[Tom Hand]

Robert,
Again, thanks for posting that article link but you do realize MagnaFlow and Walker Dynomax are two separate and quite different companies don't you? Magnaflow has no real public or private connection (that I am aware of) with Walker Dynomax UltraFlo mufflers.

Walker is a Tenneco Automotive division based out of the Midwest and Northern portion of our country and Magnaflow is from the California area.

The Dynomax folks use a very large, quite sophisticated, and very different "cold flow" air flow measuring system than Magnaflow does.

Take care,
Tom

[Z Code 400]

Tom,

My error and corrections noted on the Magnaflow/Dynomax issue. That was a typo and I was reviewing a lot of data from the two firms at the same time. I appreciate you setting me straight on that one for the record.

Your testing was very well thought out and accurate. We duplicated several tests and found that 480-500 cfm through a 2.50" pipe @ 28 in/H20 is about the limit.

Even flowing at 20.3 in/H20 (the rate is at the bottom of the flyer) 2,200 cfm from a side inlet muffler is most suspicious...Robert

[Z Code 400]

I thought it important to note that both Joe Sherman & John Kaase prefers to use a perforated core glasspack to increase collector length to roughly 40" overall. Their testing suggests the added collector length and open design of this system has a substantial influence on the engine's torque curve.

Of interesting note, chambered mufflers, such as Flowmasters, appear to the pressure waves much the same as the end of an open pipe. This means the pressure waves see no change in collector length and pressure wave reflection is largely the same as it was before the muffler was added.

A glass pack muffler can act significantly different. It does not appear to the pressure waves as the end of an open pipe, but rather as a substantial increase in collector length.

Additional dyno testing was conducted on the balance and x-pipes. Virtually all V-8 exhaust systems can be refined by the addition of a balance or X-pipe. Extensive dyno testing on both of these systems indicates balance and X-pipes are indeed successful at reducing noise. However, on engines producing between 325 to 550 horsepower, 60% of the engines tested delivered as much as 12 additional hp, with 5-8 being the most common increase. The other remaining 40% tested showed virtually no change in output either positive or negative.

We found this of particular interest since we are yet to see an improvement in output with the X-Pipe, although some do report such an improvement.

I hope you find this information of interest...Robert

P.S. When referring to the primary tube selection chart, where low-speed torque is of prime importance (especially with a stock converter and high rear end gears), use the lower line to select the appropriate primary size. For hot street machines having reasonably big cams and higher SCR's, use the middle line to size the primary tube. For race engines, use the top line.

[Jack Gifford]

Is that third image from old Isky '5-cycle' ad copy?

[Z Code 400]

Jack,

It's not an Isky image, but it does illustrate the principle. Ed Iskenderian gave me a t shirt many years ago that depicted a clown riding a bicylce, carrying a trophy that said "Iskenderian 5-Cycle Racing Cams." We also received a lot of decals from Isky back then and the clown was present on those too...Robert

[BruceWilkie]

1800 deg exhaust temps = rapidly melted pistons. 1350 degrees is pushing the edge on short bursts. (1st hand experience 5 seconds at 1500 degrees cylinder looked like it was sprayed with a plasma welder! 105HP from 501cc was nice to see while it lasted). something to think about is rapid cooling = rapidly shrinking(relatively speaking). High pressure pulse following previous pulse gives a big push to the already shrinking pulse. Somewhere in my head is a figure of 300 ft per second being an "ideal" velocity in a header tube at peak power. Dont remember my source though. Want to really get to know exhaust? Spend some time with 2 strokes. I know of more than a few 1000cc 2 stroke snowmobiles fully trail ridable on pump gas in the 220 hp range at @9000 rpm. Tail pipe(single) about 1.25". Lots of things happening in those expansion pipe exhausts! Relatively recent PHR Engine edition had some very useful info. (Your attachments look DAMN familiar too!)
Big head pipes and large body (length and width) muffler = maximum shrinkage. Take a lesson from the Jap performance cars thats just what you see. If you could find a way to fit under a "normal" car a tuned expansion system as found on 2 stroke race bikes and snowmobiles you could get some interesting results. (It would be even more interesting if you could easily convert a 400ci Pontiac to 2 stroke but Im straying too far from topic). Real world street/strip car 400 will get by fine with 2.5 inch exhaust. As you increase displacement say another 50 cubes 3" will get the job done 500 inches 3.5inches. One key to this is straight flow paths. Another is anti reversion tech wherever you can utilize it. OH and rapid expansion followed by cooling and shrinking, in the right place and time. Seems so simple doesnt it?

[BruceWilkie]

Want GOOD exhaust tech? Find and read May 2005 Popular Hot Rodding. Excellent info from David Vizard. I knew I'd seen some of those thumbnails somewhere.

[BruceWilkie]

Here is the link!

http://www.superchevy.com/technical/...exh/index.html

[Z Code 400]

Thanks!!!

[BruceWilkie]

There is a misprint in that article showing std airflow at 10.5hg! That is wrong it is 1.5hg! To answer your original question of how much air flow thru 2.5" pipe at 28"water the answer is approx 657.

[exhausted]

While there is a minimum diameter necessary to make good power for any application, another problem creeps in as you get too large in tailpipes. Larger pipes also allow ambient air pressure to be closer to the engine which can hurt performance especially if the engines headers are too big. Larger tailpipes also slow down pressure waves in the system this can both hurt or help depending on how you are tuning an using the motor. So to help wear it out, bigger is not always better. I value flow numbers as we can learn if a component offers a restriction to flow, but the point to me would be to make sure that there is not a place in your system where the flow is hindered creating a choke. Increasing diameter will not overcome the loss of a badly flowing part of a system. Unlike in the intake system, exhaust flow does not recover from a point of restriction. There is no piston pulling the flow out!