'64 RPO N11 Exhaust System
While looking at the options that were available in 1964, I found an option titled N11 - Off Road Exhaust System. I know that it's not the same as the N14 - Side Mount Exhaust System that was offered for the first time in 1965 but I don't remember what the N11 contained. Any ideas?
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Re: '64 RPO N11 Exhaust System
Michael, it's a off road under car exhaust that sounds VERY nice on HP Corvettes. 2 1/2 inch system only. Go to archives here, massive information on this system for you. Enjoy!
Dan1964 Red FI Coupe, DUNTOV '09
Drove the 64 over 5000 miles to three Regionals and the San Jose National, one dust storm and 40 lbs of bugs! -
Re: '64 RPO N11 Exhaust System
N11 was a different rear section - the assembly of rear pipe and muffler. The difference was a "two-pass" muffler that was less restrictive than the standard muffler. The front pipes were the same as base. N11 was only available on engine/trans combinations that included 2.5" pipes, and it was an inexpensive option - less than forty bucks!
This welded rear section was sold over the counter - the exact same assembly as installed at the plant, so it was easy to change a base exhaust to N11 in the field. (The base system was serviced as a separate rear pipe section and muffler that were designed to be clamped together - not the OE welded assembly.)
For those who bought these N11 rear sections over the counter when they were available in the sixties and seventies, it was probably one of the best "investments" you could make. Better than gold! Better than real estate! Better than the stock market, but who knew at the time.
It's the best performance exhaust system ever made for vintage Corvettes - low restriction with a great sound that was not excessive for normal drivng, and now a good reproduction is available.
I chuckle every time I see a side pipe car. Yeah, they look great, but they are VERY restrictive and VERY LOUD!
N11 was listed as an option for 1963, but none were sold, and it won't fit early '63s with the deep seat wells due to N11 not having the "jog" in the pipe to clear the deep seat wells. It can be fitted to later '63s with the shallow seat wells, but will also require a new front section since the '63 OE pipes have reversed center slip joint "polarity" compared to later C2s.
DukeComment
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Re: '64 RPO N11 Exhaust System
Duke,
Yup, I almost wish mine wasn't a sidepipe car. Then I look at it. They just look so good on a coupe. It's too bad they didn't engineer them for better performance.
GeorgeComment
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Re: '64 RPO N11 Exhaust System
Sorry Duke but a certain Sebring Silver ZO-6 has a set of early design around the seat well N11's on it. And they are originals, not to that car but I happend to be there when they were purchased at Bloomington in the 70's.
And another thing the N11's across the counter would fit the early 63's even though they were straight. Real close but they would work.
The darn things were so big they would slip over the 63 front pipes. Been there, done that!
JRComment
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Re: '64 RPO N11 Exhaust System
Impossible to do considering packaging constraints.
The exhaust gas flow rate is measured in CFM (Cubic Feet per Minute) maintaining a 1.5" Hg (inches of mercury, or 20.4 inches of water) pressure drop across the entire exhaust system.
Quiet (typical) = 7 to 12 PSI at the RPM for peak HP
Sporty (typical)= 2 to 8 PSI at the RPM for peak HP
Race (typical)= .5 to 3 PSI at the RPM for peak HP
Open Headers = 0 PSI
Estimated CFM Rating
Designed Engine Power (HP)............................CFM Rating
.................................................. ...Quiet.........Sporty..........Race
0 - 50............................................... 20 ............40 .............120
51 - 100.............................................60 ........... 120 ............360
101 - 150.......................................... 100 ..........200 ............600
151 - 200 ..........................................140 ..........280 ............840
201 - 250 ..........................................180 ..........360 ..........1080
251 - 300 ..........................................220 ..........440 ..........1320
301 - 400 ..........................................280 ..........560 ..........1680
401 - 600 ..........................................400 ..........800 ..........2400
601 - 1000 ........................................640 .........1280 ..........3840
1000- 2000 .......................................1200 ........2400 ..........7200
• Quiet is a production exhaust system for a family sedan or luxury sedan where a "throaty"
engine roar is undesirable.
• Sporty is a production exhaust system for performance/sports cars.
• Race is an exhaust system with extremely low back pressure, designed for classes of racing
where rules require mufflers.
• For open headers/no exhaust system, enter a very large value of CFM, for example 100000
CFM
An acceptably low restriction exhaust system for a typical vintage SBC which has not been modified, should fall into the range of about 440-600 cfm per bank @ 1.5 in-hg pressure drop from the beginning of the exhaust port to the end of the tailpipe.
The most important consideration with noise attenuation devices is the size of the chamber which is used as a means of quieting the noise. The larger the enclosure, the greater the attenuation per unit of system back pressure. Another way to say it, is, the bigger the volume of the muffler, the more flow that the exhaust system will permit while at the same time effectively quieting the noise AND maintaining low pressure at the exhaust ports.
Reread the first sentence of this post. This is one huge reason why modern attenuators (mufflers) are no longer made in pre-determined shapes. Rather, they are custom fitted to each application whereby they make full use of all available space. These modern mufflers are large, irregularly shaped, and very efficient!
