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My 68 has a 350/327. The judging manual says that all small blocks had 2" exhuast pipes except for the ones with the off-road option. The manual states on page 90 that small blocks with the off-road start at the manifold as 2" and expands to 2.5" as it reaches the center hanger. My exhaust pipes, which appear to be original, start off at 2.0" and then expand to 2.5" via a welded flanging about 8" down from the manifold. Would these be the correct pipes for the off-road option or are they some aftermarket attempt to put big pipes on a small block?? My exhaust pipes are in good enough shape to restore and use but if they aren't the off-road pipes, I will probably replace them with a full 2.0" system from manifolds back. Any comments??
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Re: 68 off-road exhaust
Jeff-----
Sometimes the judging manual can get you in trouble. For 1968, ALL Corvettes used 2-1/2" exhaust systems----from base 327 to L-88. For 1969, ALL Corvettes used 2" exhaust-----from base 350 to L-88. All N-11 systems were 2-1/2" but NO N-11 system was available for 1969 or thereafter---1968 was the final year.
For 1968 Corvettes with small block engines, all of which used 2" outlet exhaust manifolds, the forward exhaust pipe had a swaged down section of the pipe near the manifold which allowed the 2-1/2" pipe to be reduced to the manifold diameter. Big blocks, all of which used 2-1/2" outlet manifolds, did not require the swaged down section. Your forward exhaust pipes sound original as they have the swaged reduction section whereas many later SERVICE exhaust pipes apparently use a welded-on reduction section.
All PRODUCTION 1968 Corvette exhaust systems used a rear exhaust pipe which was welded to the muffler, at the muffler. This included BOTH standard as well as N-11 systems. In SERVICE, the standard mufflers were available only as a seperate part with a "bell" connector to attach to the rear exhaust pipe. The connection was then either clamped or welded at the "bell" connector. The N-11 system mufflers were available in SERVICE only as a complete asssembly with the rear exhaust pipe welded to the muffler AT THE MUFFLER, as original.
If you have an exhaust system with the mufflers welded to the rear exhaust pipes AT THE MUFFLERS, then you have either a PRODUCTION (original) standard exhaust system or a PRODUCTION or SERVICE N-11 exhaust system. The external configuration of the standard exhaust system and the N-11 exhaust system is virtually identical, the only difference possibly being numbers debossed on the outside of the mufflers. Unfortunately, there are a variety of numbers seen and I can't tell you how to positively ID the N-11 system. However, the last three digits of "735" or "736" on any debossed sequence of numbers MAY identify an N-11 system.
If your mufflers are connected to the rear exhaust pipe at a "bell" connection about 10-12" from the muffler using either a welded or clamped joint, then you DO NOT currently have an N-11 system, whether or not your car was originally so-equipped.In Appreciation of John Hinckley -
Re: 68 off-road exhaust
Joe,
I recently came across a pair of what I'm certain are N11 mufflers except for one significant observation, they had two mounting brackets on the rear face instead of just the "one". Somewhere I've seen or read that either "some" or "all" GM service replacements for the standard Corvette mufflers had the two mounting brackets on the rear face as I had found on these. Does the same "one mounting bracket" hold true for the factory original N11 mufflers, and the "two mounting brackets" for some or all of their GM service replacments? In other words, as I have come across a pair of N11 mufflers with the "two mounting brackets", then I should consider them to be the GM Service replacements, not the factory originals? TBarr #24014Comment
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Re: 68 off-road exhaust
Tom-----
I don't think that any original N-11 system would have used the "two bracket" mufflers. In fact, I've never seen a GM SERVICE N-11 system with the dual brackets. The 68-only SERVICE N-11 system had unique part numbers, although the 68 style muffler hanger bracket was the ONLY difference between the 64-67 and 68 muffler/pipe assemblies. GM NEVER offerred a "one-size-fits-all" part number for 64-67 and 68 N-11 systems. Perhaps the ones you saw were aftermarket. If not, I'd be interested to know what the GM part number for the assemblies are.In Appreciation of John HinckleyComment
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Re: 68 off-road exhaust
Joe,
Would the part number for the assembly be on the mufflers, paint stenciled or embossed maybe? If so then I'll see what I can find by tonight and post it up. Thanks for the info. TBarr #24014Comment
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Re: 68 off-road exhaust
Tom-----
If the mufflers are new, there should be a part tag taped to one of the pipes. If they're not new, then there may be a part number or part number derivative debossed on one or both of the mufflers. Since the same basic muffler is used for both sides, but its orientation changed, sometimes the debossment is on the top of one muffler and the bottom of the other. Also, usually, but not always, GM mufflers will have a "GM" debossed somewhere with the other numbers. Actually, GM did not make these mufflers, but, apparently, the prints called for "GM" to be debossed upon them by the manufacturer.In Appreciation of John HinckleyComment
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Re: 68 off-road exhaust
Joe,
After looking at both muffler assemblies again, I can find no paper or stick-on type tag, both assemblies are on the Corvette and have been slightly used. The exhaust pipes are welded to the mufflers as they should be for N11. Though I am saying "embossed", which is what I have believed "Webster's" to define, I think we are talking about the same "impressured" style of lettering. Is it the application of the "debossing process" that you are refering to or the letters themselves? I'll simply say "raised relief" to understand I am observing the same.
