replacing cat with glass pack

[andrew4266]

has anyone done this? it seems that it would keep it quiet yet still let the exhaust pass through.

[wolfrpi]

Sounds like it would make a pretty good fire under your car!

Erick

[Lawrence Coppari]

I know of a 944T that has a hollow cat. It is only slightly louder than it was before the cat mysteriously lost its innerds. An NA would be louder but don't know how much.

[1.2gees]

An NA is really not that much louder, without a cat... However, if the muffler is stock, it may rattle a bit, as it has to a few on this board, including me...

Glasspack will NOT last long, in place of the cat. Instead, I'd suggest pulling out your stock downpipe, punching the cat, and installing it back. Be ready to replace your muffler as mine started making nasty noises after the track event.
Ahmet

------------------
It's all the driver...

[matty89]

why wont the glass pack last long ? because of the heat? its made for heat no ?

[HondaDustR]

It will help with flow but it doesn't sound good, but that also may depend on the exact glasspack you get,and your tolerance for 4 cyl rasp. I tried the 26" Thrush glasspack resonator and it may as well have been a straight pipe. Lots of harsh, raspy 4 cyl exhaust sounds made it through even the stock muffler. It sounded like a ricer on steroids with the thrush 2 chamber muffler...and so loud I had to swap the stock muffler on the next day (daily driver). I did run a punched out stock cat for a few months before that and it didn't increase the sound much with the stock muffler, but did sound slightly annoying for daily use with the 2 chamber. Keep in mind that changing the backpressure while running the stock chip can cause loss of low and mid range torque, which is what these engines really do best. The 944MAX chip I run is tuned for a test pipe, so I did notice some slight gains when running the empty cat and the glasspack, but the higher flow 2 chamber muffler I switched to seems to make it run better than stock even with the stock cat I am currently running.

The downside to a punched out cat is the weird pressure wave resonances that can get going inside the empty chamber and mess with the exhaust flow ( Good video explaination of this phenomenon here at 4:30 http://www.youtube.com/watch?v=Wa0BJqTG22Y&feature=channel_video_title ). The fiberglass packing in a glasspack burns out over time, especially with the cheaper brands. The factory cat is about half cat bricks, half glasspack resonator, so between the steel mesh liners left behind that support the cat bricks in the shell and the glasspack section, the hollowed out cat does a decent job of keeping the sound under control. The 944 motor is very large for a 4 cyl, being a 2.5L, and does make lots of undesirable 4 cyl type sound that has to be quieted down.

Play this vid in 720 HD mode for the best sound and you can hear some of the results of my last project. I do need to record how it sounds with the 2 chamber and the stock cat, ans I think it is the best of all of these. Skip to the 4:00 mark to get the audio answer to your question.


YouTube - Porsche 924S Thrush exhaust project

[Rudeboy42]

Whatever you do definitely don't put a Bursch header and test pipe with nothing but a cherry bomb glasspack.

God what the hell was I thinking?

[CKniht90]

Rudeboy.. got pictures or video?

[matty89]

right now im running a straight pipe cat tube and my muffler nest is starting to make a metal noise so i think all put a MFlow highflow cat(90$) and a Mflow muffler(100$ ) but im still debating on what to do ! suggestions ?

[ernie9944]

Butting in with my combo (which will last -give you good service & will produce a deep throaty sound ) was install on my 944 quiet a few years back. S/S cat mode to fit ,dumping in the OE muffler with a 4" S/S polish exhaust tip.Glass pack do yourself & your car a favour keep away from it.

[matty89]

where di you get ur SS cat or resonator it looks like to me ?

[ernie9944]

Originally Posted by matty89

where di you get ur SS cat or resonator it looks like to me ?

This not a resonator it's a s/s cat got it at my local speed shop.

[matty89]

Originally Posted by ernie9944

This not a resonator it's a s/s cat got it at my local speed shop.

do you remember off hand how much it was like 100$ or 200$ i dont know if im going to leave my cat without the cat or not muffler is ratteling a little inside of it .... im thinking of a cat like urs or a resonator with a new muffler depends on the prices i get off with..

[ernie9944]

Matty___ this install was done I believe 8 or 9 years ago ,when my cat when nuke I started looking around for another one but didn't want to go OE ,so this guy at the speed shop had that one that someone order for a Honda.I beleive the price was around $200.oo but since it was laying around I got it for $80.oo brand new in the box,like said I had to modified it a little by using the flange on my old cat .As far as the part number is concern I don't have it and the box is long gone ,so not much help there,one thing I remember is that it had two outlet plugs on the top (front) .After the install I kept a close watch on it for adverse effects on the car performance but found none in fact it seem to work better then the OE one ,with the add of the 4" tip the car had a nice throaty sound but nothing (extreme or ricy) .It's still on the car after all them years & just doing find.You can call it (trial & error) sort a thing just happen to be lucky it did work I guess. If your's is giving up why don't you look around for an after market one ,they are some nice one out there that doesn't cost a fortune & do the job just fine.

[ernie9944]

Matty--- two exemple of what is out there, those are S/S Pace Setter cats__ first one is approx $160.00___ second $125.00,if you do buy one don't buy the cheap one at $40 or $50 they won't last. The first one you would probably have to do the same mod as I did to install, cut the flanges on your OE cat and re-weld them but any good muffler shop can do the install properly.

[Wharf Rat]

When I bought my 944 it had the header, test pipe, and stock catback and had the rattling that everyone talks about. So I installed some no-name dual outlet muffler that I inherited with the car and it was loud as hell. Then I got a Thrush glass pack to put in place of the test pipe. It quieted down considerably and is tolerable now. As far as the heat/fire, yeah it looks like it got hot down there. The paint is fried off of the last 3 inches of the glasspack. I've done about a dozen track days with it and haven't had any issues with the heat though.

[Slam]

Hmmm... How about getting a stock 944 Euro resonator from a breaker in...well...Europe?

[HondaDustR]

Someone did that a little while ago. The big challenge is that the y-pipe flanges are oriented differently, requiring cutting and rewelding so the screw holes line up with the non-euro headers. It probably sounds and performs the best, though.

[Slam]

Come to think of it, I recall seeing that thread. I think the upshot was that you'd have to get the exhaust mani with the resonator.

My 83 has a resonator, and the car's loud but it sounds good. My 84 with the sotck setup is quieter but doesn't have the same snarl on decel over-run. My wife;s 924 has a straight pipe to the muffler, and it sounds very nice indeed.