I'm Baffled

Discussion in 'Ranchero Tech Help' started by thegasman, Jan 14, 2020.

  1. Hillbilly

    Hillbilly In Maximum Overdrive

    Messages:
    5,787
    Location:
    Winchester, TN.
    Ok, I'm going to post this one last time. RPM is a killer on the 351/400M's and also on the earlier 400 engines. You can build a healthy stump pulling engine with those but you have to respect the fact that they can not take rpm above max 5,000 rpm. Yeah, you can make it breathe better and all the old school hotrodding tricks give excellent results. The problem is that rpm above 5,000 rpm sets up a harmonic vibration that causes the webbing in the block to flex. This web movement causes the cam bearings to start breaking apart resulting in a slow drop in oil pressure. Eventually you have so little oil pressure that the engine suffers failure of the connecting rod bearings along with valve train wear. My heart felt advice is if you modify those engines also invest in an ignition system that has the ability to control high rpm. I personally prefer MSD ignition systems that have the rev limiter. You can also kill those engines by downshifting the transmission in a situation that results in way too high rpm. Don't forget this.
     
  2. thegasman

    thegasman In First Gear

    Messages:
    19
    Thanks for the great advice again HB. Everything I picked out works well in the lower powerband range. Just wanted a strong and dependable 400. Not planning on racing anybody or downshifting to cause high RPM but you never know, sh** happens. I have insurance for everything else, can't hurt to have an ignition system with a rev limiter to keep the RPM's down. I'll definitely make the investment. Thanks HB.
     
  3. pmrphil

    pmrphil In Maximum Overdrive GOLD MEMBER

    Messages:
    1,141
    Location:
    central CT
    Also talk to your engine guy about decking the block .030 versus cutting the heads. It will raise the compression that much more without any more changes. Those engines the pistons were normally "in the hole" anywhere from .065 to .078, which resulted in the C.R. (in reality) to be in the 7.5 range.
     
  4. TestDummy

    TestDummy In Maximum Overdrive SILVER MEMBER

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    23,169
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    C'Ville
    And every engine ever built.
     
    ForistellFord likes this.
  5. Hillbilly

    Hillbilly In Maximum Overdrive

    Messages:
    5,787
    Location:
    Winchester, TN.
    Yes, you are correct on that point Sean. Nearly any engine can outrun the point where physics take over and give you a large "BOOM". I watched a bunch of 400's even when brand new unravel because the car owners were used to letting their small blocks scream and they got by with abusing the high winding 302 and 351 engines. Oddly, the 351-C didn't have that problem. I think Ford went too far on them in the quest for thin wall castings. Those engines made excellent power for tow trucks - - Up until the operator over reved it by down shifting the manual gear box to get more engine braking. Within days the truck was sidelined because of no oil pressure. Unfortunate life fact.
     

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