing the resonators from my exhaust:

http://www.fordforums.com/showthread.php?s=&threadid=31657&highlight=exhaust


// Jake.
 
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#3 ·
By unblock:

I would probably go back to Midas - (see other imbedded thread) and get them to cut the dead end pipe off, and join it to the other pipe, probably into a small length of 3" pipe, to my 3" chrome "dump pipe" tip.

I don't want to do this if I would lose power though!

Have you considered removing your resonators (other thread) ?
 
#4 ·
No..... but reading your thread... hmmm.......

Could be a cheap temporary alternative to getting a new exhaust system.
I dont want to do anything thats going to get attention from the police though. As long as it's not "illegally" loud :smlwink:


I don't want anything thats going to annoy on highway crusies either.

Would just getting one removed be good enough?

I'd love a louder sound with higher revving, but not idle and cruise
 
#5 ·
Put it this way, for me it's still no loud enough, my wife likes it, and I believe it gives the car more of a 'presence'. It's by no means intrusive or annoying.

I was told that there is no point changing from the VCT exhaust to gain performance, since it really is an excellent system. My only gripe was that it was too quiet for a performance car!

You could consider just removing the rear resonator, and see how you go, but I just went the whole hog. It's a cheap and easy mod, and there is no hassles with insurance as is in the case of getting a complete 'after market' exhaust.

Let me know how you go.
 
#7 ·
I would say that the engine revs a little more freely, and perhaps
there is a little more urgency. But the differences are minimal - and it could be just my perception.
 
#9 ·
#11 ·
BLACK XR6-VCT said:
I have read somewhere previously that if you un block the exhaust pipe which has been blocked off on a AU XR6-VCT then you will have a louder exhaust, but you will also lose power due to less back pressure.

Where does this theory about "back pressure" come from. I have read a few texts on exhaust design and nowhere is that mentioned.
 
#12 ·
Well I did it.

I got the Midas blokes to chop of the "equaliser pipe" and put a collector after the two mufflers, so it now forms a single 2.5" pipe out to the back of the car.

What do I think?

Now it sounds like an XR6 should sound! It is loud, and almost V8ish at idle, and just barks when taking off. I love it.

My wife says it's now a bit too loud even though she didn't mind the first step where I just removed the resonators.

Overall, this step is maybe just for those of us who love it loud!!!

PS. There is no loss of power at all - who ever came up with that crap ?

Jake.
 
#13 ·
Having no back pressure is proven to lose power, otherwise why do V8 Supercars still spend so much time/money developing their exhausts?
 
#14 ·
because they have to meet noise rules, not because they like dragging them round. Any positive pressure in the exhaust tract
when the valve opens potentially reduces the amount of air/fuel being sucked in on the intake stroke.
 
#15 ·
Aaron_M said:
Having no back pressure is proven to lose power, otherwise why do V8 Supercars still spend so much time/money developing their exhausts?
If thats the case then drag cars must be losing HP by running open headers.:MrSparkle
 
#17 ·
Here are the results for dB tests after my mods:
==================================

After Stage 1 (Both resonators off & new tip): 89 dB
After Stage 2 (Equaliser pipe also off): 93 dB

PS. We also tested a stock '02 XR6 (it was a HP, mine is VCT) and he tested at 84 dB.

Note: this was measured at 3750 RPM, which is at 75% of
the peak power RPM of 5000. The measurement was done at a 45o angle at a distance of 52cm as specified in the VicRoads document.

Note: the legal limmit in Vic for cars post 1986 is 90 dB !

Note: after stage two revving at 3200 RPM my car made 88 dB.


Regards, Jake.
 
#20 ·
Acually in terms of legal, the car is tested at 75% of the RPM
where peak power is produced, hence 3750 for the AU XR6.

This is why we tested it as above, following the VicRoads document to the letter.

Either way, like you said, if you see cops you just don't rev
the car out as far - Easy.

PS. I reckon there are about 10 V8's on my street that are about
5 times louder than my car. I don't think the cops really care.
 
#21 ·
xr8_sprint said:
i'd hate to imagine the db reading of my car on full song.

pacemakers with twin stainless 2.5" chopped at the diff no mufflers. :)

she's a screamer ;)
Do you get any hassles from cops ?
 
#22 ·
MP3 of the exhaust note:
 
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