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  1. #16
    Member damoroso's Avatar
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    I looked it up because I didn't know....

    As information, hypereutectic pistons are aluminum with silicon added to make the alloy more stable with regard to expansion. Hypereutectic means there was as much silicon added to the aluminum that can be and still have it join with the aluminum molecularly. To much, and the aluminum gets grainy and brittle. This is basically a "stabilizer" that makes the aluminum piston expand less as it gets hot allowing a better cold/hot fit. The technology came about because in the early days of smog motors, aluminum pistons were used (for various reasons) and because of the expansion when they got to operating temp, they had to have a fairly loose cold fit. This allowed unburned fuel to sit in the rings and eventually the crankcase then venting unspent hydrocarbons to the atmosphere. Getting the pistons to expand less and closing up the cold gap using hypereutectic technology eliminated this.

    If this was common knowledge, I appologize!!

  2. #17
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    Now you talking....excellent choice
    To give you some idea ..assuming you only get 375 of those HP at the RW and traction -- your vette should do the 1/4 mile in the low 12's which is very very fast for a street car ..there is very little out there that will match that

  3. #18
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    how does this sound.
    i have been talking to the local machine shop
    according to them, since there isnt a ridge in the top of my cylinder walls, they say that i can take the pistons out with the block still in the car and as long as the bearings are ok (not scored, etc showing the the crank is messed up) i wont need to pull the block to remove and reinstall the pistons.

    that would be great if it were true. what do you guys think?

  4. #19
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    That's correct- As long as there's no ridge, you can knock the pistons/rods out with no problem. I did Ol' Red a year ago- just like that. The biggest trick is getting everything clean.

    BUT- (always has to be one of those) just getting new pistons does not necessarily mean they fit. You said you're looking at hyper-u-whachcallit pistons- the piston clearance can be run tighter to take advantage of the different piston material. You can't really correctly hone to fit without taking a chance on nicking the crank- not saying that it can't be done, but there is that chance.
    the swap I did was forged to forged and the pistons I put in had been there before and were marked as to what hole they went in.

    Unless $$ is really an object, I think I'd look at going with forged pistons- some issues- clearance is looser so they might rattle a little bit cold, but the overall strength is better,

  5. #20
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    You might well regret not removing the engine , if you have gone as far as new heads , cams , lifters and so forth , go the whole hog and pull the motor and check and refresh everything and do it right.

  6. #21
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    interesting,

    well there isnt a ridge. just a smooth wall from bottom to top. i figured what the hell, its apart this far lets give it a try so i unbolted the #1 piston, put some tubing on the threads and it popped right out.

    the bearings are a little shiny in the middle but from the pictures i have seen it fits into the normal wear category.

    what the hell, whats the worse that can happen, i put it all back together and have to do it all over again?
    id probably go ahead and pull the block at this point except for the fact that at this i cant get a cherry picker into the garage to get over the car.

  7. #22
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    You will have a problem with clearances - blocks need to be honed to suit a piston , you will most likely not seat the rings to the smooth bore correctly this way and will not be able to balance the rotating assembly apart from other issues. Surely its not a problem to roll the vehicle out the garage , get the engine out and roll it back in?

  8. #23
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    Even the issue of not being able to get a cherry picker in the garage is not a problem. My garage is in the basement- 7' ceiling. I can swing a BB out of a Vette no problem.
    THe difficult part is getting it over the nose. I pull a front tire/wheel and go over the side. If you don't have a really long cherry picker that's about the only option anyway. Unless you have a narrow 1 car garage it's do-able.

    I can understand your point of not wanting to pull the block out. But why take a chance? Unless the pistons fit correctly, there's a good chance you build an oil burner that you can't get dried up. Extra true with hyper alloy pistons.

  9. #24
    help ID these pistons
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    Pull the engine and take it to a machine shop. Your chances of buying a set of new .060"-over pistons and having ANY of them fit properly are slim to none. You need a fresh hone to fit the pistons, and correct cross-hatch in order for new rings to seat, and differing piston weights will affect your balance. You can't just "change the pistons" - there's more to it than that.


  10. #25
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    damn this sucks,
    machine tells me face to face one thing,
    now i get the exact opposite.
    i probably shouldnt have already pulled the pistons.
    it was actually quite easy. caps off and pushed them right out.

    thats what i get from listening to my machine shop.

    looks like i am going to have to try and figure out a way to get the block out.

  11. #26
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    Bax, you got the block pretty well stripped now. Unbolt the bellhousing and convertor (automatic?) disconnect the block to frame ground, 2 motor mount bolts, throw a chain over it and pull.

    And I don't want to appear to be telling you that just throwing a set of pistons in won't work. It WILL WORK- I've done it. All that anyone is saying is that for max performance and engine life- (that means low oil consumption too BTW) the BEST way is to have the pistons properly fit.
    I don't know your machine shop, and I'm not about to diss them. Here's a question I always ask when I go to a different machine shop- How do you install the wrist pins?
    Different schools of thought on this one- the factory presses them in with a press. I've seen lots of small shops heat the small end of the rod in an oven or with a torch. After that, the end of the rod is usually blue. My next question is how much did the heat change the structure of the material of the rod? I'm no metallurgist, just a car guy. I did talk to a machine shop that builds some serious race stuff in KC- he told me he presses the pins- when you heat the small end, he said it never quite shrinks back to the original size. true or not, I don't know. But he didn't heat my rods when he put the new pistons on.

  12. #27
    help ID these pistons
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    Quote Originally Posted by TimAT View Post
    the factory presses them in with a press.
    Yes, they did - after induction-heating the pin end of the rod; pressing them cold can damage the pin, the rod, and the piston.


  13. #28
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    Agreed. But I've never pulled any of them out of a factory engine and saw the rods were blue.

  14. #29
    help ID these pistons
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    Quote Originally Posted by TimAT View Post
    Agreed. But I've never pulled any of them out of a factory engine and saw the rods were blue.
    Induction heating doesn't discolor them like a direct flame does - it's almost instantaneous.

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