FAQ: The Exhaust Thread

1998 Riv wrote:

turtleman wrote:

[...........so why do all the cheap or expensive headers+DP and individual DP's have this braided flex joint that seems to inevitably leak?

I haven't read anywhere about these leaks in the flex joint??? Anyways... Hogan's DP flex joint is optional, according to their website. You should be able to order it w/o.

Alex, most run of the mill exhaust shops won't have the expensive equip to do mandrel bends. Maybe a larger performance specialty place? Dunno...

Ive seen a madrel bender in an exhaust shop about a mile from my house. Like an EZ Muffler or so. Our exhaust is so simple, straight back to whatever you want.

Most places don't have a mandrel bender in my area. It's very expensive (50k+) and specialized equipment that your average exhaust shop doesn't need. You're lucky if there's one a mile from your house!

well you know what, I think im going to get the 3" DP and run 3" from there to the bend and get the gradual reducer to 2.5" and plump in the bend with 2.5" 15deg elbows and get flowmaster's Y pipe to go to the glasspacks i have. that should work well based off of the velocity theory.

AA wrote:

Most places don't have a mandrel bender in my area. It's very expensive (50k+) and specialized equipment that your average exhaust shop doesn't need. You're lucky if there's one a mile from your house!

theres also an excellent DYNO shop a mile in the other direction, and 5 bars 4 blocks away....

is the pipe of that rear bend section already 2.5" or smaller?

Smaller after the T.

One of the diagrams posted in the FAQ shows 1 7/8 after the split.

Quote :

well you know what, I think im going to get the 3" DP and run 3" from there to the bend and get the gradual reducer to 2.5" and plump in the bend with 2.5" 15deg elbows and get flowmaster's Y pipe to go to the glasspacks i have. that should work well based off of the velocity theory.

what size glasspacks? I don't believe your plan will really hold up. The principle you are referring to is called the Venturi effect. While you will be tapering down from 3" to 2.5", after your y split, the combined area will be greater than 3" (providing your glasspacks are 2.25" or 2.5" diameter).

the resonator is a huge restriction. Bigger than the manifolds. Our stock exhaust is probably only marginally better than a regal's with the single muffler.

quote: "the resonator is a huge restriction. Bigger than the manifolds. Our stock exhaust is probably only marginally better than a regal's with the single muffler."

Maybe so, but I've not seen numbers to prove this. However, from my own research and personal experience of feeling a sizable difference from headers + stock exhaust, I have reason to disagree that ours is only marginally better than a Regal GS, which has the U-Bend in there.

If you look at what the Bonneville SSEi guys are doing (same exhaust layout) it seems they've already realized that stock exhaust after cat converter isn't that bad. Take INTENSE racing's project 8-ball, as an example. They put on SLP headers and high flow cat, cam, IC, etc. This car was making over 400 hp before they replaced the stock exhaust. I asked INTENSE about this when I bought the headers, and they explained the stock exhaust flow was more than adequate for my application, based on their experience with the SSEi.

As bad as the Regal GS exhaust with U-bend would seem, Thrasher Engineered Performance did a study a few years back that showed conventional wisdom of exhaust design doesn't apply as much as we'd like to assume. They took a stock Regal GS exhaust and measured flow of various parts, cutting it off at different places for testing. What they found was, the entire cat-back stock system, including U-bend, was only responsible for a slight restriction in flow and performance. To quote their words:

"It's evident that at best, a free-flow system will gain perhaps 10HP - and that's for a noisy system, while one which controls irritating resonances and drones better would probably gain less than that. Therefore, a 5-7HP gain from a cat-back exhaust system is probably in the ballpark for achievable gains."

Reading through their experiments, I cannot see much value in spending money making my car noisy for a 10 hp gain. Instead, I'll push my car into the 13s with a civilized (and good) sounding exhaust note. I realize I could subtract a tenth from my times by improving my exhaust, but it's just not worth it right now. The car is amply quick with zero exhaust drone, no rasp, no nothing but a nice rumble at idle. Any mods I do will be for the purposes of appearance and/or weight reduction.

Hmmm well that sounds convincing

I'm not against maintaining a 100% stock exterior anyway. There are times when you don't want to draw extra attention, and I'd like to keep the Riv for a daily driver. I probably won't even do exhaust tips or rims on this car. Stealth stealth stealth!

I don't want to come off as being against exhaust tips or even a good muffler mod. I think there are tasteful additions that can be made to our cars. I just want people here to understand that (imo) they're not going to see super hp gains with a straight through exhaust like would be expected on a N/A car. Instead they're going to get a lot of noise, and maybe that will provide some psychological benefit (or anguish?), but numbers are what really matter to me. I don't mean to sound like my opinion is proven fact, it's only my personal take on things. Everyone's entitled to their own view.

Besides the parts expense and (custom) labor costs, the biggest reason I won't open my exhaust is because I personally can't stand the sound of a 90 deg V6, and I definitely will not put up with drone. Unless you are cammed, there is very little good that can come from the end of our tail pipes. A quality muffler can give it a meaner sound, but it's not like we are talking about a throaty V8 here.

