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  1. #1

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    Thumbs up 2014 Forged svho piston

    FYI , I noticed the 2014 forged svho piston top has been changed, there are nolonger valve releif cut outs in the piston. The entire top of the piston is now dished shaped causing a more smoother (even) fuel burn to be concertated more in the center of the conbustion chamber, This should help preventing detonation and possible produce a little more HP as well, Tommy Jordan


  2. #2
    Kristian Keppel Waterholics's Avatar
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    Thanks for the info Tommy. Nice to know Yamaha is on the ball game with power and reliability.

  3. #3
    wotxxxsd's Avatar
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    Nice to see Yamaha is using the learning curve to benefit us consumers!!!

  4. #4
    Quote Originally Posted by 2fast4u View Post
    FYI , I noticed the 2014 forged svho piston top has been changed, there are nolonger valve releif cut outs in the piston. The entire top of the piston is now dished shaped causing a more smoother (even) fuel burn to be concertated more in the center of the conbustion chamber, This should help preventing detonation and possible produce a little more HP as well, Tommy Jordan

    Tommy,

    Didn't Chrysler do soemthing like that in the 70's? They had the Hemi head - Great motors they were.
    Not sure which way the curve was on there head's, but they were hemespherical and it was advertised to burn fuel better and to aid in the flow of the gases in and out of the combustion chamber.

    Dave
    FX HO (2012)

  5. #5
    Hemispherical combustion chambers date back for centuries for use in mortars and cannons. Hemi referes to the head desing and not the tops of the pistons. Different comanies have been using in automobile applications as early as 1901, Peugo, Alfa Romeo, BMW ect.. . Daimler Started using them in 1914 And started putting them in their cars as soon as the 50s? The new. "hemis" are not true hemis and only have the name to make people feel good.

  6. #6
    Mod less, ride more! troyheb's Avatar
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  7. #7
    shrabber's Avatar
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    The shape of the piston bowl controls the movement of air and fuel as the piston comes up for the compression stroke. The air and fuel swirl into a vortex inside the piston bowl before combustion takes place, creating a better mixture, more efficient combustion = power

    Thumbs Up!!

  8. #8
    Vern's Avatar
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    Early Hemi motors actually had the opposite design ... the advantage was the ports and valves were canted at extreme angles, almost 45 degrees. This unshrouded the valves and allowed for serious airflow in and out of the head, creating a HP advantage over non-Hemi heads. The hemispherical combustion chamber in the head was a side effect of the optimal valve canting/placement ... the combustion chamber had to be totally different than a standard quench head to accommodate the valve placement and movement. The pistons were the opposite of the dished pistons Yamaha is using on the SVHO ... pistons on the hemis were EXTREMELY domed ... the domes almost looked like a tent ... necessary to fit into the high dome combustion chambers and still make good compression.

    Although the hemi head design allowed massive airflow, it was also more prone to detonation due to the non-quench design. With nitromethane or hi octane gas, this was a minor issue compared to the significant HP advantage, so it was a very successful design advantage for all-out HP goals. By the way, our modern 4-5 valves per cylinder head designs are the far better way to achieve 'hemi-head' flow numbers, along with great quench area, efficient combustion chamber design. Multi-valve heads have far less shrouding and are a much better design rather than two huge valves with extreme canting angle and non-optimal combustion chamber/piston dome designs.

    For street cars and crappy gas, designs eventually went the other direction. Engineers found that flat top, zero deck piston arrangements, along with very small combustion chambers yielded the best detonation resistance, maybe due to significant swirl created by that design. Most modern engines now use small combustion chambers and very small quench areas for detonation resistance and efficiency.

    Dished pistons have been around for a long time and are nothing new. They are usually the best way to keep compression at a safe level with a reasonable combustion chamber size, especially with boosted motors. Turbo-specific pistons were dished and have been available for a long time; Yamaha did not invent this and there is nothing new or unique about it.

    Just wanted to clarify - not taking anything away from the SVHO setup. I think it incorporates a bunch of great improvements and that Yamaha took a good motor and made it significantly better. Awesome engine with huge potential.
    Last edited by Vern; 01-29-2014 at 11:32 AM. Reason: added


  9. #9
    Mod less, ride more! troyheb's Avatar
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    NIce info, Vern.

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