There is a mod from Eagle Mike, dubbed as the MC mod. In this mod, the exhaust cam has been advanced with one tooth (counter clockwise). They are claiming 7%-10% torque and horse power increase thanks to this mod and no downsides. No more oil or petrol consumed.
This last statement is a bit strange for me, because you cannot get extra performance out of thin air. This made me curious about what is in the background of this mod technically.
The engine is going through the four strokes as:
Looking at a camshaft, the sequence would be as follows:
- The exhaust lobe pushes open the exhaust valve and the piston comes up to push the exhaust out, then starts to close.
- The intake starts to open, just as the exhaust is closing, piston goes down, and the intake valve closes.
- Then both valves stay closed for the compression and combustion strokes.
This means that the first lobe to come through the rotation will be the exhaust lobe, immediately followed by the intake lobe.
Overlap is the point where the exhaust valve is closing, and the intake valve is just opening. To increase overlap, you have to RETARD the EXHAUST, and/or ADVANCE the INTAKE. To reduce overlap, you have to ADVANCE the EXHAUST, and/or RETARD the INTAKE.
In our case, the MC mod is reducing the overlap between the operation of the exhaust and intake valves. In cam tuning it is known to increase low RPM power, and causing no change or reducing the high RPM power.
From the point of an outsider (me), looks like when the exhaust valve closes earlier, no air/fuel mixture can escape through the exhaust valve and also, maybe, a bit higher pressure will be present in the cylinder when the piston starts to move upwards.
For me, seems that there is no “negative” effect of this mod, because the extra power is earned from saving a bit of air/fuel mixture by not letting it escape through the exhaust valve, but I don’t have real experience in internal combustion engine tuning. If you find my logic faulty, please let me know and we can discuss it and I will update the post accordingly.
Here is a video of guys doing the MC mod.