On the left muffler: top line is a raised relief GM, below that is a raised relief 3845737 with a black ink/paint stripe covering it from end to end. Below that are the numbers 3845735 simply in black ink/paint stencil. And below those are the raised relief characters 6 1 328 8 A.
On the right muffler: All letters or numbers are raised relief and no black ink/paint stripes or stenciled numbers appear. Top line: GM, below that is 3845736, and below that is 6 1 350 8 A.
As I had previously mentioned, two mounting brackets are welded on the rear face of both mufflers. I tried the "magnet test" on the front and rear faces of both mufflers, but found they both attracted the magnet so they are either fabricated with a lower grade of stainless steel or none at all. Also, no black out paint are on these assemblies, so I am certain by my observation that they did not come originally installed from another Corvette. I am not certain what is now, or has been previously available in aftermarket, reproduction, or GM Service replacements for the N11 muffler assemblies, but with this added information I'd like to know further what you might believe these to be, Joe. Thanks. TBarr #24014Comment
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Re: 68 off-road exhaust
Tom-----
These mufflers are GM SERVICE N-11 assemblies. I was not aware that GM ever made these assemblies with dual brackets, but, obviously, they did. The last available N-11 assemblies did not have dual brackets, but had the 63-67 style brackets only.In Appreciation of John HinckleyComment
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Re: 68 off-road exhaust
Thanks Joe. This was important to me, for judging purposes I needed to know if they were acceptable for no deductions. Other than the original factory equipped N11 mufflers, the 68-69 Judging Manual states they will accept GM Service replacement mufflers only as a "no deduction" of points. TBarr #24014Comment
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Re: 68 off-road exhaust
Tom------
The only problem might be that when they say that they will accept GM SERVICE N-11 assemblies I'm not sure that they're talking about ones with DUAL BRACKETS. Like I mentioned, I've never seen a GM assembly with the dual brackets.
The 64-67 assemblies were GM #3845735 and GM #3845736. These numbers, or derivatives thereof, are what you've found on the mufflers. That's virtually certain to mean that they were GM assemblies since it's illegal for aftermarket or replacement manufacturers to use GM's part numbers without permission (which they won't get except through the relatively recent GM Restoration Parts program). Also, most GM-supplied SERVICE mufflers have the "GM" symbol debossed somewhere on the outer shell. By the way, debossed means "raised" characters as opposed to "stamped in" or "sunken" characters which are termed embossed.
The 68-only N-11 system was GM part #3931803 and 3931804. These mufflers MAY have carried the same numbers as above on the muffler shell, itself, since the mufflers were the same, as far as I know. The only difference was that the muffler brackets were different and of the 68 style. If GM had used DUAL BRACKETS (which they apparently did given the information which you reported), I don't understand why they would have used unique part numbers for 64-67 and 68. The dual bracket assemblies would work for either.
As I mentioned, I know for certain what the 3845735 and 3845736 are configured like; I've seen many and have 2 sets in the collection. I've never seen any that have dual brackets. But, once-upon-a-time they may have been so-constructed.
I've never seen a set of the 3931803 and 3931804 assemblies; they were discontinued YEARS ago. However, perhaps GM just added the 68 style bracket to the earlier assemblies without removing or deleting the 64-67 bracket. These assemblies would then be applicable to ANY 64-68, so it's hard to understand why they'd discontinue these, but keep those with just the mid year style brackets for years to come. But, that may be just what they did. Logic does not enter into all of these type of decisions for reasons known only within the inner sanctum of GM
In any event, before assuming that the "dual bracket" assemblies will qualify for a no judging point deduction, I'd recommend consulting an experienced judge. I am not so-qualified.In Appreciation of John HinckleyComment
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