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<blockquote data-quote="Pumpkin" data-source="post: 393470" data-attributes="member: 285"><p>Your are right about cam overlap. But most people running open exhaust have large cams and run their engines at high RPM's. I do think it is more the size of the tubing than backpressure. Most 22re run one size with a muffler, take the muffler out and you would have to go down in size to help with the scavenging. Most people have to large of exhaust pipe on their 4 cyl engines any way. It is all about how you use one cylinder to pull gasses from another. That is why 180* headers work so well (at higher RPM's). A lot of dirt track racers have switch to a tri-Y header. Because it helps with not only high RPM's but also with Mid-range. My yota has a 406 on propane and block hugger headers. it has 2.5in into a single 3in with a little resonator on the end. Does real good to about 5000 rpms. That is where the propane runs out and just about the max on the cam. So all in all it works for me. If I was turning 7000 plus I would not be using block huggers or a single exhaust.</p></blockquote><p></p>
[QUOTE="Pumpkin, post: 393470, member: 285"] Your are right about cam overlap. But most people running open exhaust have large cams and run their engines at high RPM's. I do think it is more the size of the tubing than backpressure. Most 22re run one size with a muffler, take the muffler out and you would have to go down in size to help with the scavenging. Most people have to large of exhaust pipe on their 4 cyl engines any way. It is all about how you use one cylinder to pull gasses from another. That is why 180* headers work so well (at higher RPM's). A lot of dirt track racers have switch to a tri-Y header. Because it helps with not only high RPM's but also with Mid-range. My yota has a 406 on propane and block hugger headers. it has 2.5in into a single 3in with a little resonator on the end. Does real good to about 5000 rpms. That is where the propane runs out and just about the max on the cam. So all in all it works for me. If I was turning 7000 plus I would not be using block huggers or a single exhaust. [/QUOTE]
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