Engine Builders-KB356 Piston Milling

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thomasfouraker

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Purchased a used 408 Long Block some time back.

It wasn't from the person that had the motor built so alot of the specs were found through disassembly.

It has KB356 Pistons that are about .040 in the hole and the quench dome has been milled flat with the rest of the piston. The KB356 specs it is +23.5 cc dish, I assume this is unmachined with the quench at zero deck. I cc'd the piston today and it took 9cc to fill it up. Does this seem about right? Trying to order my head gasket today and dial in my compression ratio the best I can.

Will attach photo from my phone.

Thanks!

Thomas
 
Picture attached

2C2A5597-D24E-48CA-A84E-A5E79613586A.jpeg
 
23 cc's is with the piston in the hole , tdc.
The piston, like that..will be entirely sub deck...below the deck. The quench pad unmachined comes up .080 above the deck normally.

You should measure with one piston n rod assembled on the crank in the block.
I spec with a 60cc...and no quench pad..that you would be near the lower 9.1 realm.
 
MOPAROFFICIAL said:
23 cc's is with the piston in the hole , tdc.
The piston, like that..will be entirely sub deck...below the deck. The quench pad unmachined comes up .080 above the deck normally.

You should measure with one piston n rod assembled on the crank in the block.
I spec with a 60cc...and no quench pad..that you would be near the lower 9.1 realm.
MOPAROFFICIAL said:
23 cc's is with the piston in the hole , tdc.
The piston, like that..will be entirely sub deck...below the deck. The quench pad unmachined comes up .080 above the deck normally.

You should measure with one piston n rod assembled on the crank in the block.
I spec with a 60cc...and no quench pad..that you would be near the lower 9.1 realm.
Click to expand...

I have a piston assembled on the rod on the crank and at TDC I am about .040 in the hole to the quench pad which is now the entire diameter of the piston since the raised area has been completely milled off. That’s with a machinist straight edge and feeler gauges but will confirm with a depth mic tomorrow.

So should I move forward with calculating my compression ratio with a piston dish of 9cc plus my volume remaining cylinder volume?
Click to expand...
MOPAROFFICIAL said:
23 cc's is with the piston in the hole , tdc.
The piston, like that..will be entirely sub deck...below the deck. The quench pad unmachined comes up .080 above the deck normally.

You should measure with one piston n rod assembled on the crank in the block.
I spec with a 60cc...and no quench pad..that you would be near the lower 9.1 realm.
Click to expand...

Is that at zero deck or .040 in the hole?
 
To get the proper measurement, the piston must be in the bore. ALL of the volume above the top ring is part of the equation. The way you're measuring the piston out of the bore will be inaccurate, since it does not include everything above the top ring. You'll also not know "where" the piston is in the bore, until you actually measure, as your block maybe different than the next, so you will have to measure.
 
RustyRatRod said:
To get the proper measurement, the piston must be in the bore. ALL of the volume above the top ring is part of the equation. The way you're measuring the piston out of the bore will be inaccurate, since it does not include everything above the top ring. You'll also not know "where" the piston is in the bore, until you actually measure, as your block maybe different than the next, so you will have to measure.
Click to expand...

I have a piston in the block on the crank fully assembled with bearings and at TDC I am about .040 in the hole. That is with a straight edge and feeler gauges but will confirm with a depth mic.
My cylinder head is 62cc magnum RT heads
Top ring land is .250
 
MOPAROFFICIAL said:
With the exception of the quench pad...the cup ledge is below deck, yes .

Can't remember if it was .040 or .080.
Search "when **** hits the fan"
And "out with the 340 and in with the 410"

Enjoy.
Click to expand...

His "quench pad" and all will be below deck now, yes? As he said and the picture shows the quench pad has been milled off, right? Or is my one eyed self missing something?
 
RustyRatRod said:
His "quench pad" and all will be below deck now, yes? As he said and the picture shows the quench pad has been milled off, right? Or is my one eyed self missing something?
Click to expand...

Yes, that's settled.
Im just giving the specs as it was to be used as cast.
None the less... the cup is lower than the pad with it cut flush...so it's looking like its been cut below flush and it may now be a 8.5 compression piston if it is indeed flat with the cup.
 
Until you have the crank, rod, and piston in the block, you have no clue what the compression ratio will be. Deck height measurement is a huge factor.
Proper way is to put the piston a measured distance down in the cylinder, seal the rings with some grease, measure the volume, just like cc-ing a combustion chamber, and compare to a calculated volume. That will give you dish volume.
Example: 4" bore, 1/2 down, calculate 103 cc. Actual measured cc, 115 cc's. Your dish would be 12 cc's. Then all you need is deck height, cyl head volume, head gasket thickness and volume.
 
33IMP said:
Until you have the crank, rod, and piston in the block, you have no clue what the compression ratio will be. Deck height measurement is a huge factor.
Proper way is to put the piston a measured distance down in the cylinder, seal the rings with some grease, measure the volume, just like cc-ing a combustion chamber, and compare to a calculated volume.
Example: 4" bore, 1/2 down, calculate 103 cc. Actual measured cc, 115 cc's. Your dish would be 12 cc's. Then all you need is deck height, cyl head volume, head gasket thickness and volume.
Click to expand...

S'what I was tryin to tell him.
 
I’m running 10.2 with 2.02 j heads. There’s a few ways to skin the cat. Run 93 non ethanol, or add some octane booster to 87, mix 100 Av gas with 87... or mix in some leaded 110 race gas to 87.
 
With a .062 thick x 4.18 bore gasket the static compression would be about 10:1 and the cam degreed in at 114* the dynamic would be 8.2:1 (border line premium pump gas)
 
Yea, thinking I may need to step up on my cam and go with a thicker head gasket to give me a little wiggle room in there.

So much for advancing the cam timing and adding boost.
 
Scody21 said:
I’m running 10.2 with 2.02 j heads. There’s a few ways to skin the cat. Run 93 non ethanol, or add some octane booster to 87, mix 100 Av gas with 87... or mix in some leaded 110 race gas to 87.
Click to expand...

If anything, he'll NEED the ethanol 93. The added alcohol helps add to detonation resistance. Alcohol is a higher octane than gas.
 
To the OP, it's my humble opinion with iron heads, you're in trouble. You're going to need a later IVC event. By a good bit.
 
Last edited:
RustyRatRod said:
To the OP, it's my humble opinion with ion heads, you'e in trouble. You're going to need a later IVC event. By a good bit.
Click to expand...

Would I need longer duration or could I retard the timing? Also, would a custom cometic get me by and if so what dynamic ratio should I shoot for?
 
thomasfouraker said:
Would I need longer duration or could I retard the timing? Also, would a custom cometic get me by and if so what dynamic ratio should I shoot for?
Click to expand...

Yeah you can go that route I guess. I don't think it's as productive as another camshaft. For something to have a later IVC it would "probably" have more duration anyway. I would recommend something in the neighborhood of 70° "or so" advertised IVC.
 
....and as far as a safe dynamic figure for pump gas, I wouldn't push any more than 7.9 with iron heads. JMO.
 
I appreciate all the replies! Not the news I was wanting to hear but would rather know exactly what I am dealing with. Looks like a conservative tune, 160* thermostat, some 93 and some octane boost each fill up will be what my formula is. Will try and find a thicker head gasket but at the same time I am opening up my quench area in doing so. I think short of ordering a custom cometic, or opening up the chambers on my cylinder heads I dont have many options.
 
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