A Student-Built Cummins Nears 1,000 HP

We’ve been following the University of Northwestern Ohio Diesel Club’s Cummins-powered pulling truck since 2011, and we’ve been pleased to see the students transform a shop truck into a serious sled puller.

Work on the project started back in 2006 with a worn-out shop truck and a collection of parts from unused training-aid piles. With the purchase of an additional truck and the donation of another, the Diesel Club soon had enough parts for a working vehicle.
The heart of the truck is a 24-valve engine dating from about 2001, an industrial engine donated by Cummins to the school. It’s one of the dreaded Brazilian 53 blocks, which have thin water jacket walls and are more prone to cracking, but so far this engine hasn’t presented any problems.

The Build So Far

Nobody remembers how the engine was originally configured, but it first made smoke for the Diesel Club with a lightly modified P-pump, no-name “100-hp” injectors (they weren’t), and a totally inadequate Holset HX-35W turbo scavenged from a parts pile. In that configuration, and with a locked-down wastegate and 34 psi of boost, the engine made 340 hp at 2,500 rpm and 730 lb-ft at 2,400 rpm on one of the school’s DTS engine dynos—and that was with excessive exhaust restriction upstream of the turbo and huge clouds of smoke, a sure sign of wasted fuel and an engine struggling to breathe.

2 Hamilton’s 232-252-105.5 cam is designed for high-revving Cummins engines. The difference in lift and duration are obvious even to the eye. The stock cam has 0.235-inch intake and 0.297-inch exhaust lobe lift. The Hamilton has 0.307 inch of lift. The stock cam has 107.5-inch lobe separation angles (LSA, also LCA for Lobe Center Angles). The Hamilton increases overlap to 105.5°. Intake and exhaust duration are 232° and 252° respectively, compared to 159° and 206° stock. All this adds up to significant improvements in breathing ability, but it does narrow the powerband significantly, moving it up to the 4,000—5,200 rpm range.
3 The cam in a Cummins B Series doesn’t use cam bearings in all of the cam bores, but a high-performance cam like the Hamilton requires them due to the increased lift and spring pressures. Normally there’s only one bearing at the front; if you do a cam upgrade, the block needs to be line-bored to fit bearings in the other six bores.
4 Along with assembly lube on the cam lobes and followers, Hamilton requires the use of their high-zinc Cam-Shield break-in lube. This is especially important for a high-performance diesel cam as standard engine oil may not provide a proper break-in.

This is the point where Diesel World got involved. The club is supported by the
University, but is required to generate a significant portion of its project revenue from fund-raising activities. DW was able to facilitate the donation of a number of good products to help them along.

Step one was an overhaul using internal engine parts from Federal Mogul and Fel-Pro. Even in a low-time engine, having fresh, top-quality bearings, pistons, rings, gaskets and seals and seals makes for worry-free tinkering down the road.

Next up, Preble County Diesel in Eaton, Ohio, O-ringed the head using BHJ tooling. ARP supplied a set of its then-new ARP2000 SAE 8740 head studs to hold down the head (see “Rings of Fire” in the November 2011 issue of Diesel World, p. 24).

The club wasn’t sure of what had been done to the donated Bosch P-pump, except that it had been “tweaked.” Dynomite Diesel Performance (DDP) sac-type injectors were added and the engine jumped to 392 hp and 854 lb-ft, but with 65 psi of drive pressure and only 35 psi of boost, it was clear that it desperately needed more air (“Injection Connection,” Diesel World, March 2012, p. 22).

5 When you think you have enough high-zinc cam assembly lube, add a bit more. This is vital in any rebuilt but is critical for a high-performance, high-lift cam with stiff valve springs.
6 The Precision Turbo 2.6 x 3.35 turbo is designed 2.6-class pulling trucks. The numerals in the name refer to the diameters of the compressor and turbine. In this particular turbo, the purchaser can choose between two A/R (Area/Radius), 1.12 or 1.28. A/R describes the size of the turbine housing; a smaller housing will spool up faster but have more restriction than a larger A/R. Low-revving engines should use the 1.12, but this being a high-revver, the UNOH Diesel Club used the 1.28. The Precision compressor wheels are CNC-machined 2618 alloy forged aluminum while the turbine is made of Inconel.

The next step was to give the engine the air it needed using a non-wastegated DDP T-4 turbo with 82mm turbine and 74mm compressor wheels (“Cummins 24V Turbo Upgrade”, Diesel World, September 2012, p. 126). Meanwhile, 110-lb. valve springs from Hamilton Cams allowed the engine to rev to 4,300 rpm. With these mods, the engine cranked out 650 hp and nearly 1,200 lb-ft on 60 lbs of boost with 55 psi of drive pressure.

Harland Sharp entered the project with a set of high ratio billet roller rockers (“Rock-and-Rollin’,” Diesel World, May 2012, p. 136). They offered an honest 0.050-inch lift increase with reduced friction, adding 13 hp and 26 lb-ft of torque while altering the power curve to improved the lower end and midrange significantly.

