Hmmm. Now i'll have to actually measure the bar on my 92.......
I'll try to get time to do that tomorrow and post back.

 

Ah, exhaust upgrades, one of my favorite little sins on Caddy's. On my last one (the '87 Coupe), the exhaust was literally falling off when I got it so I immediately put a whole new exhaust on it, mostly stock parts, but for the muffler I went with a high performance Flowmaster. That was amazing. Very quiet at idle, just the right amount of burble when cruising, but when you stomped on the throttle it just freaking roared. My '89 still has it's original factory exhaust on it, and I just haven't been able to bring myself to chop it off since it is still in pretty decent condition.

Whenever I do replace it though, I already have it all picked out. And as far as I know, there's no easy or practical way to run a true dual exhaust on the 4.x motors, with perhaps the one exception of dropping it off at a shop that specializes in custom performance exhaust systems, and handing them a blank check because way too much stuff would have to be custom fabricated.

However, I do know a great way to fake it, the muffler from a V6 Camaro/Firebird is the perfect match for the 4.1 and 4.5 motors, same pipe size, about the same case size and a good performance match to the motor, and they utilize a single inlet, dual outlet design. Any muffler shop should be able to easily fabricate a pipe over to the other side for a second tail pipe, and I have a nice set of chrome turn downs picked out. However, there is one problem with your 4.9, they increased the diameter of the exhaust system, and with the obvious increase in horsepower I don't know if the muffler would be an appropriate match. Possibly someone makes a compatible muffler for anyone who's seriously upgraded their V6 Camaro/Firebird, although most people don't bother, they usually just swap in a V8.

Anyways, when I do that swap to mine, I'm going to go with the Magnaflow muffler and high performance cat. I stumbled onto someone who had done just the muffler to his '90 Deville and had posted a video of it to youtube. It looked like a dual exhaust, and sounded amazing. I'll try to find the link and post it, it's worth checking out unless you're absolutely set on a true dual exhaust system. Honestly though, I think the only time I've come across one of these motors with a true dual was one that had been dropped into a Pontiac Fiero. (Fiero guys apparently love the Cadillac 4.x motors, and Northstar motors.)

 

Here's the clip, apparently he did it with the Flowmaster version of the muffler, but the sound should be similar. He did the tailpipes straight out, but like I said I want to use turndowns so that it maintains somewhat of a stock look.

 

I have a flowmaster that I saved off of a mid 90's camaro that had a 3" single with 2.25" dual outlets and Magnaflow tips. That is probably the route I will go. Would just be nice to come up with a bit better design off the manifolds to actually make use of bigger pipe for the flow and not just the look.
Funny you bring up the Fiero guys, that is what I originally bought the Deville for. But I ended up driving it after I sold my Suburban and decided I liked it so I did the rear suspension, gas tank, etc. and just continued driving it. But if im going to continue driving it I need to personalize it a bit. Im hoping to find a crashed one to keep around for spare drivetrain if and when the time comes that its needed.
Im hoping to find the STS or Eldrado that I was looking for and still havent found. They all seem to have a pile of issues or are priced way beyond actual value around here.
That video didnt sound bad, definately the typical Flowmaster sound though.

 

schlicky13,

You're in for a treat with the heater core, been there!

The very worst part is the clamps on the core in/out tubes on the firewall. You wouldn't think that could be so hard. It wouldn't be if there was enough space to work - there isn't.

Also, be sure to get the heater door adjusted properly as it is too easy to bump off adjustment by accident.

I left the plastic cover off under the dash until I was sure it was properly adjusted. That cover alone is a pita.

Good luck!

 

Well, most probably you should make sure that you have closed that properly Also, be sure to get the heating unit modified effectively as it is too simple to push off modification by chance.