I have the Speed pro hyereutectic pistons in my motor. There are a bunch of numbers on the top of each piston. Any help appreciated in deciphering some of them.

345NP .060
This is part number and overbore size I assume

03-337-07-C
This is what I want to know about. Anybody know?

Also upon a quick measurement with a feeler gauge (not totally accurate), these pistons are well more than .045 down in the hole. Are pistons ever this far down from the factory. (I know these aren't factory pistons, just wondering what the range was from the factory. I thought the common down in the hole dimension was around .025)

Guess I need my block decked right?

opinions appreciated.

RJ

With Dial Indicator setup it came out to .052 in the whole!!!
RJ

the 345 # is the actual part #. the second set of #'s are probably some type of internal company #'s. The actual part # tells you anything you need to know on the piston as far as specs. It has a 1.56 compression height which with a standard stroke, 5.7 rod, equals a deck height of 9.00. A stock block would be 9.025, so yes, your piston should be .025 in the hole if the block has never been decked. It is about impossible to measure accurately with a feeler gauge so I suspect you are not getting an accurate measurement. I wouldn't expect the tolerance range on the block to be that far off. Also when you are measuring you need to be at true top dead center. The balancer mark may not be exactly accurate.

Hi Mike,
Thanks for responding. I repeated the measurement with a magnet based dial indicator and got the .052 measurement after setting the piston at TDC using the dial indicator.
What do you mean by compression height of 1.56? I didn't build this bottom end and don't know for sure who did, I only did the top end. Is it possible there could be an issue of incorrect rods or crank? Should I pull the engine all the way down and check everything?

Thanks again
RJ

Probably not.

Dial indicate off the top of the pin on both sides to take into account any sort of piston rock. Shouldn't be hardly ANY at the center of the pin on top.

Stock here.........

It's 9.025" -5.7", then -1/2 the stroke ='s the compression distance.

So if you use 9.00", your piston will be DITH right at .025"..

pdq67

rj,
The 345NP is the part number. .060 is the size. The other number is probably a manufacturing date or batch code. It really does not mean anything to you or me.
Thise pistons are your standard replacement pistons and I am not a bit surprised at the .042 deck hgt.

Personally, I dont know if it will really buy you anything to bother decking the block. The 345NP's are just a plain cast piston and probably should not be in any type of real performance application anyway. They are NOT hypereutectic. The Hypereutectic version of that piston is an H345NP

tHANKS bILL AND OTHERS, hAVE BEEN THINKING OF GOING TO (oops) new rotating assembly anyway. Then I guess I would have the block machined first. Since you are in the machining business, what kind of money is involved in sonic testing line boring and assorted block work if I may ask. Ballpark figure.
Thank you
RJ

My catalog lists those as have a 1.54" compression height, not 1.56" like most online data shows. In one block of mine, after being decked .008", they ended up .040" in the hole. If I hadn't had the block decked they would have been .048" in the hole. On another block that was undecked, they ended up on average .053" in the hole.

The .020" reduced compression height was built in to compensate for the block being decked during a rebuild.

The Federal Mogul website lists the H345 with a compression distance of 1.560

tHANKS bILL AND OTHERS, hAVE BEEN THINKING OF GOING TO (oops) new rotating assembly anyway. Then I guess I would have the block machined first. Since you are in the machining business, what kind of money is involved in sonic testing line boring and assorted block work if I may ask. Ballpark figure.
Thank you
RJ

I am having my Block tanked, cleaned, new cam bearings, bored, deck plate honed, deck squared, all new soft plugs and clearnced for a stroker crank for about $500 and a case of beer. I passed on the line bore and hone.

Why didnt you have it line bored?
RJ

Honesly, I didnt think it was nesesary. The old bearings did not indicate any odd loading so I left well enough alone......

The Federal Mogul website lists the H345 with a compression distance of 1.560

Exactly my point. Unless the pistons have changed in recent years, all of them I have used end up way down in the hole. If they was truly a 1.56" CH piston, deck heights would be more in the .020"-.030" range in an undecked block...not .048" or more like I have seen on several different engines.

Have the block decked to 9.005" (.020" off of a "standard" 9.025" block), and use a fel-pro 1094 head gasket at .015" think, and you end up with a near perfect .040" quench height with a 1.54" CH piston. With a 1.56" CH, a smaller cut to get the block to 9.020" plus the 1094 head gasket still gets you .040" quench height.