Making appropriate timing changes was proving to be a problem, so Pure Diesel Power’s adjustable timing gear set was installed. This mod didn’t add any power in and of itself, but it did make it easier to set and alter pump timing. A modest 11-degree change was worth almost 25 hp, and future modifications can now be accompanied by easy pump timing changes to fully realize their benefits.

Running a T4 turbo on a T3 exhaust manifold is not optimal in terms of maximizing turbo performance and drive pressure, so the Diesel Club installed an ATS Bigfoot T4 exhaust manifold. A 32 lb-ft increase in torque was accompanied by a substantial change in the torque curve, with more low-end boost and faster turbo light-up.

In our experience, intake horns aren’t one of the bigger power producers but ATS Arc Flow horn defied that common knowledge by delivering a substantial 26 horsepower and an almost unbelievable 133 lb-ft of torque. We said then, and will say again, those results were very real but may not be typical; we think they came from a curious synergy of parts. However the power increase came about, the team was certainly happy to have it.

7 Northeast Diesel in Missouri built the P7100 pump. Kevin Glover installed 13mm plungers onto a mild cam, big delivery valve holders and laser cut high-flow delivery valves, along with 5,000-rpm governor springs. With other minor tweaks, this pump can easily support more than 1,000 hp.
8 The Diesel Club students tried setting the P7100’s fuel plate at 700, 750 and 850cc. Power was higher at 850cc but the turbo was harder to light.
9 They said it couldn’t be done—namely combining the high-lift Hamilton cam with the Harland Sharp high-ratio (0.050” lift) rockers. Here valve-to-piston clearance is being checked with a bore scope. With the thick head gasket and flycut pistons there was enough clearance, but the problems were found with valve spring and rocker geometry. While the engine made some runs like this, it was ultimately decided to go back to the stock ratio rockers. “They” were right.
10 Any high-performance engine needs stouter fasteners. The UNOH engine used mostly ARP bolts throughout. You can see the difference in appearance between the stock bolts and the 12-point ARPs. The new bolts are designed to yield at 220,000 psi.
11 The Mahle PowerPak pistons were flycut approximately 0.185 inch and with a thick marine-style head gasket offered plenty of clearance. The bowl size is the standard 44.5cc; unfortunately, this dropped the compression ratio to about 13:1, much of which is bled off dynamically by the long-duration cam. Joe Krivcikas at Hamilton Cams suggested a higher CR. Kalvinator Engines put the ceramic coating on the crowns for increased durability.
12 The Diesel Club machined off the cast intake manifold and did some mild porting. They drilled and tapped the head for a new manifold.

There comes a time in every performance engine’s life when the fuel flow to the pump is inadequate for the amount of horsepower being made. A high-volume supply pump is the answer, but if you have a P7100 pump with a stock return valve, you’ll be sending back at least a gallon of diesel per minute back to the tank—and that’s a GPM that could go to making horsepower. Extra flow is necessary for cooling the pump in day-to-day driving, but when the engine is operated only in short spurts, a device like Tork Technology’s High Performance Overflow Valve is key. This tiny, inexpensive upgrade was worth 14 hp and 42 lb-ft as well as a beneficial change in the power and torque curves.

By this time, the engine was producing nearly 850 hp and 1,400 lb-ft, and the truck put in a reasonable performance at a few pulling events in the 2.6 category. More importantly, the truck had become a valuable teaching tool for the students, instructors, and club members.

The Latest Mods

Our latest round of modifications started with something that had been on the wish list for a long time: a new camshaft. The UNOH Diesel Club went with Hamilton’s 232-252 duration (at 0.050-inch lift) cam, a popular pulling truck cam designed for high-rpm operation with heads that have not been massaged for increased flow.
Ryan at Hamilton Cams explained that this cam is ideal for pulling trucks, but not a good choice for street trucks. It moves the power band to 4,000-5,200 rpm at the expense of low-end power, which is needed on the street. It also requires piston flycut valve pockets to be cut into the piston crown for valve clearance. Hamilton says as much as 0.250 inch may be needed, but the actual depth will depend on head gasket thickness and whether the block or head have been machined. Because of the massive increase in lift, the previously installed Harland Sharp roller rockers could not be used with this camshaft.

13 The Diesel Club fabricated a new large-plenum intake. The new Scheid Diesel 0.093-inch injector lines are also apparent in this view. The Diesel Club learned the hard way that the line clamps are there for a reason; they prevent fatigue fractures from vibration.
14 To help hold the lower end together, the stock girdle was replaced by a Haisley Machine Gorilla Girdle. This is the kit contents; installers must add extra-long main bearing bolts. In this case, the stock 12mm bolts were replaced by high-strength 14mm bolts from ARP, which required drilling out and rethreading the block.

As with any high-revving engine, the valve springs need attention to avoid valve float at high rpm. A stiff valve spring is also necessary when dealing with high boost levels because a highly pressurized intake system can slow valve closure (or even prevent it) with weak stock springs. We mentioned the earlier upgrade to Hamilton 110-lb springs. Hamilton has since determined that these springs may heavier than needed for some applications, and they have introduced 103-lb springs that will reduce camshaft wear. Were we choosing springs today, we’d go for the 103-lb springs. Hamilton calls them a “Three Bears” just-right choice for most high-performance Cummins engines with high-left cams.

