I thought the collectors looked better on the Bursch headers. They look merged while others just come together suddenly and then continue.

This is a great merge collector:

http://www.spdexhaust.com/images/Sec...or/MC/MC12.jpg

Our RSR headers were designed specifically for the 3.2L engine. Sold mostly to race shops which wouldn't use them if they didn't perform. They are medium equal length primaries with F1 merge collectors tuned for 5800rpm.
We are finish up a long tube version using the same principles, true equal length 30.5 +/- 0.25 with the same F1 merge collectors. Carrera version will have 1.63" primaries and 2.25" secondaries. Larger secondaries require custom muffler inlets to match, OEM is 1.875" and our street mufflers are 2.0".


http://forums.pelicanparts.com/uploa...1574205920.JPG

http://forums.pelicanparts.com/uploa...1574205920.JPG

Brian,

This looks like a long tube header, are the primaries about 30" long?
Those collectors are very well made! Fantastic job!
I did not know you were making long tube headers now, very glad to see these.
Can you wrap heat boxes around these also?

Primaries on these are 30.5" +/- 0.25" which took a lot of work to design. Every other setup I measured had huge variance between the primary lengths, one was 2".
Yes we are working on heat exchangers right now. The last step is to add the inlets and outlets which will be test fit this weekend. I'll post them up in the thread that was started a few weeks ago. Once that is finished we'll be adapting the system for use with 997 and 991 GT3 mufflers. There will be a lot of options for secondary (muffler) systems using the V-band arrangement on the bottom photo above. This was a lot more involved than it appears, the headers were designed to fit all 911 from early to late with any transaxle from 901 to G50. They clear the early oil lines and oil tank line and might clear the late oil lines with the right secondary system. Will work with thick flange or thin flange studs just like our RSR hearers. I lost count how many times I test fit this system to different cars.

While I think that Rarely's headers are a great product you have to remember that w/ a muffler on the end of them most of the acoustic tuning benefits go away.

There are 2 main parts to exhaust design
1) flow - where you want to keep heat in and turbulence out, keep gas speed and laminar flow up
2) acoustic - where you are trying to place an acoustic rarefaction signal at the exhaust port at the right time to draw extra gas out of the cylinder and in some cases extra mixture into the combustion chamber(this is sometimes called the 'fifth cycle'.

mufflers kill the later. There are multiple acoustic signals generated in the exhaust system, varying in timing and strength, every change in diameter, merge, lip etc, generates these acoustic signals but the main and by far strongest one is the transition from collector to atmosphere. In the best systems this signal is further amplified by a precisely designed megaphone and will often include a reverse megaphone to smear the signal out and make it last longer at the exhaust port. A part of the design of these systems is pipe, properly sized in diameter and length. The minute a muffler is added all that engineering is obviated.

W/ mufflers flow is all that is left, design features that maximize flow are proper pipe size, gentle bends, tapered merges and smooth transitions, you can get some of the acoustic signal back by extending the collector pipe an inch or so into the muffler cavity(if it has one, Flowmaster works best for this sort of thing, perforated pipe mufflers not so much)

Does a cherry bomb canister muffler help here? These mimic a straight through secondary and help reduce sound a bit.

Straight through muffler design is much better than baffles and chambers. The perforations of a bullet muffler are a pressure outlet which slows velocity but nothing like hitting the wall of a baffle or chamber. The object is to disrupt flow as little as possible while attenuating noise level, a tall order. A properly tuned exhaust system will be hindered by any type of muffler, but it is always best to start with a properly tuned system. If that were not the case then headers would perform no better than OEM exchangers or other headers of a different design once the same muffler is added.

I think most automotive engineering theories agree that the maximum effect of a tuned exhaust system results from an open atmosphere at the end of the collector. The tuned air pulses that help increase exhaust gas velocity are either partially or totally negated by the muffler as a result of its function to decrease exhaust noise.

