cp pistons, eagle rods =cr?

[zdatsupra]

Does anyone know if running cp pistons .040 oversized with the eagle rods what compression ratio this should yield with minimally shaved head and block using 1.5 or 2.0 mm hg?

[avp23]

thats a good question, im using Cp pistons stock size and eagle rods my self. im using a 1.2 HG to.

[Zumtizzle]

Use a damn compression calculator online. We won't spoon feed this to you guys.

[Zumtizzle]

Basic measurements (Formulas used below)
Bore Diameter = 83.5mm
Stroke = 91mm
Bore Radius = 41.75mm
Piston Volume = 19cc
Deck Clearance = -2.8cc
Combustion Chamber Volume = 37.5cc
2.0mm x 84mm Head Gasket Volume = 11.08cc

Cylinder Volume
Bore size = 83.5mm
Stroke = 91mm
Bore Radius = 41.75mm
Volume of Cylinder = (pi*radius*radius*height)/1000
(3.1416*41.75*41.75*91)/1000 = 498.316cc
Total Bottom End Capacity = (498.316cc*6 = 2989.896cc)

Gasket Volume
Gasket thickness = 2.00mm
Bore size = 84mm
Volume of head gasket = (pi*radius*radius*height)/1000
(3.1416*42*42*2)/1000 = 11.08cc

Deck Clearance
Piston height = 0.5mm
Bore Size = 83.5mm
Volume of Exposed Piston = (pi*radius*radius*height)/1000
(3.1416*41.75*41.75*0.5)/1000 = 2.74cc

Compression Ratio
CR = Compression Ratio
D = Displacement
PV = Piston Volume
DC = Deck Clearance Volume
G = Gasket Volume
CC = Combustion Chamber Volume

CR = (D + PV + DC + G + CC) / (PV + DC + G + CC)
8.685:1 = (498.316cc+19cc-2.74cc+11.08cc+37.5cc)/(19cc-2.74cc+11.08cc+37.5cc) = (563.156)/(64.84)

.

[suprahero]

My 2jz cp pistons were .040 and they were -15.5cc. I'lll have to check my thread to be sure.

That's right for the 2jz pistons, but I don't know which motor you're talking about. If you call CP, they will tell you the dish volume.

[zdatsupra]

I dont expect spoonfeeding, I dont even expect someone to tell me exactly what my cr will be as I know every motor is different and even an online calculator is not going to be totally accurate if I dont get in there and measure what I have going on.
I know for my L series Nissan motor there are mulitiple lists that tell you what cr is expected for different heads, pistons combos etc...
This makes it much easier to plan a build and purchasing parts or like in my case looking towards what size hg I need to finish putting what I have back together...With all the different parts out there for the 7mgte it sure would be nice to have a resource available based on peoples past experiences and calculations etc....
Zumtizzle, thanks for the math, that might help me avoid having to look up my notes somewhere in the garage out there....

[zdatsupra]

For those wanting to know the dish volume of cp pistons.
for the 7mgte .040 according to cp is-18.3 cc, crevice volume above the rings is .6cc.

[avp23]

For those wanting to know the dish volume of cp pistons.
for the 7mgte .040 according to cp is-18.3 cc, crevice volume above the rings is .6cc.

what about stock size cp pistons? thanks in advance haha.

and what size is the stock 7mgte 2995cc? i dont know.

[suprarich]

Your cp pistons should have came with a build sheet that would list the dish cc's

[IJ.]

Use a damn compression calculator online. We won't spoon feed this to you guys.

Even though you did in the very next post ;)

[Zumtizzle]

Even though you did in the very next post ;)

haha i had posted it somewhere else and decided to post it up here too for future reference. ;)

[zdatsupra]

The build sheet does not list the dish volume or crevice volume, however the man at cp tech line was very helpful.

[turbo joe]

Just an FYI == if you're not needing to know down to a gnat's ass...

The compression ratio will increase by the same percentage that you change the displacement...all other things held equal. If you make a 10:1 motor displace 10% more, the compression ratio will then be 11:1.

If you want to know how much the compression ratio changes with a larger bore...figure the displacement with the old bore...and the new bore, then apply the same percentage change to the old compression ratio.