Constricted Header Collector?

[XfireZ51]

Never really noticed this before until I got car up on jack stands to do trans fluid change and bleed slave cylinder. Whaddya think guys? Needs to be re-done? Yes? No? It goes from a 3" collector to a 2.5" neckdown back to a 3". Its about 3" in length.


http://i187.photobucket.com/albums/x198/Z51Xfire/NarrowedExhaust002.jpg

http://i187.photobucket.com/albums/x198/Z51Xfire/NarrowedExhaust001.jpg

[Paul Workman]

Dom,

I'm dubious of any practical advantage to addressing that one choke point.

There is that constriction, then another 3 to 2-1/2 into the 2-1/2" "X" pipe, before entering the resonator. Once inside the rez, the twin resonator pipes aren't even 2" across before they spill out into an internal, single pipe less than 3" across before splitting again into the pair of less than 2" pipes leading out of the resonator and ending at the output collector. The outputs are approx 2-1/2" expanding to the 3" segment leading to the muffs and then transitioning again to 2-1/2" inlet to be split into two tubes leading to the muffler tips.

However, it would be no trick at all to cut off the flanges and install a slip-fit link to slide over the header collector (which I did, before further eliminating all of the MF stuff, except the muffs (which I like).

P.

[XfireZ51]

Paul,

Here is then response I got from Magnaflow regarding the muffler fitment, resonator constriction and construction.

MF: "The fitment of the system may be altered by the headers if it's a long tube or short tube. The muffler hanger should measure 1.6" high. I would recommend shorter aftermarket urethane isolators/bushings to get them to sit higher. The resonator in the catback system has a dual y-pipe with a single 3" core in the center."

Me: Doesn't the single 3" core inhibit performance. Is there any other alternative to using this resonator? Thanks again for your response.

MF: "The single 3" core provides better sound control and sacrifices minimal performance. The only other solution is using a dual/dual muffler which will increase flow and reduce back pressure at the expense of bottom end torque."

There's that higher backpressure = better low end torque thing. :rolleyes:
Essentially the MF resonator is a dual Y design with each Y connected to the other via the tail end or single 3" core in the center. Speaking with Al last week, he doesn't necessarily believe that there is an inherent disadvantage here. In essence, what you have is a dual Xpipe and additional scavenging in the resonator.
I would think the constriction immediately after the collector and at the point of highest pressure and heat could affect performance more significantly than further down the line where the exhaust has begun to cool and require less volume. But I'm certainly no expert.

[Paul Workman]

Paul,

Here is then response I got from Magnaflow regarding the muffler fitment, resonator constriction and construction.

MF: "The fitment of the system may be altered by the headers if it's a long tube or short tube. The muffler hanger should measure 1.6" high. I would recommend shorter aftermarket urethane isolators/bushings to get them to sit higher. The resonator in the catback system has a dual y-pipe with a single 3" core in the center."

Me: Doesn't the single 3" core inhibit performance. Is there any other alternative to using this resonator? Thanks again for your response.

MF: "The single 3" core provides better sound control and sacrifices minimal performance. The only other solution is using a dual/dual muffler which will increase flow and reduce back pressure at the expense of bottom end torque."

There's that higher backpressure = better low end torque thing. :rolleyes:
Essentially the MF resonator is a dual Y design with each Y connected to the other via the tail end or single 3" core in the center. Speaking with Al last week, he doesn't necessarily believe that there is an inherent disadvantage here. In essence, what you have is a dual Xpipe and additional scavenging in the resonator.
I would think the constriction immediately after the collector and at the point of highest pressure and heat could affect performance more significantly than further down the line where the exhaust has begun to cool and require less volume. But I'm certainly no expert.

MF: "The single 3" core provides better sound control and sacrifices minimal performance. The only other solution is using a dual/dual muffler which will increase flow and reduce back pressure at the expense of bottom end torque."

Ye ol' back-pressure=more low end torque, eh? Sacrifices minimal performance??? I'd like to say to MF; Define "minimal"!

Well, I'm dubious of their claims... Then again, it is a system designed for a 300-330 hp engine. Like you, I'm no expert here. But, a fully ported, 500 hp LT5 is another animal when it comes to factoring in "minimal" losses. I dunno how to find out except to dyno your car and switch the exhaust for a true 3" and run it again. :dontknow: But, I agree that a restriction closer to the front would have more effect than one at the end of the system (the reason I'm not overly concerned about the 3" to 2-1/2 constriction at the muffs on my system).

Could be a lot about nuttin, but I will say your system sounds "bitchen" (am I dating myself?).

P.

