That would be some very useful and inciteful information.

Duke

If the minimum ID is 2.5" then a flow rating of 500 that I use for the OE 2.5" systems is probably in the ballpark, but if any projections into the flow stream reduce the diameter to under 2.5" that's the dimension you should use, then factor the flow by the area ratio. It's important to use the minimum ID. If you have a 4" pipe with one 2" restriction, it's going to flow like a 2" pipe! A corollary to "a chain is only as strong as it's weakest link" is "a duct will only flow as well as its minimum cross section."

A slightly smaller tailpipe diameter out of the muffler, especially if it's short is not a big deal due to exhaust cooling.

To get 750 CFM flow you're going to need 3" pipes and very low restriction mufflers with at least 2.5" internal passages, preferably straight through type like Dynomax Ultraflows or Magnaflows.

Duke

I'll see what I can do. And I agree 100% with your #20 post, (the others as well, of course).....you need to "Engineer" the complete package, or system, for a specific usage. I'll be doing some dyno stuff this winter and I'll pass on what I learn. I'm trying to design a balanced combination, that optimizes all the "stages" of the system, within a specific RPM range based on my intended usage, considering factors like chassis/tire limitation, gearing, etc.

On the factory sidepipes..... from what I gather (and I'm sure you know better than I), the race cars of the day had "loud side pipes", and someone in marketing said "make us some good looking loud sidepipes" for the production cars, and Engineering had little input. Hence, the C-2 "good looking loud sidepipes" that....well, flowed whatever they flowed.

JohnZ has previously stated that the sidepipe option was driven by marketing, not engineering considerations.

Back in those days I think they designed the car and then added the exhaust system wherever it would fit, but the C2 was an exception.

The "holes in the frame" showed that the exhaust system was considered from the begining, and placing the mufflers at the extreme rear of the car was not only a good packaging solution, but improved exhaust system performance as well.

Duke

dang I was afraid of that....I don't know that the pipes have any reduced diameter point but it is possible around bends etc. the internal diameter or the chambered sections seem to stay at 2.5. I wished I had done 3 inch at least back to the chambers...oh well this is was just a cheap an experimental pipe system for me, once I get it worked out I'll have it redone in stainless. Finding the right muffler is the trick...the off-roads would be perfect if they existed at some price that using them up didn't bankrupt me....I'm guess they flowed ok. I had hoped the bigger chambers would flow well. I will have to do some open vs closed tests and see what happens...Thinking some DynoMax next time...without the spare carrier I could maybe get an extra pair or something under the car....not sure how I would work the exits....wonder how loud those race mufflers would be.

Duke do you think Crossover Tubes really help especially at lower RPM? I haven't found how to get it represented in the Engine Analyzer, except by just guessing and adding some to the flow numbers...However I would expect that is not really real, since adding the crossover probably just allows you to get closer to the full flow potential, not really increase it....guess it depends on how the flow numbers are derived.

for what it is worth I found this....

http://www.dynomax.com/news/Downloads/SEMA-Flowv2.doc

If you're working on an under-car system, you may want to review what this guy has done...... I've seen this car in action, it's not excessively loud, and it's faster than Stink!, and he's moving 511" @ 6500 RPM, or so, worth of air thru it.

(just put the address in your browser, and then remove the space in the word "document", i don't know why that space is there, but i can't get it removed lol )

http://www.fastraces.org/members/fastraces/fastraces.nsf/822dcaaaa26c6da985256dd80023623d/c10e85e88cc2ec19852571360045fb07!OpenDoc ument

and who ever worked up those 2.5" "Rams Horn" manifolds did some good work..... very compact, and efficent (as you've said numerous times).

What was the air/fuel ratio between the side exhaust engine and the under car exhaust engine?

No way to model a crossover in EA that I know of. I believe it assumes two isolated systems on an eight cylinder engine. A crossover probably helps the torque curve at various points, but the effect is likely minor. The main purpose of a crossover is to soften the low frequency noise by allowing eight evenly spaced pulses on each side rather than four uneven pulses.

The human ear prefers higher frequencies.

If your current exhaust system model is causing high backpressure, spread out the LCA and see what happens. Exhaust backpressure will not be affected that much, but the torque curve should be improved if the effective overlap was over 4 sq-in-deg to begin with.

Duke

Duke, one of my buddys even spoke of hooking a gauge in the exhaust to get a real world test of an exhaust system. Never though of side pipes on my body style. I have 2.25" back until the Exit of the mufflers. It was as much as the muffler shop guy wanted to tangle with. Still have to adjust a hanger every now and then.

A gage would provide some good info. One could drill and tab an old heat riser and plumb in at that point pretty easily.

Duke, I understand how jaded you can get with the aftermarket. I am so frustrated trying to hot rod my car in a sensible manner. How hard can it be to flow a #$%@^ muffler???????? This data should be as available as the muffler case size.

Here's a Vizard article on developing a muffler system with minimal impact on performance. I thought it had some good points:

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

I've agreed with most of your statements in this thread except this one. The example you gave of "If you have a 4" pipe with one 2" restriction, it's going to flow like a 2" pipe" is inaccurate. It will actually flow somewhere in between depending on the transition to and from the restriction, where the restriction is located, how long the rstriction is, etc.

I guess it boils down to what you're trying to represent with that statement. If you're attempting to make general recommendations concerning good design, then yes, if you're trying to put empherical data to a design, and be reasonably accurate, then no.

The rest is good information.

What you need is LARGER FLOWPATHS!!! The OE & reproductions do not address this vital issue.

Check this out: http://www.classicchambered.com/clas...rformance.html

Since I don't know hot to attach a file here, someone want to volunteer to post a pic. for me? PM me with your E-mail.

Pay close attention to figure #9 in the article, and the accompanying text that addresses expansion chambers.

I believe that is the only thing that could have boosted my torque appreciably in certain RPM ranges.

Doug

Duke,
I've read some articles on extending the collector for added
power gains... so, I must admit I was a little surprised by your
findings.... Have you studied collector length in relation to power and
.. would it be safe to asume that an extended collector exhaust
with traditional high performance pipes/mufflers aft of it is different
than just plain sidepipes??? apples and oranges???

Kyle


Edit- this would obviously be in a stituation where headers were used

In the early/mid '60s many of the NHRA stock class record holders all used Stahl Headers. For a relatively short period of time "Stahl's" theory was that longer collectors added more power. The cars with his headers ranging from I/Stock up to FX (Chev Z-11's) had the headers exit the front fenderwell and then had a collector the full length of the rockers back to the front of the rear wheels. They all sounded kind of funny with this set up. It wasn't too long before Jere's next theory cut the length of the collector to about 1-2" from the front wheel well.

Here's a Vizard article on developing a muffler system with minimal impact on performance. I thought it had some good points:

http://www.popularhotrodding.com/eng...exh/index.html[/QUOTE]

What a great article. Two points are really important: one you can build a tuned header system and get the benefit of it's tuning as long as you have an expansion box (plenum) or some such (why would the wave care if it's reflected from an expansion into a 14.7 psi space or a 16.7 psi space) and (I'm not sure he covered this) mufflers don't like to be pulsed, they want to be steady state flowed. A plenum in the exhaust helps to approach this. Gee given appropriate design even a stock motor might benefit form headers.