wallaper72

Can anyone tell me if this catalytic converter is stock or aftermarket? I thought it was a aftermarket high flow cat but I am not sure. That cat physically looks good but I am having problems with high back pressure, guessing its the culprit. The rest of the system is Hedman shorty's / Y-pipe to a 3 inch Flowmaster cat back.

Drew

iTrader: (58)

Considering it doesn't have any GM or AC stamps and doesn't look stock, I'd say it's aftermarket.

jeremyb1988

So...probably a dumb question bc you posted all this...but is there any reason you dont just do straight pipes...worried about inspections in your area I assume? Or trying to keep the car all original as possible, just curious.

NoEmissions84TA

iTrader: (1)

https://www.arb.ca.gov/msprog/afterm...amcatlabel.pdf

It is a Walker Super Converter. Approved for use in CA.
http://www.ebay.com/itm/Walker-Super...xYCnnz&vxp=mtr

jeremyb1988

Haha...I like ur SN...no emissions...fitting you replied to this post...think I have seen you on here before...but yeah...sorry had a little chuckle when I seen ur sn. Good info tho! Images saved!

NoEmissions84TA

iTrader: (1)

Thanks, and you're welcome.

wallaper72

I started looking at the cat as I am troubleshooting performance problems, the car feels way to slow for the 383 that is under the hood.

I ended up hooking up a back pressure gauge into my 02 and taking it for a drive. Everything looked good until I hit about 3k RPM. By the time I hit 6K RPM I was getting about 12psi of back pressure. From what I understand that is way to high.

I am going to have the exhaust shop build me a straight pip this week and test.

I would love to strip that cat out of the system but the car get so loud without it! lol

Thanks for the help.

NoEmissions84TA

iTrader: (1)

12 psi - yeah that's too high.
Good job testing instead of guessing and randomly replacing parts.

wallaper72

If anyone is interested in results from removing the cat. Maximum back pressure dropped 3psi, and my air/fuel at WOT went from from 11.5 to 12.5.

NoEmissions84TA

iTrader: (1)

So your backpressure is still 9 psi???
That's still too high. Where was your pressure gauge installed?
A stock automotive exhaust might have over 5 psi OF BACK PRESSURE, AT PEAK RPMS WHERE EXHAUST FLOW IS AT MAX, or even more in a few cases, of back pressure in the exhaust system if measured at the collectors at max engine rpm, with a decent accurate pressure gauge, while a good aftermarket exhaust system will roughly cut that in half to the 3-5 psi range. BUT An excellent performance exhaust will get down in the 1-2 psi or LOWER restriction to flow range at max engine rpm. from http://garage.grumpysperformance.com

wallaper72

The gauge is going into the exhaust just before the stock cat location.

I dont know about the accuracy of the gauge, I got it from amazon.
Tool Aid 33600 Exhaust Back Pressure Tester.

NoEmissions84TA

iTrader: (1)

Unless the gauge was dropped, it should be reasonably accurate.
You now have a test pipe in place of the cat. What is the rest of your exhaust system?
If it is already upgraded, then your muffler is quite a restriction.
Is there any way you could repeat the test with NO MUFFLER?

wallaper72

Headman shorty headers (I think 1 5/8) - matching Headman Y-pipe.
Flowmaster muffler, stamp on side of muffler is 42583.

NoEmissions84TA

iTrader: (1)

WOW. A Flowmaster has baffles, unlike a glasspack which can burn out and gets louder.
You have nothing there to clog - unless a mouse built a nest inside your muffler.
I'm stumped.

Decades ago, I has a friend with a 68 Camaro with a built 350. The car had 3 chamber Flowmasters on it when he got it. He changed to turbo tubes (straight pipe with fiberglass packed around it and crimped) and man was that loud! But super responsive. He had to quiet it down, so he had regular oval case turbo mufflers installed. Much quieter, but it killed the top end performance. It is not easy to have a reasonably quiet exhaust system that is not restrictive.

NoEmissions84TA

iTrader: (1)

I just read that your muffler has a 2.5" inlet. That could be your bottleneck.
You probably have to increase the size of your intermediate pipe and muffler to allow your 383 to breathe.

TTOP350

iTrader: (8)

Unhook the muffler or the intermediate pipe after the cat if that pipe is 2.5 inches and retest BP. The muffler may have issues.