FAQ: The Exhaust Thread

I'm sure this has been covered before, but I couldn't find it. I have a 98 Riviera. I got the ZZP Shorty 3" Downpipe. I was under the assumption that this will bolt right up to my exhaust manifold. Is this correct or will I have to cut and weld on a different flange to bolt it up? The car is in storage. So I'm not able to go and measure mine.

I'm not 100% sure but I suspect you'll be able to bolt it to the manifold, but not the lower flange at the cat.

the lower part I'll have welded most likely. I just wasn't entirely sure on the mating of the exhaust manifold.

Well I ordered the MagnaFlow 99306HM cat and a pair of the MagnaFlow 12226 mufflers. I guess what I'm not sure of how loud is this going to be. Piping is going to be 2.5" with my 3" dp. I don't know if I should get a resonator or just see how it sounds with what I have. I want it to have a nice tone to it, but I don't want it stupid loud either. What do you guys think?

I have no resonator with glasspacks for mufflers and its not too loud for me, if i were you id just try what you have already and if its too loud you can always add a resonator.

That's kinda what I was thinking. Test it out first then go from there. Thanks though. It always helps to have a second opinion

Has anyone added just a high flow cat to the stock system? Without headers or downpipe change? Just curious what the difference in noise/power might be.

jlaw wrote:

Has anyone added just a high flow cat to the stock system? Without headers or downpipe change? Just curious what the difference in noise/power might be.

FYI someone passed along to me that the stock cat uses a high-flow version of this Corning substrate for the catalytic converter:

www.corning.com/WorkArea/downloadasset.aspx?id=6281

If what was passed to me is true then the stock converter is probably not the choke point in the exhaust system. Nor the mufflers. For my $$$ I'd be looking hard at that downpipe. Now, isn't it true that on the '95 the downpipe and converter are kinda one piece? I don't have one but on my friend's '95 they seemed to be but he's such a gearhead I don't know if he'd modified it - anyway, is so then that's a different issue, and on those models a new cat with a larger downpipe might buy you something.

Bottom line for me is that as has been said on this forum a bunch of times (although not in so many words) a larger downpipe on the stock exhaust should buy you some HP.

albertj wrote:

Now, isn't it true that on the '95 the downpipe and converter are kinda one piece?

Yes its all one piece.

If one could find performance mufflers with the same diameters as the stock mufflers and installed them wouldn't there only be positive performance effects? My theory is that the same size diameter would keep the heat of the gases the same as stock, but have less restrictions in the muffler. I don't see how any torque could be lost.

RidzRiv wrote:

If one could find performance mufflers with the same diameters as the stock mufflers and installed them wouldn't there only be positive performance effects? My theory is that the same size diameter would keep the heat of the gases the same as stock, but have less restrictions in the muffler. I don't see how any torque could be lost.

No, because the stock mufflers are not as restrictive as the stock downpipes. They are only easier to see and easier to replace, hence easier to sell to some people.

I wasn't saying that changing the mufflers would give you more gains than changing the downpipe. I was just stating that it would be possible to keep the gases as hot as stock so that they don't slow down, while having less of the restrictions of the stock muffler. Where as using a larger diameter muffler would allow the gases to cool down more and slow down. I was just putting out an idea, because it's hard to compare the effects of a performance muffler vs. stock when you are using different sizes, because of course different diameters will change the exhaust flow.

albertj wrote:

No, because the stock mufflers are not as restrictive as the stock downpipes. They are only easier to see and easier to replace, hence easier to sell to some people.

Dont forget about the front manifold either.....

According to the guys on the pontiac bonneville club forum the series 1 3800 exhaust manifolds are some of the best manifolds gm has made.

ahhh, wasnt paying attention. Thought we were referring to Series II haha

ok i read through about 20 somethingpages and it all looked like afgan script to me lol..i got lost so....i have a 97 buick riviera i want exhaust work done and im probably gonna get it done within the next week or two..

i have no mods YET..except for a intake ..but i plan on lowering sc pulley ..better tires so i can do pcm work for governor.. msd wires (unless there are better that you all know of???) 180 or 160 thermostat... plugs....kyb shocks/struts...and thats probably it...

i dnt know if any of that matters on what type of exhaust i get but ...
WHAT SIZE AND KIND OF MUFFLERS AND PIPES WILL DO ME BEST WITH SOUND AND PERFORMANCE for my car?????????
thanks in advance

My 2 cents - consider putting on a larger (3") downpipe (easy to get), use the *stock* resonator (the aftermarket downpipes just will bolt to it) or a Corsa (tell 'em it's for a Seville), put more or less the mufflers of your choice on after the Y-split, and same as tailpipes use stainless to the end with decent (your choice of style) tips. If you look back in the thread for Rick Wakefield's posts, I think he had some of the best insights.

