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Old 05-28-2013, 08:25 PM
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What pistons are these?

Pulled the head off a 355 I had built several years back. Maybe y'all can tell me what CC pistons these might be, So I can more accurately find the compression ratio. There is a number stamped on them, Its H345NP and they are .030 over. I'm unsure of the brand.




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Old 05-28-2013, 08:50 PM
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These them?

Sealed Power Hypereutectic Pistons ZH345NP - Mobile SummitRacing.com
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Old 05-28-2013, 09:05 PM
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Originally Posted by Sixshooter45 View Post

Oh man, To be honest they look like them. But unsure to be honest. I didn't personally build the motor. A retired machinist built it that has now pasted on. Thanks for the link,
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Old 05-28-2013, 09:17 PM
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Yeah, the eyebrows are 5cc's, but the part number bothers me. I'm thinkin' they're 1.540" pistons instead of 1.560", even though the link by SixShooter45 says 1.560". There's something strange about that part number and there is conflicting information available.

Bring any cylinder to TDC. Stand a steel rule on its edge across the bore, about a half inch from the edge of the bore. Insert feeler gauge blades until you determine the exact piston deck height (measurement from the crown of the piston to the block deck). Play with the crank a little one way and then the other to make certain that you have found TDC. Insert the feeler gauge blades at 3PM or 9PM as you are standing at the side of the motor to prevent rocking the piston on its pin at Noon or 6PM.

If it's a virgin block (never decked) and the pistons are 1.540", I would expect to find a piston deck height of around 0.045". With a conventional thickness head gasket of 0.040", the squish (or lack of squish) with this arrangement would be 0.085". If the piston deck height plays out at around 0.025", then the block is virgin and the piston is 1.560".

Last edited by techinspector1; 05-28-2013 at 09:25 PM.
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Old 05-29-2013, 06:47 AM
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Originally Posted by techinspector1 View Post
Yeah, the eyebrows are 5cc's, but the part number bothers me. I'm thinkin' they're 1.540" pistons instead of 1.560", even though the link by SixShooter45 says 1.560". There's something strange about that part number and there is conflicting information available.

Bring any cylinder to TDC. Stand a steel rule on its edge across the bore, about a half inch from the edge of the bore. Insert feeler gauge blades until you determine the exact piston deck height (measurement from the crown of the piston to the block deck). Play with the crank a little one way and then the other to make certain that you have found TDC. Insert the feeler gauge blades at 3PM or 9PM as you are standing at the side of the motor to prevent rocking the piston on its pin at Noon or 6PM.

If it's a virgin block (never decked) and the pistons are 1.540", I would expect to find a piston deck height of around 0.045". With a conventional thickness head gasket of 0.040", the squish (or lack of squish) with this arrangement would be 0.085". If the piston deck height plays out at around 0.025", then the block is virgin and the piston is 1.560".
Thanks for the help tech. I will check it after work today and report back with the results.
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Old 05-29-2013, 07:57 PM
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Originally Posted by techinspector1 View Post
Yeah, the eyebrows are 5cc's, but the part number bothers me. I'm thinkin' they're 1.540" pistons instead of 1.560", even though the link by SixShooter45 says 1.560". There's something strange about that part number and there is conflicting information available.

Bring any cylinder to TDC. Stand a steel rule on its edge across the bore, about a half inch from the edge of the bore. Insert feeler gauge blades until you determine the exact piston deck height (measurement from the crown of the piston to the block deck). Play with the crank a little one way and then the other to make certain that you have found TDC. Insert the feeler gauge blades at 3PM or 9PM as you are standing at the side of the motor to prevent rocking the piston on its pin at Noon or 6PM.

If it's a virgin block (never decked) and the pistons are 1.540", I would expect to find a piston deck height of around 0.045". With a conventional thickness head gasket of 0.040", the squish (or lack of squish) with this arrangement would be 0.085". If the piston deck height plays out at around 0.025", then the block is virgin and the piston is 1.560".
Tech, I checked the deck height this afternoon and came up with a .028,

If I take that and do the math.

