A while back, I posted some questions related to a v-twin I am working on.

Here is another puzzling one.  The engine is a v-twin, dual overhead cam, 4 valve configuration - designed from a clean sheet of paper - not really a copy of anything.

The motor has severe intake reversion that comes on at around 4-5k rpm.  At the same time, the engine will not make peak power past low 5k rpm/gate valve.  
Things tried have been:

1. Cam timing and duration changes - we have been all over the map with possible changes and combinations and the engine does not really respond positively or negatively to cam changes.
2. Intake manifold configs: dual IR runners, one carb to divide to either cylinder, 48mm and 56mm throat carbs.  All had reversion.

Is it safe to say that the engine will not be able to realize its power potential unless the reversion goes away?    Also, what other factors could contribute to reversion besides cams and intake systems?  Really look forward to some experienced opinions on this topic.

What RPM is the engine designed for? What's the volume of each cylinder? What type of carb are you using - automotive fixed-venturi, constant-velocity with the slide actuated by venturi vacuum (standard motorcycle carbs), or flat-slide-type carbs in which the slide and needle also act as the throttle?

My experience, which is motorcycle engines with a separate carb / throttle body per cylinder, is that you will *always* have some degree of flow reversion, particularly at low revs. If the cam timing is long enough for the engine to make decent power at high revs then it will be long enough so that at lower revs it fills the cylinder first and then pushes some of it back out. If you run the engine without the airbox you can often see a mist of fuel being pushed back out.

If your problem develops at high revs and full load, it sounds like there is some sort of resonance developing between the intake runner and the cylinder (acting like a Helmholtz resonator). I can only see that situation happening if your intake ports or intake runners are WAY WAY too big and/or too short. You need to keep the velocity up so that the column of air stuffs the cylinder full but doesn't let any of it back out when the engine is in its powerband. I've never seen a production-design engine have that problem, but if you've gone out of bounds, maybe there's a first time.

The bike engines are just designed to deal with whatever reversion happens at lower revs. Constant-vacuum carbs have the slides close down at lower revs, which partially reflects the reversion wave; the carb is jetted to deal with whatever reversion is left. Modern fuel-injection systems use a drive-by-wire throttle that stays mostly closed at low revs, even when the rider asks for full throttle. Flat-slide carbs don't deal with the reversion; they have terrible bottom-end response ...

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