Miura piston question | FerrariChat

Miura piston question

Discussion in 'LamborghiniChat.com' started by Joe250, Apr 11, 2017.

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  1. Joe250

    Joe250 Rookie

    Oct 4, 2013
    13
    California
    #1 Joe250, Apr 11, 2017
    Last edited: Apr 11, 2017
    In the article below, there is talk of "porous pistons" on the Miura. This is the first time I'm hearing of this. Can anyone share some more information on the subject?

    https://drive-my.com/en/blogs/entry/epic-restoration-1971-lamborghini-miura-sv.html

    Part of what already had me thinking about pistons was the fact that of the 3 Miura restorations/rebuilds that I've found on the web, all 3 went for modern pistons and conrods. I realize there are a number of advances in the technology that likely prompted each of them to upgrade, but I'm just curious if there is something more.

    Restoration Log 9 « The Motoring Enthusiast

    Lamborghini Miura Restoration and Lamborghini Miura Restoration

    Scotts Mura
     
  2. hashiriya

    hashiriya Formula Junior

    Feb 26, 2010
    351
    I don't know if OE pistons are available, but "it's okay" for an old die-cast piston to have some porosity. Of course, it's really really bad and can result in some catastrophic damage.
    The problem is that literally no one is making custom die-cast pistons, only forged CNC machined ones.
    While die-cast pistons have their advantages in lower expansion ratio and lighter weight (due to lower specific gravity). So in colder climates die-cast pistons work better.
    Disadvantages: they have lower hardness, so a forged piston would have less ring land wear over time.

    As for connecting rods - not sure if those are really needed.

    What's really acceptable to me is a better cylinder liner material. In the old it was grey cast iron which is not really hard, so they tend to have quite significant wear in the ring land area. Modern ductile iron liners would be more durable and likely result in bigger power over time.
     
  3. Martinkdf

    Martinkdf Karting

    Jan 18, 2015
    67
    Germany
    Hei, during the last 50 years there is a certain development on material and design of pistons, piston rings and conrods. If one of the rods or pistons fails during running the engine a fatal crash will be the result. To use new and state of the art pistons and rods improves the reliability and performance of the engine. I would say that the use of oldfashioned parts is a mistake in an engine like that. Martin
     
  4. Joe250

    Joe250 Rookie

    Oct 4, 2013
    13
    California
    Thank you both for your responses. Sounds like maybe the others are being cautious. Considering the costs in replacing the original block, modern pistons and conrods (and possibly even liners) seem like cheap insurance.
     
  5. Martinkdf

    Martinkdf Karting

    Jan 18, 2015
    67
    Germany
    #5 Martinkdf, Apr 12, 2017
    Last edited by a moderator: Sep 7, 2017
    Hei, I decided to keep the original conrods on my last P250-project but only after having examined them by x-ray and ultraviolet vacuum-fluorescence. They were not bended and free of microcracks. The pistons and piston rings came from CPS in Italy. They offer various types of pistons for Lamborghini. They are CNC made and approximately 80 grams lighter than the 40 year old original items. The surface of the pistons is partially coated with graphite / Teflon and the rings are made in current technology. During the first 3000km running-in-period the engine consumpted 0.5 Liter 5W50 Mobil1 lubricant. Of course - an Urraco engine is not that expensive than a Miura but you can spend easily 25.000 for an complete overhaul and if it crashes because you used poor parts it is a very sad thing. Martin
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  6. Bertocchi

    Bertocchi Formula 3
    Consultant

    Jan 28, 2004
    2,176
    Austin, Texas
    Full Name:
    David Castelhano
    With the values of these cars skyrocketing and originality a concern, the preservation of castings is one of my biggest concerns. Scrapping an original, matching numbers, block is not an option.
    All precautions should be made to prevent an engine from "putting a leg out of bed" as the Brits would say. Piston/conn rod failure often takes irreplaceable castings with them.
     

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