Synopsis (I covered this in earlier posts)

What I did - I bought a 2004 Park Avenue Ultra exhaust from my local GM dealer (in part because Jason said it would fit and he was of course correct), it was made for me in Wixom by GM, it was the RPO (regular production option) for the PA Ultra, with the round stainless tips and what appear to be somewhat oversize mufflers (they **just** fit under the Riv). It came with hangers and bolted right on. Slight relocation of O2 sensor wire needed but nothing major - no wiring changes at all, just needed to make a extension of the heat shield for the wiring out of a little piece of aluminum.

Why I did that - When my mufflers rusted out I had a custom stainless exhaust (you saw it earlier in this thread with pointers to youtube vids) made for me and installed by NeverRust in Avalon PA, custom made of T304 including a Jones 4" glasspack as resonator and custom mufflers. Problem for me was... well it was a *blast* to drive on trips of 25 miles or less but the drone was a bit much on longer trips. Pretty near all my driving is longer trips. So I sold that exhaust to a friend (who liked the sound to put on his Riv and bought the 2004 PAU RPO exhaust to replace it.

Good luck and don't don't get sucked into spending too much time on this. Exhaust system won't really add horsepower, maker's claims aside, unless you are making mods on a car that had an exhaust tuned primarily and almost solely for attenuation and that's not the case on the Riv to begin with. The stock exhaust flows really well, has a trick resonator that gets rid of the chronic 3800 90-deg-vee drone, and has a nice burble at idle.

Albertj,
I like your reasoning, and the mostly stock approach. If I were to use your recommendations, that is, how you finally configured your own car, what might it cost, ballpark?

denim wrote:

Albertj,
I like your reasoning, and the mostly stock approach. If I were to use your recommendations, that is, how you finally configured your own car, what might it cost, ballpark?

Short answer - You have to ask dealers for price quotes. Because the PAU exhaust comes in one piece so shipping can be -- well -- interesting. That means expensive. It could be as much as a grand or more to your door.

Better (and cheaper) answer - PN of the PAU exhaust assembly was 25749911. This is *important* - it shows up in the GM system as a "converter" and lists for almost $810. A rookie parts counterperson is not going to get that it really is the *whole* exhaust and hangers - there's some goofiness involved like no picture in the system or some stuff. Oh yeah you get $80 for return of your old cat.

You should be able to get for less than $810 but you will have to ask around and negotiate. You might want to check Monsterpartsonline.com and gmpartsdirect.com using the part number 25749911 and print those prices out and ask the parts counter person to come as close as he can to the pricing without an Act of Congress. I think dealer cost on it runs $350 to $450. So the thing is an experienced parts counterperson with some discretion or a parts manager is not usually going to charge you a 100% markup for something like that. I do not remember what I paid but it was less than the then-price for GMPD if you included shipping. And the dealer even had the lot attendant drive the thing to my house... it's all one piece and clumsy, we hadda tie a red flag to the part that hung out the tail of the S-10...

As you know the parts managers have some discretion. So what you pay may depend a little on who you talk to at the respective dealers. I am thinking they should come close to the GMPD price, if only because they don't actually have to pay shipping from GM. Yeah, shipping is another matter. GMPartsDirect wants almost $150 to ship the sucker.

I guess the point is if you can buy it from a dealer for less than $650 all-in for pickup at the dealer you Found A Deal and might/should consider it.

They will (may) want a "reason " for replacing the cat and assuming your mufflers are rusty you can just say "Preventive maintenance." Which is what it is... unlike the aftermarket aluminized systems the factory system is T409 stainless. (you should clean it off with clean rags and alcohol and then paint it before install more on this below).

So as I confessed before I earlier had a custom stainless exhaust fabricated and put on. For that exhaust I bought and provided a new Walker cat (they have actually about the best aftermarket cats I don't care what magnaflow says) to weld onto the system. When I sold the custom system I asked for and got my buddy's old cat as part of the trade (it was part clogged and the heat shield had rusted off the case). He sawed it off with a hacksaw. I turned that in for my $80.- some weeks after getting the "converter" from GM. And called it "preventive maintenance."