[XfireZ51]

Paul,

Let's not forget that no less an expert than Marc Haibeck continues to say that
he feels there is no practical loss in performance between a 2.5" Corsa system vs. another 3" system.

[todesengel]

Paul,

Let's not forget that no less an expert than Marc Haibeck continues to say that
he feels there is no practical loss in performance between a 2.5" Corsa system vs. another 3" system.
While that may be true, as well as the fact that most n/a cars need SOME restriction to maintain low end torque, I do not think what is shown is what Marc had in mind.

It is one thing to have a "free flowing" 2.5" exhaust, and something entirely different to have a 3" exhaust flowing into a 2.5" restriction, and back to 3" again. Restrictions like this create turbulance in the exhaust flow and disrupt it's release. Think about it, what are the benefits of a mandrel bent system v. a crush bend?

If it were mine I would remove the restriction, and make the entire system no less restrictive than the header outlets themselves, or you are really gaining nothing imho.

[XfireZ51]

While that may be true, as well as the fact that most n/a cars need SOME restriction to maintain low end torque, I do not think what is shown is what Marc had in mind.

It is one thing to have a "free flowing" 2.5" exhaust, and something entirely different to have a 3" exhaust flowing into a 2.5" restriction, and back to 3" again. Restrictions like this create turbulance in the exhaust flow and disrupt it's release. Think about it, what are the benefits of a mandrel bent system v. a crush bend?

If it were mine I would remove the restriction, and make the entire system no less restrictive than the header outlets themselves, or you are really gaining nothing imho.

That's 2.5" OD btw.

[todesengel]

I would also like to add that I do not buy magnaflows response to a restriction towards the tail end of the exhaust. It just seems contrary to theory.

First ask yourself what happens when exhaust gases cool, they expand. With expansion of gases it slows and requires more area to evacuate. For this reason you see a lot of people run 2.25"-2.50" headers which dump into a larger system down the line and/or a exhaust system that "megaphones" towards the tail end to compensate for the expansion of these gases as they cool. For this reason, imho, it would seem "better" to have a restriction on the front end, where the gases are still hot, than the back end. The "better" solution, again imho, is to have a consistent system OR one that expands to take into account the expansion of gases, OR the best solution which would be a system that is coated, or wrapped, to limit gas expansion AND enlarges towards the discharge.

[flyin ryan]

I find all this talk rather interesting. On my Stingray, I have SPD build a choke into my collectors on purpose. This one is identical, Divergent & Convergent angles, to the ones on my Stingray, I just have an extra set for dynoing only as the ones on my Stingray are welded to the exhaust.

http://i228.photobucket.com/albums/ee142/flyinryan_ZR1/IMG_1634.jpg

http://i228.photobucket.com/albums/ee142/flyinryan_ZR1/IMG_1635.jpg

[Paul Workman]

I would also like to add that I do not buy magnaflows response to a restriction towards the tail end of the exhaust. It just seems contrary to theory.

First ask yourself what happens when exhaust gases cool, they expand. With expansion of gases it slows and requires more area to evacuate. For this reason you see a lot of people run 2.25"-2.50" headers which dump into a larger system down the line and/or a exhaust system that "megaphones" towards the tail end to compensate for the expansion of these gases as they cool. For this reason, imho, it would seem "better" to have a restriction on the front end, where the gases are still hot, than the back end. The "better" solution, again imho, is to have a consistent system OR one that expands to take into account the expansion of gases, OR the best solution which would be a system that is coated, or wrapped, to limit gas expansion AND enlarges towards the discharge.

Well...Gasses do NOT expand as they cool; just the opposite (or a lot of thermal dynamics texts books got it all wrong!). Put the cap (seal) on an empty plastic milk jug at room temp and put it in the fridge, if ya wanna see for yourself.

But, I agree, from a fluid dynamics perspective, that a consistent size (i.e.) uniform throughout is important - as opposed to varying diameters abruptly (especially abruptly!) along the way:thumbsup:. Otherwise, there are acoustical energy consequences (turbulance being one byproduct); hence the funnel designs you see on some intake porting jobs, AND, (to your point) the same is true on some exhausts, tho not so much on anything but rice burners and...and tubas, of course. (Electronics engineers refer to the taper concept as "impedance matching" - a physical reality in waveguide design...But, I digress.)

P.

[XfireZ51]

FR,

"I find all this talk rather interesting. On my Stingray, I have SPD build a choke into my collectors on purpose. This one is identical, Divergent & Convergent angles, to the ones on my Stingray, I just have an extra set for dynoing only as the ones on my Stingray are welded to the exhaust."

It's clear that the choke illustrated by your header collector is gradual and represents a single point. My constriction, OTOH, is more abrupt and significantly longer length. It just doesn't make sense to me that this isn't affecting performance coming from the left side of the motor. I'm willing to listen since addressing this is gonna cost a few bucks to eliminate.

