Mufflers-Black?

[Joe L.]

Re: Mufflers-Black?

In the above photos it appears (to me) that the mufflers were blacked out on the TOP side, leaving the bottoms that are more easily seen natural. I thought the purpose of black out was to disguise the shiny mufflers and lighter colored fiberglass from view. On most of the C3 cars I saw new (76-82), the mufflers appeared to have been sprayed from the bottom. Was top side blackout common or typical on C2 cars? Chip.

Paul------


I have no idea what the origin of that "top coating" of the mufflers is. However, I don't think that was ever done at the factory.

Interesting note: once-upon-a-time there were available SERVICE mufflers for 2" 1969-72 Corvettes under GM #3960601 and 3960602. I purchased quite a few of the right side 3960602 mufflers when they were still available for my 1969 inasmuch as the right side would rot out about every 3 or 4 years (yes, even in California since the rotting out was always from the inside out). Every one of these I purchased was supplied in a box and the muffler was coated black on the bottom, sides, and end.

Also, I have purchased quite a few of the last available 63-72 2-1/2" SERVICE mufflers over the years, GM #3943385 and 3943386. Some of these were supplied coated black on the bottom, sides and end and some were not. However, I also purchased several of the 64-67 N-11 SERVICE muffler assemblies with rear pipe over the years and looked at many others for sale over the years and I've never seen one in which the mufflers were coated black.

[Scott S.]

Re: Mufflers-Black?

Is not the intention to cover the bottom side of the muffler black so it is not a dominate viewing under the car looking from the rear?

Gene,

I thought the same thing. Viewed at eye-level from directly behind a car with rear exhaust, I thought the stainless steel exhaust tips were supposed to disappear into a "black hole" (to be accomplished during the blackout process), and a shiny rear-muffler surface should not be visable.

Similarly, when viewed from the side, I always notice what seems like a large "gap" between the rear wheel and the rear fender lip on side exhaust cars, because there is no muffler filling that space. From the right angle, you can see daylight through that "gap". On a rear exhaust car, it's just black, presumably from the mufflers filling the "gap" and being dark from the blackout process, no silver-gray aluminum color is visible.

The blackout process shown in Adams (p. 318) would certainly accomplish both tasks.

[Scott S.]

Re: Mufflers-Black?

Russ -

Actually, the chassis blackout operation was done with the fully-assembled chassis right-side-up, in the last station on the Chassis Line, right before Body Drop, using airless spray guns fed from drums with Johnstone pumps.

John,

Was the chassis blackout in the muffler area sprayed from the top down by someone standing on ground level, or was it sprayed upward from below, while standing in the "pit", e.g., like during the wheel alignment procedure photo you have posted in other Threads, with the crowd of visitors watching?

What I'm getting at is this, if it was sprayed from below, it would be hard to get a lot of blackout paint on the top surface of the mufflers. If sprayed from above, unlikely to get a lot of blackout paint on the bottom surface of the mufflers, unless it was common practice to angle the spray gun all over for thorough coverage.

The photo in Adams (p. 318) you've referenced in old Threads sure looks like the mufflers were well coated.

[Terry M.]

Re: Mufflers-Black?

Paul------


I have no idea what the origin of that "top coating" of the mufflers is. However, I don't think that was ever done at the factory.

Interesting note: once-upon-a-time there were available SERVICE mufflers for 2" 1969-72 Corvettes under GM #3960601 and 3960602. I purchased quite a few of the right side 3960602 mufflers when they were still available for my 1969 inasmuch as the right side would rot out about every 3 or 4 years (yes, even in California since the rotting out was always from the inside out). Every one of these I purchased was supplied in a box and the muffler was coated black on the bottom, sides, and end.

Also, I have purchased quite a few of the last available 63-72 2-1/2" SERVICE mufflers over the years, GM #3943385 and 3943386. Some of these were supplied coated black on the bottom, sides and end and some were not. However, I also purchased several of the 64-67 N-11 SERVICE muffler assemblies with rear pipe over the years and looked at many others for sale over the years and I've never seen one in which the mufflers were coated black.

One of the differences (among many) is that the C3 mufflers you reference were made by Walker, but the mid-year N11s were made by Arvin.

[Scott S.]

Re: Mufflers-Black?

