More siamese simulation.. inner vs outer cylinder part 2

A while back I posted something  about the difference between the outer and inner cylinders.  In that case the inner cylinders made a lot more power at first to to into a weird limbo zone while the outer picked up later. This  behaviour however did only occur this case . After checking the model I found out that I had one pipe section incorrectly defined. Meaning that the section where it expands to split the was at the carburettor side and the pipe section did not expand at the split.

 

I re- ran a few models and the  behaviour is still there, just more subtle ( sometimes with very specific intake configurations you do get a similar if not identical behaviour to my first findings). Depending on the intake you still get the situation where inner pair produces a bit more power at first then the outers take over. What is interesting is that the outer cylinders are much more sensitive to tuning the intake ( both these where on the same run of the mill LCB) than the outer pair.

 

inner-outer-test

Only difference is in the intake tract. (different manifold and a long rampipe) note the minimal change in the outer cylinder compared to the inner cylinder

All good and nice but why should you care ? Well my screw up indicates that you can manipulate the inner cylinders quite a bit, reasonably independent on the outer ones.

 

If you could get the inner cylinder to play along nicely you could gain a whopping 10 kw in his case just by changing the intake.

I have run a whole bunch of simulations with various intake (some of them quite weird)  configurations and it is quite hard to get a handle on what does what, but some of them do perform a lot better than others and they are not very logical at first glance.

 

 

better-intake

A better intake can improve the inner cylinders quite a bit ( red is inner cylinder, black is outer ). It is allso possible to shift the powerband down a lot but at the cost of a limited rpm capability

If these would do the same in real life remains to be seen. It would require fabricating a manifold or having one 3D printed, not cheap but certainly well within reach when building a mid budget engine.

 

 

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