9.025
5.700
1.740
-------
That comes to 1.585 and my deck height is .028? man im so lost haha. Does this mean that my block has been decked?
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Old 05-30-2013, 04:02 PM
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Quote:
Originally Posted by Slammedsi View Post
Tech, I checked the deck height this afternoon and came up with a .028,

If I take that and do the math.

9.025
5.700
1.740
-------
That comes to 1.585 and my deck height is .028? man im so lost haha. Does this mean that my block has been decked?
OK, first off, let's get the nomenclature correct. In your first sentence here, you say "deck height". You are not checking the "deck height", you are checking the "piston deck height". "Deck height" refers to block deck height, the dimension from the centerline of the main bearing bore to the block deck where the heads bolt on. "Piston deck height" is the measurement from the crown of the piston to the block deck where the heads bolt on, with the piston at top dead center.

9.025" would be the standard block deck height of a small block Chevy motor. It could be a little less or a little more, depending on margins in place at the time of manufacture and machining of the block itself.

Your "stack" of parts would be as follows.....
Stroke of a 350 crank is 3.484". Half the stroke, or the "radius" of the stroke, would be 1.742", so that is one of the values in the stack dimension.

Second would be the rod length and we'll assume you're using a standard 350 rod measuring 5.703" center to center.

Third would be the "piston compression height", or measurement from the centerline of the wrist pin to the uppermost part of the piston crown just above the top ring, not including any pop-up. On a 350 Chevy, this can be anywhere from 1.540" to 1.565", with 1.560" being the factory blueprint dimension.

Now, if we add the standard dimensions of 1.742" and 5.703" and 1.560", we find a stack dimension of 9.005". If we add the piston deck height that you found (0.028") to this, we find a block deck height of 9.033".

The piston could still be a rebuilder special, with a piston compression height of 1.540", reflecting a stack of........
1.742" plus 5.703" plus 1.540" for a total stack of 8.985". Adding your 0.028" piston deck height dimension to that would leave you with a block deck height of 9.013", which is entirely possible.

The most important thing to you though, is that you have determined the piston deck height. Armed with that information, you can now choose a head gasket with the proper thickness to set your squish.
0.028" + 0.016" (Fel-Pro 7733) = 0.043" squish
0.028" + 0.020" (Mr Gasket 1130G) = 0.048" squish
0.028" + 0.026" (Victor Reinz 5746) = 0.054" squish
0.028" + 0.028" (GM 10105117) = 0.056" squish

All gaskets shown above are for use with iron heads. Aluminum heads require a thicker composition gasket to prevent brinelling of the aluminum.
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Old 05-30-2013, 05:34 PM
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Quote:
Originally Posted by techinspector1 View Post
OK, first off, let's get the nomenclature correct. In your first sentence here, you say "deck height". You are not checking the "deck height", you are checking the "piston deck height". "Deck height" refers to block deck height, the dimension from the centerline of the main bearing bore to the block deck where the heads bolt on. "Piston deck height" is the measurement from the crown of the piston to the block deck where the heads bolt on, with the piston at top dead center.

9.025" would be the standard block deck height of a small block Chevy motor. It could be a little less or a little more, depending on margins in place at the time of manufacture and machining of the block itself.

Your "stack" of parts would be as follows.....
Stroke of a 350 crank is 3.484". Half the stroke, or the "radius" of the stroke, would be 1.742", so that is one of the values in the stack dimension.

Second would be the rod length and we'll assume you're using a standard 350 rod measuring 5.703" center to center.

Third would be the "piston compression height", or measurement from the centerline of the wrist pin to the uppermost part of the piston crown just above the top ring, not including any pop-up. On a 350 Chevy, this can be anywhere from 1.540" to 1.565", with 1.560" being the factory blueprint dimension.

Now, if we add the standard dimensions of 1.742" and 5.703" and 1.560", we find a stack dimension of 9.005". If we add the piston deck height that you found (0.028") to this, we find a block deck height of 9.033".

