What exactly is "Off Road" exhaust?

[Sams '66]

What exactly is "Off Road" exaust?

Sounds like something I might add to my Jeep.......

LoL

Sam:confused

 

[67HEAVEN]

Off Road Exhaust was Chevy's way of implying louder than normal, and those naughty boys ordering same should be sure to race their cars "off the road" on race tracks.

 

[Sams '66]

ahhh Haaaa
So .......it is more open? and lots louder?
Or chambered just for the noise?

Sam

 

[SebringBill]

For my 57 (and through 62) the mufflers were round instead of oval. I believe that the "off road exhaust was less restrictive, hence louder. I like the sound of mine both at idle and at speed.

 

[Dave65]

The mufflers had three baffles rather than the five on the normal mufflers. Otherwise they looked identical.

Dave

 

[396 RAT]

I have never had 'em, but I thought off road exhaust was a chambered system that exited out the rear?

 

[bossvette]

I had "off road exhaust " on a 69 z-28 and they were chambered pipes that exited from the rear.

 

[Sams '66]

Sounds like it is an exsaust system that is louder and more restictive??
Reduces performance?.....like side pipes?


Sam

 

[78SilvAnniv]

Sounds like it is an exsaust system that is louder and more restictive??
Reduces performance?.....like side pipes?
Sam

Nah...more like louder, less restrictive and more performance.
That is what I experienced with my switch to chambered exhaust which is termed "for off road use only".

I think FORUO is a legal term that absolves the manufacturers/providers of responsiblity towards smog changes to on-road vehicles, since legally (Federal) we are not supposed to change any emissions on our vehicles.
Heidi

 

[Tom Bryant]

As Dave said the off road mufflers for the midyears looked just like the standard mufflers but were less restrictive. Sounded great too. This was option code N11. Side mounted exhaust was chambered and was option code N14. The off road mufflers for the solid axles were round and had 2 smaller tubes straight through with no baffles. They didn't have a seperate option number but came as standard equipment on the high horse fuelies.

The chambered exhaust used on Camaros and 442s and maybe other GM muscle cars was made up of the same chambered type pipe sections as the Corvette sidepipes (midyears). This was developed by Walker and they still sell it in replacement muffler configuration under the brand name Walker Turbo Tubes (also NAPA). Off road refers to 2 different type of systems here. As a matter of fact N14 Side Mounted Exhaust was footnoted in the parts manual as off road use only also.

Tom

 

[78SilvAnniv]

Tom,
Is the For Off Road Use Only exhaust you are discussing different from what I am thinking it is?

It seems from your comments that FORUO exhaust could be ordered for the early vettes, but by today's definition (my understanding) we are not supposed to change anything about the emissions and companies who sell the exhaust use FORUO as a disclaimer?
So...you used to be able to have FORUO installed at the factory, and now you must use-at-your-own-risk according to the disclaimer?
Heidi

 

[Tom Bryant]

That's about it Heidi. Pre-emission era cars used the off road disclaimer mostly because they were kind of loud. Now it can mean that the exhaust is louder lthan is commonly accepted by law enforcment and also that it isn't emissions certified.

Tom

 

[78SilvAnniv]

Thank you!
I see that I was on a TOTALLY different page than everyone else...but I learned something new.
Heidi

 

[bossvette]

Back in the good ole days us old f***ts remember It was like Tom said you could order "Off Road" exhaust and other go fast parts from the manufacturer, which simply meant they were louder and or more performance orientated not for normal street driving. The first Corvette I ever had a ride was a 65 396 Big Block with the 425 HP engine and had side pipes(off road) and 4.56 rear gears(gas was $.30 a gallon for high test) It would pin you back in the seat thru most of third gear.
As emissions laws took over the term "Off road use only" came to be a disclaimer that aftermarket manufacturers used so they could sell their "illegal equipment" The larger companies have the resources to become "50 state legal" while the smaller ones don't.
the 69 z-28 I had was equipped with "off road" exhaust, camshaft and had dealer installed headers with 4.11 gears beyond the standard z-28 package. As long as you kept it under 3000 rpm it drove like your grandmas 6 cylinder after 3000 was a different story.

 

[wallyknoch]

Off road exhaust was included with the fuel injection at no extra cost for the 1962 Vettes. Look close to seventh line down, which reads, 441A off road exhaust. cost $00.00. Close to 3000 cars were so equiped and that probably included some or all of the 340 cars too. This is a true copy of my dealer invoice that I found in my old law school notes about a week ago. I have been looking for it for years and if I still had it, the notes were a logical place to look and I finally got lucky.

