Diesel Performance

Building a 1200 Horse Power Common Rail Cummins
Building a 1200 Horse Power Common Rail Cummins

Building a 1200 Horse Power Common Rail Cummins   

Doug Hockenberry – Interview with Vinny Himes of DX2Parts.com



Photos Courtesy of Vinny Himes










Vinny, I am doing a paper for school on how to build a 1200 horse power common rail. What would be your approach to a project of this caliber?


Doug, honestly this is a loaded question, the old saying “there’s more than one way to skin a cat” Really comes to mind right now.

There are so many shops out there that have put together a 1200+ horse power Common Rail Cummins.

The real questions here should be…..

How do you build a 1200 horse power Common Rail that you can still drive?

That being said reliability is hit and miss at that power level, some guys can make them live for a long time because they either, never drive the thing except on the weekends when they are competing, or they drive it every single day but only get on it hard every now and then.

If the right steps are taken during the engine build there is no reason you can’t get some good miles out of an engine like that.

You will break it eventually and people expecting to build something like this and have it last forever need a reality check. I have actually had guys call me telling me how worthless some other shop is because they built a 1000 horse engine and then after countless sled pulls and drag races the engine blew up. Now that customer is all mad at the shop and wants them to warranty the work.

This is ridiculous. The fact that these engines hold up as long as they do is nothing short of amazing but be realistic in your expectations. Something will eventually break, that’s what you get when you start playing the high performance game.

What are the steps you would take to build a “Somewhat” reliable 1200 horse power Cummins engine?

Well I would start by making sure I had a nice sound engine to begin with. I would have the cylinder head pressure tested with heat to ensure there are no existing stress fractures or cracks. Once I knew the cylinder head was sound I would have the intake tray milled off the side of the head to allow access to the intake runners. Industrial Injections has been providing me with top of the line cylinder heads and I will continue to use their services. This is the kind of work you can expect from them.

With the tray removed you can get a good port and polish on the intake side. I would perform the same port and polish on the exhaust side of the cylinder head.
I would have oversized valves installed by a very good machine shop and port the valve bowls. With a good port job these heads can flow 100 CFM more than a stock cylinder head.
You will have to get an aftermarket side mount intake manifold now that the factory one has been removed. Hellmann Performance is the only one I sell and they really are a work of art.

There is a row of freeze plugs down the passenger’s side of the head. These are just a pressed in soft plug and they will blow out under high boost. I would pull those out and drill and tap the holes to accept a threaded coolant plug.

I would install a set of 110 lb. valve springs with titanium retainers. Switching from a steel retainer to a titanium retainer makes a huge difference when you are running an engine at high RPM’s.

For example, 1 gram of weight is equivalent to 800 pounds at 8000 RPM’s that’s based off a rotating weight but you can see how much stress can be relieved just by lightening up the valve train in a high performance engine.
Factory steel retainers on left, Hamilton Titanium retainers’ right

While we are discussing rotating weight and valve train, I would like to mention Harland Sharp billet roller rockers.

I would highly recommend their products for a build of this caliber. You can remove up to 100 grams from the valve train by using a set of Harland Sharps’ billet roller rockers, while also reducing friction in the valve train. This can ultimately gain you 30 additional rotating horse power while lowering engine temperatures and increasing longevity. You may hear some people say these roller rockers are not meant for daily driving. 100% not true, I have used these roller rockers on daily driven and competition builds. The brass bushed roller rockers will work perfectly for both scenarios.

Harland Sharp Roller Rockers: When using oversized valves make sure you take a measurement of the distance from outside to outside of the valve stems, also check valve stem diameter. Give these measurements to Harland Sharp before ordering, this extra step will ensure you don’t run into any fitment issues.

Wow Vinny, so with the cylinder head and valve train dialed in is there anything else you suggest before we move on to the block and rotating assembly? What about push rods? Do you recommend billet pushrods?

Doug, whenever you are working on or building a high performance engine or pulling truck you need to have weak points. No matter how strong we build things, there is always a weak point. I always try to make my weak point a quick, easy, cheap fix.

Stock Cummins push rods are $10-15 ea. If I install a set of aftermarket billet push rods, then yeah, they are stronger and will hold up to some crazy RPM’s but if they don’t give when things go wrong we are going to break some very hard to replace, expensive parts. In my personal opinion push rods are a good weak point to have. If you bend one it’s as easy as removing the six 10mm valve cover bolts and pulling the rockers off and dropping in a couple of new push rods.

That is a lot more cost effective and time effective than tearing the engine down to fix a kissed piston or a bent valve.

Okay! I’m glad I asked that question.

So what do we need to do with the rotating assembly to make sure we don’t send rods through the block at 1200 horse power?

First thing you need to do is ditch the split forged Common Rail rods. A stock Common Rail rod is forged as one piece and is then fractured to give us the rod cap.

These rods will start to walk on the crank at 4,000+ RPM and are known to fail at or above 900 horse power.

You can get a set of machined 12 valve or early 24 valve rods and those will hold up to 1000+ horse power. For added insurance I would have them shot peened and polished to give them even more strength.
Shot peening a metal surface will relieve the tensile stresses built up during the manufacturing of the part. This more than doubles the strength of that part, especially parts that have to be drilled or ground on after the initial casting of the part.

