It sure is a shame about the 4.5 and 4.9 not being hotrodable

[osiris]

There's some dude on another Caddy site that apparently has a Hell of a nice running 4.9 liter Seville like Fred mentioned.

[WarrenJ]

Absent a link, we'll never know about it.

Care to provide one?

[Cadillac Jim]

If I wanted to pump up a 4.9, there are lots of parts out there, and even complete engines. There is an old mention on our links page:

Prestige Engine Co.

214-905-9933

They custom manufacture high performance 4.1, 4.5 & 4.9 Cadillac block engines in a variety of configurations. I do not know if they do Northstars or not.

If I wanted a quick, simple Cadillac sleeper, I would get one of the LT1 cars cheap, like Ed Hall says, and an LS7 (427 cid, 505 hp) or other less expensive small-block crate engine, a transmission beef-up or upgrade, and a custom exhaust system (see below). Suspension and brake upgrades would be appropriate. For the current GM crate engines, see

http://www.gmpartsdirect.com/perfPackages....l=Crate+Engines

The exaust can be a simple 2.5" with dual low-restriction catalytic converters and something like Borla Pro XS mufflers to the stock tips, or it can be a custom ultra-quiet to make a true sleeper. It might go something like this: high performance headers, dual low-restriction cats, optional Borlas or equivalent, then a large transverse cutom-built collector/resonator that emulates the outside to the performance exhaust system, and then some quiet low-restriction mufflers to the tips.

This will keep you in the $10K-$15K range for the whole project, unless you go for the LS7, which will add nearly $10K to it over other small block crate engines.

Borla, Edelbrock, and others will sell you a crate engine to your specifications and a price appropriate to those specifications, and work with you on the installation and exhaust.

[The Fred]

I don't want cats on my car,

My reason for not wanting cats is an odd one but here goes

The exhaust doesn't smell as good with cats

*shrug*

[Cadillac Jim]

If the cats are part of an overall system, including EGR and possible A.I.R or whatever, it actually should smell better. I remember early catalytic converters in the 1970's that would leave a sulfur smell sometimes. But, after the engine redesigns were complete about 1976 or so, the exhaust is very clean and odor-free, and it should be on modern cars. However, if your sense of smell is unusually acute, you may differ.

The catalytic converter also offers a dual function as a resonator in most cars. This means that the header up to that point has a pressure release point, or a known reflection coefficient, and the header to that pont can be tuned to offer peaks in the torque curve. This allows placement of the mufflers near the rear of the car where the silencing operation is less audible inside the car. And, the long tube(s) between the cat and the mufflers allows a low-frequency resonance that can be the key to oomph off the line. If you take out the cat, you need to replace it with a similarly-sized resonator. The reflection coefficient (percentage of gas blast pressure that is reflected each time a cylinder fires) won't be the same, so some change in the torque curve can still be expected. Remember, when The Fred took off his cat to see if it was obstructing, the motor had no torque.

Note that, for racing systems, exhaust system manufacturers generally say to put the racing muffler within 18 inches of the last collector in the header(s). That's where the cat is in most cars.

[The Fred]

I like a sulphur smell.. also love diesel smell

I'm odd

[Bill K]

The Cats are there to (in the long run) protect your lungs and ours.

Not everyone wants to smell your gas.

[Texas Jim]

The catalytic converter also offers a dual function as a resonator in most cars. This means that the header up to that point has a pressure release point, or a known reflection coefficient, and the header to that pont can be tuned to offer peaks in the torque curve. This allows placement of the mufflers near the rear of the car where the silencing operation is less audible inside the car. And, the long tube(s) between the cat and the mufflers allows a low-frequency resonance that can be the key to oomph off the line. If you take out the cat, you need to replace it with a similarly-sized resonator. The reflection coefficient (percentage of gas blast pressure that is reflected each time a cylinder fires) won't be the same, so some change in the torque curve can still be expected.

Remember, when The Fred took off his cat to see if it was obstructing, the motor had no torque.

I totally agree about changes to the exhaust system affect the torque curve.

I had a low restriction dual exhaust system installed on my 2002 Taurus, replacing the stock single exhaust.

It had almost ZERO torque. Also was way too loud inside the car. Loud drone at cruising speed. Took it back and had them add a resonator which brought the noise to a acceptable level. But still no torque off the line. Above 4000 RPM it would scream. Chirp the tires on 1-2 shift. Below that almost nothing.

Disconnected the battery several times ... sometimes for several hours. FINALLY it relearned the new setup. Then it regained "MOST" of the torque it had lost. Now from 2500 on up it is a lot stronger than it used to be.

