Will I Get Overboost/leanout? Cutting Middle Muffler Out Of X-Force 3&

[joshmcmillan]

I posted this on another forum and I thought I'd post it here as well to get the best range of answers.


So, my XR6 Turbo has a 3" Xforce catback along with high flow cat and dump. It's a mild steel system and has been on the car for about 6 years.

The middle muffler has recently developed a few holes, you can hear it from the side of the car, and was also pointed out during its 90k service.

Now, the car has had a custom tune at CV Performance in Sydney and on the 98 tune which I run 100% of the time (less aggressive boost), it is doing 11.5 PSI, which goes down to 9 PSI after a few seconds WOT. It also has the F6 secondary intake, K&N Filter, but is otherwise stock.

Firstly, if I cut the exhaust out completely and replace with a 3" straight pipe, would I be likely to see over-boost, lean out, or damage the engine in any way?
Secondly, does anyone would to have a guess at how loud it would be, the second muffler is pretty massive with two pipes coming out of the muffler.

My other option I guess would be to replace it with another XForce muffler, or a hotdog or something. I don't want it insanely loud but wouldn't mind it a little bit louder.

[Cameron02]

As far as middle muffler removal goes. You can do a search as plenty of people have done it. It will probably put your over the legal limit of 90dba so I would hang on to your old system if I was you. I have a completly sock system. With the centre muffler removed my car tested at 89dba and 93dba on deceleration due to gargle/poping sound.

[joshmcmillan]

As far as middle muffler removal goes. You can do a search as plenty of people have done it. It will probably put your over the legal limit of 90dba so I would hang on to your old system if I was you. I have a completly sock system. With the centre muffler removed my car tested at 89dba and 93dba on deceleration due to gargle/poping sound.

I know a heap of people remove the standard middle muffler without a problem, I just thought that as mine is a complete aftermarket exhaust with a tune, that it might be different. I'd be more worried about lean outs than overboost.

[Pazzo]

I would say you would have to put it on dyno for touch up... If exhaust was stock the cat would be your restriction... You have a full exhaust with a high flow cat.. Your middle muffler will be your restriction now..

If you cut it out might flow to well now and have no restriction so I would atleast throw it back on dyno to check things out to be safe.

Edited 11/01/13 07:02 PM by Pazzo XR6T

[JETURBO]

^^^ this guy ^^^

[xr6t_ute]

It will definately change your tune since you have the 3" aftermarket exhaust, it will definately boost spike and run leaner,that's why your safest bet is to do what ^^^^^ that guy said and throw it on a dyno for a run. And you will see how much it changed.

[joshmcmillan]

Thanks for the replies. Ok so as an alternative, if I was to put say a 3" redback hotdog on it, would that make the situation better?
Getting the tune checked out isn't the worry, but as it's been years since it was tuned, I'm still running the old CAPA flash tuner, and don't like the idea of forking out $1500 for an X3 and tune (not yet anyway, I'll do so when I change injectors, intercooler etc...)

If that wouldn't make it safe, well I guess it's try find an exact muffler replacement from X-Force.

[Pazzo]

What ever you do get it checked after on dyno

[joshmcmillan]

I surely will Pazzo. If it's not safe after an similar muffler replacement well I'd have no option but to get it retuned.

For the mean time I might use some muffler putty and see how long I can get it to last

[ratter]

even if the afr is acceptable it does not mean it is safe!

if the boost level is even a little more than when tuned, the spark tables most likely not have been set to any higher than when tuned and damage may occur, and if the afr is even slightly leaner than when tuned, but what others consider safe it still may cause knock issues as leaner AFR's can not tolerate as much spark.

End of the day, if the boost remains identical and the afr is identical to when tuned it may be safe, but that still does not allow for wear and tear if the tune was done long time ago