Jeep 4.0L vs 4.6L Stroker

    Camshaft, Fuel System, Exhaust, and other considerations when going from 4.0L to a 4.6L stroker

    I am building a 4.6L stroker (4.0L with a 4.2L crank and rods) for my 1994 Cherokee Sport and would appreciate your experience and input on cam and valve spring choice. This is a daily driver, but while I had it apart, I decided to increase the cubic inches. The plan includes appropriate fuel injectors and a Gale Banks header to go along with the increased stroke. My first cam choice was the Comp Cams 68-200-4 but other suggestions include 68-232-4 to avoid engine code lights.

    William D. Cutler
    Via email

    For starters, you're correct in factoring larger injectors into the mix; the factory 19 lb/hr units might not be able to keep up with the needs of a hot 4.6L stroker. My 4.6L would technically run with the factory injection/calibration, but it detonated badly at anything over three-quarter throttle. I used Ford injectors from Accel—either 23 or 24 lb/hr, but I can't remember. I also used a Hesco adjustable fuel pressure regulator and a Turbo City adjustable MAP sensor.

    Unfortunately, Turbo City has gone out of business. I have zero experience with the company, but Leigh Performance Machine has an adjustable MAP sensor on its website. It's about the only one for a Jeep I know of. Don't forget a larger (at least 62mm) throttle body. There should be some aftermarket ones still for sale, but if not, you can remove the butterfly and shaft and have a machine shop bore your stock throttle body so there's no taper. If you go this route, take a little die grinder and create a few small vertical notches on the top of the idle air control port opening to prevent whistling. All of those components are necessary to make sure the engine is getting enough air and fuel to support the larger displacement. Good choice on the Banks header.

    In regard to tuning a stroker engine, neither myself nor my buddy Pete Trasborg had much success in the long run with either OBDII or OBD1 systems. The Chrysler ECUs are sort of like water; you can divert them for a while, but they're eventually going to meander back to their original flow. It's a difficult prospect getting them to continue supplying the correct fuel mixture to support the extra cubes, so my advice is to pay close attention with your ears, and if you start experiencing detonation (indicative of a potential lean condition) dig out the multimeter and diagnostic tools and see what the system is up to. Most JeepSpeed/KOH/class-racing guys I know who build hot strokers to remain class-legal (rather than just running a V-8) would ditch the factory Mopar injection system for something like a FAST or Holley Sniper system which don't have a base tuning to worry about. That said, some work just fine. It can be frustrating; Iwish there was something else I could honestly tell you.

    As for the camshaft, I ran a Comp Cams Xtreme 4x4 268 cam in the 4.6L I built for my '99 XJ, and it passed the California sniffer test back when they used to stick a probe up the tailpipe and measure levels. It didn't trip any codes or check engine lights in my OBDII emissions system, so your OBD1 would almost certainly have no problem. However, I eventually flattened a cam lobe. I think it was a combination of my spring pressures and the engine oil not containing enough zinc to prevent excessive wear on the flat-tappet lifters. When that cam went flat, I replaced it with the Comp Cams 68-232-4 you're considering as one of your options, and it seemed to be a much happier engine.

    Here's the cams you're considering:
    Comp Cams 249-68-200-4
    Duration - 252 intake/252 exhaust
    Duration @ .050 - 206 intake/206 exhaust
    Lift (inches) - 0.433 intake/0.433 exhaust
    Lobe Separation - 110 degrees

    My take: With a 110-degree lobe separation you're going to pull comparatively less vacuum at idle and have a choppier intake signal than with the 68-232-4 cam. In fact, some of the older literature on these cams state: "for carbureted engines, not for fuel injection". Although the valve lift is much "safer" than the Xtreme cam below, the equal intake/exhaust grind and moderately narrow LSA were designed in the days of drafting tables with no consideration for computer-controlled ECUs. It'll work, but it's not optimal.

    Comp Cams 68-232-4
    Duration - 250 intake/256 exhaust
    Duration @ .050 - 206 intake/212 exhaust
    Lift (in)- 0.460 intake/0.476 exhaust
    Lobe Separation - 113 degrees

    My take: The 113-degree LSA is wider, so the idle will be much smoother and will pull a stronger signal for the injection system at idle and low rpms. Furthermore, the cam is ground on a 110-degree intake centerline, so by installing it straight up you're essentially advancing slightly for improved low-end and off-idle performance. The unequal intake/exhaust lobes favor the weaker exhaust flow of the AMC head, allowing the engine more duration and lift to purge the exhaust gasses and scavenge the incoming air/fuel charge more efficiently. The one caveat is the relatively high lift numbers. That does two things: first, it places greater pressure on the valve springs and as a result, more contact pressure on the lifter-to-lobe face. It also requires you to pay close attention to compressed spring height. If you use the company's recommended valvetrain components and don't get fancy with your cylinder machining, you should be fine. As an extra precautionary step, I'd strongly suggest adding a bottle of ZZP additive to your engine oil at every oil change to help the cam survive.

    So bottom line, I think you'll be much happier with the Comp Cams 68-232-4 cam. Mine ran very strong, passed emissions, and never blipped a trouble code or check engine light. And in reality, it's a stronger performing cam in one of these engines compared with the 249-68-200-4

    Finally, here's a little light reading. I apologize that not all the photos/captions have caught up with our most recent website upgrade. They will in time, but considering I wrote these back in 2006 or so, it's all still fairly relevant tech.

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