Another option on the rods is to purchase a high performance aftermarket rod intended for competition use. Carrillo Rods and Crower Rods are two of the aftermarket rods I have used on high horse power builds. They aren’t cheap but they won’t break!

To further insure your rotating assembly holds together you will want to balance the rotating assembly at 5-6000 RPM, even if you never plan on running the engine that hard it is a good time to go overboard.

I also use the Industrial Injections Gorilla Girdle for all of my customer’s seeking a high horse power engine. They come with ARP main studs and keep the block from deflecting at high RPM. The top of the block is obviously solid, but the bottom of the block has nothing keeping the sides of the block from flexing.

The Gorilla Girdle ties the sides of the block together while also connecting them to the main caps, this makes for a very strong bottom end.

Okay, so it sounds like the bottom end of the engine and rotating assembly are pretty well bullet proof at this point, what about pistons? What do you recommend?


A guy could get pretty carried away with pistons; I would love to be able to throw a set of Monotherm’s in every engine. It’s hard to justify $3,100 for pistons when we know we can push a chamfered, ceramic coated piston to well over 1000 horse power without any issues. So I would have to say most guys will be just fine with a set of pistons from Industrial Injection.


                      Monotherm Piston                                    Chamfered Coated Mahle Piston


What about the freeze plugs in the block? I have heard of guys blowing them out, what’s up with that?

Well you can blow the freeze plugs out of the block on a fairly stock truck. It’s as simple as starting a truck up cold and flogging it right from the get go. 40 PSI of boost pressure will blow the freeze plugs out of the block on a cold engine.

On a high horse power engine you can blow the freeze plugs out of the block due to the massive amount of boost you will see under wide open throttle especially if there is a substantial load against the engine, Sled Pulling would be a perfect example.

I generally try to talk guys into getting a set of billet freeze plug retainers if they are going to be building more than 80 pounds of boost. It’s just good insurance.


Okay, so now we have a dialed in long block. Where do we go from here?

Well you need fuel and air to make this whole build really worth it. Let’s start with the fuel side of things.

I am not a big fan of big single modified CP3’s they are grumpy in a daily driven truck and aren’t going to live a long happy life.

I would recommend twin 33% over CP3’s. I have used this setup on a daily driven truck and they have very good street manors and will support 1200 horse power no problem. Industrial Injections has really invested a lot of time and money into making their modified CP3’s the best on the market. I use their pumps on my personal truck as well as many satisfied customer’s trucks.

Some people say dual feeding the fuel rail will damage injectors. This is not true; the common misconception here is based off the fact that you have to get rid of the rail pressure relief valve. With the valve removed you now have two ports to feed the rail. Some guys think that since the rail has no way to return fuel you will over pressurize the injectors causing them to crack or split. The bottom line here is, you would have to be able to command around 40,000 PSI to split an injector body. Between the FCA and Rail Pressure sensor we do not have the ability to command or read pressures that high. I ran a dual feed line setup into the fuel rail on my 2003 Cummins for more than 300,000 miles with the same set of injectors. I am running the same dual feed setup on my current 2007 Cummins. It will work just fine and ensures the rail is never sucked dry.

Some good information I have received from Brady at Industrial Injections, don’t push these CP3’s too hard. The old P-7100 Bosch pumps love a lot of supply pressure. A CP3 pump does not, 8-10 PSI of supply is plenty? I run two FASS 150 pumps mounted on the frame for a build like this. Each pump feeding its own CP3 and feeding at only 10PSI.  

For injectors you are going to need something substantial, I would start with a set of 65 liter per minute injectors. Those will move enough fuel for 1200 horse and with a good tune they will not be horribly smoky.

So what about air, what kind of turbo combo are you thinking?

Man you could do about 10 different turbo setups for a build like this. I would just keep it simple, Industrial Injections race twins have been in production for years and people have been pushing them well over 1000 horse power. I go to their dyno event every year and see at least one truck with those compounds that lays down a cool 1200 horse.

I am running the Silver 64 over and S483 and that setup spools awesome on the street and makes the power needed for the sled and the track.

If I was doing a purpose built pulling truck I would go with an Aurora 5500 Clipped 2.6 with a 66mm Inducer. The 0.90 A/R that Clint uses in this turbo makes it easier to spool. This turbo will spool 400 RPM’s faster than your standard S475 and produces an extra 100 horse power, they come with a billet wheel and utilize an 83mm turbine wheel. It isn’t going to make 1200 horse but it will keep you in the 2.6 class and you will still be able to spool it.

Well Vinny I think we have just about everything covered on the engine side of things. I would love to get into the rest of the truck but we are just trying to cover the engine build for now. Thanks so much for your time and information, the pictures are great!

Doug the pleasure was all mine! Your school is doing some really great things, most diesel programs just cover class 8 basics and never give the new generation of diesel enthusiasts any information about Performance based light duty diesels. It really is addicting once you see what these trucks are capable of.

About the Author
Vincent Himes

Diesel service technician and mechanic with experience inspecting, repairing, installing and upgrading, trucks and anything else with a diesel engine. DX2 Parts Sales Rep., Married with two children and two dogs.