Today is the Day

And you could loose power.

Looks & sounds like its a combo of both key & jet

OK so basically I am gonna figure y'all understand what a camshaft is/does, and simply say it's the timer in the engine that determines when the valvetrain is gonna open/close, for how long, and how far the valves will open.

In the image below you have what would be an overhead cam pushing directly on a valve, however the concept for a vtwin is the same, different method of moving the valves but same basic events. Notice as the camshaft rotates the cam lobes move the valves, as it moves further up the ramp (lift) you can see as the lobe rotates it goes from the back (zero lift) to the ramp and it begins to open the valve, pushes the valve open farther as it turns (lift) and then back down a ramp to close. Once the opening timing event starts, duration or time of the lift occurs

These are the events that Timing duration and lift encompass.



Timing

The relationship between the rotation of the camshaft and the rotation of the crankshaft is of critical importance. Since the valves control the flow of the air/fuel mixture intake and exhaust gases, they must be opened and closed at the appropriate time during the stroke of the piston.

For this reason, the camshaft is connected to the crankshaft either directly, via a gear mechanism, or indirectly via a belt or chain called a timing belt or timing chain.

In some designs the camshaft also drives the distributor and the oil and fuel pumps. Some vehicles may have the power steering pump driven by the camshaft. With some early fuel injection systems, cams on the camshaft would operate the fuel injectors.

In a two-stroke engine that uses a camshaft, each valve is opened once for each rotation of the crankshaft; in these engines, the camshaft rotates at the same speed as the crankshaft. In a four-stroke engine, the valves are opened only half as often; thus, two full rotations of the crankshaft occur for each rotation of the camshaft.

The timing of the camshaft can be advanced to produce better low RPM torque, or retarded for better high RPM power. Either of these moves the overall power produced by the engine down or up the RPM scale respectively. The amount of change is very little (usually < 5 deg), and affects valve to piston clearances.


So basically JB changed the timing of the events on his camshafts AS THEY RELATE to the timing of the crankshaft in relationship to when the piston is at a specific position.

Doing this allows the engine to have more compression (not the 10.5 to 1 you read about) but to create more cylinder pressure. More pressure means more power, it's kind of like taking a few thousands off the heads to tighten up the quench (space) and allow more higher pressure. However this way is done not by changing the shape and space but when the event occurs in that same space.

JB wish I had thought to have you check compression on each cyl prior to and after the +4 key install. You should do that now so you know what PSI each cyl has at this point.

In any event doing this creates more TQ, it's not expensive, it's like putting in new cams with different timing but the same life and helps with lower to mid range power.

Click Here to see an animated Twin Cam cutaway

Now in the cam chest you see the large upper gear, it has a mark that aligns it with a mark on the smaller crank pinion shaft gear, these are aligned when cams are installed so the events happen as they are designed in the cams profile in relation to the time the piston is doing its thing

What JB did is change the key that is in a slot in the large gear from one that is straight to one that moves the gear +4 degrees. So when he slides that tab (key) into the slot on the cam it moves the alignment position relationship with the pinion (smaller gear below) on the crank.

When this gear with the +4 key is put on the rear cam (both cams are driven in the back by gears or chains) this moves the time at which the cams are designed to move forward or +4 degrees in timing as it relates to the pinion, so when you change the key, install the gear you end up rotating (advancing) the cam position when you align the marks, so the cam event happen 4 degrees earlier than they did when installed straight up or as manufactured to happen.

Well, you changed the timing of the events and increased the ability of the cylinders to be filled to some extent, basically raising the pressure allows you to increase the power, which may require a bit more fuel, a bit earlier on as the events are happening sooner.

The change shouldn't have been too drastic in fuel,

BTW one of the byproducts of EFI is that you can have your power and economy
combined due to mapping of cells, something that is difficult to do with a three stage fuel system in a carb.

The dynamics changed and so the needs changed. Pretty much it.