Math Test - Compression Ratios and Compression Testing
07-27-2012, 03:06 AM
#21
Teching In
Join Date: Oct 2006
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Ok Guys, I've got a math test for you. (This is actually to help a friend out who is worried about his Compression test results).
Scenario:
He swapped in a LR4 (4.8 L Vortec) truck engine, stock heads, no porting etc.
Given that the LR4 has a factory compression ratio of about 9.5 to 1
Reference: http://www.new-cars.com/2003/chevrol...hoe-specs.html
(Lets assume it's from a 2003... it supposedly has 70k miles on it)
He did a dry compression test (did NOT add teaspoon of oil to cylinder) on all cylinders.
Questions:
1) What is the Maximum psi that he could expect to see on each cylinder
2) What is the lowest acceptable psi that he could see on any cylinder
I know his results and I have my answers to Questions 1 & 2 above in my head... but just wanted to get some feedback from the community... hopefully to put his mind at ease. (Please give some reasoning for your answer... not just a number... for example... x*y=z.... thanks!)
Bonus Question: What if this were a stock LS1 motor with 10.5 to 1 CR... same questions...
Any constructive input is appreciated.
Scenario:
He swapped in a LR4 (4.8 L Vortec) truck engine, stock heads, no porting etc.
Given that the LR4 has a factory compression ratio of about 9.5 to 1
Reference: http://www.new-cars.com/2003/chevrol...hoe-specs.html
(Lets assume it's from a 2003... it supposedly has 70k miles on it)
He did a dry compression test (did NOT add teaspoon of oil to cylinder) on all cylinders.
Questions:
1) What is the Maximum psi that he could expect to see on each cylinder
2) What is the lowest acceptable psi that he could see on any cylinder
I know his results and I have my answers to Questions 1 & 2 above in my head... but just wanted to get some feedback from the community... hopefully to put his mind at ease. (Please give some reasoning for your answer... not just a number... for example... x*y=z.... thanks!)
Bonus Question: What if this were a stock LS1 motor with 10.5 to 1 CR... same questions...
Any constructive input is appreciated.
07-28-2013, 12:11 AM
#24
I just use this calculator:
http://www.rbracing-rsr.com/comprAdvHD.htm
Don't input IVC @ .050" use .006" or it doesn't work right.
Without knowing the cam's effect on dynamic compression and altitude, you can't know cranking compression.
Given that this is a stock 4.8L. I know it's 3.78" bore, 3.27" stroke, and 6.276" rods and I know it's 9.5:1.
I have no idea on the cam specs... cept that it's a 190/191 .466/.457 114 LSA. And that doesn't help me.
http://www.rbracing-rsr.com/comprAdvHD.htm
Don't input IVC @ .050" use .006" or it doesn't work right.
Without knowing the cam's effect on dynamic compression and altitude, you can't know cranking compression.
Given that this is a stock 4.8L. I know it's 3.78" bore, 3.27" stroke, and 6.276" rods and I know it's 9.5:1.
I have no idea on the cam specs... cept that it's a 190/191 .466/.457 114 LSA. And that doesn't help me.
07-28-2013, 05:44 PM
#27
TECH Resident
Thread Starter
No, the block was fine actually. He was going to rebuild it but got orders to Germany. Its been sold to a friend who is planning on building it.
