Mod referrals?!
Senior Member
Joined: 06-15-2008
Posts: 109
From: Ohio
Not really
Just punch out the cat guts in the 2th cat.
Than slide a piece of perforated 2.75" tubing into the back of
this stock downpipe, tack in place, & your done.
Better torque, under the curve, this way.
Looks stock, & passes emissions too.
Add a K&N intake, some corn whiskey,(E47.5), some traction, &
Your set to run 12's at the track.
Just punch out the cat guts in the 2th cat.
Than slide a piece of perforated 2.75" tubing into the back of
this stock downpipe, tack in place, & your done.
Better torque, under the curve, this way.
Looks stock, & passes emissions too.
Add a K&N intake, some corn whiskey,(E47.5), some traction, &
Your set to run 12's at the track.
Senior Member
Joined: 04-26-2009
Posts: 669
From: City of Champions
Actually I bought a SS muffler, then cut out the 2.75" perforated tubing, inside the SS muffler.
The automatic muffler has twice the perforation, then the manual muffler.
Either will work fine.
I then placed it in the back of the stock downpipe.
By hand, I turned it back & forth a few inches, while putting some pressure,
on the tubing, while turning it.
After about 15 minutes, I bored a nice 2.75" hole thru the cat.
This way you still have cat guts in place, when you put the empty,
tubing back in place.
After knocking out the 2.75" cat 'core', that's stuck inside the tubing, I slid it back
into the back of the downpipe.
I then marked it, & trimmed it flush to the back of the downpipe.
I tack welded it in place.
If you can't tack it, just drill & tap ,for one screw, to hold it in place.
This is only to prevent any rattling.
When your done, what's left of the 2nd cat, will still heat up, be very
Hot, when you touch it, or if any emissions guy touches it, to check for
Cat operation.
The perforated tubing is just to allow hot air to heat the remaining cat,
& the tubing holds this remaining cat guts in place, very well.
This mod removes the restriction of the 2nd cat, & still keeps it working.
The large, 1st cat is needed, to keep the torque up, & it flows well.
Aftermarket catless, or the ones with a small cat, hurts torque.
Yes, I've tryed aftermarket downpipes, with, & without the small cat.
The stock downpipe, with the 2nd cat restriction removed, works best.
The automatic muffler has twice the perforation, then the manual muffler.
Either will work fine.
I then placed it in the back of the stock downpipe.
By hand, I turned it back & forth a few inches, while putting some pressure,
on the tubing, while turning it.
After about 15 minutes, I bored a nice 2.75" hole thru the cat.
This way you still have cat guts in place, when you put the empty,
tubing back in place.
After knocking out the 2.75" cat 'core', that's stuck inside the tubing, I slid it back
into the back of the downpipe.
I then marked it, & trimmed it flush to the back of the downpipe.
I tack welded it in place.
If you can't tack it, just drill & tap ,for one screw, to hold it in place.
This is only to prevent any rattling.
When your done, what's left of the 2nd cat, will still heat up, be very
Hot, when you touch it, or if any emissions guy touches it, to check for
Cat operation.
The perforated tubing is just to allow hot air to heat the remaining cat,
& the tubing holds this remaining cat guts in place, very well.
This mod removes the restriction of the 2nd cat, & still keeps it working.
The large, 1st cat is needed, to keep the torque up, & it flows well.
Aftermarket catless, or the ones with a small cat, hurts torque.
Yes, I've tryed aftermarket downpipes, with, & without the small cat.
The stock downpipe, with the 2nd cat restriction removed, works best.
Last edited by 2005HHRauto; Aug 27, 2012 at 09:01 PM.
Senior Member
Joined: 06-15-2008
Posts: 109
From: Ohio
Actually I bought a SS muffler, then cut out the 2.75" perforated tubing, inside the SS muffler.
The automatic muffler has twice the perforation, then the manual muffler.
Either will work fine.
I then placed it in the back of the stock downpipe.
By hand, I turned it back & forth a few inches, while putting some pressure,
on the tubing, while turning it.
After about 15 minutes, I bored a nice 2.75" hole thru the cat.
This way you still have cat guts in place, when you put the empty,
tubing back in place.
