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Old 04-13-2007, 12:08 PM
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Dished pistons and quench

I was curious of a few things while putting together this low rent 350 I was trying to use a thin head gasket to get within the .045 quench distance on this engine it turns out though the cast dish pistons actually sit below the factory .025 deck height I measure .039 from the heighest part of the piston so without decking the block i aint going to meet the .045 height. Anyhow I started to think about it a little and wonder if the reccomended quench distance applies to dished pistons because the dish with the head gasket thickness is over the .045 in most cases. Does the quench distance only apply to flat top pistons?

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Old 04-13-2007, 12:26 PM
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Quote:
Originally Posted by KGRIFF
. Does the quench distance only apply to flat top pistons?
No but the factory style pistons with a full dish don't have enough flat surface to provide any appreciable quench. You would need to use a D-cup or "reverse dome" piston to get any quench benefit.
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Old 04-13-2007, 03:57 PM
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Hippie is right. A well designed dish piston will have a flat top on the portion of the piston that corresponds to the flat part of the chamber and the dish will be where the open portion of the chamber is. This gives you quench in the non chamber area.

In the piston pic area 1 would be the area that you would want to get the ~.045" piston to head distance with. This part of the piston top should correspond to the flat portion of the head.

2 is the dish and should be the approximate shape of the chamber portion of the head.

They should match the same numbered areas in the pic of the head as best as possible. NOTE - the piston and head I used for examples don't match each other they're just the stuff I had pics of.
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Old 04-13-2007, 05:50 PM
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That certionally makes sense, it creates a small pocket for most of the combustion to occur vrs a larger and thinner area for combustion to occur reducing the chance for detonation. I was thinking in way the wrong direction on this one lol.
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Old 04-15-2007, 10:09 AM
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Here's a side by side look that is similar to what SLOW is trying to point out.

Note the smaller quench pad at the bottom in addition to the large top quench pad and the one around the outside edge of the piston.
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Old 04-16-2007, 10:47 PM
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Also, some cheaper aftermarket pistons are up to .020" shorter in compression height than stock pistons.
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Old 04-17-2007, 09:33 AM
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Quote:
Originally Posted by KGRIFF
That certionally makes sense, it creates a small pocket for most of the combustion to occur vrs a larger and thinner area for combustion to occur reducing the chance for detonation. I was thinking in way the wrong direction on this one lol.
and the quench area stimulates the charge, inducing swirl, which is was really reduces the detonation. That quench is definetely important to consider.
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Old 04-19-2007, 12:00 PM
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I am kind of without a good quench on this one the pistons are full dish and they sit below the deck at .039 at the highest point. The 350 is just going to be kind of a test fit to make sure everything works right before the little more serious 406 goes in. The 350 was always intened for a test engine I was trying to build the best performing 350 for the littlest cost but in reality I think we cut to many corners on it for cost sake but its nearly together now so we will see what happens. The engine specs : engine was previously bored to 4.04 its a 010 block 2 bolt main, I bought it for $70 because it threw the damper. We tore it down checked the clearances and felt it was close enough to just hand hone it and put new rings on the zollinger pistons, I had a factory crank polished (a different one) and installed it with a high volume oil pump. The main bolts were replaced with arp bolts. True roller timing chain a used 270 magnum cam with crane antipump lifters, a pair of junkyard vortec heads which I ported the exhaust side ground in the valves shaved .010 off the retainers and replaced the springs with stiffer ones. Picked up the summit stage 3 intake and have a 3310 holley or a 600 elderbrock(thinking about trading for a 750 though) we will see what happens in a few weeks
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