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  1. #1
    LTX Member


    Status
    Offline
    Join Date
    Jul 2020
    Name
    Jim
    Vehicle
    1996 Roadmaster wagon
    Location
    Minnesota
    Posts
    19

    Default Enigne freshen and tweak for mulituse RMW

    I am finalizing the engine upgrade design for my 96 RMW that is a daily, hauler, cruiser, tow vehicle, errand runner, all of which don't add up to many miles per year as we are retired. Not usually used for long trips as we have a van based motorhome for that on an Express 3500 extended van. Currently all stock with the 2.56 rear gears and actually drives quite nicely. Suspension, steering, new paint, etc all done so now will be freshening the drivetrain this winter so never (hopefully) have to worry about it later.

    The goal of the setup is to keep near stock torque curve, but with a bit more torque and a bit more hp up higher. Gear change from 2.56 to 3.08 and an Eaton Truetrac.

    Things I want to address are getting more lift without more overlap, accurate ratio (1.5) rockers, tighter quench, better design pistons. General tightening up of tolerances and cylinder match, accurate compression ratio at 10.5/1. Nothing remotely high performance and original converter stall speed desired. Just want responsive, relatively quick/responsive, but not blazing, and most of all fun to drive, which low end torquers certainly can be.

    Will be using the stock block and iron heads but with work on both.

    Scat 5.7 generic small block crank in standard weight, as needed to handle balance with piston choice.

    Scat forged full floating stock style I beam rods

    Pistons will be KB120 Hyper flattops in appropriate oversize. These are full flattop with two valve reliefs instead of the 4 on stock pistons which mess up the quench and mix.

    Total Seal classic rings 5/64-5/64-/3/16 standard tension

    Cam from Comp as a custom ground using lobes off the lobe selection chart. 200/206 at .050 on 116* separation. .473/480 lift with 1.5 rockers. This cam will give the same overlap at .050 as the stock cam at -14.5* and actually give less overlap at .006 at +11.5*.

    High volume oil pump with ported bypass to prevent pressure climb

    Rockers PRW cast roller tip in 1/5 ratio self guiding.

    Other stuff normal, roller timing set, hydraulic roller lifters, etc

    Block will be cut to zero deck for the pistons and generally checked, deburred, deflashed, return drains cleaned up, etc. Not a big fan align honing mains as I have seen too many spin bearings after honing, but will check bores and straightness.

    On the heads, I will CC the chambers and do a bit of port work but not change the volume very much. Taper stem boss, unshroud, remove any flash. 4/5 angle valve job on standard valve size, and new guides, face straightened out. Install improved strength exhaust studs.

    Balance the rotating assembly.

    Check the intake/head/exhaust manifold port match and correct as needed.

    Clean up flash, bumps, etc on exhaust manifold ports.

    Will probably need to send for a tune as gears will change and I want to keep the same RPM for shift points as now, but not same speeds (I think the shift map goes by mph like on the LS engines). Also will do EGR delete, air injection delete, and turn down the fan on/off speeds to keep tighter temp control. This is a MAF engine so don't know if the fuel map will need changing for the better airflow, but am a bit worried it may have lower TPS opening and put too much timing in so that may need to be backed off a bit for light loads/low tps.

    One question I haven't found the answer to yet is the max you can cut the block deck on a stock LT1 iron block. Anybody go an idea on that? How much I need to have it cut will vary depending on where it is now and the actual crank, rod, and piston dimensions so the cut will have to come after some trial fitting. Target at zero to .001 down the hole so .039 gasket gives .040 quench which is fairly tight so stuff needs to be consistent.

    Also any information of what to get for a tune as this is pretty much a non standard type engine for the most part, but closer to stock the high perf. I am used to doing my own tuning, but my HPtuner won't work on the 96 even though it is OBD2, and it is very expensive, it appears, to get a suitable tuner for the setup.

    Any input or suggestions welcomed!

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