Roaring Aurora!

[G2Northstar]

I got such a kick out of my little experiment that it had to be shared.

It started when noticing the airfilter box has very little room in it. Matter of fact I've never seen one so constricted. it's actually smaller in terms of volume than, well probably a lawn mower. I was appalled.

There is about 1" between the air filter and the internal baffle that placed into the filter housing case. It also restricts as it leads to the large ducting to the throttle body.

The intake air horn is also pretty small and has a harmonic section with small chambers. Mine was filled with debris and rocks. Now removed it can pull air from the side and bottom, instead of just the side-- fender area. The undercarriage protects from direct exposure to the elements.

The main restriction in my viewpoint is the large baffle installed downstream of the air filter (on top, as the air flows bottom to top/up). It's obvious the engineers did every trick in the book to prevent ANY intake sound from "disturbing" the passengers, no doubt effecting (negatively) ultimate HP/TQ and possibly MPG, too.

Why develop and manufacture a state of the art engine and then "choke" it down? Whith relatively high compression, 4 cams and 4 valves per cylinder, the design is meant to sing, all the while providing good emissions and MPG.

Now I wouldn't say it's an ultimate design, but solid none the less. The Europeans tend to offer that, but then you have to pay for it. My last Audi had a 4.2 V8, FIVE/5 valves per cylinder, 4 cams, variable valve timing, high 11.1/1 compression, a 3 stage variable intake and she made 385HP/360TQ with an intake and sport exhaust (340Hp stock at 7,000rpm/ 302lb/ft tq). It would also breach 60 in 5 seconds flat and would run 170mph in 6th gear.

So, anyway--

I was fairly confident removing the harmonic restrictors would both allow more air flow and let some sound out when "on the throttle".

Boy was I surprised. That Northstar 4.0 sounds great "on the boil"!

It's fairly subdued, but still just a bit "muscley" sounding up to about 3500 rpm and at 4500 rpm on up it just Roars. Now I don't mean that in terms of a decibel leavel, which is is pronounced but not excessive or shrieking. It's just a nice deep and strong intake sound. Sure made me smile and laugh. Poppa's car just "grew a set", as some would say

Normal driving and it's pretty quiet, not too much more sound/noise than stock but at least you know there is an engine up there. I like it.

With any luck the extra breathing, due to eliminated intake tract restrictions, might even help the MPG.

It surprised me and I'm not sure if the sound makes it any faster, but the powerband does seem more even, not running out of breath at higher rpm's. In the Sport/Power mode the engine pulls strong to 6K rpm, shifts to 2nd at 4500 rpm, right where the deep sound comes in, then shifts to 3rd at 75mph. I really think the car is faster, especially from mid range on up.

If anyone is intersted I took pictures of my "procedure" and can post them.

Wonder what could be done with the exhaust.....?

[chemicall]

Good job man I always delete accordion tubes, get a k&n, upgrade smal piping and remove restrictions, a bit louder but better throttle response and a bit better gas mileage...great for me!

Your biggest exhaust restriction is your cats(especially if they are original that came with the car), some magnaflow hi-flow cats. about $60-70 a piece. Magnaflow mufflers would be a great choice too. Real smooth and loud when you want it to be you coud put a sweet exhaust on it that would not only make it hall a$$ even more but with them magnaflow's you would be suprised just how smooth the sound is. Old resonator's you could do away with also...

[G2Northstar]

Thanks for the good words and advice.

Once the paper element gets old, I'll most likely put a KN in. I have for almost every car I've owned in the last 20 years.

I noticed the exhaust has a 'T' at the rear suspension and looks suspect too me for significant restriction. In addition, the exhaust tubing steps down some, post-cat. No doubt in part to reduce any unwanted "engine" sounds that a nice V-8 might make

Upstream of the cat, the tubing looks to be 2.5" or better. For hot high velocity gases that should be a-okay. But at it cools off and density goes up, theoretically when combined with yet smaller tubing it will just exacerbate the restriction issue, again and especially, when it hits the sharp 'T' bend section.

If I get crafty and do anything, which I probably will, cause I just can't leave "well enough alone", that nasty little 'T' section including the post cat section, which is about 4' long will morph into something more fitting. I used to make custom exhausts and sure wish I had access to the machine to bend up a new rear section. Hopefully one of our good local exhaust shops will be on board with my idea and do the grunt work for me.

