taking the 83 motor .030 over to straighten out the bores,, ordered a set of Silvolites to match the new bore size,, in some brief comparison checks of the stock and silvolite pistons,,noticed the following

http://www.flickr.com/photos/13718356@N ... 614078265/

the silvolites are not so light,,the lightest of the set of .030 overs is 539 grams or 19.00 oz,, checked 3 of the stock pistons,, these are standard size , rings off,, not cleaned,, they weighed 470, 471 and 466,, allowing for the crud on the stock pistons, the Silvolites are about 3+ oz heavier,, where is the weight?

Looking at the first photo, the inside diameter of the Silvolite on the left has a single step, and two diameters inside the body of the piston,, the stock piston has two steps and three diameters,, measuring the extreme tail of the Silvolite piston, it is 3.73 to 3.53 mm thick,, the Silvolite is 4.93 to 4.90,, thats over a mm there.

Another difference is pin bore oiling,, the second photo shows a stock pin bore oil hole,,on the leading side of the pin bore diameter,,to oil this hole lube that has accumulated on the outside of the pin bore boss would fall into the passage to the piston pin,,, photos 3 and 4 show that Silvolite has substituted in a set of grooves that run the width of the pin bore at 4 and 8 o'clock,, to oil here lube that passes by the ends of the pin would need to be pulled in..

comparing compression heights,, and this is a really rough measurement,, but matches what I see visually when I put the pistons side by side,, crown to top of pin bores on the Silvolites is running about 500 microns less than the stock pistons, so the compression achieved will be less,, we are talking measurements in the .001 here, so this is windage.

the appearance of the casting and machining of the Silvolites is excellent,
but certainly every feature on these pistons looks "full" when compared to the stock pistons..
maybe a good thing in a heavy vehicle like the D-150..

Can you put a wrist pin in so that both pistons have part of the pin in them? If you can would you post a picture.


Richard

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Part of Tyrde-Browne Racing

Are the OEM pistons standard or 0.030" Over? Apples and apples as far as weight goes?

With a larger bore, I've found that the compression height is lower with rebuild parts. Likely in an effort not to effect compression on the aftermarket's part.

CJ

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Part of Tyrde-Browne Racing

here are photos of the pistons side by side on a common pin

http://www.flickr.com/photos/13718356@N ... 743079972/

1st photo is a close up shot,, i cleaned the carbon off the crown of the stock piston, inserted a pin into each. The gap under the silvolite piston measured with a feeler gauge,, is about .020 to 025,, these .030 oversized silvolites do have a reduced compression height.
2nd is a side by side comparison of ring land location,, very comparable,, the silvolites have a much larger radius at the ring groove edges,, the radius would reduce the piston ring support area fractionally, but also offers resistance to fatigue cracking or having burrs left from the machining process. The no radius and the large radius each would have +'s and -'s
The slot in the oil control ring groove is also a bit different. On the stock piston the slot is centered behind the expander, on the silvolite a section of the slot also picks up the bottom ring. Again, here I can't say one is better than the other,,,
3rd is a photo of my garage surface plate,,, a pane of glass,,

back on the pin oiling question, drilled hole on the stock vs slots on the silvolites,,I'll speak with some of the piston design guys,, none of our HD diesel pistons have either, we do direct the oil from the oil control ring with slots on the bottom ring groove land to the outside pin bore edges,,

regards
DT

measured the top deck thickness using a dial caliper with extended tips.
the stock piston is .300 at the center and .330 towards the OD
the silvolite piston is .380 at the center and .400 towards the OD

Just looking at the 2 pistons side by side you can tell the silvolite is going to be heavier than the stock piston. The space between the oil ring and the wrist pin is much thicker, the pad on the bottom side of the wrist pin, and the measured difference in the crown thickness....thats where the heavier weight is coming from.

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There's no such thing as too much cam....only not enough engine!

I agree, don't know if it is a stronger alloy, but it is certainly a "thicker" part,
usually thickness = strength