Thinking about trimming piston skirt

Discussion in 'Performance Mods' started by MrHungwell94, May 28, 2015.

  1. MrHungwell94

    MrHungwell94 New Member

    I don't plan on doing much modification to my engine but one thing I do want to do is trim off the small part of the piston that blocks the air intake when it is at top center to get better airflow, but should this be done to a brand new never ran before engine? I'm waiting on my new motor to come and I know the first thing I'm going to do is take it apart and inspect the jug, particularly the transfer ports, as I had a fairly new motor have a piston catch on one and gash the piston and take some small pieces off the port and it looked to me like it was a bad mold so I might just give the transfer ports a gentle sanding to make sure the edges don't give the piston anything to catch on to and I figured while I had it apart I'd perform that modification as I've seen on many YouTube videos and have heard it greatly helps but I'm worried it might be a little too much for an engine that hasn't been broken in yet, so basically, is it safe to perform any modifications on a brand new motor before it's break in period?

  2. jaguar

    jaguar Well-Known Member

    it don't matter that it's new.
    it don't work by opening up the intake*, it works by increasing the intake port duration.
    Ideal duration is 120 degrees. Best to measure what your is before you go cutting away.

    *At TDC is when the intake flow is about to completely stop, so intake flow area there is not a consideration. If you want more flow as the piston is rising then just widen the port.
  3. butre

    butre Well-Known Member

    It's best to do all your internal modifications before you ever even fire the thing up.
  4. HeadSmess

    HeadSmess Well-Known Member

    from memory its 96degrees stock...for the 48.

    scribing line at tdc at top of port and grinding to said line ended up around the ideal...less is better if you want it to start and run.

    make it the same curve as the port, not just a simple straight cut.

    remember to chamfer slightly.

    widen the port if possible...

    transfers often need a good cleanup.

    race engines use new parts all the time with no ill effects...

    these things are cheap enough to play with, have some fun blowing them up, shrugging, and doing it all over again :)