I imagine a 3" post cat section, with nice transitions to the "dual" exhausts would work. Otherwise there might be room enough for dual 2.25" pipes. this might help to graft them into the dual exhaust branch at the T section. Even dual 2" pipes would have substantially more cross section-- and reduced back pressure-- than a single 3", which would probably be fine for a daily driver. Don't want to loose too much low end torque-- which the Aurora is a bit lacking on, IMHO, but no doubt in part to the fairly high gearing. Good midrange though.

Polar opposite would be the $1400 hi-flow cat's (2) and downpipes for my Audi S4. The complete exhast was $3,600 w/o installation. Yes, it was nice (very, okay, extremely nice)! And the nearly $800 monthly payment certainly is not missed, either.

If the Magna Flow cat were that cheap it would be hard to pass up. If you have a link on where I can find them, that would be great to look into it a bit further.

Being that my wife staked her claim to the car, we'll see how much exhaust noise is exceptable, if I get the chance to fiddle with it. She's pretty cool and liked our Audi (the straight pipes were a wee bit excessive, however...!) so it probably won't be an issue.

If i get stuck with the mildely "blinged" Honda Ridgeline (sport brakes and wheels, plus S/S add-ons) I'll still live

[lelandl]

Your theory of "density goes up" doesn't seem to take one thing into account, density goes up because as temperature goes down, so does volume. And as volume goes down in a particular size pipe, so does velocity. Larger pipes as temp drops are going to drop the velocity of the gases even further due to this loss of volume. This is one of the theories behind stepped headers which drop pipe size as you move further down the tube. Huge pipes or open exhaust can actually cost you power in the low and mid range.


Leland

[G2Northstar]

Originally Posted by lelandl

Your theory of "density goes up" doesn't seem to take one thing into account, density goes up because as temperature goes down, so does volume. And as volume goes down in a particular size pipe, so does velocity. Larger pipes as temp drops are going to drop the velocity of the gases even further due to this loss of volume. This is one of the theories behind stepped headers which drop pipe size as you move further down the tube. Huge pipes or open exhaust can actually cost you power in the low and mid range.
Leland

That's a great second post. Congrats!

And as density goes down, it's resistance to movement goes up...

Perhaps you're over looking the fact an exhaust is rather long and combined with various turns will cause a back pressure stack up, making the velocity issue a (nearly) moot point, except when exiting the cylinder heads.

You might want to double check this: "as temperature goes down, so does volume.", at least how it relates to the actual workings of an exhaust system-- so, consider this a 'contexual issue', not one per se against physics.

There is also the relationship between velocity and density, which I think in a round about way is addressed by my comment on limiting the diameter to help preserve some backpressue due to it's effect on engine torque output.

I guess we could go one step further and address engine design, cam design/timing and the relationship between emissions and driveablity. That'd be fun!

[lelandl]

How far velocity is important is a bit farther than leaving the cylinder head, especially if headers or tuned manifolds are involved. The velocity is directly related to scavenging and the tuning of the pipes/runners and this is all affected by the total system. Smoothing out turns and bends is always good, as you say, and even something as simple as going to mandrel bends instead of "crushed" bends can make a big difference.



Leland

[chemicall]

Originally Posted by G2Northstar

:
If the Magna Flow cat were that cheap it would be hard to pass up. If you have a link on where I can find them, that would be great to look into it a bit further.

I got mine at Canadian tire, was $60-$70, 2.5" polished hi-flow, partssource also sells them (I believe these are canadian only) but I'm pretty sure advance auto parts has them, ebay has them 2 inch and up for $65 us free shipping, here's a 2.5" for your reference http://cgi.ebay.com/ebaymotors/2-5-M...Q5fAccessories

the heatshield doesn't seem polished though, like it matters they face just upwards towards your underbody. There obd1/2 compatible, I noticed no power loss from going catless to the magnaflow cat, worked out good. I'll never think about spending big bucks on a cat again.

