Quiet, high flow, legal exhaust?

I am planning to get a better exhaust for my '96... The downpipe from ZZP is 48-state legal, as I may move to CA, it is out of my league right now... Is there any exhaust that would give me slightly more hp while being quiet and 50-state legal? Exhausts from name brands or other GM cars?

The most obvious improvement for the exhaust would be headers. I bought some on Ebay for around $200. Since each cylinder will now have more room to push out exhaust gas, you can actually drop a couple of pulley sizes on the supercharger, maybe a 3.6 or 3.5.
If you do get headers, make sure to buy the transmission dipstick from a W-body car like the Buick Regal. The tranny dipstick on the Riviera will sit right against the header tube and get burned.
One thing to keep in mind, adding headers will and a smaller pulley will result in more horsepower, but in less torque. Before the headers I could easily spin the tires when hitting the throttle. After the headers not so much.
As far as exhaust sound, I removed the OEM mufflers to get more sound, and I liked it for a while, but on long trips the loud drone sound has gotten annoying.
I am actually about to replace the OEM muffler to get it to quiet down again
I say 'muffler' not 'mufflers' because I'm gonna replace the Y pipe after the resonator for a single exit pipe. It's the OEM pipe for a 98 and up Buick Park Avenue.
I'm curious about how it will affect performance but I don't think it will change too much. Fingers crossed

OrangeCat3800 wrote:

 I am planning to get a better exhaust for my '96... The downpipe from ZZP is 48-state legal, as I may move to CA, it is out of my league right now... Is there any exhaust that would give me slightly more hp while being quiet and 50-state legal? Exhausts from name brands or other GM cars?

I had this problem some time ago.

I put on a larger downpipe, and a piece of aluminum flashing over it to serve as a heat shield b/c the pipe runs real close to the firewall.  Depending on whose pipe you get, this may or may not be a thing for you.

I tried a custom exhaust but it droned.  I sold it to a friend who liked the drone (and who does not drive his Riv on the highway all that much)

I got an exhaust made for my Riv by GM.  This was about 10 years ago.  It was custom made, but 'custom' is a polite stretch - by law carmakers have to provide spare parts for cars they sell in the USA, for 10 years.  I think it was 2012 (I don't have my maintenance log on me ATM).  Abaddon mentioned that the Park Avenue exhaust(s) fit the Riv (pretty much). I went to my nearby GM dealer and asked Parts to order one for me.  They noted in the memo field on the order that the exhaust was for a Riv and entered my VIN.   Because there were no exhausts around for the 2004 PA Ultra - so by law GM had to make one.  My exhaust was made at GM's Wixom Performance plant in Wixom, MI.  I still have the build tag for it.  It is a one-piece, cat-back unit, and showed in the GM catalog as a "catalytic converter."  Yeah right, a cat that comes with the exhaust pipes, tail pipes and mufflers, and new elastomeric hangers, crated for shipment by truck to anywhere.   It **JUST** fit the Riv.  I had to push the mufflers up under the rear bumper fascia.  They fit fine but they extend above the fascia; they kinda snap into place then you slip the hangers on.  The folks at Wixom were nice enough to make sure the hanger pins were all in exactly the right places.  But... The bung for the oxy sensor was/is about 4" or 5" off; the OE wire pigtail fits with no issues whatever. I made a splash shield extension for it out of aluminum coilstock and popriveted it onto the existing steel shield.  That's been fine for a decade.

The thing is, the PA Ultra exhaust is darn near silent but breathes with excellence.  With the stock exhaust I had a flat spot in acceleration around 2000 - 2100 RPM.  I'd be pulling onto a highway and around that speed the engine's acceleration would slow to a crawl; holding the accelerator down the car would eventually start accelerating again.  *Not* with the PA exhaust, it just screams along.    