After knocking out the 2.75" cat 'core', that's stuck inside the tubing, I slid it back
into the back of the downpipe.
I then marked it, & trimmed it flush to the back of the downpipe.
I tack welded it in place.
If you can't tack it, just drill & tap ,for one screw, to hold it in place.
This is only to prevent any rattling.
When your done, what's left of the 2nd cat, will still heat up, be very
Hot, when you touch it, or if any emissions guy touches it, to check for
Cat operation.
The perforated tubing is just to allow hot air to heat the remaining cat,
& the tubing holds this remaining cat guts in place, very well.
This mod removes the restriction of the 2nd cat, & still keeps it working.
The large, 1st cat is needed, to keep the torque up, & it flows well.
Aftermarket catless, or the ones with a small cat, hurts torque.
Yes, I've tryed aftermarket downpipes, with, & without the small cat.
The stock downpipe, with the 2nd cat restriction removed, works best.
The automatic muffler has twice the perforation, then the manual muffler.
Either will work fine.
I then placed it in the back of the stock downpipe.
By hand, I turned it back & forth a few inches, while putting some pressure,
on the tubing, while turning it.
After about 15 minutes, I bored a nice 2.75" hole thru the cat.
This way you still have cat guts in place, when you put the empty,
tubing back in place.
After knocking out the 2.75" cat 'core', that's stuck inside the tubing, I slid it back
into the back of the downpipe.
I then marked it, & trimmed it flush to the back of the downpipe.
I tack welded it in place.
If you can't tack it, just drill & tap ,for one screw, to hold it in place.
This is only to prevent any rattling.
When your done, what's left of the 2nd cat, will still heat up, be very
Hot, when you touch it, or if any emissions guy touches it, to check for
Cat operation.
The perforated tubing is just to allow hot air to heat the remaining cat,
& the tubing holds this remaining cat guts in place, very well.
This mod removes the restriction of the 2nd cat, & still keeps it working.
The large, 1st cat is needed, to keep the torque up, & it flows well.
Aftermarket catless, or the ones with a small cat, hurts torque.
Yes, I've tryed aftermarket downpipes, with, & without the small cat.
The stock downpipe, with the 2nd cat restriction removed, works best.
Great info.....thank you!
Senior Member
Joined: 04-26-2009
Posts: 669
From: City of Champions
I have a CIA downpipe up in the 'rafters', of the garage,
covered with dust...
I bought a larger $300 aftermarket cat too, from Random Tech, & tryed
it in the CIA downpipe, down towards the end of the downpipe.
Nothing beats the size & volume, of the stock, 1st cat, in the location,
that it is in.
You just need to free up the restriction, of that 2nd cat, & just sliding in a
2.75" piece of tubing, does the job.
If you just gut the 2nd gut, without the tubing, flow is screwed up, been there, done that...
Senior Member
Joined: 06-15-2008
Posts: 109
From: Ohio
Those little 'soda' can size aftermarket cats.
I have a CIA downpipe up in the 'rafters', of the garage,
covered with dust...
I bought a larger $300 aftermarket cat too, from Random Tech, & tryed
it in the CIA downpipe, down towards the end of the downpipe.
Nothing beats the size & volume, of the stock, 1st cat, in the location,
that it is in.
You just need to free up the restriction, of that 2nd cat, & just sliding in a
2.75" piece of tubing, does the job.
If you just gut the 2nd gut, without the tubing, flow is screwed up, been there, done that...
I have a CIA downpipe up in the 'rafters', of the garage,
covered with dust...
I bought a larger $300 aftermarket cat too, from Random Tech, & tryed
it in the CIA downpipe, down towards the end of the downpipe.
Nothing beats the size & volume, of the stock, 1st cat, in the location,
that it is in.
You just need to free up the restriction, of that 2nd cat, & just sliding in a
2.75" piece of tubing, does the job.
If you just gut the 2nd gut, without the tubing, flow is screwed up, been there, done that...
Senior Member
Joined: 04-26-2009
Posts: 669
From: City of Champions
Still 3" in this area.
I turn mid 12's @ 111mph at the track with this modded stock downpipe...