Oh yeah these cat's aren't a huge lug like the originals, so you'll be shaving some weight off the exhaust too. My girlfriend runs around with magnaflow cat/muffler and she doesn't complain at all, it's not loud until your getting right into the peddle, it amazed me how smooth magnaflow's products are though.

Most exhausts I hear around here, if they downshift or whatever, just pop n crackle, even this kid with a 350 lt1 firebird, I laughed at him after he left and heard the thing crackling when he was stopping. Moral of the story, my magnaflows don't do that. The muffler's are about $100 a piece and up, not too bad, considering all the $ you can save on magnaflow cats.

on my 3800 it costed me about $325 for a full single exhaust, 2.5" dp, all 2.5" stainless pipe front to back, 2.5" magnaflow cat and muffler, 2.5" tail pipe. The original was all 2.25, and at the bends wow did they ever get small.

I paid $119 plus tax for my muffler so about $138 after tax(canada), i could have got it across the river for 95 bucks plus 4% or whatever it is and saved about $40, but I didn't know this until it was too late....ohwell I still got a good price on my exhaust.

[G2Northstar]

On a family car like the Aurora, despite it's modern engine design, must have good driveability. An extremely "open" exhaust would no doubt create a low RPM torque loss, something noted in the previous post, and would be addressed with reasonable sized tubing.

Not only are flow dynamics important, but OEM's also heavily factor in NVH, or in this case just the "noise" aspect. Not only for the exhaust but for the intake, as demonstrated by the intake modification I did.

Whereas on my Audi v-8, where it was tuned for performance, they also seemed to factor in harmonic scavenging effects. The stock dual S/S exhaust, with dual cats, was no slouch, with a bypass flat valve built into the exhaust for high RPM use (peak HP is 7,000rpm, increased to 385). The performance exhaust added substantial HP increase, but more importantly bolstered the TQ by some 40 lbs (at the wheels in a AWD system). Being made in Europe their noise and performance standards are extremely strick. See TUV (like our DOT)for more info.

Now I'm not going to put a $3,600 exhaust on a $500 car, but the principles still apply.

[G2Northstar]

Hey Chemicall, thanks for the info!

[lelandl]

Just a little story about how lack of knowledge (or just lack of thought ;-) ) can cause problems.

A local drag racer and "engine god" built a full bore 427 big block Chev. (I'll tell about the assembly someday) This had 12.5:1 compression, big roller cam, large valve rectangular port heads, I believe a Victor intake, 850 double-pumper, 5500 stall converter, and 2" headers. On the track he shifted it at about 7000.

One day I could hear this engine screaming, but it just didn't sound right. I went outside and here is the guy with the Camaro outside his garage trying to rev it but it would only go to about 5000 and just stop, like you had it on a trans brake. I noticed how quiet the exhaust was, so I went over and looked under the car. Much to my surprise there were two big, oval, stock mufflers bolted to the headers. I asked him what was up and he told me he couldn't figure out why the engine wouldn't rev. I told him he had too much back pressure. "No way, those mufflers are off of a Caddy 500."

I looked at him and said "you don't think that a muffler that takes a 500 cube engine and makes it sound like a sewing machine has too much back pressure?" "Nope, should flow lots" was his answer. Needless to say once he took the mufflers off the engine worked fine again.


Leland

Originally Posted by G2Northstar

On a family car like the Aurora, despite it's modern engine design, must have good driveability. An extremely "open" exhaust would no doubt create a low RPM torque loss, something noted in the previous post, and would be addressed with reasonable sized tubing.

Not only are flow dynamics important, but OEM's also heavily factor in NVH, or in this case just the "noise" aspect. Not only for the exhaust but for the intake, as demonstrated by the intake modification I did.

Whereas on my Audi v-8, where it was tuned for performance, they also seemed to factor in harmonic scavenging effects. The stock dual S/S exhaust, with dual cats, was no slouch, with a bypass flat valve built into the exhaust for high RPM use (peak HP is 7,000rpm, increased to 385). The performance exhaust added substantial HP increase, but more importantly bolstered the TQ by some 40 lbs (at the wheels in a AWD system). Being made in Europe their noise and performance standards are extremely strick. See TUV (like our DOT)for more info.

Now I'm not going to put a $3,600 exhaust on a $500 car, but the principles still apply.