68 deville convertible exhaust - can I put dual exhaust on the car?

[cadillac_joe]

Just curious if I can put dual exhaust on my 1968 Coupe DeVille Convertible.

[The Tassie Devil(le)]

Yes.

Bruce.

[Scot Minesinger]

One nice thing about doing that is service.  You will no longer have to drop the "Y" pipe to remove flywheel cover (shimming starter) or dropping oil pan.  Keep away from the fuel lines on passenger side.  This does help performance and gas mileage on the highway, but it does not make much difference at low rpm.

The disadvantage is you get points taken off at shows and it is usually not as quiet as single exhaust.

Recommend you make them look as factory as possible, no 1' chromed straight extensions out the back.  This will preserve value.  I might be able to send you some pictures of my 1970 DeVille RWD with my dual exhaust system.

[Gene Beaird]

IIRC, the trans crossmember only has one 'hump' for the exhaust on the passenger side. The driver's side exhaust pipe may be close to that crossmember, requiring careful alignment to keep it from hitting the crossmember. Just something to think about.

[The Tassie Devil(le)]

With regard to the trans crossmember, I would be having a look for a '68 Chevrolet or Pontiac Big Block powered vehicles to see if they has crossmembers that has the twin "humps".

You never know, what GM did back then.   One might interchange.

Bruce.

[cadillac_joe]

Thanks to everyone that responded.
I was just wondering since an add I've seen in the Self-Starter that lists...
- single exhaust for "Cadillac 1964-'74" and
- duals for "Eldorado 1967-'70"
I know they have the same motor, so was just curious there wasn't something I was overlooking/missing.

[Scot Minesinger]

All,

Got the request for pictures and will send them soon.  Tried to keep true Cadillac mounting method and make it look like it was a factory option.  The trans mount bump for exhaust is not an issue in adding dual exhausts.  The only major issue is in the back adjacent to gasoline tank if you want resonators to keep the car reasonably quiet.  The space between frame and gas tank on driver side is generous and accommodates the resonator no problem.  The space between tank and frame on passenger side is much smaller, and to avoid having a dropped resonator exhaust that looks bad and not factory, you have to use a narrow rear resonator on both sides.  Then I paint the resonators barbeque (a paint that takes high heat) flat black so they are not easily noticed when approaching car from side at a distance.  The aluminized metal really holds up and shines, and you do not want to see the bottom sliver that the rear quarter does not hide as the car is approached.

Planning to drive the Cadillac to GN in NY, and you can get a close up look there.

[Scot Minesinger]

Also, on the 67-70 Eldorado, the exhaust system in the 1970 shop manual shows two exhaust pipes (the majority of the system length) from exhaust manifold to muffler at rear (two inlet pipes) and a single exhaust pipe with resonator leaving the muffler. 

Perhaps the option to use dual exhausts uses this concept with two mufflers or dual exits out of a single muffler and dual resonators.  The long dual pipes to rear muffler instead of Y pipe was likely to accommodate front drive system.

[Scot Minesinger]

Pictures of 1970 dual exhaust system.  Did not jack up car, just crawled underneath.  Note heat shielding for fuel lines on passenger side.  Note replication of factory hangers w/orange high heat rubber.  Can only load three pictures at a time, so several responses posted.

[Scot Minesinger]

more pictures

[Scot Minesinger]

last of the pictures, let me know if you need more