Here are two resources for understanding your engine as a complete system.

The first is an exhaust article by David Vizard in Popular Hot Rodding. The key part of this article is David's discussion of high performance Otto cycle (4 stroke) engines as really 5-stroke engines, due to interaction between the exhaust system and the overlap cycle. What does a long tube header really do? How does it interact with your cam? This is a pretty short, easily accessible article for understanding those topics.

http://www.popularhotrodding.com/eng...exh/index.html


The other resource discusses not just exhaust tuning, but all of the gas dynamic interactions in a running high performance engine. This is actually the user's manual for the updated Dynomation engine simulation program, but beginning on page 231, there is an extended chapter on gas dynamics that is quite complete but much more accessibly written than my old Internal Combustion Engine textbook. To really understand how your intake, exhaust, and cam form a system in your engine, this is a must read. Unfortunately, the PDF file is 44mb, so dial-ups are out of luck (:


http://www.proracingsim.com/download...sersManual.pdf

 

I read the first article when it was in the magazine. It's a good read.

The second link doesn't work.

 

Link fixed. Sorry about that.

 

I really liked the Vizard article. It's hard to talk to companies though when selecting a muffler, especially when asking them flow numbers on a muffler cause they all say that " flow numbers don't mean crap, we have dyno tests that.....". Without knowing all the variables it's hard to make a final decision. I was trying to use this information to select a baffled style (no glass pack) kind of muffler for my n/a 434 cause of the fact that they appear as a termination in the exhaust system as far as collector lengths and pressure wave tuning are concerned. Mr. Vizard indicates that glass pack mufflers serve to elongate the collector as far as pressure wave tuning is concerned but does not indicate by how much. I guess it's all very dependant on the specific "glass pack" muffler of concern and the diameter to indicate at which rpm they become effective.

 

I built an exhaust expansion chamber for my supercharged MG-powered Morris Minor back in (gulp!) 1968, based on similar recommendations in Philip Smith's book on exhaust tuning. It really punched up the mid-range and made the thing sound like a BMW boxer twin on nitro!

 

The expansion chamber is a great idea.... terminator boxes. I have two of them in the shop.

Bret

 

The Brookland's "Silencer"?.

As SStrokerAce just mentioned, he used terminator boxes in 2002 for a SBC. I had fun helping on them.

I hate to admit that I read Smith's book when it first came out ('62?) when I was in college. I may have you by a few years, Bill.

 

Both good reads, thanks for the heads up.

I wish the exhaust companies would make real resonator/termination boxes. Whenever you look for resonators you find glass packs.

 

If Flowmaster made a 80 series with absolutely nothing inside, it would be a fairly good terminator box. One problem with an empty muffler shell is not much support on the wide fairly flat panels so it booms or vibrates a lot.

Terminator boxes generally don't do much quieting. I don't think I'd like them on my street car especially because the'd be just about under your feet or seat. Resonators are meant to get rid of certain (annoying) frequencies. The glass pack technology does that. There are other ways.

 

Do you know of any flowmaster style (spintech or anything with an open box, not a glass pack design) muffler in the 3.5" and up range that flows around 800 cfm? It would be nice to kill two birds with one stone.

 

I don't think any of the "open box" designs would help much because they don't flow enough, as you said. The Dynomax or Magnaflow high-flow designs which flow way over 800 cfm still make the engine think they are part of the secondary header length.

I don't know how to do it without the box and the muffler unless you don't need the muffler at all.

 

Lots of great stuff here!
1. Hadn't thought of the Brooklands-required design, OSS! (Didn't it include a rather stifling fishtail though?)

2. Late '43 vintage here, OSS, how 'bout you? (o:b

3. For anyone who hasn't yet read the Proracingsim download, you'll lust for the "how to" after reading the excellent tech stuff starting, as per 71C, on P. 231. BTW, there appear to be a ton of improvements in the speed and functionality of the new Windows-based version, and the tech section is a lot more detailed and much better written and illustrated. Actually running the program is a blast (even in my DOS version), as you watch all those pressure traces do their dance. You can understand at last what's really happening. (And by the way, Vizard is a strong proponent of DM. He says he turned an engine designer friend onto it in the late nineties and the guy used it to greatly improve a Formula One engine he was working on...) Two thumbs up!

4. I haven't found a bench big enough to properly flow my 4" 40 Series Flowmasters, but they look (and Vizard mentions in that article that they are) empty enough to qualify; just enough baffles to keep the sides from flapping! At 5" x 12" x 17" or 930 c.i. volume, they are also plenty big enough: 15X one cylinder's displacement of my 495 BBC (also aluminum, 71C!). Now all I have to do is figure how to get them under the floor of my '70 Camaro and still have some ground clearance! I would think the Spin Tech design would also work. (Or maybe we could line empty boxes with glass wool to cut the cackle?)

 

I forgot the fishtail. Just leave it off?

Early '43 vintage here. I told you we went to different schools together!
BME (Automotive) '66

 

E.O.I.T. Mechanical, Ottawa ON, '67
(o:b

 

is it just me or is vizard in his article just trying to add some sort of anti revertion to the ex system but not call it that ? becouse a far as I can tell the reason that the flowmaster race mufflers make more power then most is becouse they are not only high flow but anti revertion .......

 

Well most aren't high flow. It's not anti-reversion per se, it's tuining the length of the header collector to a certain length for best power. His terminator boxes act like the atmosphere, or the tailpipe. You can put whatever you want behind that and be happy.

Bret

 

that is my point a terminator box lets the air speed drop as it comes out of the pipe and therefor becouse the air has little energy left do to expansion it cannot flow back into the pipe I.E. anti revertion ......and there are some other high flow mufflers out there like borla but in looking at the plates in a flowmaster the air can flow well one way but not the other though personly I do not like the sound I wonder if I could gain any power by adding a race muffler after the headder then on to the rest of the ex with muffler though I am not sure there is room .....

 

If you ever want to be suprised throw them on a motor in the engine dyno. Try something like a Dynomax or Magnaflow and then compare that to a flowmaster, you will see a big difference. You gotta take into account the length of the system when you are doing that but either way you will see the flow differences pretty quickly.

Bret

 

If the exhaust gasses expand as they enter the box and slow down, then pressure will increase. Pressure and velocity are inversely proportional. That's how a carb venturi works, only here the velocity increases and the pressure drops so fuel can be "sucked" in. Actually atmospheric pressure forces it in.

Because the terminator box is not "as big as all outdoors", the gasses flow out the other end. The cfm out = cfm in minus any cfm that is lost because the gasses cooling in the box. Here's where flow is directly proportional to the temp of the flow. So, there is not much pressure build up in the box, and if there is, the outlet is the least restriction,so that's where the gasses go. Oh yeah, the boxes DO get hot when you are pumping max hp thru them.

A good t'box has a bellmouth leading to the outlet. It generally sticks well into the box, so most of the gasses just pass directly from the inlet pipe to the outlet bellmouth. At least that's how it is on the ones I've seen.

Th t'box is there to cause a pressure reflection back up the header extension, not to slow down the gasses or take flow energy from them.

Mufflers take heat out of the gasses which decreases their volume and slows them down. These are all things you probably don't want to do right behind the header. The farther the muffler is from the engine, the fewer cfm of exhaust flow it sees, so the less restrictive it is. You put the t'boxes in the system to cause the tuning pulses you want.