1969 nos chambered exhust

[William]

Chambered exhaust became a problem for Chevrolet.

Initially standard equipment on Z/28s, 350 & 375 hp 396s people were getting excessive noise tickets prompting Chevrolet to discontinue the system as standard equipment as of November 25, 1968. Undoubtedly caught short of some exhaust system components for Camaro there was an interim system of a transverse muffler without resonators, same as the 67-68 "deep-tone" dual exhaust. Later systems included resonators as depicted in the Aug '69 Hi-Perf Cars road test of ZL1 #3 - assembly line systems had the resonators welded to the exhaust pipes. People that had been ticketed could have the standard dual exhaust system retro-fitted at no cost and this is what the letter explains, listing the parts to be used.

As shown in the assembly manual [NC8] the RH rear chambered muffler was welded to its tailpipe. The LH rear muffler used a conventional tail pipe secured with a U clamp. Each muffler had 2 tabs and were bolted together. The ebay system is a collection of mismatched parts: 2 LH rear chambered mufflers and standard muffler 2nd design tailpipes.

Chambered is not a hi-performance exhaust system. True ZL1 guru Bill Porterfield built a ‘resto’ ZL1 engine and dyno-tested it for the February 1995 Chevy Hi-Performance magazine. Simply removing the chambered exhaust system added 80 hp. Todays Flowmaster systems cost 0 power.

[Chevy454]

William: I don't have my copy handy, but does the assembly manual show the tailpipe/muffler welded on the transverse muffler system?

Also, I've read that article Porterfield did on the ZL1, but check this: we ran the chambered exhaust on our Y-Camaro up until a couple years ago, and I went low 12.8s with it...I put a Flowmaster system on it as well as a rebuilt tranny and it didn't gain ET or MPH! Never could figure hat one out?? Anyay, it looks to me like the worst part the chambered system is where it flattens out to go under the crossmember...

[William]

On the standard muffler system the tailpipes were not welded to the mufflers.

The ZL1 cam probably magnifies the limitations of the chambered system - 4 mufflers, lots of bends and small pipe diameter. If your Flowmaster system was 2.5" it may not have been much better than stock or other changes in fuel volume/timing may have been required to bring up the power. One of our customers did a COPO clone that he raced and I recall at one point the car just shut off at about 1000 feet - the engine was using fuel faster than the pump/lines could supply it. Intake/exhaust is a delicate balance and a change in one generally requires a change in the other.

[Chevy454]

It looks like the diagrams on page 4 of the stuff I posted are backwards then? Looks like they have the chambers clamped and the mufflers welded?

And the ZL1 cam would definitely magnify the problem...too much duration and a very restrictive exhaust is a bad, bad combo! Yeah, our system was the 2.5" transverse Flowmaster system...the engine was rebuilt to factory specs, and was a whopping 10.2:1 compression, but was bracket car consistent...I did pretty decent at a couple bracket races, even on the skinny tires. Anyway, it's interesting you mention fuel...I bumped the compression up to 12:1, and am now running 12.3 @ 113+ (on Polys) with the stock AC fuel pump and factory lines. I did an A-B-A test with a 130gph pump this summer, and the car ran just as well with the stock AC, so that's what's on it, and what looks best!

[Jeff H]

Was the big block chambered system larger than the small block chambered system? If they put 2" pipes on a big block, then I don't care if you're running chambered or transverse, it's too small either way. And comparing Flowmaster to the chambered isn't the best comparison because Flowmaster is not the best flowing exhaust, it's lucky if it's middle of the road. But it sounds cool!

[William]

The only difference between sb chambered and bb are the manifold pipes.

HRM did a great exhaust tech article a few years ago. The car used was modified '70 442. I recall the system that ended up at no power loss was 3" with an X pipe. X is supposed to be better than H.

Many years back one of the Illinois crowd told me his '69 Z/28 had more power on the chassis dyno after he replaced the OE chambered system with the standard transverse muffler.

[Belair62]

If nothing else it loses "seat of the pants" feel with the chambered on my Chevelle for some reason...not sure if real numbers would bear that out.

[Rick H]

[ QUOTE ]
As shown in the assembly manual [NC8] the RH rear chambered muffler was welded to its tailpipe. The LH rear muffler used a conventional tail pipe secured with a U clamp. Each muffler had 2 tabs and were bolted together.

[/ QUOTE ]

There is an original GM chambered system on ebay right now that shows that very setup.

http://cgi.ebay.com/ebaymotors/ws/eB...tem=4520947137

Rick H.

[Salvatore]

Very good Rick. Thanks for keeping us informed again. Sam

[Chevy454]

I see the headpipes and intermediate pipes are missing from that particular system...those intermediate pipes are the REAL power killers...they flatten out to clear the tranny crossmember and are as crooked as a dog's hind leg!

BTW, our system looks just like that in the last link (rear pipes bolt together etc.) but the pass. side pipe is NOT welded on...so what do we have?