One of the differences (among many) is that the C3 mufflers you reference were made by Walker, but the mid-year N11s were made by Arvin.

Joe and Terry,

In regard to Joe's most recent post, if N11 off-road exhaust was installed on the assembly line, the N11 muffler system would receive the same blackout process as the "regular" mufflers, correct?

[Terry M.]

Re: Mufflers-Black?

John,

Was the chassis blackout in the muffler area sprayed from the top down by someone standing on ground level, or was it sprayed upward from below, while standing in the "pit", e.g., like during the wheel alignment procedure photo you have posted in other Threads, with the crowd of visitors watching?

What I'm getting at is this, if it was sprayed from below, it would be hard to get a lot of blackout paint on the top surface of the mufflers. If sprayed from above, unlikely to get a lot of blackout paint on the bottom surface of the mufflers, unless it was common practice to angle the spray gun all over for thorough coverage.

The photo in Adams (p. 318) you've referenced in old Threads sure looks like the mufflers were well coated.

Scott,
I know your question is confined (although not stated) to mid-years. FWIW: On the C3s I have seen with original black-out usually the coating is on the back end and bottom and the runs go up toward the top. That could happen if the coating was applied to them while the chassis was upside down, but John has posted pictures of that section of the line and no coating is taking place there and the mufflers were not in sight. The other option is they were coated before installation, perhaps not even in St Louis. Of course they may have done the C2s differently, and I woo am anxious to see John's answer to your question.

[Paul D.]

Re: Mufflers-Black?

I seem to remember seeing a set of supposedly original "off road" mufflers that had been taken off a L-88 (68 I believe) and they had a part number stamped on the bottom over top of a black out coating. It seemed odd to me at the time, but makes sense if the mufflers were treated to some black out at the manufacturer. Also would explain the upward runs that Terry spoke of. Now, do any of you recall mufflers showing two different forms of black out? Seems reasonable that some black out from the assembly line would get on the mufflers and be of a different shade or have runs going in two directions. Not losing any sleep over it, just curious. Chip.

[Terry M.]

Re: Mufflers-Black?

I seem to remember seeing a set of supposedly original "off road" mufflers that had been taken off a L-88 (68 I believe) and they had a part number stamped on the bottom over top of a black out coating. It seemed odd to me at the time, but makes sense if the mufflers were treated to some black out at the manufacturer. Also would explain the upward runs that Terry spoke of. Now, do any of you recall mufflers showing two different forms of black out? Seems reasonable that some black out from the assembly line would get on the mufflers and be of a different shade or have runs going in two directions. Not losing any sleep over it, just curious. Chip.

Again, on C3s we occasionally see minor black overspray on the spare tire tub. I can only conclude that any scratches int he muffler coating, or incomplete coverage were "touched up" at some point on the line when the chassis was more complete.

[Joe L.]

Re: Mufflers-Black?

Joe and Terry,

In regard to Joe's most recent post, if N11 off-road exhaust was installed on the assembly line, the N11 muffler system would receive the same blackout process as the "regular" mufflers, correct?

Scott------


Yes, once installed on the cars in PRODUCTION they would have received the same black-out as other mufflers. That is also most assuredly why they were not coated from the manufacturing source. However, there's no reason why the SERVICE assemblies, even though of the same part number as PRODUCTION, could not have been coated. As a matter of fact, sometimes SERVICE parts are painted whereas PRODUCTION pieces are not even though they are of the same part number.

The standard exhaust SERVICE mufflers were, of course, of a different part number than PRODUCTION due to the different SERVICE configuration. However, as far as I know, they were manufactured in the same plant. As I mentioned, the 3943385 and 3943386 are seen both with and without black coating. Here's what I've observed over the years:

63-67 2" SERVICE mufflers---not coated black; all bare metal

63-67 2-1/2" SERVICE mufflers (single hanger bracket)----(I don't recall seeing any; they were discontinued in 1969)

69-72 2" SERVICE-----coated black on bottom, sides and end

68-72 & 63-67 2-1/2" SERVICE (after 1969) (dual hanger bracket)----some coated black on bottom, sides, and end and some not coated, bare metal

64-67 N-11-----not coated; bare metal.

[Michael H.]

Re: Mufflers-Black?

