Gary_321
Mechanical
- Dec 4, 2017
- 56
I've noticed something glaringly obvious.
My six-cylinder engine is effectively two three-cylinder engines with a common crankshaft.
Cylinders 1-3 have a common exhaust manifold as do cylinders 4-6.
The intake has individual throttle bodies with all six cylinders have a common plenum.
A six-cylinder has a cycle phase of 120° and because the inlet valve has a duration of 293°, there is a 173° overlap.
Graph showing six-cylinder inlet valve interaction
In the linked image, the red line shows the cycle that is following the blue. Positive values show "air" moving from the cylinder into the plenum, negative values show "air" moving from the plenum into the cylinder. You can see that some "air" would move from 3 to 5.
The firing order is 1-5-3-6-2-4. 1 & 5 are four cylinders apart and 5 & 3 are two cylinders apart. This means that 5 will influence 1 less that 3 will influence 5.
To almost eliminate this inlet valve interaction, I propose to split the plenum in two. As the phase is now 240°, the overlap will be only 53° and the flow from consecutive cylinders would be significantly reduced. Here is the inlet valve overlap graph...
Graph showing three-cylinder inlet valve interaction
The proposed modification...
Plenum before...
Image of unmodified plenum
Image of unmodified plenum
Plenum after...
Image of modified plenum
I'll replace the cardboard template with aluminium sheet and secure it with epoxy resin.
Do you think this is a sensible thing to do?
My six-cylinder engine is effectively two three-cylinder engines with a common crankshaft.
Cylinders 1-3 have a common exhaust manifold as do cylinders 4-6.
The intake has individual throttle bodies with all six cylinders have a common plenum.
A six-cylinder has a cycle phase of 120° and because the inlet valve has a duration of 293°, there is a 173° overlap.
Graph showing six-cylinder inlet valve interaction
In the linked image, the red line shows the cycle that is following the blue. Positive values show "air" moving from the cylinder into the plenum, negative values show "air" moving from the plenum into the cylinder. You can see that some "air" would move from 3 to 5.
The firing order is 1-5-3-6-2-4. 1 & 5 are four cylinders apart and 5 & 3 are two cylinders apart. This means that 5 will influence 1 less that 3 will influence 5.
To almost eliminate this inlet valve interaction, I propose to split the plenum in two. As the phase is now 240°, the overlap will be only 53° and the flow from consecutive cylinders would be significantly reduced. Here is the inlet valve overlap graph...
Graph showing three-cylinder inlet valve interaction
The proposed modification...
Plenum before...
Image of unmodified plenum
Image of unmodified plenum
Plenum after...
Image of modified plenum
I'll replace the cardboard template with aluminium sheet and secure it with epoxy resin.
Do you think this is a sensible thing to do?