off road exhaust

[Ted K.]

Bought a 68 L89 project car. Tank sticker indicates off road exhaust. What is off road exhaust? Is it under car, side exhaust, or what.
Thanks

[Gary S.]

Re: off road exhaust

My 66 had off road exhaust and it is an under car exhaust. Can't tell you the specifics but I believe it to be a bit less back pressure and a little more noise.

Gary

[Mike M.]

Re: off road exhaust

gery's got it right--off road system was installed under the car like base exhaust systems and off road mufflers had less baffles so less restriction to exhaust escape(little more horsepower) and a little louder. mike

[Bob Foster]

Re: off road exhaust

Does that mean that off road exhaust systems are street legal so long as the sound level when measured by a state authorized inspection station doesn't exceed any state allowable maximums?

[William C.]

Re: off road exhaust

A) they aren't that loud (much quieter than sidepipes for example)

B) the Government was not in the noise business back then.

[Tom R.]

Re: off road exhaust

I was going through the archives and believe I read that N11 has three baffles versus five for stock mufflers. Also, all pipes are 2 1/2 whether smallblock or big block.

[Dave McDufford]

Re: off road exhaust

For what it is worth, it is my understanding that Allen's Exhaust in Indiana build's their systems with either 5, 3, or 1 baffles in the mufflers. I bought a three baffle system for my restoration but since the restoration is not complete I have no idea how it sounds.

Dave

[Joe L.]

Re: off road exhaust

Ted-----

As others have mentioned, off road exhaust is an undercar exhaust system. 1968 was the only year for C3s that off road exhaust was available. It was not available after 1968. NO 1968 Corvette was ever originally fitted with side exhaust.

The off-road (N-11) mufflers used 2 tubular baffles instead of 3 for standard undercar exhaust. The only difference between the 64-67 N-11 system and the 68 N-11 system was the muffler hanger brackets welded on the rear of the muffler. Otherwise, the systems were the same. The 1968 N-11 mufflers/pipes assemblies were discontinued MANY years ago. However, the 64-67 pieces were available until about 6 or 7 years ago. Curiously, unlike the standard mufflers for 2-1/2" systems which were supplied for SERVICE for many years with dual brackets (i.e. for 63-67 AND 68-72 applications), the N-11 pieces were NEVER supplied with dual brackets. So, the muffler/pipe assemblies for 64-67 and 1968 were different and unique to each.

ALL N-11 systems were 2-1/2". However, for 1968, ALL Corvette exhaust systems, N-11 or standard, were 2-1/2" regardless of engine option from base engine to L-88. Of course, the forward pipes were different for small blocks and big blocks.

[Tom R.]

Re: off road exhaust

Joe:

I'm looking at muffler PRODUCTION numbers and that from 68-69 and from 70-72 a single part number was used for either model year series in all applications except N11 and N14. Yet in 73 and 74, we see a spike or proliferation in muffler part numbers by engine and transmission...what goes?

I can only imagine that once EGR was introduced, it caused more "dialing in" on exhaust gas which must have influence the baffling. Your thoughts?

[Joe L.]

Re: off road exhaust

Tom------

The 68-69 and 70-72 information that you're looking at is incorrect. For those years there were several different parts and configurations. For instance, for 69-72 there were both 2" and 2-1/2" systems used, depending upon application. Forward exhaust pipes varied by big block/small block and also manual or auto trans.

[Chuck M.]

Re: off road exhaust

So, if I am understanding this correctly, you CAN NOT have N11 off-road exhaust with side pipes? I did not know that, learn something new everyday.

[Joe L.]

Re: off road exhaust

Chuck------

Yes, that's the way it is. You absolutely CANNOT have N-11 and N-14 on the same car. For 1965-67 both N-11 and N-14 were available but, as I say, the two options could not be installed on the same car. For 1968, N-11 was available. However, N-14 was NOT available. For 1969, N-14 was available but N-11 was NOT available. After 1969, neither exhaust option was available.