P-Pump Cummins Project: Timing Makes Power

12 to 18 Degrees–How Much Time Will We Gain?

We hear it all the time, timing makes power. But how much power? Well, there are a number of variables but it was a question we decided to try and answer with our pretty much stock 12v P-Pump Cummins project Green Monster. In our last installment we had put in a set of Scheid Diesel 5×0.018-inch injectors and gained a whopping 117 horsepower on the dyno. Since we were driving the turbo harder, boost also went from 19 pounds to 38 pounds which was part of our vast increase in power. To make the most of these new injectors though, we needed to add timing.

The first step of our timing change involved removing a 24mm cap and removing a small plastic “bullet” that is used to pin the pump so it won’t move. A small amount of oil will come out which is ok, since it will be replenished as soon as the truck is restarted.

The timing pin is removed, and will be reinstalled backwards later in order to hold the pump at a set timing. But for now we just needed to remove it. If you’re worried about breaking the small plastic pin (which can happen if you’re not careful) metal ones are available from various vendors.

Injection timing in a diesel works very similar to the timing curve that you would find in a gasoline engine. One of the main differences however is that you can run a lot more timing with boost in a diesel engine thanks to their direct injection and robust nature. The factory sets timing at 12 degrees, which is fine for cold startups noise concerns and overall power, but we wanted to tell the balance a bit towards the power part of the equation. This meant ramping up the timing well above our 12-degree starting point.

Next we removed the back #6 valve cover so we could see the rocker arms and then turned the engine backwards by the alternator to get close to TDC. With the valves on #6 on overlap (the rockers are crossing each other rising and falling) #1 should be close to Top Dead Center (TDC) on the compression stroke, which is where we’ll need it to check timing.

Moving up to the top of the engine, we loosened the #1 injection line from the clamps and bent it slightly in order to clear the pump’s delivery valve. If you don’t feel like bending the line you can always just remove it.

One of the main considerations when it came to setting timing is that we were still on the stock 270,000-mile head gasket with factory re-tightened headbolts. We have run up to 30 degrees on trucks with ARP 625 head studs and fire ringed head gaskets but we would be limited (for now) by our factory parts. Many hot street trucks or folks that tow and want a little better mileage ought to go just a few degrees over stock which is what we did. We felt that a 5 to 7 degree bump would be adequate, and in the end we decided to go from 12 degrees up to 18 degrees of timing.

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Next we used a specialty delivery valve tool to remove the delivery valve from the pump, which will come out in a number of pieces. Don’t lose any of these! Or get them dirty.

Technician Erick Brown mounted a dial indicator on the pump that extended down into the pump and measures pump camshaft lift. This will be used to determine timing.

When we got close to TDC, we took the valve cover off the number 6 cylinder and had one mechanic go under the truck and turn the engine slowly by the flywheel teeth until the rockers crossed over. This meant cylinder number one would be on the top of the compression stroke. Other popular methods of finding tdc are pushing on the timing pin right below the injection pump, or using a dial indicator set to the piston on the number 1 injector hole.

We had the folks at Brown’s Diesel help us in setting timing the “correct way” which is to use a dial gauge on the delivery valve holder. You’ll need the specifications of your pump (160hp, 180hp, or 215hp) but as long as you have that you should be good to go. The actual process didn’t take that long, but it was good to have two people on the truck. We also marked one side of the crank position sensor to see how far it moved for those who may not have a dial indicator. The rumor was that moving the engine from one side of the crank sensor pickup to the other with the pump gear off was worth about 10 degrees, as it turned out, the Internet was close, and it actually turned out to be closer to 12 degrees.

We marked TDC on the balancer on either side of the crank sensor with a screwdriver for future reference, and to see how much the damper would turn when our pump was re-timed.

After we found TDC, the oil filler was taken off, which gave us access to the large timing pump gear nut.

Once on the dyno the truck was a little louder, but nothing that bad, and cold start and other driving aspects of the truck remained unchanged. It should be noted that we did have to adjust the idle up which was performed at the back of the pump with a 19 mm wrench. On the dyno, we were quite pleased with the power game, as we picked up an additional 30 horsepower over what we had made with just the injectors alone. The additional timing also actually made the boost drop from 38psi to 35psi so in an apples to apples comparison the extra six degrees of timing may have been worth even more than 30 horsepower. With 400 in sight, our next move will to be to install a lift pump from Power Driven Diesel to see if we can break the 400rwhp mark. As for now, we learned that even six degrees will make quite a difference in power, and in our case was worth almost 10 percent!