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| | |-+ Dish piston at 10.50 WILL make more power than a flat top at 10.50???
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Author Topic: Dish piston at 10.50 WILL make more power than a flat top at 10.50???  (Read 60985 times)
FoxBodyBlur
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« Reply #15 on: January 09, 2007, 11:31:14 pm »

worth a try lol
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« Reply #16 on: January 09, 2007, 11:57:43 pm »

at bdc you would have a little more room to fill the cylinder with the air. which means more air

And finally someone gets in the right time zone!

Keep going.......This is good.

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« Reply #17 on: January 10, 2007, 12:16:34 am »

so the volume of the dish increases the amount of air/fuel in the cylinder, therefore increasing cylinder pressure at tdc?

how about a quench type piston compared to a full dish?  would the improved flame travel of the quench piston offset the additional volume?
« Last Edit: January 10, 2007, 01:00:54 am by knucklefux » Logged

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« Reply #18 on: January 10, 2007, 12:59:24 am »

Dished pistons offer more surface area compared to flat top pistons.  But it's not the 'volume' of the dish, it's the fact that the dish is FARTHER down than the piston top in the cylinder at BDC.  As the piston travels down in the intake stroke, the air is drawn inward and the increased distance created by the dish causes more air to be drawn into the cylinder.  Since the only difference being considered is the type of piston, the dish creates a higher demand for air to fill the cylinder.  Since the intake runner, intake valve, lift and duration are being kept equal between the two piston options the velocity of the air being drawn into the cylinder is increased.  In other words the increase in the distance created by the dish demands more air and fuel to be drawn into the cylinder in the same amount of time as the flat top pistion.  Higher velocity allows more air to be scavenged into the cylinder by tailoring the valve timing events of both the exhaust and intake valves which will create more power.
« Last Edit: January 10, 2007, 01:14:52 am by Its1FastCat » Logged

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« Reply #19 on: January 10, 2007, 01:00:44 am »

Wow lol.
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knucklefux
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« Reply #20 on: January 10, 2007, 01:19:25 am »

damn fastcat...who's dissertation did you dig up for that one?

so, if fastcat is right...it still leaves my question up for debate.  which is better, the full dish or the quench? 

my vote is for the quench piston...it has the low floor of the dish, higher cr, and better flame travel.  well, that's my guess, anyway...
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« Reply #21 on: January 10, 2007, 01:27:10 am »

No one's dissertation. It just makes sense if you think about it.
« Last Edit: January 10, 2007, 01:30:34 am by Its1FastCat » Logged

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mikemustang289
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« Reply #22 on: January 10, 2007, 04:38:28 am »

So it is better then to reduce the combustion chamber volume and offset that by gaining volume in a dished piston? Why then all the hype over the Hemi' design?
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« Reply #23 on: January 10, 2007, 05:12:03 am »

Dished pistons offer more surface area compared to flat top pistons.  But it's not the 'volume' of the dish, it's the fact that the dish is FARTHER down than the piston top in the cylinder at BDC.  As the piston travels down in the intake stroke, the air is drawn inward and the increased distance created by the dish causes more air to be drawn into the cylinder.  Since the only difference being considered is the type of piston, the dish creates a higher demand for air to fill the cylinder.  Since the intake runner, intake valve, lift and duration are being kept equal between the two piston options the velocity of the air being drawn into the cylinder is increased.  In other words the increase in the distance created by the dish demands more air and fuel to be drawn into the cylinder in the same amount of time as the flat top pistion.  Higher velocity allows more air to be scavenged into the cylinder by tailoring the valve timing events of both the exhaust and intake valves which will create more power.

Yes, but isn't the dish farther down than a flat top at TDC as well? How could a dish then draw in more air. The velocity of the air would be the same between both pistons. Yes, the piston will sit lower in the cylinder at BDC, but if the volume of the combustion area (combustion chamber, head gasket, etc.) is kept the same between a flat top and dished piston, both the pistons will displace the same volume and essentially be the same distance from the cylinder head. Think about it like removing all of the volume in the cylinder head and essentially making it flat, then taking that volume and putting it into the piston as a dish. The compression ratio would stay the same and so does the volume inside the cylinder at BDC.

The dished piston will displace the same volume (bore x stroke) as a flat top piston. I'm assuming the velocity of the incoming air is determined by piston speed and cylinder volume; I could be wrong, but how could a dish have any affect on the velocity of the air or the amount of air that is able to enter the cylinder.

Maybe the dish piston has some type of effect on the way air moves inside the cylinder, helping to force air inside the cylinder (and exit the cylinder) based on the shape of the piston.
« Last Edit: January 10, 2007, 05:40:36 am by mikemustang289 » Logged

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« Reply #24 on: January 10, 2007, 08:08:12 am »

Wouldn't the shape of the dish naturally draw more air than a flat top? Besides... the actual volume of the cylinder between the dish and flat could be the same (hence the same compression ratio) but the dish would pull more air to fill it.
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« Reply #25 on: January 10, 2007, 09:30:22 am »

i think that what fastcat is getting at is that since the dish piston is lower by some amount, the incoming air will "see" it as having a stroke that is longer.  the deeper the dish, the longer the stroke the air sees...
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« Reply #26 on: January 10, 2007, 11:37:47 am »

Exactly, and since the air has to travel deeper into the cylinder in the same amount of time the velocity of air flowing into the cylinder is greatly increased.  So it draws more air in from the intake track.
« Last Edit: January 10, 2007, 11:42:12 am by Its1FastCat » Logged

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« Reply #27 on: January 10, 2007, 01:01:43 pm »

I think the piston beingn farther in the cylinder at BDC is like day light savings times.  Sure we can move the clock around but there are still only 24 hrs in a day.  Lets look at what we have a work here.  You have atmospheric pressure (minus the losses in the intake track) as the pistom move increasing the cylinder volume.  This creates a pressure diffferntial to force the a/f into the cylinder.  Now if we are talking about two engines with everything the  except dish volume & combustion chamber size,haw are we any more air?  Now if we are cutting the head at an angle & laying back the valves you might free up restriction but this is apples & oranges to jsut saying the dish is better simply with the dish. 
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« Reply #28 on: January 10, 2007, 01:05:52 pm »

I think the piston beingn farther in the cylinder at BDC is like day light savings times.  Sure we can move the clock around but there are still only 24 hrs in a day.  Lets look at what we have a work here.  You have atmospheric pressure (minus the losses in the intake track) as the pistom move increasing the cylinder volume.  This creates a pressure diffferntial to force the a/f into the cylinder.  Now if we are talking about two engines with everything the  except dish volume & combustion chamber size,haw are we any more air?  Now if we are cutting the head at an angle & laying back the valves you might free up restriction but this is apples & oranges to jsut saying the dish is better simply with the dish. 

This is very typical thinking.  The concept involved is a relatively forward concept.  Not an easy thing to grasp...but once you have, it makes perfect sense.  I'll let Jay come let the cat out of the bag...it's his question =).

Cris 
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mikemustang289
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« Reply #29 on: January 10, 2007, 01:06:57 pm »

Yes but the volumes are kept the same. That is like saying you are adding cubic inches to your engine by going with a dish pistons. The lengths should not matter since what you are concerned about is volume. An engine with a 4 inch bore and 3 inch stroke would not create more velocity than a 3 inch bore 4 inch strocke (if volumes are equal). Maybe I am wrong but I still think the only way a dish can be better is if it has some type of effect on the airflow in the cylinder.
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