[todesengel]

You are 100% correct, I had it backwards (my apologies). I just re-read what I wrote, and it should have read cool as they expand, not sure where my head was, but the point is still valid that a restriction is going to adversely affect the flow.

I am not quite sure about this being isolated to rice burners, as I have seen many buick, and 89 t/a people utilizing the same technology

Again, sorry for my brain lapse Well...Gasses do NOT expand as they cool; just the opposite (or a lot of thermal dynamics texts books got it all wrong!). Put the cap (seal) on an empty plastic milk jug at room temp and put it in the fridge, if ya wanna see for yourself.

But, I agree, from a fluid dynamics perspective, that a consistent size (i.e.) uniform throughout is important - as opposed to varying diameters abruptly (especially abruptly!) along the way:thumbsup:. Otherwise, there are acoustical energy consequences (turbulance being one byproduct); hence the funnel designs you see on some intake porting jobs, AND, (to your point) the same is true on some exhausts, tho not so much on anything but rice burners and...and tubas, of course. (Electronics engineers refer to the taper concept as "impedance matching" - a physical reality in waveguide design...But, I digress.)

P.

[flyin ryan]

It's clear that the choke illustrated by your header collector is gradual and represents a single point. My constriction, OTOH, is more abrupt and significantly longer length. It just doesn't make sense to me that this isn't affecting performance coming from the left side of the motor. I'm willing to listen since addressing this is gonna cost a few bucks to eliminate.I understand your system. Just don't know if there is as much in it as one may think or want to believe. The majority of the exhaust gasses are concentrated toward the center of the pipe & gradually diminishes' as they approach the wall, so how much of that exhaust gas volume is being affected...maybe 5%? Of coarse all this depends on pipe diameter being discussed for a given combo too. I've mentioned on here in the past my thoughts about exhaust sizing on our cars (Way, Way too big on average) but don't say too much as to not have the entire community hate me, LOL. The collector I showed might surprise some guys the size it is versus the HP it supports. I'm actually contemplating a little smaller set. So bottom line, don't think I'm trying to discourage, just trying to shed some light on the situation. To physically & visually look at your exhaust, the obvious answer is to automatically assume it is a problem, I mean how can it not be?...but may not be so much in reality. :wave:

[tpepmeie]

The collector I showed might surprise some guys the size it is versus the HP it supports. I'm actually contemplating a little smaller set.

Right on, FR. In fact, a 2.5" diameter choke would not be unexpected for my 700 hp engine. Recommended, in fact. There is a relationship between primary pipe size, and length to the choke size, too.

todd

[XfireZ51]

Right on, FR. In fact, a 2.5" diameter choke would not be unexpected for my 700 hp engine. Recommended, in fact. There is a relationship between primary pipe size, and length to the choke size, too.

todd

Todd/FR,

Thx for the input. Could expand on the relationships you are discussing?
If I am understanding FR, you are saying the bang for the buck isn't there in removing the constriction.

[jonszr1]

i not to long ago posted the difference between the 21/2 in corsa and thew unique 3 in system my kids came up with . the car with the corsa the car with the corsa went 12.71 114.77 with the change over done between rounds on the same day at fointana the car went 12.23 .@116.40 the 3 in they came up with had a unique dual crossover witch was a 3 in wide by 3 in deep reqtangular pipes that look like 2rulers done at the area where the pipies bend to go down the tunnel . they then put in 2 21/2 in super turbo mufflers. they then changed to 3 in super turbo mufflers and found that the et got better but not the mile an hr . hopefully i can get to bill boudreaus house to take some pics to show what they did . all i can say is this exhaust makes more poiwe than the corsa and is even quieter than the corsa also . i do believe that it is the best of both worlds unless one wants a very loud exhaust . i will say i dont like the collector that stainless works puts on their headers

[XfireZ51]

Took a trip to Brakes Plus yesterday to "address" the constriction issue, thanks to Al. Seems like when there's some work to be done on a ZR-1 in Chicago, some of the luminaries show up. Low and behold, Pete comes over to mount some Nitto's on Kevin's car for BG. Paul Workman showed up also. Helpful that they were there to lend a hand. Completely impromptu on an FBI Friday afternoon. Besides the narrowed header pipe, we also tacked the muffs. They'd rotate when the motor torqued over giving them a cockeyed look.
The piece we eliminated comes from Magnaflow. The system is meant for a stock exhaust LT-1/LT-4 motor so it makes sense but not for the LT-5 with headers. Here's what it looked like: :jawdrop:

http://i187.photobucket.com/albums/x198/Z51Xfire/OEM%20Z06%20Wheels/Constricted%20Exhaust/OD.jpg

http://i187.photobucket.com/albums/x198/Z51Xfire/OEM%20Z06%20Wheels/Constricted%20Exhaust/ID2.jpg

http://i187.photobucket.com/albums/x198/Z51Xfire/OEM%20Z06%20Wheels/Constricted%20Exhaust/Sideview.jpg

http://i187.photobucket.com/albums/x198/Z51Xfire/OEM%20Z06%20Wheels/Constricted%20Exhaust/ID.jpg

