How to Double the Power of a First Gen Cummins

In the shop today is a beautiful 1991 Dodge Ram equipped with a 1st gen 12 valve Cummins. This is the first generation Cummins with a VE pump, not known to generate much horsepower. We’re gonna throw it on the dyno and see how much horsepower and torque it makes stock. Then we’re going to double it.

Road Testing and Dyno Testing the First Gen Cummins

We took the 1st gen Cummins out for a road test and this thing is pathetic. It is very slow, and took more than 14 seconds to run ⅛ mile. The first gen Cummins are rated 160hp from the factory so hopefully it will make 128 to 130 at the tire.

After the road test, we did a dyno run from 1500 to 2500 rpm and the truck seemed to flatline and not rev any higher. The dyno test revealed a whopping 140 horsepower and 387 ft lbs of torque with about 14 pounds of boost. Now, our goal is to double this to 280 horsepower and roughly 800 pound feet of torque. We are always up for a good challenge.

Adding New Parts to the First Gen Cummins

One of the first things we’re going to do is install some 5×14 injectors in this truck. This might be a little more injector than we need to double the power, but we want to make sure we have plenty of fuel to reach our power goals. We were able to get the first two injectors out, then cylinder three stuck, so we used our Power Driven Injector Puller tool to remove the remaining stuck injectors.

With the new fuel injectors installed and the first gen Cummins still strapped on the dyno, we’re going to see the power difference from just adding injectors.

With just a simple injector upgrade, we hit 199 horsepower to the tire, picking up just shy of 60 horsepower. Torque went to 545 ft lbs from 387 ft lbs. Next, we’ll adjust the fuel screw in the pump to see where that gets us.

We started by turning the fuel screw up three turns. As an FYI, be careful when adjusting the fuel screw. If you turn the fuel screw in and you have a deeper fuel pin, you can get to the point where the pump can travel so far that it can get into a runaway. If you’re doing this, you need to know what you’re doing and have an assistant to help block the air intake if a runaway starts.

With three turns of the fuel screw, we hit 213 horsepower to the tire and 593 ft lbs of torque. We were hoping for more gain from the fuel screw but we have some options to get more out of this truck. We could turn the fuel screw all the way to run away and then back it off slightly. We can modify timing, and we can also look at a built fuel pump or transmission.

We were able to get ½ turn more out of the fuel screw and push to just over 230 horsepower. However, we are also dealing with lift pump fuel pressure dropping to zero. Looks like both a lift pump upgrade and injection pump modifications are in store. We’re going to go with one of our high volume-low pressure lift pumps and install a 3200rpm governor spring in the VE injection pump.

Changing the Govenor Spring and Lift Pump

After swapping injectors and adjusting the fuel screw, our next move was to swap out the lift pump and governor spring.

And after the dyno test…

…we did it. We doubled the horsepower of this 1st gen Cummins. With the increased RPM from the governor spring and fuel pressure from the new lift pump, we were able to hit the power goal on the dot. Peak boost hit 25.9 psi and peak torque shows 758 ft lbs. Next, we’re going to see what we can achieve with a lockup transmission.

So this first gen Cummins started off with140 horsepower, and we got it to 280 before installing an upgraded transmission. And now we’re getting 322 HP and 753 ft lbs of torque out of a first gen Cummins.

Then we did a burnout

Call Us With Questions About Your Diesel Engine

It took some work to double the power of this old first gen Cummins, but it is doable and it makes it a lot more fun to drive. If you have questions about the work we did on this truck or any other diesel truck, give us a call at the shop. Our team is here and ready to answer your questions and make sure you have the best parts for your truck. Give us a call at 435-962-9555 or text us at 435-962-9506 or leave us a comment below. Don’t forget to follow us on YouTube, Facebook, and Instagram for more product tests. Leave us a comment below about what you’d like us to cover next.