That experiance is about the only reason I have not went with performance mufflers on my '06 DTS. It runs real strong and I don't want to mess it up. You have to be pretty careful at a light or you will chirp the tires just taking off more or less normally.

[Cadillac Jim]

The hot setup if you are adding a dual exhaust to a FWD car, V6 or V8, is to have a low-restriction catalytic converter within 18 inches of where each header goes to one pipe, then a long piple to the back of the car, with performance mufflers under the trunk. Of course, I'm assuming that you are getting peformance exhaust headers, and you should work with the vendor about selection and placement of the catalytic converter. These guys may be less concerned with the bottom end.

The exhaust system resonances can be considered as happening in several places, most notably: between the ports and the cat, and between the cat and the mufflers. There are two types of resonances: volume and length. volume resonances occur at frequencies determined by the volume and the reflection coefficient at the bouandaries of the cavity. Length resonances occur when the quarter wavelength or half wavelength of sound at the exhaust frequency matches the avaiable length, with adjustments for the reflection coefficient at each end. At the header end, you may consider the reflection coefficient at the ports to by 1.0 when the valves are closed but near zero when the valves are open, so you may get two length resonances out of the header. There is often a collector where the four piples go to one, and this is usually a pressure release point, separating the length resonances in the header -- but not the volume resonance.

The frequency is determined by the firing rate, not half the firing rate, unless you have a really exotic header that hooks to cylinders that fire every other time. For a 1-8-4-3-6-5-7-2 firing order, the headers would need to hook to 1, 4, 6, and 7, then to 2, 3, 5 and 8, for example -- somthing I've never seen done. A really tood 8-to-4-to-two-to-one equal-length header would work best, which is why they use them in racing, but they take too much space to use in street cars. Thus the frequency is the RPM divided by 60, then multipled by half the number of cylinders. For a V8 at 2200 RPM (typical GM cruise), this is just under 150 Hz. At 5,500 RPM we have 367 Hz. Half-wavelength would be about 18 inches. Thus the 18-inch recommendation for the lenth from the collector to the first resonator or catalytic converter.

[Texas Jim]

The hot setup if you are adding a dual exhaust to a FWD car, V6 or V8, is to have a low-restriction catalytic converter within 18 inches of where each header goes to one pipe, then a long piple to the back of the car, with performance mufflers under the trunk. Of course, I'm assuming that you are getting peformance exhaust headers, and you should work with the vendor about selection and placement of the catalytic converter. These guys may be less concerned with the bottom end.

The exhaust system resonances can be considered as happening in several places, most notably: between the ports and the cat, and between the cat and the mufflers. There are two types of resonances: volume and length. volume resonances occur at frequencies determined by the volume and the reflection coefficient at the bouandaries of the cavity. Length resonances occur when the quarter wavelength or half wavelength of sound at the exhaust frequency matches the avaiable length, with adjustments for the reflection coefficient at each end. At the header end, you may consider the reflection coefficient at the ports to by 1.0 when the valves are closed but near zero when the valves are open, so you may get two length resonances out of the header. There is often a collector where the four piples go to one, and this is usually a pressure release point, separating the length resonances in the header -- but not the volume resonance.

The frequency is determined by the firing rate, not half the firing rate, unless you have a really exotic header that hooks to cylinders that fire every other time. For a 1-8-4-3-6-5-7-2 firing order, the headers would need to hook to 1, 4, 6, and 7, then to 2, 3, 5 and 8, for example -- somthing I've never seen done. A really tood 8-to-4-to-two-to-one equal-length header would work best, which is why they use them in racing, but they take too much space to use in street cars. Thus the frequency is the RPM divided by 60, then multipled by half the number of cylinders. For a V8 at 2200 RPM (typical GM cruise), this is just under 150 Hz. At 5,500 RPM we have 367 Hz. Half-wavelength would be about 18 inches. Thus the 18-inch recommendation for the lenth from the collector to the first resonator or catalytic converter.

JIm,

Thanks for the information. I am gonna save it for future referance.

On the Taurus, I think the system ended up being TOO efficent, if thats possible. One of the mistakes I made, (against the recomendation of the muffler shop owner) was I wanted 2 1/2 inch pipe from the cats all the way back to the dual Flow Masters at the rear bumper. The exhaust ends of the cats were opened up to match the 2 1/2 inch pipe I wanted. The original pipe was 1 3/4. He did it EXACTLY the way I wanted it, but that was probably not the optimal way it should have been. I can only blame my own stupid self for THAT.

