Published GM specs on exhuast decibel values?

[Richard M.]

Did such a document ever exist, or is there 3rd party test data available anywhere?

In particular, 1967 Standard, Offroad, & Sidepipe values?

Our new member in Norway has his L71 with GM service replacement N14 exhaust system. We believe this is likely the only L71 in Norway. The car was restored as close as possible to spec. Engine rebuilt to spec with stock internals, stock fuel system, properly tuned and running perfectly there. Upon delivery to the port in Norway last month, he drove the car 280KM for 3 hours to his home.

He has failed the Norway DMV inspection process due to "Loud Exhaust". It passed all other criteria. Just yesterday he was told by the DMV inspectors that they believe...... "GM would NEVER supply a exhaust this loud" They used sandpaper on the pipes to reveal the stamped GM part numbers, and they still are not convinced that this is a "as-originally-equipped" system.....which it is. There is no criteria for their rejection, thay simply say....."It's too loud and not original." They have the last word.

They tested the decibel level of the exhaust and recorded it at 106 db. I'm not sure at what RPM.

I am trying to get him some published data with specs to help him convince the DMV inspectors that his exhaust is stock. Ideally if the data shows N14 is in the range of 106 db it could help his cause.

Rich
p.s. his name is Odd Vehusheia #52530, and he asked me to ask for your help. His computer and English writing skills are cumbersome so I told him I would write it for him.

[Michael J.]

Re: Published GM specs on exhuast decibel values?

Having lived in Norway for many years, I feel for him and understand the government control and redtape involved there. I don't know about any decibel values, etc. from GM, but I seem to recall a thread not too long ago where someone explained that the sidepipe option was officially listed by GM as an "off road" configuration option so they could avoid government rejecting the cars for street use on just such issues. As such, GM could claim the car was configured for off road (i.e. track) useage, and not intended for street use if the sound was too loud for any local government regs. Anyone else know about this nuance?

[Bill M.]

Re: Published GM specs on exhuast decibel values?

From the '67 brochure: dual side-mounted off-road exhaust.

[Clem Z.]

Re: Published GM specs on exhuast decibel values?

a trick we used back in the day when we drove the NASCAR race cars with open exhaust to the track we would install coarse metallic pot scrubbers in the exhaust pipes and hold them in with a wire screen clamped across the outlet to hold them in place. i think the pot scrubbers were made from copper shavings. maybe something like would work just to get you thru inspection.

[Richard M.]

Re: Published GM specs on exhuast decibel values?

Michael, Yes I recall seeing that doc in a thread recently, but I think it was in 1969.
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Bill, My '53-'67 Spec Guide says....
N11 - "Off-Road Exhaust System"
N14 - "Side Mounted Exhaust System"
Would a Order Copy show N14 as it is in the brochure, or as in the Spec Guide?
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Clem, We were thinking of that but it may still fail.

[Anthony P.]

Re: Published GM specs on exhuast decibel values?

I even used steel wool in the pipes back in the mid 1970's with my cherry bombs. Did not last long, but long enough to get me through inspection with reduced sound.

a trick we used back in the day when we drove the NASCAR race cars with open exhaust to the track we would install coarse metallic pot scrubbers in the exhaust pipes and hold them in with a wire screen clamped across the outlet to hold them in place. i think the pot scrubbers were made from copper shavings. maybe something like would work just to get you thru inspection.

[Clem Z.]

Re: Published GM specs on exhuast decibel values?

I even used steel wool in the pipes back in the mid 1970's with my cherry bombs them. Did not last long, but long enough to get me through inspection with reduced sound.

we did not use steel wool but pot cleaners made from copper shavings. i think they were called "chore boys" or something like that.

[Bill M.]

Re: Published GM specs on exhuast decibel values?

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Bill, My '53-'67 Spec Guide says....
N11 - "Off-Road Exhaust System"
N14 - "Side Mounted Exhaust System"
Would a Order Copy show N14 as it is in the brochure, or as in the Spec Guide?

From the '66 GM options list:

Exhaust System, Dual Side Mounted: (for off-road serice only).....N14

My interpretation of "off-road": This is loud, and if you get a loud muffler ticket, we're not gonna replace it under warranty with a standard exhaust system.