The other thing - the 3800 on the Riv already has a rear header, effectively. Look at it from under teh car. It's just not tuned with equal length runners; it's a group of short tubes.  I got some improvement doing what some of the folks on this list suggested - porting the *front* manifold.  What happened - my original manifold cracked enough to throw codes.  It took a while to find it though, the crack was on the pavement facing side of the manifold near the ignition module.  I looked at buying a powerlog but they were out of them at ZZP with no backorder fulfillment estimate.  Soooooooo... I got a junkyard OE manifold (I had read I should avoid the new replacements in favor of a new or used original) and using the new gasket as a template I ported it using a Dremel and grinder bits.  Hee hee, I shoulda done that way sooner, it worked a treat.  

The 3.6" pulley would be fine, just be sure to burn Premium.  

Albertj

Thanks AlbertJ for the info! Glad it worked out for you. What was the part number of the one piece exhaust GM made for you? My 99 Riviera has the flat spots in acceleration as you mentioned. The mufflers have been replaced by the PO. They appear to be AP brand. I would like to go back to an all stock setup. The PAU exhaust seems to have worked for you. That’s the route I would like to take. Please advise Thanks again
Vince

VinnyD wrote:

Thanks AlbertJ for the info! Glad it worked out for you. What was the part number of the one piece exhaust GM made for you? My 99 Riviera has the flat spots in acceleration as you mentioned. The mufflers have been replaced by the PO. They appear to be AP brand. I would like to go back to an all stock setup. The PAU exhaust seems to have worked for you. That’s the route I would like to take. Please advise Thanks again
Vince

I thought I knew where the tag was last night but didn't find it. I will look again tonight. There *might* be a scan of it on this site, look in the exhaust sections maybe.

Those AP mufflers on your car might have come to it via rock auto.

In the meantime, the base part number was for the 2004 Park Avenue Ultra with the dual exhaust option including stainless steel tips. I think 25749911 was the one with plain tips. Which woulda had the same mufflers.

Found the tag - interesting, my # was in fact 2574911.   Pack station was GM SPO, 4400 West Mt. Hope Rd, Lansing MI 48917.  I have not located the build decal yet, it shows the build location was Wixom. My old posts about it are around here: https://rivperformance.editboard.com/t2258p315-faq-the-exhaust-thread

VinnyD wrote:

Thanks AlbertJ for the info! Glad it worked out for you. What was the part number of the one piece exhaust GM made for you? My 99 Riviera has the flat spots in acceleration as you mentioned. The mufflers have been replaced by the PO. They appear to be AP brand. I would like to go back to an all stock setup. The PAU exhaust seems to have worked for you. That’s the route I would like to take. Please advise Thanks again
Vince

Just checking in on your exhaust situation.

Albertj

Thanks Albertj for checking. I bought an exhaust manifold from zzperformance. Just got it Wednesday. Can’t wait to install it!
Didn’t want to spend that much but you know how that goes.
Thanks for providing the part number from your exhaust. I’m hoping the manifold will make a noticeable improvement. I will make a decision about replacing the mufflers after driving for a while with the new manifold. How is your riviera? Have you had time to work on your Volvo?

VinnyD wrote:

Thanks Albertj for checking. I bought an exhaust manifold from zzperformance. Just got it Wednesday. Can’t wait to install it!
Didn’t want to spend that much but you know how that goes.
Thanks for providing the part number from your exhaust. I’m hoping the manifold will make a noticeable improvement. I will make a decision about replacing the mufflers after driving for a while with the new manifold. How is your riviera? Have you had time to work on your Volvo?

Which mani did you get, front, rear, or both? I installed a front ZZP manifold and it doesn't sound much different but the power band is better for sure

VinnyD wrote:

Thanks Albertj for checking. I bought an exhaust manifold from zzperformance. Just got it Wednesday. Can’t wait to install it!
Didn’t want to spend that much but you know how that goes.
Thanks for providing the part number from your exhaust. I’m hoping the manifold will make a noticeable improvement. I will make a decision about replacing the mufflers after driving for a while with the new manifold. How is your riviera? Have you had time to work on your Volvo?

The ZZP manifold will make a noticeable difference, but not necessarily more than simply porting the cast manifold. You could tell on a dyno I think, but not a butt dyno.

