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.
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.
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.
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.
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!