SS fan

So who has a stock auto SS down pipe they aren't using, might cure my problems.

breds2k

i cannot understand how you really have any gains with changing the dp slightly like this, seriously bet just catless will be fine. That low RPM torque probably doesnt make too much of a difference on the track with a cat.

2005HHRauto

Been there, done that.
Cat less CIA DP was tried, it's in the picture, of the 1st post.
If anyone wants it, $100 + shipping, it has a single cut, & I paid $350 for it,
3 years ago. It weighs 9lbs, stock DP weighs 18lbs.

I've tested a lot of DPs, & this one that I'm using now, is the best...

The gains from eliminating the 2nd cat, from a stock DP, is awesome,as the 2nd cat is a restriction. By just putting a 2.75" hole in it, it isn't a restriction anymore.
The low rpm torque means nothing at the track, I brake-boost, at 3,000 rpm,but on the street, I wouldn't trade it for anything.
It's a DD, 99.9% of the time, & is such a pleasant DD, with this DP, that I am now using.

hhrfreek

Ok just clear this up for me. I think you stated you tacked a tube in place of the second cat on one setup. Then you stated you cored a hole in the second cat on another setup. On the setup with the second cat cored out the cat doesn't fall apart? Why didn't you just completely gut it.

Trying to figure out options for my Solstice, but the difference is I just have one big a$$ cat instead of 2.

Evad

Am I correct that the Downpipe that works best for you is a factory GM Downpipe and a stock factory Cat in the first position and the second Cat is a factory original and has a 2.75 hole cut through it, is that right?

2005HHRauto

Yes...

2005HHRauto

Same DP
I 1st cored a 2.75" hole in the 2nd cat, so that I could tack in place, a piece of perforated tubing.The tubing was holding the remaining cat-guts in place.
I left the remaining cat-guts in place to see if it would get really hot, like a normal cat, in case an emission, tester would touch the cat, to check if it was a cat.
It worked, it gets just as hot as a normal cat.
When testing this DP, last year, I really liked how it felt on the street, & I got a 12.86 at the track, with drag radials, at the end of last year. 4 weeks ago, i got a best of 12.51 @ 11.66mph at the track, with slicks, with this DP.

I kept this cat on until 2-3 weeks ago, to test what I thought would be a better DP.
Since I had the 'cored' DP out of the car, I removed the piece of perforated tubing, to see if any cat-guts remained.
It was still fully in place...
So, since the track is shut down for the year now, I just put this DP back in, to see if the cat-guts would remain in place, without the perforated tubing in place.
I'll check it in the spring, & if the cat-guts are gone, I'll just tack the piece of perforated tubing, back in place.

2005HHRauto

Maybe some pics will help...



The piece of tubing I used, & what is pictured, is from inside a spare HHR SS automatic muffler that I had.
No you don't need this for your tubing inside the cat. Any 2.75" tubing will work...LOL

A little HHR SS muffler history lesson now...LOL
Both manual & automatic HHR SS mufflers use straight thru ,2.75" tubing.
This is a why you never have to replace your muffler, it's a straight thru, free flowing muffer, that is all we need.
Hay, I got 12.51 @ 111.66 out of a stock muffer, it works, leave it alone..LOL
But the holes are different on the tubing, between the two mufflers, which is so strange.
The automatic muffler has 2 sets of 6 rows, of 'holes'. You can see one set of the 6 rows of holes, in this picture.
The manual HHR SS muffler has 2 sets, of only 2 rows of holes...LOL
So they needed more rows of holes on the automatic, for noise control, I guess...
So there is some real engineering going on at GM, even down to the number of holes, in the muffler tubing....LOL
You would think that they would use the same 2 sets of 6 rows of holes, for both mufflers, & called it a day.
And you think that I'm crazy for what I do...LOL
Hay, you want to do something silly...
Go outside at night, when it's really dark, & shine a flashlight into your muffler, too see if you have 2 sets of 2 rows of holes, if you have a manual, & 2 sets of 6 rows of holes, if you have an automatic.
Don't tell your wife what your doing, as she will think that your losing it...LOL
I can here it now. Honey, I'm going out into the dark of night, to see how many rows of holes, that I have in my muffler...LOL

Big cat pictured is the 1st cat in our DP , it's 4.5" in diameter x 4.625" long

Picture of 2.75" 'core' inside, & outside tubing, from the 2nd cat.
The 2nd postion cat in our DPs, is smaller than the 1st postion cat, & is a restriction, & is why this cat needs 'cored', or removed.
I don't have a 'complete' 2nd cat, to show you it's size, but it is 3.5" long x appox: 4" diameter

When looking at the piece of perforated 2.75" tubing, where it's really black on the left of the picture, is the back of the DP.
You can see where the remaining cat-guts is causing the tubing to get super hot, as seen by how white the area of the tubing is, in the middle, & to the right in the picture, & by how 'cooked' the metal looks, from overheating.

Also 4 of the DP's in the picture of the 1st post, are for sale @ $100 each, + shipping, as I'm done with DP testing now...
1. Stock manual DP
2. Stock manual DP with 2" hole 'cored' thru both cats.
3. Stock manual DP with both cats 100% removed, with a piece of 2.75" tubing placed in the 2nd cat housing. The 1st cat housing was cut open, so that I could weld in a piece of 3" tubing. This housing was then welded back in place. So both cat housings in this DP, are now resonators. This is a stock appearing DP that is a quiet free flowing catless DP. This is the DP that I was using, before installing the present DP ,that I am now using.
4. CIA 9lb catless DP that has a single cut, in the middle. I paid $350 for it 2 or 3 years ago. This will fit both manual, or automatics.
1st 3 OEM manual type DPs, come with a 'dummy' O2 sensor, as shown in that picture.

MIKEYfixit

Thanks for sharing all your info!

breds2k

So did you actually lose power with a 3" catless DP over the stock 2.75" with 1 cat and 1 gutted?