The piston could still be a rebuilder special, with a piston compression height of 1.540", reflecting a stack of........
1.742" plus 5.703" plus 1.540" for a total stack of 8.985". Adding your 0.028" piston deck height dimension to that would leave you with a block deck height of 9.013", which is entirely possible.

The most important thing to you though, is that you have determined the piston deck height. Armed with that information, you can now choose a head gasket with the proper thickness to set your squish.
0.028" + 0.016" (Fel-Pro 7733) = 0.043" squish
0.028" + 0.020" (Mr Gasket 1130G) = 0.048" squish
0.028" + 0.026" (Victor Reinz 5746) = 0.054" squish
0.028" + 0.028" (GM 10105117) = 0.056" squish

All gaskets shown above are for use with iron heads. Aluminum heads require a thicker composition gasket to prevent brinelling of the aluminum.
Tech, I do thank you for your help with all this.

I guess my next question would be if I used a set of Cast Summit racing Vortec heads with 67 CC chambers and 185 runners P/N SUM-151124, that should bump my compression up to 9.91:1 while using the Mr Gasket 1130G .018 head gasket. Is this Going to affect my ability to run pump gas any?

To be honest my first choice was to use the Edelbrock performer RPM heads P/N 60895. But in doing so, Like you said i would have to use a thicker gasket. I guessed about a .040 gasket and it would drop my compression to 9.74:1

At 310 bucks each for the vortecs and 650 for the Edelbrocks, i think the best bet is to run with the edelbrocks. Am I in the clear to run them with the way my pistons and everything else is set up?
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Old 05-30-2013, 07:42 PM
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OK, lets run the SCR to make sure we're on the same page.....
.7854 x 4.03 x 4.03 x 3.484 x 16.387 = 728cc's in the cylinder
Edelbrock 60895 64cc's in the chamber
.7854 x 4.03 x 4.03 x 0.028 x 16.387 = 6cc's in the piston deck height
Piston crown = 5cc's
GM 10105117 composition gasket (can be used with aluminum heads according to GM) 6cc's
If this gasket does Brinell the heads a little, it will only take a very light cut on the mill to bring them back to dead flat for using them on your next build.
728 + 64 + 6 + 6 +5 = 809cc's total.
Deduct cylinder cc's from total cc's, 809 less 728 = 81cc's
Divide 809 by 81 and find 9.99:1 static compression ratio with a 0.056" squish. (Call it 10 to 1.) Ideal squish is 0.035" to 0.045", but we cannot always have "ideal".
10:1 should be fine for aluminum heads and pump gas on the street. Use a camshaft with 0.050" duration of somewhere between 212 and 230, depending on operating range you want. The sweet spot for 10:1 SCR would be a cam with 220 degrees duration on the intake valve.
An Edelbrock Performer RPM high-rise dual-plane will make more power from idle to 6000 than any other intake manifold. Max power from a 350 calls for a 750 carb (vacuum secondaries if using a tight converter, double pumper with a loose converter or stick shift). If a fellow is not after max power, a 500, 600 or 650 will work fine. Those fellows looking for max fuel mileage will use a RPM Spreadbore intake manifold and mount a Quadrajet on it.

If you'd like, I can DynoSim the package with your cam choice.....or my cam choice.....

Last edited by techinspector1; 05-30-2013 at 08:00 PM.
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Old 05-30-2013, 08:36 PM
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From a thread at Speedtalk:
Quote:
Post by BigEd36 Wed Dec 12, 2012 6:42 pm
According to the Speed Pro electronic catalog hypereutectic piston H345ACP (545 grams for +.030") has a 1.548" compression height, hypereutectic piston H345NCP (546 grams for +.030") and H345NP have a 1.560" compression height. Cast piston 345NP has a 1.54" compression height.
If this is correct, your pistons are hypereutectic and have a 1.56" CH.

