piston weight question
06-28-2007, 03:06 PM
#3
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That's a heck of a piece of paper if it weighs 9 grams
I'm with mdacton, it's about 3 paper clips worth of metal. Shave it off evenly and weigh it periodically to make sure you don't take off too much.
I'm with mdacton, it's about 3 paper clips worth of metal. Shave it off evenly and weigh it periodically to make sure you don't take off too much.
06-28-2007, 10:11 PM
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06-29-2007, 06:43 AM
#9
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They are within 3 grams of each other but I thought they were supposed to be close to 0. When I measured themeach on my scale they were within 3 of each other. about half were right on, 2 were within 1 and two were within 3.
06-29-2007, 02:51 PM
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07-01-2007, 11:56 AM
#13
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Few things here....
1. I've yet to see a piston that is 100% ready to go out of the box yet. Good article by Larry Widmer here on how they are not ready out of the box. http://www.theoldone.com/articles/en...ppistons1.html
2. You need to start looking at this in terms of percentage differences here if you have a 700g BBC Dome then 3g's is basically nothing. Now a 350g ultralightweight SBC piston it's a larger difference. Still under .5-.6% is dam close.
3. Depends on the quality of piston you are looking at here. A shelf KB piston for a SBC that is easliy acceptable for what you are getting, hell I've had custom Wiesco's that I ordered to my spec be 2g+ different from one another.
4. HOW GOOD IS YOUR BALANCE GUY ANYWAYS? 3g's might sound like a lot but different people doing the balance work might find that and some might not.
5. How good is your scale? I use a digital scale accurate down to .1g for finding a part's mass. A scale working in the 1g accuracy range is not going to help when it's accuracy is a 1/3rd of your difference.
6. Do you really know the best place to take mass out of the piston without weakening the structure of the piston? Some pistons that's easy, on others not at all.
Here is a good of example of not easy: http://usera.imagecave.com/sstrokera...coPistons5.JPG
Those pistons were within 2g probably on a sub 500g mass as they came to me. I still had to take 25g out of each dome to get them where they needed to be (but I ordered them that way) I wasn't worried about getting them closer in mass but worried about getting the dome shapes the same and equal volume. This is in a motor that has to take 900+hp and 5000+ ft/sec piston speed. Someplace that worrying about balance and strength is more important than a street motor. Even on the extreme end of street motors a 396 going 6500rpm is only 4200ft/sec, that's a 20%+ gain in speed but the forces are 50%+ higher!
Basically what I'm saying is either way, I wouldn't worry too much about 3g for what your most likely using it for. Spend that timing making sure the cam is degreed in correctly, or the bearing clearance is correct.
Bret
1. I've yet to see a piston that is 100% ready to go out of the box yet. Good article by Larry Widmer here on how they are not ready out of the box. http://www.theoldone.com/articles/en...ppistons1.html
2. You need to start looking at this in terms of percentage differences here if you have a 700g BBC Dome then 3g's is basically nothing. Now a 350g ultralightweight SBC piston it's a larger difference. Still under .5-.6% is dam close.
3. Depends on the quality of piston you are looking at here. A shelf KB piston for a SBC that is easliy acceptable for what you are getting, hell I've had custom Wiesco's that I ordered to my spec be 2g+ different from one another.
4. HOW GOOD IS YOUR BALANCE GUY ANYWAYS? 3g's might sound like a lot but different people doing the balance work might find that and some might not.
5. How good is your scale? I use a digital scale accurate down to .1g for finding a part's mass. A scale working in the 1g accuracy range is not going to help when it's accuracy is a 1/3rd of your difference.
6. Do you really know the best place to take mass out of the piston without weakening the structure of the piston? Some pistons that's easy, on others not at all.
Here is a good of example of not easy: http://usera.imagecave.com/sstrokera...coPistons5.JPG
Those pistons were within 2g probably on a sub 500g mass as they came to me. I still had to take 25g out of each dome to get them where they needed to be (but I ordered them that way) I wasn't worried about getting them closer in mass but worried about getting the dome shapes the same and equal volume. This is in a motor that has to take 900+hp and 5000+ ft/sec piston speed. Someplace that worrying about balance and strength is more important than a street motor. Even on the extreme end of street motors a 396 going 6500rpm is only 4200ft/sec, that's a 20%+ gain in speed but the forces are 50%+ higher!
Basically what I'm saying is either way, I wouldn't worry too much about 3g for what your most likely using it for. Spend that timing making sure the cam is degreed in correctly, or the bearing clearance is correct.
Bret
07-07-2007, 10:19 AM
#14
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Thank you! I appreciate your time explaining what you believe. Most people on here seem to "cut-n-paste" . I've always respected your opinions. And your right, for what I'm doing I think 3 grams won't matter and the machine shop will compensate. Like I stated earlier, the 3 grams on my digital scale amounted to the brown coated paper that came in the box of pistons. As heavy as these pistons are, they are one choice given for the class I'm building the engine for, and when it's all done I'll most likely get flamed for running stock untouched heads and stock rockers too.
07-11-2007, 09:22 PM
#15
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When I weight matched my Lunati's I tried getting them to within .05 grams of each other on a pharmacists's scale. The extra mass, which amounted to about +1 gram on the heaviest one, came not from the wrist pin but from the wrist pin beam itself, inside the piston. It was in essence a rectangle when it started, and I turned it into a "D" on the end, toward the bottom of the skirt. I wish I had a picture to show you, but I can't find it. I used a die grinder with a sand paper roll to do the job as a carbide takes off too much material way too fast for this application.