A little trivia - The new exhaust will come with an EmCon converter, which will be TINY and very close to the downpipe. Don't wig out. it is small because it uses a newer technology "thinwall" substrate and flows better than stink (or any cat it replaces). It does not have to be big. Oh and you don't have to but I also fabricated an extension to the undercar heat shield out of sheet aluminum flashing (mill finish) and secured that with exhaust repair epoxy and I think pop rivets or teeny sheet metal screws I forget which. And in order to be sure I got my moneyworth out of the replacement I painted it (except the cat) with silver 'high heat' engine paint before install. It took weeks for the paint to cure (heh heh).

A little more insight: Have a buddy help you with the install, the one-piece exhaust is a bit much to get into place and does not look like it fits -- until it is all hung on the hangers, then it's great. The mufflers just tuck inside the rear bumper skin. They will scrape the skin going in but rest just above and inside it once it is all hung at the right height. They are big. Getting it on, you pop the hangers off the new exhaust and swap them in for the old ones one by one in their respective places. Use the old ones as paperweights or some such or sell them. The factory hangers are some sort of black miracle elastomer, I doubt they ever wear out.

When I did my install I (well I didn't do it keep reading) broke the center hanger, repaired it with same grade stainless bolts and used galvanized pipe nipples over the bolts for ferrules to go in the hangers. Only reason was my bud (a very good manufacturing engineer by the way) mistook the swaged bolt in the hanger for a bolthead to turn (it happens) and busted it when we were removing the old system. I am responsible for my car so I say I broke the hanger... Not a big deal, I am good at making once-and-done solutions out of common/odd hardware and the hanger can be easily copied form common hardware once done being peeved about breaking it.

Hey, thanks for the wealth of knowledge.
As you can tell by my cross-category posts, I'm considering multiple fixes to my Riv, mostly to get mechanically original performance, with some for upgrades. All the help I've received in the short time I've owned this car is greatly appreciated. It's stuff hardly available anywhere else. This forum is a valuable asset.
Strewn between house work projects (and I don't mean sweeping up) I'll get the Riv project list in order soon.
I won't be doing the exhaust without a close inspection of what to keep and what to chuck. But I'll always refer back to your post.
Best!

HEY ABOUT MUCH DOES THE 3" DOWNPIPE COST ABOUT??

try calling ZZP or the other suppliers listed on the Dash of this site. I am thinking less than $150, but I don't really know.

The "thrush turbo" is a carbon copy of the stock muff. After dicking around with mine,I can honestly claim that It would have been better to leave the system alone. I might have more flow,but The noise inside the cab is boring. I like my toons too much.I have a 3" exhaust pipe running through a 27" cherry bomb and into a single 2 1/2 thrush turbo.the sound is very good.the system is lighter now,but I cant say for sure if its a real performance gain.

robotennis61 wrote:

The "thrush turbo" is a carbon copy of the stock muff. After dicking around with mine,I can honestly claim that It would have been better to leave the system alone. I might have more flow,but The noise inside the cab is boring. I like my toons too much.I have a 3" exhaust pipe running through a 27" cherry bomb and into a single 2 1/2 thrush turbo.the sound is very good.the system is lighter now,but I cant say for sure if its a real performance gain.

That's what got me to sell a *beautiful* T304 custom system and put on the PAU. What suprised me, however - for some reason on the stock system when you're accelerating there's a "flat spot" between 2000 and 2500 RPM where the acceleration seems impeded. When I put the SS system on that flat spot was GONE. The surprise was when I put the PAU system on it did not come back.

The PAU system is darn near silent to my ears. I think I may use a sound meter to check that, though. The general sound attenuation strategy GM used on these cars, I think, was to push the resonance of the exhaust down to a very low frequency and damp it out in part with the padding under the carpet (pull yours up sometime & you'll see what I mean the pad is... ummmmm... "generous." When the SS exhaust was in I added padding and eDead butyl panel damper under rear seat and in rear passenger footwells.

Albertj

SO IF I WAS TO GET A 3" DP AND JUST ADD MUFFLERS AND TIPS TO MY EXISTING EXHAUST SYSTEM I SHOULD BE OK? I WAS THINKING ABOUT MAGNAFLOWS JUST TO GIVE IT A LITTLE GROWL OR NOISE