A muffler is used to attenuate (reduce) the exhaust sound and not to increase power. However, a muffler change can restore lost power produced by a less efficient muffler. Thus, the ideal muffler is one that produces the desired exhaust note while producing the least power loss.

Not sure if the above helps aftermarket muffler selection.

Sherwood

No, Cherry bomb use a perforated core wrapped w/ f/g or steel wool or some similar product

Here's what they do / Flowmasters to reinforce the acoustic signal
http://forums.pelicanparts.com/uploa...1574289302.jpg



You could do something similar w/ stock or GT3 mufflers which also have a chambered design
http://forums.pelicanparts.com/uploa...1574289302.jpg
http://forums.pelicanparts.com/uploa...1574289302.jpg
http://forums.pelicanparts.com/uploa...1574289302.jpg


But not w/ 993 types
n/a 993
http://forums.pelicanparts.com/uploa...1574289302.jpg

993t this one flows better than the n/a version
http://forums.pelicanparts.com/uploa...1574289302.JPG
some other perforated pipe systems
http://forums.pelicanparts.com/uploa...1574289302.gif

http://forums.pelicanparts.com/uploa...1574289302.jpg





Ricardo has been doing the work for Porsche on their more modern systems
http://forums.pelicanparts.com/uploa...1574289302.jpg

http://forums.pelicanparts.com/uploa...1574289302.jpg

Installed my headers from William Knight today, together with the Dynomax 17231 mufller. Spent all day cutting and welding (I suck at welding)

Out with the 2.4 heat exchangers and in with Knightrace headers

What a difference. This is a fresh rebuilt 3.6 with a SW chip. Completely standard otherwise. With the 2.4 heat exchangers, it was fast, good torque, but had a noticable drop after 4500rpm.

Now......oh boy. It's a rocket. Idle tone is so-so,.but when you get on it, it Sounds like a mad chain saw. It's loud, but not too loud. However, this is my daily driver, so we'll see.

Before and after:

http://forums.pelicanparts.com/uploa...1580156268.jpg
http://forums.pelicanparts.com/uploa...1580156268.jpg

GREAT JOB ! On the sound it looks like it exits the sides, it is fine, I am posting this in case others have questions, If you add an additional 90 degree sweep and send the exhaust out the back it cuts sound levels quite a bit. Great work and it takes me over a day myself, William Knight
KNIGHTRACE@MAC.COM

Yeah took me all day. Almost done, just need to trim the pipes a bit.

http://forums.pelicanparts.com/uploa...1580158066.jpg

do they have a one out muffler with same flow characteristics? prob a lot quieter

Not developed one thus far, I may in the future but it will be a while, catching up still, WK

Do you guys have any sound clips of the Dynomax flow-x muffler?

I’ve building a 912, and considering that the flat-4 fires each cylinder bank sequentially, if you merged each bank into a Y, then into the muffler, I'm thinking you'd get some decent scavenging in the crossover, or at the very least, wouldn't get get much if any back flow.

I’m curious what they sound like and how loud are the compared to the stock muffler.

https://uploads.tapatalk-cdn.com/202...93bed43465.jpg


Sent from my iPhone using Tapatalk Pro

We have had problems with that muffler. it blows the fiberglass out.

I can see how that happens, evidently a lot of people seeing the same issue.

How did it sound though? I'm thinking about using the Magnaflo 11386, which is a similar X design, but it's all welded, with no glass pack.

http://forums.pelicanparts.com/uploa...1580953483.png

I've wondered if those cross flow mufflers are really a good option on a 911. Due to the engine/exhaust arrangement on a 911, we tend to have the exhaust entry on opposing sides of the muffler. So basically the flow from the left bank meets the flow from the right bank almost head on at the X (destructive interference). I'd guess that these mufflers are intended to be used with the two inlets on the same end.

I worked on the magna flow mufflers and an engineer from magna flow helped named Nick Howe, ultimately they work but hurt the top end hp on preformance based engines. I have all the internal diagrams if someone would like them. William Knight KNIGHTRACE@MAC.COM