AA wrote:

I don't want to come off as being against exhaust tips or even a good muffler mod. I think there are tasteful additions that can be made to our cars. I just want people here to understand that (imo) they're not going to see super hp gains with a straight through exhaust like would be expected on a N/A car. Instead they're going to get a lot of noise, and maybe that will provide some psychological benefit (or anguish?), but numbers are what really matter to me. I don't mean to sound like my opinion is proven fact, it's only my personal take on things. Everyone's entitled to their own view.

Besides the parts expense and (custom) labor costs, the biggest reason I won't open my exhaust is because I personally can't stand the sound of a 90 deg V6, and I definitely will not put up with drone. Unless you are cammed, there is very little good that can come from the end of our tail pipes. A quality muffler can give it a meaner sound, but it's not like we are talking about a throaty V8 here.

I Agree with you totally...and for 95% of The Riv's here...there not really any reason besides personal preference to modify the exhaust in hopes of gaining HP....In fact, a lack of back pressure reduces low end torque. You make a good point with Todd Allen's SSEI....That car has too much power for its own good and it is quiet except for the S/C.

And Our ENGINES DO SOUND LIKE SHIT UNLESS YOU HAVE A GIANT CAM....In which case they do sound very very sexy, But once they get up to temperature...your ears feel like theyre about to bleed....Its fun

Ive got a 3" magnaflow resonator that toned it a down a bit for just the resonator....I hope the 3" perforated magnaflow muffler does a little bit more.

And I would agree there are times when it's appropriate to open things up, regardless of the noise. If you're going all out, every last bit of flow counts. You can make up for some of that lost torque by increasing boost, right? I agree cams sound nice. I met the owner of a white GTP named Chris at the track last year... totally open 3" pipe, sounded great.

I don't think the stock exhaust is sufficient. the 1 7/8" mufflers simply don't cut it. If you use the dynomax super-turbo muffler as an example (keep in mind these are performance mufflers and flow more than OEM), you can see why the oem dual 1 7/8 isn't good enough for performance applications.

Code:

#          shell dia    o/a length    shell length      ID    OD      CFM      HP single/dual
17771  3¹⁄₄ x 7³⁄₄    18¹⁄₂              14                    1³⁄₄  1³⁄₄      160        73 / 146
17762  3¹⁄₄ x 7³⁄₄    18¹⁄₂              14                    2      2        180        82 / 164
17730  4¹⁄₄ x 9³⁄₄      18¹⁄₂              14                    2      2        260        118 / 236

this was pulled from the super turbo pdf

The formula for max loss free hp supported by a muffler is cfm/2.2

Looking at the chart shows us that not even a single 3" super turbo muffler would do to support 300 hp. I can see why the riv exhaust would be better than the stock regal gs (which has a single 2 1/4 muffler, i.e. less area than 2 x 1 7/8")

for and interesting read, compare to the ultra flo muffler, very similar to the hooker maximum flow and you'll see that a single 2 1/4 muffler would support 433 hp. These flow about as much as straight pipe.

Jason, am I reading the chart right? It looks like dual dynomax super turbo mufflers are only good for 236 HP at best, 164 at worst? Which are our stock mufflers closest too?

I couldn't tell you without testing them with the same kind of equipment they have. The stock riviera mufflers are closest in shell size to the 17730 with an ID/OD of 1 7/8 (halfway between the above sizes).
Suffice to say that the OEMs don't flow as well as a performance muffler of the same diameter, and even less than one with a bigger diameter. If I had to to guess, I would say that it flows less than the 17762

Max loss free horsepower just means that after that level, your exhaust is holding you back. If the exhaust is holding back 7-10 hp, then exhaust work is that's a fairly cheap way (in hp/$) to make more power. Can you still run 12s or 13s ? yes. But why would you want to throw money at other mods that won't even give you that ?

The GP has 2 x 2.25 so it is much better after the split than our system.

When I do my exhaust this week, I will cut the resonator and a muffler open to show you guys how much they suck. I saw the resonator on my GF's GS when It was replaced. It is terrible.

Does someone make a hipo resonator, or are you leaving it off?

Yes. Magnaflow makes some, as does dynomax (a bullet ultraflow). I am going to use a 3" magnaflow straight through (4" shell, 14" body). I have some mufflers lying around, namely a pair of 2.5" superturbos (17749) and a pair of 2.5 hooker maxflows, as well as a pair of dynomax 2.5 resonator/tip. If the resonators/tips don't fit with the super turbos, I'll use the maxflows.

alright im doing a CAT delete... how long is the cat

As I type, my turtle is at a shop having the exhaust run.
Running 3in pipe all the way back with the 3in DP and fabbing a 3>2.5x2 Y pipe to put the 2.5in glasspacks on

We'll see how it comes out in a little while...

Great!!!

I can't wait to here the results. I plan on doing the same to my car with 2.5" hooker aerochamber mufflers.

That's going to be SO loud!

goood nice to hear that you finnally found a place to do it

ok it's basically done. just gotta get tips on it.
Let me tell you though, the glasspacks didn't stay on long..
I got a pair of Dynomax superturbos on there from work cause it was extremely loud and just an out of control sound. I don't know if it makes any sizable difference but they had put the glasspacks on backwards and those ones had a directional design. Don't think it would have made much difference at all though.

but now its very functional and still much louder than before with the stock + glasspacks on it. its all welded and hung nice and solid 3 in all the way to the back muffs

some pics will come, shortly