Piston head volume and piston dome/dish volume.

[JamesR]

Hi,

Sometimes piston specs are listed with piston head volume while other times they are listed as piston dome/dish volume. I'm trying to decide on a set of pistons for 454/.030 with a pair of Edelbrock RPM Performers that Ive had sitting around for abit, but I'm not sure how to correlate piston head volume to dome/dish volume. I'm looking to run between 9.0 and 9.5:1. Nothing too radical, just a good pump gas street motor somewhere in the 450hp - 500hp range.

 

[grumpyvette]

read thru these links

lets assume your building a 454 chevy with edelbrock heads with 100cc combustion chambers and your looking to find the STATIC COMPRESSION RATIO

read this link

measuring piston dome volume

\" how do you measure piston dome volume" I just bought a 454 from a yard sale, the seller has no clue as to the pistons used" https://www.summitracing.com/newsandevents/calcsandtools/compression-calculator http://www.grumpysperformance.com/cop2.png...

garage.grumpysperformance.com

you can purchase a 1/2" thick 6" x 6" lexan sheet you can drill and modify to cover a heads combustion chamber or a blocks bore to cc a combustion chamber volume or piston dome volume for under $16 on the internet/amazon /ebay

Amazon.com

http://www.carcraft.com/techarticles/ca ... index.html

http://www.kb-silvolite.com/calc.php?action=comp

http://www.csgnetwork.com/compcalc.html

http://golenengineservice.com/calc/calccr.htm

http://www.circletrack.com/techarticles ... mples.html

viewtopic.php?f=55&t=2718&p=7057&hilit=octane+compression#p7057

viewtopic.php?f=52&t=727

ok, lets assume your cylinder head volume is 100cc
and your looking at use of a .032 thick head gasket with a 4.310 diam.
and your piston is .010 below the block deck when measured,
and a flat top piston is selected as a start point,
and your bore diam. is 4.281(.030 over)
and your using a stock 4" stroke crank
and stock rods
lets use the calculator above from KB
you see you have a 9.58:1 cpr

now lets assume you select three different pistons and compare results, with the only change being the piston dome or dish

the first has a 5cc valve clearance notch
which would result in a 9.2:1 cpr

the second piston choice has a 18cc dome
which would result in a 11.26:1 cpr


the third piston choice has a 20cc dish
which would result in a 8.26:1 cpr

Mahle pistons are designed for specific applications with the alloy that is best suited for that particular application.
but keep in mind the better versions of forged pistons tend to have the advantage in both strength and heat tolerances

......................Piston Alloy Comparison
4032...................................................... 2618
High silicon............................................No silicon
Low expansion........................................expansion
Tighter piston-to-wall clearance................More Piston-to-wall clearance needed
Quiet Operation......................................Noise when cold
Less ductile............................................More ductile
More stable & consistent.........................Higher resistance to detonation
Longer life cycles....................................Shorter life cycles
Harder...................................................Softer

 

[JamesR]

Thanks for the reply. Ive gone through most of those links and I feel I'm either missing something obvious or its just not clear in the descriptions.

Ive used several calculators and thats what is confusing me at this point. For example this is how Summit lists one the speed pro pistons:

Bore (in) 4.280 in.
Bore (mm) 108.712mm
Piston Style Dome, with single valve relief
Piston Material Hypereutectic aluminum
Compression Distance (in) 1.640 in.
Dome Height (in) 0.100 in.
Piston Head Volume (cc) -10.50cc
Wrist Pin Style Press-fit or floating
Pin Diameter (in) 0.989 in.
Piston Ring Thickness 5/64 in. x 5/64 in. x 3/16 in.

Also this is how Northern Auto list the same piston:

454 BASED; .100 Dome w/ 1 valve relief, 4.250 bore x 4.00 stroke, press or floating pin, coated skirts. Pistons sold in sets of 8, price shown is each.

Ring dimensions 5/64, 5/64, 3/16
Dome Shape; .100 Dome w/ 1 relief
Compression dist 1.640
Deck Clearance .025
Skirt Clearance .0015

With the KB calc I get ~10.0:1. However if I use a calculator that uses piston dome volume like this calc: http://www.csgnetwork.com/compcalc.html , I would have to have a domed piston volume of about 17cc to achieve the same compression of the KB using the piston head volume of -10.50cc. So what is the correlation here between these two terms?

Or is one cal wrong and the other right? Should the magnitude of these two be the same?

Also to add to the confusion, the Northern Auto listing has the table below which would seem to suggest with a 110cc head that the compression would be in the low 9s. Unfortunately they dont state the spec of the gasket used for the those results.

 

[grumpyvette]

thats a very common question,
notice neither chart or description of the pistons from either source gives you all the info needed to calculate accurately
but the answer is that without knowing the blocks deck height and the gasket thickness and diam.
and the pistons deck height and dome or dish volume, plus the bore diam. you can,t accurately calculate the true STATIC compression.
because theres NO standard for engine gasket thickness, or diam. or block deck height, used.
many company's ASSUME either a ZERO DECK ( block decked to spec.) or a .025 deck,(common stock un-machined block) and what ever gasket height was commonly used, the problem is that those measurements tended to be changed over production runs so only measuring not ASSUMING will give you the correct answer, (btw try to keep the quench distance in the .038-.044 range on a stock BBC)
youll need to know your true block deck height and piston to deck clearance plus the gasket dimensions and then get the quench calculated before making a valid selection

viewtopic.php?f=53&t=726&p=5640&hilit=quench+squish#p5640

 

[JamesR]

Ok, I run into this issue at work as well. Its an issue of the manufactures/suppliers not using the same standards to describe their products.

So to clear up one last issue...lets say you have all the information for the block, gaskets, etc (measured) which includes the piston head volume but this information does not explicitly state the piston dome volume. How can you determine the dome volume from the head volume and vice-versa? Are they actually describing the same thing? That is if the piston head volume is -10.50cc, then its piston dome volume is 10.50cc. These are just two terms whose magnitudes describing the same effect on the total combustion chamber volume @ TDC?

Thanks for taking the time to address this for me.

 

[grumpyvette]

Ok, I run into this issue at work as well. Its an issue of the manufactures/suppliers not using the same standards to describe their products.

So to clear up one last issue...lets say you have all the information for the block, gaskets, etc (measured) which includes the piston head volume but this information does not explicitly state the piston dome volume. How can you determine the dome volume from the head volume and vice-versa? Are they actually describing the same thing? That is if the piston head volume is -10.50cc, then its piston dome volume is 10.50cc. These are just two terms whose magnitudes describing the same effect on the total combustion chamber volume @ TDC?

Thanks for taking the time to address this for me.

a flat top piston has zero volume, in the compression calculation, and valve clearance cuts or recessed/ dished designed piston add volume to the combustion chamber, and reduce compression, any DOME or piston extending above the quench area reduces effective combustion chamber volume, increasing the compression ratio

http://www.chevyhiperformance.com/tech/ ... index.html

flat top piston has ZERO effect

reduces effective combustion chamber volume increasing the compression

http://www.probeindustries.com/

https://www.flatlanderracing.com/trwpistonschoose.html

http://aftermarket.federalmogul.com/en- ... 7ibJ7FwU4M

http://www.jepistons.com/

http://www.venolia.com/

http://www.wiseco.com/

http://www.trickflow.com/search.asp?Ntt ... wordSearch

http://www.flatlanderracing.com/manleypis-chevy03.html

http://www.rosspistons.com/information/

http://www.ariaspistons.com/

https://www.uempistons.com/