Oh, the Volvo... I ordered some fuel injectors that are stuck in FedEx (in this rural area they have problems retaining drivers - not for any bad reasons, it's just that around here the labor market at $25 and under/hour that will pass employment screening is *really* tight at the moment). There is a fellow in Albany who'll overhaul them for me, then we'll install them. Between that and the new fuel rail should fix the misfire and I'll be driving it. Oh - I'm getting a couple connectors for the injector wiring in case I bugger any pulling the current ones. I think it'll be end of next week before those injectors are done. Fellow in Albany says the OE Denso injectors are, in general, among the best he's seen on any passenger vehicle.

The only remaining issues are the PS rack (important but not immediate urgency) and a filter for the transmission.

The Riviera is fine. I had the local GM dealer do the NY state inspection (passed, no issues), and I replaced the drivers side front wheel bearing with an SKF. Did both front wheel bearings with SKFs back in 2016, so I guess after being in service for about 90,000 miles (around 6 years) the drivers' side WB had had enough of highway driving. We'll see how soon I can sell the Riv.

Spacecowboy067 wrote:

VinnyD wrote:

Thanks Albertj for checking. I bought an exhaust manifold from zzperformance. Just got it Wednesday. Can’t wait to install it!
Didn’t want to spend that much but you know how that goes.
Thanks for providing the part number from your exhaust. I’m hoping the manifold will make a noticeable improvement. I will make a decision about replacing the mufflers after driving for a while with the new manifold. How is your riviera? Have you had time to work on your Volvo?

Which mani did you get, front, rear, or both? I installed a front ZZP manifold and it doesn't sound much different but the power band is better for sure

I just got the front mani. Glad you have more power now. Hope to have the same result with mine. I think I have an exhaust leak in that area. My exhaust sounds louder than stock. It has aftermarket mufflers on which is not something that sits well with me!

VinnyD wrote:

Spacecowboy067 wrote:

VinnyD wrote:

Thanks Albertj for checking. I bought an exhaust manifold from zzperformance. Just got it Wednesday. Can’t wait to install it!
Didn’t want to spend that much but you know how that goes.
Thanks for providing the part number from your exhaust. I’m hoping the manifold will make a noticeable improvement. I will make a decision about replacing the mufflers after driving for a while with the new manifold. How is your riviera? Have you had time to work on your Volvo?

Which mani did you get, front, rear, or both? I installed a front ZZP manifold and it doesn't sound much different but the power band is better for sure

I just got the front mani. Glad you have more power now. Hope to have the same result with mine. I think I have an exhaust leak in that area. My exhaust sounds louder than stock. It has aftermarket mufflers on which is not something that sits well with me!

Well a leak is certainly possible, especially after getting that front mani on. A lot of guys complain it doesn't seal well so they use either rtv or a metal gasket. I'm lucky and mine must've sealed pretty well so no problems here. I know porting would effectively be the same job but for $100 it was totally worth just bolting a new one up, plus now a can use the old one as a spare or club or something

Spacecowboy067 wrote:

VinnyD wrote:

Spacecowboy067 wrote:

VinnyD wrote:

Thanks Albertj for checking. I bought an exhaust manifold from zzperformance. Just got it Wednesday. Can’t wait to install it!
Didn’t want to spend that much but you know how that goes.
Thanks for providing the part number from your exhaust. I’m hoping the manifold will make a noticeable improvement. I will make a decision about replacing the mufflers after driving for a while with the new manifold. How is your riviera? Have you had time to work on your Volvo?

Which mani did you get, front, rear, or both? I installed a front ZZP manifold and it doesn't sound much different but the power band is better for sure

I just got the front mani. Glad you have more power now. Hope to have the same result with mine. I think I have an exhaust leak in that area. My exhaust sounds louder than stock. It has aftermarket mufflers on which is not something that sits well with me!