Mahle supplied the PowerPak pistons that were custom-flycut by 0.185-inch for valve relief in combination with a thick marine head gasket. These forged pistons feature skirts coated with Grafal, Mahle’s proprietary friction-reducing material, and Mahle low-friction rings. Kevin Frische at Kalvinator Engines ceramic-coated the piston crowns with Techline CVX to protect against high combustion temperatures.
To enhance breathing, the UNOH Diesel Club decided to machine off the cast intake manifold and do some mild head porting. No major changes were made but the major restrictions were taken out of the ports and all edges radiused and smoothed. The valves and seats were also worked over to enhance flow. An intake manifold was built and the head tapped to mount it.

You’ll recall that our DDP turbo had been custom-designed for a 700-hp application. With the UNOH Diesel Club’s goal of nearly 1,000 horsepower, the turbo had reached its limit. After a donated used turbo from a retired 2.6 competition truck died a spectacular death—fortunately without hurting the engine or anyone around it—Precision Turbo stepped up to the plate. Joe Krivickas at Precision generously supplied 2.6 x 3.35 sled-pulling competition turbos for the truck engine to keep the project rolling.

15 The Haisley Gorilla Girdle requires extra-long main studs. After installing the special washers over the nuts, a straightedge is used to make sure the washers are within 0.015 inch of even with the pan rail.
16 The block girdle stiffens the block to help prevent cracking due to extreme torque. Haisley recommends using the supplied gasket, but RTV can be used on street engines that will go years before being disassembled.

Unfortunately, the higher injection pressures, wear and tear, and heavy handling had resulted in a succession of cracked and leaking injector lines. Scheid Diesel sent a new set of 0.093 inside diameter lines that are both a little stouter than stock and flow more than the stock 0.075-inch lines. But oversize lines are only useful when the injection pump capacity is increased significantly; if the pump doesn’t have the capacity to fill the line with each stroke, injector opening is erratic at low speeds. That wasn’t a problem after Northeast Diesel rebuilt the Bosch P7100 and opened the door to reaching the 1,000-hp goal.

To beef up the bottom end, the Diesel Club installed a Haisley Machine Gorilla Girdle along with 14mm main studs. The crew also took a set of good English-made 12-valve rods from another training aid engine, polished the beams and shotpeened them for extra strength, and installed new pin bushings and ARP rod bolts.
It was time to put the new engine on the dyno and see what the Diesel Club hath wrought.

Dyno Results

When the smoke settled at the UNOH dyno facility, the Diesel Club engine had made a high power run of 939 hp at 3,700 rpm and a high torque run of 1,547 lb-ft at 3,100 rpm. Averages ran about 920 hp and 1,525 lb-ft of torque—enough to make the truck competitive, if not put them in the money. Unfortunately, we mean what we said about the smoke settling—the engine managed to break the dyno, which was built for gas engines, before the Diesel Club could make minor tweaks such as injection timing.

17 Spacers are used on top of the block girdle, over the studs. These are backed up by hardened washers and nuts. The spacer block goes over the rear main cap and uses special 12-point nuts. Install the Nyloc nuts in the kit and torque all bolts to 120 ft-lb. Turn the crankshaft to make sure nothing hits or binds. Next steps are to install the oil pickup tube, spacer and gaskets, as well as the oil pan.
18 Instructor Justin Sorenson, normally rather reserved, suggests one last performance upgrade. Wait, shouldn’t this engine have a Carter Thermoquad?
19 The UNOH Diesel Club “Cross Thread” stoked up at a pull in the summer of 2014. The 2.6 truck was donated by Scott Klausing, intact but in need of an engine. The UNOH Diesel Club is also working on a 3.0-class truck, and plans to compete in both classes.

This isn’t the end for the UNOH diesel project, as the students will continue to learn how to strengthen the engine as well as how to campaign a pulling truck. If you attend pulls in the western Ohio or eastern Indiana area, keep an eye out for the black UNOH Dodge—and be sure to encourage the students who built such a fantastic truck. DW

Meet the UNOH Diesel Club

In the time Diesel World has been associated with the UNOH Diesel Club, we’ve had the great pleasure of getting to know instructors Aaron Roth, Justin Sorenson and Fred Newhouse, who are the club’s official advisors. They are tireless in their devotion to the club and give generously of their free time in supporting it. Randy Lucius and Paul Higgins are instructors who help out as needed. Our participation couldn’t happen without the support of Deans Tom Grothous and Andy O’Neal, both of whom come by to get sooty on occasion. But the best part of this experience has been meeting the students. They come and go as their school careers progress, but we’ve met many standouts who are poised for a stunning career in diesel technology.


ATS Diesel Performance

BHJ Products

Dynomite Diesel

Fel Pro

Haisley Machine

Harland Sharp

Kalvinator Engines

Northeast Diesel Service

Preble County Diesel

Precision Turbo

Pure Diesel Power

Scheid Diesel

Tork Teknology

University of
Northwestern Ohio

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