| three runner ports open, but what value would that information have? Only one cylinder per side is ever in an exhaust stroke (240-degree seperation, >90 degree event) so only one runner has exhaust flowing through it at a time, which is why I tested each runner independently from the others. FWIW, the adapter for the manifolds to mount to the flowbench flowed ~340CFM, which is about what I would expect the collector on the manifold to flow, minus a little bit, of course. But that information is not valuable as the manifold is never flowing gases through all three runners at the same time. Flow equality for each runner is very important - I'm not sure why you would think otherwise, but I am happy to explain my thoughts: As each cylinder enters its exhaust stroke and pushes the exhaust gases into the manifold, there is a latent amount of "over pressure" still in the cylinder at the end of the exhaust stroke due to a quantity of hot exhaust gases which were unable to evacuate the cylinder. This is due to the fact that there is restriction in the exhaust tract and in the time period of an exhaust stroke event, there is insufficient time for the pressure in the cylinder to completely fall to atmospheric conditions. The greater the restriction in the exhaust system, the more latent pressure and heat exists in the cylinder at the time the exhaust event is completed. Given that only one cylinder per bank is in an exhaust stroke at a time and given that they are all pushing through the same turbine and exhaust system, the only difference in the amount of latent pressure and heat existing in a given cylinder is due to the restriction presented by the exhaust manifold itself. In Jon's manifolds, this is clearly the rear runner (#5 and #6). This will create a condition where the #5 and #6 cylinders have more left over heat within them at the end of the exhaust stroke. That condition limits the amount of boost, timing advance, and A/F mixture you will be able to use in the next combustion event as the mixture will be higher in temperature at the time of ignition. By having a manifold that flows equally for each runner, each cylinder will evacuate to equal amounts, having equal amounts of latent pressure and heat within them at the time the exhaust event ends. This "balancing" eliminates the tuning for the weakest link bottleneck, as well as prevents a sort-of runaway thermal condition in those restricted cylinders when the car is run for a longer duration of time. Balancing the cylinders is key in every respect from piston-bore clearance, A/F mixture, compression, plug gap, etc etc etc. I stated at the time I posted the results of Jon's manifold flowtest that I was concerned with the amount of variation between runners, namely the restrictive nature of the #5 and #6 ports, but at that time I also had no other data to compare with to know whether or not this condition could be improved upon. After seeing how the MS manifolds performed in this respect, it was clear to me that there is room for improvement on Jon's design. I can guarantee you that Jon will be spending some time looking at his casting patterns, both the old version and his upcoming new version, specifically focusing his attention to these two ports. Although he may not be too happy right at this moment, hopefully he will realize the benefit of the data available and put it to good use on his upcoming design. Without the testing, having built something is just the first real step in the process of R&D. I hope everyone can take some bit of this as helpful information, which has been my only incentive in the matter.
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[ agpowers@bellsouth.net ] Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the tailor.
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16:49:46 02/15/07
