Project Paw-Paw: Part 4
Last time, Project Paw-Paw received the second largest hybrid fuel injectors you can buy for a 7.3L Power Stroke. Now, we’re addressing the other side of the HEUI equation: high-pressure oil supply. While a factory high-pressure oil pump (HPOP) can support most hybrid injectors’ needs, a larger displacement, higher flowing HPOP is required to get the most performance possible out of the Stage 4 injectors we’re running. Specifically, we need a pump that can maintain 3,000-psi worth of high-pressure oil supply (also known as injection control pressure, or ICP) while commanding the kind of pulse width (injector on-time) that’s required to meet our power goals.
Unfortunately, other than dual HPOP systems there aren’t any direct replacement HPOP’s currently on the market that can meet the needs of our 350/200’s. However, there used to be—and we’ve secured an HPOP from yesteryear that will support our hybrids. It’s called the SRP1.1. It was manufactured by Stealth Industries and was once all the rage for budget-oriented 7.3L owners looking to get by with running a single HPOP (it retailed for $899). While the SRP1 that preceded it had some issues, the SRP1.1 proved more reliable. Sadly, it’s no longer in production (and hasn’t been for some time), so you’ll have to hunt one down on your own. Below, we’ll explain why, if you can find one out there in 7.3L land, the SRP1.1 is sufficient if you want to campaign a single HPOP/big hybrid setup.
For a readily-available dual HPOP system that can meet the oil needs of any 7.3L injector under the sun, look no further than Full Force Diesel’s kit. Additionally, the Gen3 HPOP available from Swamps Motorsports can be added in conjunction with your stock location HPOP, which will also support any HEUI injector on the market.
Meet The SRP1.1
Believe it or not, the “SRP” in SRP1.1 stands for stock replacement pump, although it’s capable of supporting much more than the demands of stock injectors. With the potential to support up to 300cc injectors, our SRP1.1 will be on the ragged edge of what it can handle thanks to our 350cc units. However, with good PCM tuning in the mix it should have no problem maintaining enough high-pressure oil to allow us to hit our mark: somewhere between 550 and 600rwhp (and 1,100 lb-ft of torque). We’ll cover all the ins and outs of custom PCM tuning a little further down the road in this series.
SRP1.1 HPOP Price: $200 to $800 used or still in the box (new pumps are no longer available)
Big Bore HPOP
Like all HPOP’s used on the 7.3L Power Stroke, the SRP1.1 is a 7-piston, fixed displacement, axial piston pump. To increase displacement, Stealth Industries concentrated its efforts in upsizing these seven pistons. The outer diameter of the pistons found in the SRP1.1 measure 0.500-inches (above left) vs. the factory pistons’ 0.436-inch o.d. (above right).
Vastly Increased Flow
In the grand scheme of things, the larger pistons are one of the key reasons why the SRP1.1 outflows a factory ’99.5-’03 7.3L HPOP by 32-percent. In the case of the ’94.5-’97 HPOP (which was what came on Paw-Paw from the factory), the SRP1.1 outflows it by more than 40-percent. For utmost performance, efficiency and durability, Stealth held the outer diameter tolerances for its pistons to 50 millionths of an inch (0.000050-inch).
New Cylinder Block
To keep the brass cylinder block that houses the larger pistons rigid, a completely new piece was manufactured. When reengineering the cylinder block, increased wall thickness was paramount for adding strength. It’s also worth noting that new piston springs (which ensure the pistons maintain contact with the swash plate), manufactured to Stealth’s specs, were included in each SRP1.1.
Stock Angle Swash Plate
The swash plate, which sits stationary at an angle to the cylinder block and is what the pistons ride on, retains the common 17-degree angle found in factory ’99.5-’03 HPOP’s. This is done so the pump remains highly reliable. Too much piston stroke and you see excessive side loading. For an added safeguard, the SRP1.1’s swash plate features a keyway to keep the pump from ever getting out of time.
Larger Output Ports
Although the SRP1.1 was based on the factory 7.3L HPOP housing, a host of improvements were made. For one thing, and in knowing that the output port threads were infamous for blowing out, Stealth machined the pump’s output ports to accept larger O-ring boss fittings (#8 SAE ORB vs. #6 SAE ORB stock). The output ports on the SRP1.1 measure 0.360-inches whereas the stock ports were only 0.210-inches, and crucial areas within the internal passages were also enlarged. This provided a huge improvement in oil flow to the cylinder heads.
The snap ring at the rear of the HPOP is what holds the entire pump together. Instead of relying on the OEM snap ring, Stealth opted for a 360-degree, locking spiral ring to hold the rear cover in place. And because the factory HPOP is notorious for leaking at the rear cover, they also added a raised O-ring land to guarantee a leak-free seal.
A Leak-Proof, Direct Replacement
For the best seal possible between the pump and front cover, Stealth re-machined the surface mounting area of the pump’s housing for exact trueness and also included a fresh OEM gasket. The housing of the SRP1.1 appears different than a factory HPOP due to being bead-blasted and then coated with a high temperature, ceramic-based paint. While the HPOP’s not having to be timed with the engine makes its installation easier, it’s vitally important that the drive gear is fully seated on the pump before you reinstall the drive gear bolt and washer.
Super Duty High-Pressure Oil Lines
During the install, we switched to later style (Super Duty) high-pressure oil feed lines. These are the lines that route high-pressure oil from the pump’s output ports to the oil rails in the cylinder heads. The factory ’94.5-’97 lines on Paw-Paw were threaded, whereas the Super Duty versions incorporate quick-connect fittings. The passenger side line carries part number F81Z-9J323-E, the driver side line is PN YC3Z-9J323-E and the two corresponding fittings hold PN F81Z-9N332-AA.
High-Pressure Oil Lines and Fittings: $200
The Injection Pressure Regulator
So if the HPOP supplies the HEUI injection system its oil volume, what creates the pressure? The answer is this little guy. Called the injection pressure regulator (IPR), it’s an electromagnetic dump valve that controls the output pressure of the HPOP. Essentially, the IPR converts the electrical signal it receives from the PCM into hydraulic pressure. Depending on demand, it varies high-pressure oil pressure between a range of 500 psi (idle) to roughly 3,000 psi (WOT). Needless to say, the IPR means everything in terms of injection pressure. It’s always a good idea to install a fresh IPR any time you change out an HPOP.
IPR Price: $185 - $215
HPOP Install FYI
During an injector or HPOP swap, air inevitably infiltrates the high-pressure oil system. Because of this, it usually takes a few cranking sessions (of 20 to 30 seconds apiece) before enough injection pressure is built up to start the engine (at least 500 psi). Don’t worry about priming the HPOP when you do this, as one of its biggest advantages is its ability to dry run for short periods of time. Once running, the engine may run a bit rough and hard-starts may be common for the first 50 miles. During this period, some “spirited” driving is recommended to purge all air from the injection system.
Getting Power to The Ground
Although Project Paw-Paw’s newfound power will probably lead to us digging ourselves a bigger hole, we do intend to see what these Nitto Ridge Grapplers are capable of once the truck is up and running again. We have every intention of subjecting the hybrid terrains to snow, mud, rain, drag strip abuse and everything in between in the months and weeks ahead. Just as Paw-Paw will be expected to perform every task we ask of it (commute, tow, race), so too will the Ridge Grapplers.
To find out why we upgraded Paw-Paw’s high-pressure oil pump, read up on the big hybrid injectors we installed in Part 3.