Well a leak is certainly possible, especially after getting that front mani on. A lot of guys complain it doesn't seal well so they use either rtv or a metal gasket. I'm lucky and mine must've sealed pretty well so no problems here. I know porting would effectively be the same job but for $100 it was totally worth just bolting a new one up, plus now a can use the old one as a spare or club or something

$100 is a really good deal space cowboy!
I have not yet installed the new mani so the exhaust leak will hopefully be quieted with the new zzp front mani. Thanks for the tips though! I’m waiting for the new manifold and crossover bolts to arrive. Good luck with your Riv!

VinnyD wrote:

Spacecowboy067 wrote:

VinnyD wrote:

Spacecowboy067 wrote:

VinnyD wrote:

Thanks Albertj for checking. I bought an exhaust manifold from zzperformance. Just got it Wednesday. Can’t wait to install it!
Didn’t want to spend that much but you know how that goes.
Thanks for providing the part number from your exhaust. I’m hoping the manifold will make a noticeable improvement. I will make a decision about replacing the mufflers after driving for a while with the new manifold. How is your riviera? Have you had time to work on your Volvo?

Which mani did you get, front, rear, or both? I installed a front ZZP manifold and it doesn't sound much different but the power band is better for sure

I just got the front mani. Glad you have more power now. Hope to have the same result with mine. I think I have an exhaust leak in that area. My exhaust sounds louder than stock. It has aftermarket mufflers on which is not something that sits well with me!

Well a leak is certainly possible, especially after getting that front mani on. A lot of guys complain it doesn't seal well so they use either rtv or a metal gasket. I'm lucky and mine must've sealed pretty well so no problems here. I know porting would effectively be the same job but for $100 it was totally worth just bolting a new one up, plus now a can use the old one as a spare or club or something

$100 is a really good deal space cowboy!
I have not yet installed the new mani so the exhaust leak will hopefully be quieted with the new zzp front mani. Thanks for the tips though! I’m waiting for the new manifold and crossover bolts to arrive. Good luck with your Riv!

From ZZP, the front Plog header is most important 'cause of how it is tuned. The rear 'manifold' from ZZP is not that much different from the rear stocker, which you can get a good 'pop' from just by porting it.

Well the ZZP stuff isn't a bad deal if you can get it cheap. I have no power tools for that or knowledge to port anything and would rather not screw up my pipes, and no one is exactly offering to do it for me either, so in my opinion I don't mind bolting a new stainless manifold to the car since it's something I'm actually capable of doing

Spacecowboy067 wrote:

Well the ZZP stuff isn't a bad deal if you can get it cheap. I have no power tools for that or knowledge to port anything and would rather not screw up my pipes, and no one is exactly offering to do it for me either, so in my opinion I don't mind bolting a new stainless manifold to the car since it's something I'm actually capable of doing

I understand.

I successfully ported my front manifold using a handheld Dremel moto-tool, with a round and a bullet-shaped abrasive stone. Success just means that you keep in mind that all you are really doing is grinding a little off the surfaces that otherwise would reflect back toward the cylinders. Doing so changes the angle of the area around each opening so that the airflow will not "hit" the side wall of the head port wall and reflect back toward the source so that you reduce or eliminate turbulence in the exhaust flow. To do this, you get the manifold off, clean it (for your convenience), and get a Sharpie(R) and a new gasket. Line up the new gasket on the manifold then trace inside the exhaust ports with the Sharpie(R). The parts you inked up in the tracing, mostly will be OK but some will be flat. Just grind those flats such that the manifold openings are more like little trumpets whose outlines match the gasket holes. You don't need to take a whole lot off. You don't need to polish the insides of the pipes - that is, if you have a ball hone you can smooth the insides of the manifold, but really if you just get rid of the areas that appear that they would reflect sound back toward the source. If you want, you can check that with a laser pointer aimed straight in at an angle normal to the opening. The rounder the dot is the more it's reflecting exhaust back and causing turbulence. The more elongated or oval the dot is, the less back-reflection you will get.

People who are selling porting wax poetic about polishing the inside of the manifold and so on. However, if you just smooth things by the openings, you'll win.

Yes it is really that simple.

Albertj