Never mind the modern mufflers for the purposes of this discussion. Let's suppose that we could engineer a side exhaust muffler for a midyear Corvette which could attenuate sound to the "sporty" level, while providing restriction somewhere between "sporty" and "race". This means that we'd need about 700-800 cfm per side. We'd start with full length 2 1/2" piping for a SBC and 3" pipe for a BBC. If we were going with a single pass chambered or "glasspack" style muffler, we'd need to incorporate an inner tube size (GM side exhaust mufflers used 1 3/4" ID inner tubing) of at least 2 1/2" for a SBC and 3" for a BBC. The outer casing of our "engineered" side mount mufflers (assuming the enclosure ran the full length of the rocker panels, or about 44") would need to be more than 6" in diameter! That would transform the beautiful lines of a midyear Corvette to something akin to a pontoon boat.......................Comment
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Re: '64 RPO N11 Exhaust System
[quote=Joe Ciaravino (32899);541319]Impossible to do considering packaging constraints.
The exhaust gas flow rate is measured in CFM (Cubic Feet per Minute) maintaining a 1.5" Hg (inches of mercury, or 20.4 inches of water) pressure drop across the entire exhaust system.
Quiet = 7 to 12 PSI at the RPM for peak HP
Sporty = 2 to 8 PSI at the RPM for peak HP
Race = .5 to 3 PSI at the RPM for peak HP
Open Headers = 0 PSI
Estimated CFM RatingComment
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Re: '64 RPO N11 Exhaust System
Russ,
I don't believe that I said this anywhere in the above post. If I did, please point out where I said so.
It is probable that you refer to that which has been common knowledge, at least around here, for years now: sidepipe mufflers are loud yet restrictive. The statement, in itself, sounds like an oxymoron, and it is, until you realize the very first sentence of my post above mentions "packaging constraints". In plain English: there is just no way to engineer an efficient (i.e.: quiet AND free flowing) muffler which will be hung adjacent to a car's rocker panels and not make the car resemble a pontoon boat.
The shape of the hypothetical muffler prohibits it. Straight-through mufflers (which are typically constructed using a perforated inner tube surrounded either with a "chambered" or fiberglass packed shell) are inherently MUCH less efficient than multiple baffle mufflers. In order to contain the necessary volume which will effectively and efficiently attenuate noise, to the level approaching that of a conventional muffler, the container's diameter would have to be on the order of at least 6" (assuming that the hypothetical muffler ran the entire 44" length of the rockers).
We didn't talk about the perforations yet. How were/are the inner tubes "perforated"? Original GM sidepipe mufflers inner tubes were formed by (probably 20-22 ga) sheet metal which was operated on by a stamp which cut rectangular louvers into it. These louvers were unattached on three sides, and attached on the fourth side. The sheet steel was then cut, rolled, and welded longitudinally. The louvers were configured such that they protruded into the flow path, so the original 1 3/4" inner tubing's ID was further choked by the rectangular protrusions. To make matters even worse, those protrusions were presented to the flow path with their open ends facing upstream! This causes great turbulence within the flow path, enhancing heat transfer to the outer shell, subsequent cooling, and resulting in decreased velocity and increased pressure. As if that is not enough, the physical protrusions effectively decreased the ID of the inner flow tube to a value somewhat smaller than 1 3/4"! Reproduction mufflers are made in much the same way, and, depending on the manufacturer, the shape of those protrusions may be rectangular (louvers as original), or triangular (like shark teeth). Some muffler companies allow you to specify the directional orientation of those projections (facing the openings downstream rather than upstream, for instance), but any variation from the standard config will result in more noise. There will be less turbulence and less slowing of the exhaust gas, and less internal pressure as a result. The cost of this is more noise.
Multiple baffle mufflers are irregularly shaped, primarily used under a car's chassis, and much more efficient at attenuating sound than long, relatively small diameter canisters which are straight-thru ("glasspacks" or "chambered") mufflers which are used along the sides of sports cars.Comment
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Re: '64 RPO N11 Exhaust System
Joe, No you didn't say that.I have just always thought that. So back in my young days when we put Doug Thorely (SP) or Hooker side pipes on our cars for better performance I am now assuming that what you say would be true of those pies also.Right?Comment
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Re: '64 RPO N11 Exhaust System
I'll have to assume that the exhausts that you used those mufflers on were offensively loud; if they were even "moderately" quiet (like the stock GM sidepipe mufflers), then they were too restrictive for a powerful engine's exhaust system.
If you used any of the straight-thru type of mufflers, either then or now (e.g.: "Cherry Bomb", "Thrush", "Hollywood", "Hooker Sidepipe", "Spiral Turbo Baffles", "Cobra-Packs", "VettePacks", or the various and sundry chambered mufflers available), then your noise level would be higher than had you fitted a conventional (multi baffled) muffler. I did NOT say that your exhaust would necessarily be more restrictive. I did say that with a straight-thru design, "quiet" and "free flowing" are mutually exclusive, by virtue of the mufflers' design. With a straight-thru muffler, decibel level is inversely proportional to restriction.
This inverse proportionality is not so with a conventional muffler, as can be proven with the advanced designs, SHAPES and SIZES of mufflers used on such cars as the 2005-2011 Corvette. With a conventional muffler, restriction can be "engineered" to a minimum, while retaining pleasing and comfortable exhaust notes. The reason is because there are multiple variables involved in multi baffled muffler design, including, but not limited to: number of baffles, number of passes, config and number of chambers, shape of baffles and chambers, but most importantly SIZE and SHAPE of the container.Comment
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Re: '64 RPO N11 Exhaust System
They were offensively loud and sounded GREAT. I loved them.Comment
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