I am a lot more used to working with 7 liter engines than I am with 3 liter. Big motors need big exhausts. I translated the same thing to the 3 liter Ford and it didn't work too well.

If I am reading yout post correctly, I messed up the resonance on it big time. Also the volume ratio.

Anyway, thanks again for the info.

Do you have any idea if the mufflers on the 2006 regular DTS and the Performance Sedan are the same ?

[Cadillac Jim]

If the original system had 1 3/4" piping on a single, then 1 3/4" dual would probably have been a good starting point. It sounds right for a 3 litre engine. What you were probably missing was the low-frequency resonance in the long pipe between the cat and the mufflers.

I don't have the formula for volume resonance handy, but it's really low. If you had too much volume and not enough length in the cat-back pipe, then you have lost two resonances. That would account for a lack of bottom end. Resonances in the intake manifold are at very high RPM because the runners can't be more than a foot long. Some 32-valve engines, like the Corvette, actually resonate one intake runner at a slightly different RPM than the other to broaden the torque peak just below redline; with a close-ratio transmission this trick can dramatically improve performance. There may be a volume resonance in the intake plenum behind the throttle body, or in the total piping between the air cleaner and the intake runners. That would give you two resonances, one at light throttle and an even lower RPM at WOT -- the tire-chirping throttle-blip resonance.

Look at the exhaust sites for cubic feet per minute (CFM) capacities required for different engines. It's a revelation if you run the numbers. With a dual 3.5" system on a 3 liter engine, for example, you would have an exhaust volume of perhaps 300 CFM, or 150 CFM per side, at 5,000 rpm. With dual 2 1/2" pipes, the exhaust gas would travel at about 50 mph. Using 1 3/4" pipes would double that. This is very crude, and the velocity slows as the gas cools. But, yes, you should have listened to the muffler guy.

It's not too late. You have another car now. Remember, the Northstar is a small engine too. You need only about 300 CFM per side. Two-inch is probably enough for a dual exhaust system. The stock system for my 1997 ETC uses 2 1/4" in the cat-back pipe and 2" after the Y.

[Cadillac Jim]

Sorry, I forgot to address your main question. I don't know whether the mufflers on the DTS are the same as other Devilles, but I would suppose that they are. On the 1993-1999 Northstars, the only differences in the whole powertrain for the Touring system cars was the intake cams, the final gear ratio, and the PCM programming, which probably could be changed back and forth by toggling a bit by a dealer's code reader (or programming with VIN from a VIN Y or VIN 9 car).

[Texas Jim]

If the original system had 1 3/4" piping on a single, then 1 3/4" dual would probably have been a good starting point. It sounds right for a 3 litre engine. What you were probably missing was the low-frequency resonance in the long pipe between the cat and the mufflers.

I don't have the formula for volume resonance handy, but it's really low. If you had too much volume and not enough length in the cat-back pipe, then you have lost two resonances. That would account for a lack of bottom end. Resonances in the intake manifold are at very high RPM because the runners can't be more than a foot long. Some 32-valve engines, like the Corvette, actually resonate one intake runner at a slightly different RPM than the other to broaden the torque peak just below redline; with a close-ratio transmission this trick can dramatically improve performance. There may be a volume resonance in the intake plenum behind the throttle body, or in the total piping between the air cleaner and the intake runners. That would give you two resonances, one at light throttle and an even lower RPM at WOT -- the tire-chirping throttle-blip resonance.

Look at the exhaust sites for cubic feet per minute (CFM) capacities required for different engines. It's a revelation if you run the numbers. With a dual 3.5" system on a 3 liter engine, for example, you would have an exhaust volume of perhaps 300 CFM, or 150 CFM per side, at 5,000 rpm. With dual 2 1/2" pipes, the exhaust gas would travel at about 50 mph. Using 1 3/4" pipes would double that. This is very crude, and the velocity slows as the gas cools. But, yes, you should have listened to the muffler guy.

It's not too late. You have another car now. Remember, the Northstar is a small engine too. You need only about 300 CFM per side. Two-inch is probably enough for a dual exhaust system. The stock system for my 1997 ETC uses 2 1/4" in the cat-back pipe and 2" after the Y.

Thanks again for the reply and the (extra) information. I will remember it and try not to make the same mistake I made before. I may learn slow but I learn GOOD.

I wrote down the number of the Corsa mufflers you recommended in another thread.

I may try them on the '06 DTS. I have some exhaust sound now and have kinda been wondering if maybe it already has low restriction mufflers on it. My brother in law remarked on it, said it surprised him that he could hear the exhaust when driving.

Will check with the dealer to see if all 06 DTS's use the same muffler.