I bought a new kit but we will be using the flanges and some of the tubes from those, nothing goes to waste.

I might add that they are a lot like Teds EMC headers so I would think performance would be close. The new ones will have some interesting bends to get around the steering box and even the pass. side will have to be close to the same to even things out.

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias

Scotty

From the book entitled

Scientific Design of Exhaust and Intake Systems-Philip H.Smith and John C.Morrison

"It may be considered that the slightly increased area at this point is of benefit in reducing pressure,particularly as there is often a sharp bend in the cast manifold bolted thereto."

Its due to the bends encountered being so close to the flange.

I also remember reading something on exhaust by Bill Jenkens.

It stated that since there is a high pressure charge being released thru the opening of the exhaust valve that there was turbulance in the flow.This resulted in possible contamination of the incoming charge due to the camshaft overlap sucking the spent charge back into the cylinder.

Basically the spent charge would creep up the outer edges inside the pipe.By keeping the flange at a greater opening than the pipe diameter the spent charge has a more difficult time getting back thru the exhaust valve.The spent charge is blocked by the actual head material exposed by the flange opening.

Oldmics

Old Mics has pretty touched on many of the points regarding why the ports in the headers or the manifolds are shaped like they are. I’ll add that if the heads are ported to the common rectangular shape, then a round port at the header flange can be obstructing part of the exhaust flow into the header. A rectangular port at the header will allow for the same cross-sectional surface area as a round port but will be a much better fit to the port at the head. On the stock exhaust ports at the heads, most are small enough that a round header port at the flange will not present any kind of obstruction so round ports can be found on the flanges of some of the older Y-Block header offerings simply due to the ease of manufacturing them. As far as the use of round tubing for headers goes, that’s what is readily available. Square tubing actually looks to have a flow advantage but is difficult for the average shop to perform the necessary mandrel bends to keep that flow advantage to the forefront. Hence, 99.9% of the headers you see use round tubing.

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The ported aluminum heads on the EMC project engine have a very rectangular or oblong exhaust port which fits up to a very similar shaped exhaust port on the headers. Flow restrictions at the header to head are thus minimized. General header design typically points to having an exhaust port at the header that’s slightly larger than the port at the head so that reversion pulses coming back up the header tube hits the head rather than going back into the cylinder. As the overlap cycle in a camshaft is increased, also is the propensity for some of the exhaust to be pulled back into the cylinder during that cycle. By maintaining a larger header port size than the port size at the exhaust exit at the head, some of the potential for dilution of the fresh intake charge going into the cylinder is minimized.

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Here’s a link to a past thread showing some different exhaust porting techniques which in turn requires appropriate header ports or flanges to match.

I appreciate all of the work you did on the different exhaust manifolds.  Great results!!

A couple of questions on my 60 ford 4x4 which now has single crossover exhaust to stock muffler coming out midway down the truck:

1.  Thinking of using ram horn or sanderson truck headers. Would you use 2 and 1/4  on ram horn and 2 and 1/2 pipes on Sanderson truck headers?

2.   I need to have some type of noise suppression  but would like to have minimal resistance to flow, would you recommend mufflers or something like a glass pack?

3. Also the exhaust comes out mid way down the truck.  Would you continue with the  route or go full length and exiting out the back? Do you recommend a certain length between manifold and muffler as well as tailpipe length?

Appreciate feedback from all

aussiebill (2/28/2011)

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Ted, i chuckle and think back as a kid when there was no technology except seat of the pants street tuneing coupled with youthfull exuberence and often ported my exhaust ports to 1 1/2" dia , figuring the ex valve was that dia, it then matched up to pipes good, but if the truth be known by todays testing etc would have made little difference? At least it seemed better? ha,ha.

Know what you mean.  I did the same but by the same token, it was equal footing for all back then.  In retrospect, that older stuff still ran good.  Most of the testing back then took place in the car and if you were lucky, on a drag strip with timers.

Lorena, Texas (South of Waco)