 

[Sams '66]

That is very cool!
Thanks for sharing!
Sam

 

[Tom Bryant]

What a great find. I was going by the NCRS Spec Guide where it doesn't list an RPO number. It makes sence that it would have to have a number but was standard on the FI and 340 and not listed where you could check the box and get it on the base engine.


I have the off road system on my '59. Bought all the pieces from GM in '73 when I got my first Chevy parts job. I use the 2 1/2" FI manifolds and '62 pipes/off road mufflers back to the '59 tail pipes. I love the sound. Nothing like it. I have read some sources that say the off road mufflers were introduced in '62 but I think they are confused with the introduction of the 2 1/2" manifold. '62 may have been when the last incarnation of that muffler was introduced though.

My Oct '72 parts book lists mufflers pn 3813533 and 3813534 (LH and RH respectively) with footnotes A (w/ High Perf., Special High Per., and F.I., C (w/exhaust pipe extension), and E (For off road service and track use only) for the '62 Corvette. This would cover the 300, 340 and 360 hp cars. I would be interested to see if there are documented 300 hp cars with off road mufflers. The same part numbers are listed for '56 through '61 with basically the same discription. The difference is they are only footnoted for Dual/4bbl and FI with high lift cams. The base engine and Dual 4/bbl and F.I with hydraulic cams get the low noise muffler.

In another Chevy parts catalog that includes Corvette (dated April 1 1960) I find the off road mufflers listed as '57 Corvette and '58-'60 Corvette with high lift cam. These part numbers are 3736957 and 3737644 LH and RH respectively. The footnote says that the corrosponding low moise muffler can be substituted at the customers option. this would be as a dealer ordered replacement and not at the time of ordering the car.

The mid year off road mufflers were pn 3845735 and 3845736. These were the same on all '63-'67s including '65-'67 big blocks (all 2/1/2" mufflers). '68 was the last year for off road mufflers showing pn 3831803 and 3831804.


Tom

 

[wallyknoch]

The original mufflers were 2 1/2 inlet and 1 7/8 outlet. The closest sound that I could obtain from the originals were Walkers. Several years ago I went to a complete stainless exhaust 2 1/2 inlet and 2 1/4 over the axle and went straight out the back. The mufflers we used were the so called Walker Hollywood tube type short mufflers. They are noisy but acceptable. Hell of a nice lope and sound at around my 850 idle. Forget about the radio, it can never make that sound Tom.

 

[JohnZ]

I have read some sources that say the off road mufflers were introduced in '62 but I think they are confused with the introduction of the 2 1/2" manifold. '62 may have been when the last incarnation of that muffler was introduced though.

Tom

There were lots of "functional" service applications for the round off-road mufflers (as listed in the parts book), but in production, all '56 and '57's had round straight-through mufflers, and all '58-'62's had oval reverse-flow mufflers EXCEPT 62's ordered with RPO 441 "off-road" exhaust (the only year it was available as an option from the factory, and about 20% of production was ordered with it).

 

[396 RAT]

I am in the process of trying something new.
STS Baffles. Several C3 Folks use the 4" baffle with Hooker side pipes.
C2 folks with stock side pipes use the 3.5 set up.
And while at the "dyno day" last Sat. the shop owner
had nothing but praise for them.
(25-30 midyrs all turning the big wheel)
Results will shown in the Corvette Fever mag, and
http://www.midyear.org/
It gave all of us some insight on our cars, and was an absolute blast.
So, I am building a full 3 1/2" side pipe system off my headers under the stock covers. Have tried the restrictive (off road exhaust) and Glass packs. (side pipe car)
This should be my last time fooling with my exhaust.
Here is the link,

http://www.spiralturbobaffles.com/customers.html

If you look around on it, you will see some dyno
comparisons. Sat. my (retarded timing to run 91) car made 300.3 RWHP at 5750, (I know, they let off way too soon as it was still climbing)
and 335 RWTQ at 3800. Will run my car with the exhaust swap, and let you know the results. According to Superior Automotive
in Anaheim the new exhaust & a little tuning it could be worth an easy 50+ RWHP.
On 502's they said they see 70+ RWHP (uncapped) going from Hooker side pipe inserts to STS Baffles.
Should be a fun experiment either way!
BTW as far as HP or Torque goes chabmered exhaust sucks.
Sad but true.... Have a brand new GM set in the rafters
with stock manifolds just in case it ever becomes a trailer queen.
)