Dissapointing performance

So i take it that since we have been rambling for a couple pages without you! You didn't read this on the previous page?
IF YOU LIKE "DAVID VIZARD" STUFF YOU SHOULD LOVE READING THIS!?!?!
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"AJ/FormS Wrote"
Dusterguy
You probably understand the 4-stroke cycle as Intake/Compression/Power/Exhaust.What you may not understand is overlap/scavenging. George (post 110) has a good handle on this. But with bigger cams there is a 5th cycle called scavenging that is supposed to occur during the overlap period when both valves are open. That is the whole idea of having tuned headers and overlap period in the first place. This scavenge-cycle does more than just help exhausting; it actually helps to pull in a larger fuel/air charge than the engine can physically pull in by itself. So if the engine could pull in 10% more charge with scavenging, it will feel 10% bigger than without.If you prevent scavenging from working, by forcing the exhaust into positive pressure with too small an exhaust system, then scavenging cannot work.
-But it is worse than that.If you force the exhaust into positive pressure, the pressure backs up, and when the exhaust is supposed to be leaving the engine, it is possible, during overlap, for the exhaust to back up and enter the intake manifold. It can get so bad that the exhaust will try to exit the intake through the carb.Guess what that does to power.Your cam has a lot of overlap, making this phenomenon a very real possibility.If the exhaust ends up in the intake, it reduces the pressure differential across the venturies, which means a much smaller A/F charge can enter.
-So now your engine is under a tripple whammy. Loss of scavenging, loss of induction, and intake charge dilution.
-The proof is very easy;just drop the pipes and watch the trap speed.You can also see the proof in the intake manifold; pop the carb off, and look towards the ports.You will see the head ports filled with soot, and the worse it is, the further into the intake,the soot will extend.Alternatively, you can braze a length of brake tubing into an exhaust pipe (leave at least a foot sticking out), and measure the back-pressure. The closer to zero, obviously, the better and more than about 2 or 3psi will seriously affect the scavenge-cycle. By 4 psi your high-performace engine, isn't anymore. This test has to be performed at full throttle,full load, and the bigger the gauge the better,cuz the engine is very sensitive to back-pressure and the more accuracy in the gauge the better.Your 10 psi vacuum/fuel pump tester won't cut it, except to ballpark it, or to point out an obviously bad condition.Neutral blips will never find it! Get a helper......drive safe, I ain't paying your speeding ticket.....................
-Chrysler knew all about this EGR back in the 70s and used it to good effect in that it delayed the use of EGR valves for a couple of years after every body else had them.