A more open exhaust make a hot cam to idle worse (hotter)? (less back pressure)
I have a rather modified engine with big bore, ported head and a DP315 cam (Russ Collins 315 profile).
The engine had a very stable and low idle when I had No numbers 4-4 (HM300 replica) without baffles.
Now when I have more open, nice singing Lotus Root 4-4, the idle is more like when I had with CX-7 or Megacycle 125-20 cam with rather open 4-1.
The carbs could have various fuel screw settings and not perfect ignition earlier, still idle really low, as 1000 rpm.
The less flowing exhaust (HM300 replica) back pressure made the hot cam nicer at idle, right? The rather high overlap is seen now with less back pressure?
I had to find out more about this that can verify what I have noticed with my engine. I think the worse idle is increased reversion I see and can explain the behaviour.
Here a little about it.
http://www.veryuseful.com/mustang/tech/engine/exhaustScavenging.pdf