If you measured how far down the piston is at TDC and got 0.028", that would tell me that the block has not been decked (stock is nominally 9.025", which gives 0.025" "piston down the hole" w/a 1.56 CH piston). The "extra" 0.003" is well within tolerances.

OR

That could also mean the block has been decked ~0.020", and the pistons are 1.54" CH. If you look at the block deck surface, the factory finish is different than the finish that almost all machine shops will leave after milling the decks.

So in the end, w/o measuring the piston CH and/or the block deck height, you're going to be guessing. But either way, figuring the compression ratio is unaffected by how the piston deck height got to be what it is (unmilled deck and 1.56" CH or milled deck and 1.54" CH).

Static compression ratio calculator
A couple calculators for dynamic compression ratio:
Kelly DCR calculator
Wallace Racing DCR calculator
KB/Silvolite DCR calculator
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Old 05-30-2013, 08:44 PM
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Couldn't help myself.....
Screwed a hydraulic flat tappet cam into the block, Crane 274-HO6, retarded 4 degrees, 750 carb, small tube headers with mufflers.......
Cam installed at 102 degree intake centerline angle, 110 degree exhaust centerline angle on these 0.050" numbers......
Intake opens (3) degrees BTDC
Intake closes (35) degrees ABDC
Exhaust opens (35) BBDC
Exhaust closes (3) ATDC

RPM....HP....TQ
2000...148...387
2500...188...395
3000...240...420
3500...295...442
4000...343...450
4500...383...448
5000...414...435
5500...420...401
6000...388...340

Max volumetric efficiency 89.9% @5000
Max BMEP 193.8 lbs @4000
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Old 05-30-2013, 08:52 PM
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Couldn't help myself.....
Screwed a hydraulic flat tappet cam into the block, Crane 274-HO6, retarded 4 degrees, 750 carb, small tube headers with mufflers.......
Cam installed at 102 degree intake centerline angle, 110 degree exhaust centerline angle on these 0.050" numbers......
Intake opens (3) degrees BTDC
Intake closes (35) degrees ABDC
Exhaust opens (35) BBDC
Exhaust closes (3) ATDC

RPM....HP....TQ
2000...148...387
2500...188...395
3000...240...420
3500...295...442
4000...343...450
4500...383...448
5000...414...435
5500...420...401
6000...388...340

Max volumetric efficiency 89.9% @5000
Max BMEP 193.8 lbs @4000
Tech, Thank for running that. If you dont mind running it again with the cam im using for this build. The cam is a summit racing unit P/N 1785 it as a dur @ 50 of 218/218, lift is 450/450 and a 106lsa. I really do thank ya for helping me out.
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Old 05-30-2013, 08:55 PM
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Tech, Thank for running that. If you dont mind running it again with the cam im using for this build. The cam is a summit racing unit P/N 1785 it as a dur @ 50 of 218/218, lift is 450/450 and a 106lsa. I really do thank ya for helping me out.
Opps shoulda read better i guess. Thats the same cam i believe? just a Crane unit.
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Old 05-30-2013, 09:00 PM
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Quote:
Originally Posted by Slammedsi View Post
Opps shoulda read better i guess. Thats the same cam i believe? just a Crane unit.
Yep, same cam. Out of the thousands of different cam profiles, how the heck did both of us hit on the same grind? My psychic abilities scare me sometimes. Yours are beginning to scare me too.

Is that enough power for you? The motor has a real nice torque curve.
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Old 05-30-2013, 09:04 PM
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Yep, same cam. Out of the thousands of different cam profiles, how the heck did both of us hit on the same grind? My psychic abilities scare me sometimes. Yours are beginning to scare me too.

Yes Sir, Like you said great minds think alike!

I do have one more question, I looked the GM head gasket P/N 10105117. It said it has a 4.000 Bore size. Isn't this going to cause Preignition being that my bore is 4.030? Or am i still in the clear?

To be honest I was hoping to hit 400 mark so I guess that's a good one.

Last edited by Slammedsi; 05-30-2013 at 09:18 PM.
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