Perfect Circle Pistons on eBay again, should I?

Discussion in 'Small Block Tech' started by MrSony, Dec 19, 2019.

  1. MrSony

    MrSony Well-Known Member

    Are they good? I know they're cast, should I just save my money for forged? These would go into an aluminum headed engine. The guy wants just over $100 for em. Any input as always is appreciated.
  2. Stevem

    Stevem Well-Known Member

    There only a C hair better then factory Pistons!
    Seing as cast Pistons run hotter then forged Pistons and with the battle with today's fuel and tomorrow's fuel in terms of knock and ping I would not want cast Pistons in my motor just for the sake of having more good things on my side build wise!
  3. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    If you are eventually going to put out the $$$$$$$$$$$$ for the TA sbb 350 heads, you should definitely get pistons with a quench pad on them so you can take advantage of that feature on those heads.

    I don't even need to see the pistons without a link to know that they are full dish pistons. A full dish piston with closed chamber heads is the same as having an open chamber heads with pistons that have a quench pad = no quench for either scenario.

    Its bad enough that you're going to use factory cast rods with the TA heads.:rolleyes: With factory rods and those cast pistons with the TA heads without any porting, you're not going to see that 30 extra HP that TA claims unless you spin the engine higher than the factory rods can handle!:eek: So you'll basically be spending all those $$$$$$$$$$$$$ for a slight weight savings.:(
  4. Jim Blackwood

    Jim Blackwood Well-Known Member

    I have to agree with Derek on this one. I understand we all have budgets, but some things make sense and some do not. There can of course be other reasons to use aftermarket heads besides performance. We bought the SE Eliminator heads for the MG-Roadmaster because the short ports gave us room for an exhaust. But absent such considerations, does it really make sense to spend upwards of 2 grand for one thing and not support it so that it can be used properly due to the budget? It isn't an all-or-nothing proposition either, because you could just as easily build the bottom end properly, wait a year, and spring for the new heads. You could even then wait another year and get the roller cam. But the bottom end really should come first.

    Houmark, MrSony and 300sbb_overkill like this.
  5. MrSony

    MrSony Well-Known Member

    I was toying with the idea of using my capscrew rods... Afaik after new bolts and balancing theyre good to 600hp, no?

    I dont plan on making 500hp with this combo, right away. But if I ever want to I want to know the bottom can handle it. Do the new forged rods TA offers drop right in without any special work other than balancing?

    And lastly, bushed or press fit for those rods? Does it matter? After seeing the $600 price tag, they aren't all that expensive. Not Chevy cheap but for a Buick 1300 for a 2/3 forged bottom end isnt terrible. And the crank is basically nodular so it should hold up well.
  6. Mark Demko

    Mark Demko Well-Known Member

    RPM kills rods not horsepower.
    MrSony and 300sbb_overkill like this.
  7. Stevem

    Stevem Well-Known Member

    If you need any convincing to the above comment here you go!

    This info shows the G force loads that the Rods need to handle.
    These numbers I will post are not for a Buick V8 per say, but none the less are eye opening!
    I will post the G for loads for 3 different stroke motors, 3.750" 4.00" and 4.210".
    These G force load are calculated by serveral factors, one of which besides the stroke is the reciprocating weight of the Pistons, rings, piston pin and the rod small end .

    For these examples given this total weight came out to 1250 grams.

    Here are the G force loads at TDC at 1000 rpm for each stroke I listed.

    3.750" = 68.34 G

    4.00" = 73.97 G

    4.210" = 78.80 G

    Now if you do not think that this sounds like much then concider that the loads the Rods need to deal / live with are 36 times higher at 6000 rpm then at 1000 rpm.

    A motor with a 3.750" stroke with the weights like the above would see load of 6780 Gs at 6000 rpm when the piston gets yanked away from TDC.
    The same condition for a 4.00" stroke would make for a load of 7339 G.
    The 4.210" stroke has a force of 7818 G.

    Yes, the loads go up as the square of the rpm, so at 6000 rpm the loads at 1000 rpm are times 36 greater.

    If you wanted to see what the load reduction would be at 5500 rpm then times the 1000 rpm numbers by 30.25.

    Also interesting is the piston velocity in ( Ft/Min) for these 3 strokes listed.

    The 3.750" stroke has a piston speed of 1016 at 1000 rpm, its 1088 for the 4.00" stroke and 1148 for the 4.210" stroke.

    At 6000 rpm the piston in the 3.750" stroke motor has traveled 6096 Ft per Min, or 1.15 miles!!

    Oh, and by the way in getting back to the piston question and it's strength , the area of the piston that houses the wrist pin see's these same G force loads!

    Sorry for the detour here with the above info but just some food for thought here for ya!
    Last edited: Dec 20, 2019
    patwhac, Mark Demko and MrSony like this.
  8. patwhac

    patwhac Well-Known Member

    What an excellent, informative, and also scary post!! :eek: I think about how 1 to 2 Gs in a car going around the track feels, I'm trying to imagine what 60 Gs feel like haha
  9. Stevem

    Stevem Well-Known Member

    Thanks, your welcome!
  10. Stevem

    Stevem Well-Known Member

    In my haste to get out the door and get to work on that morning when I posted the info in number 7 in this string , I made a mistake that I will correct here now.

    The number I gave of 7818 was not the G force seen by the Connecting Rod, its the tension force in Lbs trying to pull the rod apart, the G force for example at 6000 rpm would be 78.8 X 36 which would be 2836.8G.
    If you times 2836.8 by 2.772!that's how you durive the tension force.

    Sorry for the mistake!
    Last edited: Dec 27, 2019
    MrSony likes this.

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