Last month, we spoke extensively on how important cam selection is for the stroker and mentioned that we had chosen a Crane 753905 cam, with .456/.484-inch cam lift and 204/216 degrees duration at .050-inch lift. We installed the recommended unit (PN 99833) with 95-pound valve springs and Crane lifters. Our past experience has shown this is a great cam in the 4.0L. Crane recommends a 9.0:1 to 9.5:1 SCR with it, and we were at the upper end of that recommendation.
After looking at the dyno results and some others, we think we could have used more cam. If we were doing this again, we'd have installed the hotter Crane 753941, which has .484/.512-inch lift and a 216/228-degree duration. We wouldn't have lost any low end to speak of, but would have gained in the mid-range and upper end and reduced the possibility of pinging. As it is, the engine is ping-free on premium fuel and will run on mid-grade or regular with light loads. The hotter cam would likely have made this engine a regular fuel user.
We installed Quadratec's spectacular roller rocker setup. At the time we started the project, Quadratec had just debuted these beauties. We glommed on for many reasons. High-lift cams will increase the wear on the valve stems and guides by inducing more side loading. This side loading increases with increased lift, and the roller rockers reduce it to zero. The roller rockers also reduce internal friction and oil temperatures.
4. Our 707 rods were resized, polished and shotpeened, and balanced. The bolts were also r
...Basically, you grind away the forging seam on both sides of the beam and then polish it
5. The intake ports were match-ported to the manifold. Then both ports were smoothed and r
Any stroker will require some mods to the fuel injection. That stands to reason because of the increase in displacement. The most important step is to increase the size of the fuel injectors. Injectors are rated by fuel flow in pounds per hour (pph) or cc's. Power output is limited by the injectors' maximum flow. The OE manufacturers size them with little reserve. That's the smart thing to do, because to finely control them at low speeds and meet emissions standards, they can't be too large.
We proved that 24pph injectors would provide the fuel flow we needed to avoid running lean at higher speeds but would also be controllable at the bottom end and have an 80- to 85-percent duty cycle-the amount of time the injector is activated. An occasional short spurt over 80 percent is not necessarily harmful, but if you need to consistently run at or over 80 percent just for normal work, you'll have trouble. Many stock-type injectors will overheat and "fibrillate," or even fail, if consistently operated at high duty cycles. Also, if the unit is running at near 100 percent, there is no reserve for those moments when the engine needs to run richer momentarily to avoid a potentially damaging lean condition.
To answer your next question, yes, increasing fuel pressure will increase fuel flow. Injectors are rated by the amount of fuel they deliver at a given pressure, either 39 or 49 psi for 4.0Ls depending on year. Raising fuel pressure is a useful tool for fine-tuning but is also a popular band-aid for lots of problems with better answers. An injector rated for 21 pph at 39 psi will flow 22 pph at 49 psi.
6. All cylinder-head improvements were verified on a Super Flow 600 flow bench to note any
7. The Quadratec roller rockers install more or less like the OE pieces. In order to set t
...In theory, you could use any hardened washer/shim with the proper dimensions to gain li
The problem is that a particular injector is designed to operate at a given pressure and it's more difficult for it to open against higher pressure. Not only that, the high pressure will increase pressure spikes in the fuel rail. These come when the injectors close and fuel pressure momentarily spikes a lot higher until the fuel pressure regulator can react. What happens when another injector is trying to open just as pressure spikes? It may not get fully open and momentarily starve that cylinder for fuel. That's not only bad for power output-it can cause damage.
As paragons of EFI, we got some valuable training at Technical Services. As part of the learning process, they went one step further by building us a programmable EFI system that was tuned for our engine. It consisted of GM-based parts, a Delphi module and coil driver. They spent the better part of a day custom programming before running our "for the record" dyno test. Little did we know at the time that our project provided some R&D for them to help Painless Wiring develop a stand-alone system for Jeep 4.0L engine conversions (more on this later).
A stand-alone programmable system isn't necessary for the average stroker. We "unconverted" ours, going back to the standard EFI, and it still runs incredibly strong. Generally speaking, a 24pph injector will suit most strokers along with an adjustable MAP (Manifold Absolute Pressure) sensor. Another useful tip is to move the IAT (Intake Air Temperature) sensor into the airbox from the relatively hot intake manifold. An adjustable fuel-pressure regulator is useful for fine-tuning. All that said, you may need more or less than that, depending on your setup, and we can't cover it all here. The ideal, of course, is a stand-alone programmable system tuned specifically for the engine as built.