[John H.]

Re: Published GM specs on exhuast decibel values?

How about sending him the Section N14 sheets from the '67 Assembly Manual, the illustration on page 8-25 from the '67 Chassis Service Manual, and the photo showing side exhaust on page 7 of the '67 Corvette sales brochure? That's pretty good evidence that sidepipes were "factory".

[Richard M.]

Re: Published GM specs on exhuast decibel values?

John,

I sent him several things last night. The AIM page as you mentioned, and the page in the 53-67 Parts Book showing the Exhaust parts, including the part numbers for the big block N14. I also sent photos that I took here showing the actual part numbers on the pipes themselves.....of which they sanded the high-temp silver paint to see.

Good idea on the Service Manual pages......He has a original manual so I'll tell him that. Unfortunately I don't have any Sales brochure images handy.

He's going to take the images I sent him for a re-inspection next week to help prove that it is "all real". If we could get some actual data on decibel values when originally supplied it may help his cause.

Rich

[John H.]

Re: Published GM specs on exhuast decibel values?

John, Unfortunately I don't have any Sales brochure images handy. If we could get some actual data on decibel values when originally supplied it may help his cause.

Rich

Rich -

Scan below from page 7 of the '67 brochure showing the photo of sidepipes; I also have it at full resolution (1.24MB) if you need it (PM me with your e-mail address).

I doubt if there is any GM data on decibel levels, including exactly how the test was done. When the Walker chambered exhaust system was standard equipment on the early '69 Chevelle SS and '69 Camaro SS big-blocks and Z/28's, customers started getting excessive noise tickets, and the chambered systems were made optional (replaced in production by conventional muffler systems), and the optional chambered systems were cancelled entirely in May, 1969. See TSB below.

[Richard M.]

Re: Published GM specs on exhuast decibel values?

John, The brochure image you attached here is perfect as is....thank you. I'll get it to him for reference.

It is very interesting that the text of the brochure mentions "off-road" in the description of the side exhaust, as Bill also mentioned above. Maybe it was a way to hint to a potential buyer that it was "Loud".

Every other reference, i.e. specs, RPO info, etc, never reference the term "off road" for N14.

Thanks,
Rich

[Joe L.]

Re: Published GM specs on exhuast decibel values?

John, The brochure image you attached here is perfect as is....thank you. I'll get it to him for reference.

It is very interesting that the text of the brochure mentions "off-road" in the description of the side exhaust, as Bill also mentioned above. Maybe it was a way to hint to a potential buyer that it was "Loud".

Every other reference, i.e. specs, RPO info, etc, never reference the term "off road" for N14.

Thanks,
Rich

Rich------


Two things to keep in mind:

1) If Norway has a decibel limit, it may not make any difference to them if the N14 was a factory option, or not.

2) If the fact that the system was classified as for "off road use only" comes to their attention, that gives them the perfect out. In other words "we don't care that it was an original option, it was never intended for on-road use". As a matter of fact, that same reasoning could be used by any DMV or police authority here in the US to justify citations for excessive noise. Actually, I'm surprised it does not happen more often.

[Joe L.]

Re: Published GM specs on exhuast decibel values?

John, The brochure image you attached here is perfect as is....thank you. I'll get it to him for reference.

It is very interesting that the text of the brochure mentions "off-road" in the description of the side exhaust, as Bill also mentioned above. Maybe it was a way to hint to a potential buyer that it was "Loud".

Every other reference, i.e. specs, RPO info, etc, never reference the term "off road" for N14.

Thanks,
Rich

Rich-----


...from the 1966 Chevrolet Order Guide...

[Richard M.]

Re: Published GM specs on exhuast decibel values?

Joe.....good points. However I learned that there is a "grandfather" clause there relative to pre-1972.

I recall he told me that even though the car is not subject to the full requirements as those in place post-1972, he said that the inspectors don't adhere to that. He may have to pursue a higher bureaucratic process there to argue the situation. Unfortunately he said that process can take many weeks, with no guarantee of positive results. Also, the European Holiday season is upon them, where everything shuts down for a month or so.

As far as the term "off-road" goes, I'm still confused. The only place it ever shows up is in the brochure.

Rich