Here's a link to a discussion about muffler blackout from way back in 2004. I would have thought that all of the Judging Guides would have eliminated the process and term "mitting" by now.

https://www.forums.ncrs.org/showthread.php?t=26863&highlight=blackout&uid=3414

Mufflers for 63-67 were spray coated with chassis black. The coating was applied on the outer top surface and much of the bottom surface. The inner surfaces and end panels usually didn't receive any coating.

Search the archives for "muffler blackout" and/or "mitting".

At some point in the late 60's or possibly early 70's, I think the process changed. The chassis black coating was dropped and replaced by what looked like flat black spray paint. It's possible that the process was also completed before the exhaust system was installed on the chassis.

[Patrick N.]

Re: Mufflers-Black?

I have not added the black to my mufflers yet, but my understanding was that the black was added on the bottom surface of the muffler while the chassis was being assembled upside down. Therfore drips / excess balck would be running "up" the muffler when righted- Is that accurate?

[Mike M.]

Re: Mufflers-Black?

Scott------


Yes, once installed on the cars in PRODUCTION they would have received the same black-out as other mufflers. That is also most assuredly why they were not coated from the manufacturing source. However, there's no reason why the SERVICE assemblies, even though of the same part number as PRODUCTION, could not have been coated. As a matter of fact, sometimes SERVICE parts are painted whereas PRODUCTION pieces are not even though they are of the same part number.

The standard exhaust SERVICE mufflers were, of course, of a different part number than PRODUCTION due to the different SERVICE configuration. However, as far as I know, they were manufactured in the same plant. As I mentioned, the 3943385 and 3943386 are seen both with and without black coating. Here's what I've observed over the years:

63-67 2" SERVICE mufflers---not coated black; all bare metal

63-67 2-1/2" SERVICE mufflers (single hanger bracket)----(I don't recall seeing any; they were discontinued in 1969)

69-72 2" SERVICE-----coated black on bottom, sides and end

68-72 & 63-67 2-1/2" SERVICE (after 1969) (dual hanger bracket)----some coated black on bottom, sides, and end and some not coated, bare metal

64-67 N-11-----not coated; bare metal.

I take it from Joe's quoted response that the replacement mufflers that I am about to put on my '65 coupe need no black coating at all; that there would be no deduction for a service replacement that had no black coating. Advise if I assume wrongly. Thanks for all the responses. Mike

[Scott S.]

Re: Mufflers-Black?

I take it from Joe's quoted response that the replacement mufflers that I am about to put on my '65 coupe need no black coating at all; that there would be no deduction for a service replacement that had no black coating. Advise if I assume wrongly. Thanks for all the responses. Mike

Mike,

That was indeed the reason for my question to Joe. I have the N11 exhaust system and wanted to understand whether it should be blacked out, or not. Unless I am mistaken, for Judging purposes, the mufflers must appear as they did when the car rolled out of the factory, not as it would appear with service replacement mufflers.

Therefore, the N11 mufflers should receive the same blackout treatment as any other mufflers on a car traveling down the St. Louis assembly line.

If this is not correct, someone please say so!

[Scott S.]

Re: Mufflers-Black?

I have not added the black to my mufflers yet, but my understanding was that the black was added on the bottom surface of the muffler while the chassis was being assembled upside down. Therfore drips / excess balck would be running "up" the muffler when righted- Is that accurate?

Patrick,

I'm hoping John will provide more details that will help us to replicate the factory blackout process, but this excerpt from a series of articles in back issues of Corvette Enthusiast says the chassis was right side up when the blackout process occurred:

"On the Chassis Line, occurs the assembly of the fuel and brake lines, fuel tank, exhaust system, installation of the engine/transmission, brake bleeding/testing, body mount shims and cushions, and chassis blackout. The chassis is upright in car position on a floor conveyor during this process." - John Hinckley, Corvette Enthusiast Magazine, December 2006 (emphasis mine)

[Russ S.]

Re: Mufflers-Black?

I have not added the black to my mufflers yet, but my understanding was that the black was added on the bottom surface of the muffler while the chassis was being assembled upside down. Therfore drips / excess balck would be running "up" the muffler when righted- Is that accurate?

This is what I have been told for many years but according to John Hinckley it is incorrect. He states chassis was right side up and the blackout was sprayed on with airless spray guns.