The OD of the pipe was 3", while the ID was 2.75". However, there it slipped over onto a 2.25" inner pipe that was attached to the female ball flange. We replaced all of that with a 3" female ball flange which slip fit into the swedged portion of the original 3" portion of exhaust pipe. Al then welded it.

[Paul Workman]

Right on, FR. In fact, a 2.5" diameter choke would not be unexpected for my 700 hp engine. Recommended, in fact. There is a relationship between primary pipe size, and length to the choke size, too.

todd

The discussion is missing the point, methinks... We're not talking about a 2.5" path vs. a 3" path and choke points or tapers reached over a significant transition... No! Dom's issue is a transition length near zero, which is quite different from a "megaphone" type transition (like Ryan pictured).

I don't know how laminar flow is affected by pulsing, but that aside for a minute, maintaining laminar flow thru a transition from one diameter tube to another depends on the RATE of transition between pipe diameters.

Gas has mass, and therefore a given volume of flow from say a large to a smaller tube requires the gas to accelerate. And, we all know the (equal but opposite) force the mass has against the force attempting to propel it increases with the rate of acceleration, right?

So, as this applies to the volume of a gas pulse traveling down a pipe, if the pipe diameter is decreased, then the gas will have to accelerate. But, it is that rate of acceleration that determines how much force will be required to accelerate the mass. If the transition is relatively gentle (like the choke transition Ryan showed us), so will be the acceleration rate and the resistance will less. But, on the other hand, if the transition is instantaneous, the transition time factor goes to zero.:jawdrop: Power = work/time and so it would take an infinite amount of power to make that happen...and therefore it won't. So, what happens is the resistance to the sudden change is in the form of the pulse energy being reflected back; colliding with other gas pulses and the result is laminar flow is replaced by turbulence. Like rocks in a stream of fast moving water, you get disruption of the flow - rapids!

So, I believe the same is true for gasses in (Dom's) exhaust meeting an abrupt obstacle. As Todd pointed out, There is a relationship between primary pipe size, and length to the choke size" We're not talking about laminar flow through a tapered transition, but "square lips" (as Ryan once referred to such transitions). And, what would reflected energy mean to flow should the reflection arrive at the exhaust valve at the moment it opens??

This is the place where I start getting a headache - starting to revive the math to determine null and nodes and at what frequencies... So, for my 2 cents, my intuition has me totally thinking Dom was right in removing that ridiculously abrupt constriction, especially as close to the exhaust valves as it is. But, w/o doing the numbers, I wouldn't want to say for sure just what practical effect that (abrupt) choke point would cause. Yep...Could be a lot about nuttin, I suppose. (But I eliminated that same POS choke point in my system for the same reason Dom saw fit to do so...Great minds n all that chit!...For what it's worth.

P.

[FU]

i not to long ago posted the difference between the 21/2 in corsa and thew unique 3 in system my kids came up with . the car with the corsa the car with the corsa went 12.71 114.77 with the change over done between rounds on the same day at fointana the car went 12.23 .@116.40 the 3 in they came up with had a unique dual crossover witch was a 3 in wide by 3 in deep reqtangular pipes that look like 2rulers done at the area where the pipies bend to go down the tunnel . they then put in 2 21/2 in super turbo mufflers. they then changed to 3 in super turbo mufflers and found that the et got better but not the mile an hr . hopefully i can get to bill boudreaus house to take some pics to show what they did . all i can say is this exhaust makes more poiwe than the corsa and is even quieter than the corsa also . i do believe that it is the best of both worlds unless one wants a very loud exhaust . i will say i dont like the collector that stainless works puts on their headers

Like to see a pic if possible Jon.

[jonszr1]

frank i will try to get one posted hopefully by fri . i have to have a friend do it as i only have very basic computor knowledge . heck i dont even own a cell ph. boy i do like this exhaust quiet as stk with headers till ya get on it. there is a vid on u tube of the car at the strip not oine of the better runs but gives one a good sound clip . its under jetta vs corvetteat acd. you have to print it that way as the guy that made the vid didnt space betweencorvette at