305TBI

There are a lot of looks and performance differences among the different types of headers. If you are looking for the best performance, and most of us are, then you must consider the type of header to install on your engine. If you want peak performance at one specific RPM, then 4 into one equal length headers will work best (4 primary tubes meeting together at the collector). The RPM for peak performance is determined primarily by the length and diameter of the primary tubes. This header will provide only one best performance RPM. The Tri-y headers (4 into 2 into 1) will provide two best performance RPM's. That is due to two of the header primaries being the same length and the other two primaries being a different length. Shorty headers are used many times when there is not enough room to install Tri-Y's or 4 into 1 headers. There primaries tubes are generally much shorter, requiring a much higher RPM for best performance, and they do not provide exhaust gas scavenging at any RPM. Performance wise, they may not even be as good as the stock exhaust log manifolds. Looks wise they are better. Scavenging is necessary in order to "pull" the exhaust gases out of the combustion chambers (high pressure in the combustion chambers and low pressure in the collectors). The more exhaust gas that is removed from the combustion chamber then the more air/fuel mixture that can be injested and ignited for the next firing - that produces more horsepower. There is a lot to exhaust systems and I only understand a small part of it. There are many books that explain exhaust systems in detail, so you may want to check them out.

Good luck,
Don

Mark A Shields

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