Magnum 360 swap questions

Engines, Exhaust and Fuel Systems

  1. rcmaniac791

    rcmaniac791 Well-Known Member

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    So I'm just tossing around the idea of swapping in a magnum 360 crate engine into my car, and I've had a question arise about the flex plate. I know that I need an externally balanced magnum flex plate, and according to magnumswap.com, I can't use an LA 360 flex plate, but rather a magnum specific one. I found this one on summit:

    ATP Flexplates Z-332

    says that the outer diameter is 11.5 inches, and in my service manual, I see that the torque converter (originally a 318) is 10.75 inches. I don't know if they mean the bolt hole diameter is 11.5 on the flex plate, or if that is the actual outer edge. What do you guys think? or is there another alternative for a flex plate? Would something like this work?

    B&M Flexplates 10239
     
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  2. BudW

    BudW Moderator Staff Member

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    A Magnum 360 will fit into your car – but there are a few minor differences to be aware of.
    One of those differences is the Magnum 360 is externally balanced engine – so flexplate (or flywheel) weights will be different from a non-Magnum 360 (and from either 318).

    The measurement you mentioned is between torque converter bolts. The Magnums went to a common converter bolt pattern (the smaller one).
    All A904/A998/A999/A500/41TH series transmissions all used the smaller bolt converter bolt pattern.
    The A727/A518/46TH series transmissions could use either bolt pattern, depending if using a low-stall or a high-stall torque converter. The larger bolt hole is for 426 HEMI’s which use a larger diameter torque converter bolt. The larger diameter bolt pattern is A727 style with low-stall converter (which is not a performance converter).
    This gives a better explanation of the bolt measurements:
    FP BM-10236 360.jpg
    This a BM-10236 (for older 360's).

    If using a Magnum engine, you will want to use the Magnum flex plate. The newer design doesn’t crack as often as the older style does and it also has a provision for electronic fuel injection (if using the factory style injection system). If not using fuel injection, then the rectangular stamped holes are just along for the ride. Your original torque converter can be reused.

    So, to answer your question, you will want to use ATP Flexplates Z-332 and not B&M Flexplates 10239 in your case.

    FP ATP Z-332.png
    ATP Z-332 plate. The red arrow is the external weight.
    With this plate, you can use a stock 318 converter (internally balanced).

    Does this answer your question?
    BudW
     
  3. rcmaniac791

    rcmaniac791 Well-Known Member

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    Yes, but just for my pea brain to understand, even though the 2 measurements I found are slightly different, the ATP flex plate will fit the stock converter the A998?
     
  4. BudW

    BudW Moderator Staff Member

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    I haven’t tried it personally, but friends of mine says it works great.
    Keep in mind, the bolt pattern on crank hub and bolt pattern on converter are not symmetrical. Both will only attach (to crank and to converter) in one position. The crank bolts are not hard to figure out. The torque converter bolts are a bit more difficult and can be “a pain” when placing bolts into the converter after transmission is attached.

    I recommend either: placing the flexplate on the converter when converter is in bellhousing OR placing flexplate on converter with converter upside down on bench, and spraying a small amount of spray paint (or whatever) when the bolt holes match up – on or by one bolt hole, just as long as you get a visible amount of paint on/by that bolt hole that can be visible (on converter) from under the car.
    FP ATP Z-332 b.png

    I understand a person can move the converter to meet that spot to the flexplate when bolting things together the first time – but I recommend doing this, “not for the first time going together” but for any future repairs that might occur down the road.
    If you have bolted/unbolted as many torque converters from flexplates as I have, you will find this to be a “necessary” and time saving step.

    The color doesn’t matter or even which bolt hole. A person might even be able to get by with a sharpie marker or clear-coat paint, if wanted.
    BudW
     
  5. rcmaniac791

    rcmaniac791 Well-Known Member

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    That's all I needed to know. Thanks Bud.