Ran into some interesting info and fomulas.

[dbrick]

.I was looking around and found this on a Chrysler engineering site.
Would be useful for anyone favricating fuel injection manifolds.

Here it is
Someone, I think a brilliant engineer by the name of Bob Graham, deduced that if we tuned our intake runner to the point where the resonance was greatest, it would give the maximum push to the air and fuel when the intake valve opened at any given speed. The theory proved correct in the tests on the single cylinder and the results were reduced to a formula that was used from that day forward for ram manifolds on Chrysler engines. The runner as measured from the valve seat to the plenum (the open area where they normally meet under the carburetor,) can be determined by dividing 84,000 by the length of the runner = the speed the runner will work the best. An example is:

84000 (constant) = 5250 rpm
16 (runner length)

The formula worked with all camshaft designs tested, engine displacements, compression ratios, and bore and stroke combinations of the time.

An exhaust tuning formula was also developed on the single cylinder test stand. An example is:

205000 (constant) = 5256 rpm
39 (length of exhaust runner to collector)

On the exhaust tuning we found that we could flatten out the torque curve by adding length to the collector (the point where all the runners meet.) The collector on an engine with all cylinders operating was usually a tube measuring about 20% smaller than the total of all the exhaust runners.

[Daryl Smith]

Nice find Dave!
It is pretty close to what I have read as optimum lengths for the intake and exhaust.

Trouble is trying to fit anything near that length into our cars! For the intake, I think that is why most of the OEM manifolds have "U" bends and crossovers etc. For typical "street" rpm you need a fairly long runner. I've managed to get about 10" runners on my intake (straight).

For the exhaust, on the available header, one of the runners (#3 0r #4) is only about 18 or 19" long. Even at that there is, IIRC, bairly 12" between the end of the header and where it runs through the frame . Barely enough to mount a flex connector and connect to rest of exhaust system.
I've been trying to figure out how to best fit a longer header, including modifying the frame, or different routing. It is on hold till the rest of my mods are finished.

Just as important as length, is the diameter of both runners. This seems a little harder to determine. I am running 1 3/8" runners on my intake.

I have read/heard where many track small block Chevy's are running 1 1/2" diameter headers. Of course these will be of optimal length and rpm specific..... What do you do when your headers are not of optimal length and lower rpm? Larger diameter? Smaller? I have decided that mine will be either 1 1/4" or 1 3/8" on my 1800cc ( 1 1/2" or 1 5/8" available from vendors), but still looking for more concrete info on how to size them. I will also be looking for a better/longer collector design (4-2-1 header).

Also, on the length of the collector......I "think" those comments were for an unmuffled system, and results may differ on a car with a full exhaust system.......???

Oh yeah, I haven't forgotten about those songs. I just haven't figured out how to convert to MP3 to email to you........