Compression ration completely off ? Too high !?
Thread Starter
Intermediate
Joined: Dec 2019
Posts: 47
Likes: 0
From: 616,Michigan
Compression ration completely off ? Too high !?
So I’ve plugged my numbers into a calculator and got the following ;
Bore : 4.155
Stroke : 4.125
Cylinder Head Volume : 70cc(LS7)
Effective Dome volume : -22 ( dish pistons)
Deck Clearance : 0.005
Gasket Thickness : 0.040 (Cometic )
END RESULT : 16.8 : 1
I honestly doubt my engine is running this high. What’s off ?
Bore : 4.155
Stroke : 4.125
Cylinder Head Volume : 70cc(LS7)
Effective Dome volume : -22 ( dish pistons)
Deck Clearance : 0.005
Gasket Thickness : 0.040 (Cometic )
END RESULT : 16.8 : 1
I honestly doubt my engine is running this high. What’s off ?
Last edited by Electron447; Dec 28, 2019 at 05:52 PM.
Drifting
Joined: Sep 2009
Posts: 1,862
Likes: 595
From: Prescott, Arizona
I get 9.085:1, check if I made a mistake-
pi D squared/ 4 = cylinder area = 4.155 x 4.155 x 3.14159/ 4 = 13. 559 sq. inches x stroke 4.125 = cylinder volume = 55.93 sq inches.
Combustion chamber volume = 70 + 22 = 92 cc x .0610237 cubic inch per cc = 5.614 cubic inches, (plus gasket);
gasket @ 0.040 = 13.559 x 0.040 = 0.542 cubic inches, total combustion chamber volume =5.614 + 0.542 = 6.156 cubic inches
55.93/ 6.156 = 9.085:1
pi D squared/ 4 = cylinder area = 4.155 x 4.155 x 3.14159/ 4 = 13. 559 sq. inches x stroke 4.125 = cylinder volume = 55.93 sq inches.
Combustion chamber volume = 70 + 22 = 92 cc x .0610237 cubic inch per cc = 5.614 cubic inches, (plus gasket);
gasket @ 0.040 = 13.559 x 0.040 = 0.542 cubic inches, total combustion chamber volume =5.614 + 0.542 = 6.156 cubic inches
55.93/ 6.156 = 9.085:1
Drifting
Joined: Sep 2009
Posts: 1,862
Likes: 595
From: Prescott, Arizona
Ooops I forgot the deck clearance-
13.559 x 0.005 = 0.0678 cubic inches
6.156 + 0.0678 = 6.2238 combustion chamber volume
55.93/ 6.2238 = 8. 986:1
Probably should add the clearance around the top land also-
13.559 x 0.005 = 0.0678 cubic inches
6.156 + 0.0678 = 6.2238 combustion chamber volume
55.93/ 6.2238 = 8. 986:1
Probably should add the clearance around the top land also-
Safety Car
Joined: Mar 2017
Posts: 3,777
Likes: 941
From: Orlando Florida
My back of the envelop (Excell, actually) says 10:1. For absolute compression, we'd need more information: piston to cylinder clearance, distance from piston top to upper ring, head gasket bore diameter to start. You list deck at .005, but is that + or -, i.e. piston proud .005 or recessed .005?
I calculate:
piston stroke: 916.55 cc
gasket; 8.89 cc
deck (-.005): 1.11 cc
dish: 22.00 cc
chamber: 70.00 cc
Summed, I see A) 7.33 liters (impressive!) and B) maximum cylinder volume of 1018.55 cc, and a minimum cylinder volume of 102.00 cc. Dived max by min and I get 9.99 to 1. If the deck is reversed, then I get 9.96 to 1.
I calculate:
piston stroke: 916.55 cc
gasket; 8.89 cc
deck (-.005): 1.11 cc
dish: 22.00 cc
chamber: 70.00 cc
Summed, I see A) 7.33 liters (impressive!) and B) maximum cylinder volume of 1018.55 cc, and a minimum cylinder volume of 102.00 cc. Dived max by min and I get 9.99 to 1. If the deck is reversed, then I get 9.96 to 1.
Last edited by redzg; Dec 29, 2019 at 09:14 PM.
