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.

[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.
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]

Originally Posted by 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.
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. 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]

Originally Posted by 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.

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]

Originally Posted by todesengel

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.

[Paul Workman]

Originally Posted by 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.

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. 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.