LQ4 6.0 w/ Milled 243s
12-26-2007, 01:49 PM
#25
ok, so basically pick the cam that i want and then decide what gaskets i want then find out the compression after you take what the cam/head gaskets/heads will give you then you decide to change gaskets or mill heads however much to reach what compression you want?
wow that was probably the STUPIDEST sounding sentence i've ever typed.
sorry if you don't understand what i'm talking about because i honestly don't either.
wow that was probably the STUPIDEST sounding sentence i've ever typed.
sorry if you don't understand what i'm talking about because i honestly don't either.
12-26-2007, 02:49 PM
#27
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Dammit, I typed a whole big response, but my computer froze and I lost it. Here we go again, only I'm parting it out this time.
Part I
Static Compression Ratio (SCR) is the ratio of the total cylinder volume at BDC v. the cylinder volume with the piston at TDC. To calculate it you need your number of cylinders, bore, stroke, piston dish or dome volume, combustion volume chamber, gasket bore, gasket thickness, and whether the piston is in or out of the bore at TDC.
Part I
Static Compression Ratio (SCR) is the ratio of the total cylinder volume at BDC v. the cylinder volume with the piston at TDC. To calculate it you need your number of cylinders, bore, stroke, piston dish or dome volume, combustion volume chamber, gasket bore, gasket thickness, and whether the piston is in or out of the bore at TDC.
Last edited by tdrumm; 12-26-2007 at 03:42 PM.
12-26-2007, 02:55 PM
#28
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Part II
Dynamic Compression Ratio (DCR) uses the SCR we just calculated and also factors in the valve events of the cam you have selected. You can only build compression in a moving engine when both valves are shut. Calculating your DCR uses the valve events of your cam to only consider the portion of your stroke where both the intake and exhaust valves are shut, where as the SCR calculation considers the entire stroke. This is why DCR is always lower than SCR. There is a good DCR calculator over on ls1tech. But first we need to find your valve events.
Dynamic Compression Ratio (DCR) uses the SCR we just calculated and also factors in the valve events of the cam you have selected. You can only build compression in a moving engine when both valves are shut. Calculating your DCR uses the valve events of your cam to only consider the portion of your stroke where both the intake and exhaust valves are shut, where as the SCR calculation considers the entire stroke. This is why DCR is always lower than SCR. There is a good DCR calculator over on ls1tech. But first we need to find your valve events.
12-26-2007, 02:59 PM
#29
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Part III
Calculating valve events. There are four valve events that need to be considered to calculate your DCR. They are intake valve opening, intake valve closing, exhaust valve opening, and exhaust valve closing. These will be expressed in crank shaft degrees. To calculate valve events you need to know your cam's intake and exhaust lobe durations at .006 lift (not .050) and the intake center line (not LSA). Again on ls1tech, there is a good calculator to do this for you.
Calculating valve events. There are four valve events that need to be considered to calculate your DCR. They are intake valve opening, intake valve closing, exhaust valve opening, and exhaust valve closing. These will be expressed in crank shaft degrees. To calculate valve events you need to know your cam's intake and exhaust lobe durations at .006 lift (not .050) and the intake center line (not LSA). Again on ls1tech, there is a good calculator to do this for you.
12-26-2007, 03:41 PM
#30
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Part IV
Putting it all together:
Using some generally accepted data, we can calculate your SCR
Bore - 4.00"
Stroke - 3.62"
Piston Dish - 7cc
Combustion Chamber - 65cc
Head Gasket Bore - 4.005" *educated guess
Head Gasket Thickness - 0.040"
Piston deck height - -0.008" (out of the bore) *average for Lsx engines
This results in a SCR of 10.5:1. To reach 11:1, you would need a head with a 61cc chamber. Using the general rule for 243 heads of 1cc = 0.006 mill that works out to about a 0.025 mill.
Assuming that you have picked cams using Comp Cam lobes, we can calculate your valve events. I am assuming that there is no advance ground into these cams (i.e. ICL = LSA). Grinding advance will change the valve events.
For your 230/236, 112 cam - These are comp XE-R lobes 3725 int, 3728 ex.
IVO 27.5* BTDC
IVC 71.5* ABDC
EVO 74.5* BBDC
EVC 30.5* ATDC
ICL - 112*
For your 230/224, 111 cam - These are comp XE lobes 3718 int, 3715 ex.
IVO 30.5* BTDC
IVC 72.5* ABDC
EVO 69.5* BBDC
EVC 27.5* ATDC
ICL - 111*
Using this info to calculate your DCR gives us..... Drum roll please.....
10.5:1 SCR, 230/236 cam - 7.9:1 DCR
11.0:1 SCR, 230/236 cam - 8.25:1 DCR
10.5:1 SCR, 230/224 cam - 7.8:1 DCR
11.0:1 SCR, 230/224 cam - 8.2:1 DCR
As you can see, big durations bleed off quite a bit of compression. Everyone seems to be keyed into 8.5:1 - 8.7:1 as the magic DCR number to hit, but I if you actually sat down and figured it out ,the majority of the trucks here would be in the high 7s.
Putting it all together:
Using some generally accepted data, we can calculate your SCR
Bore - 4.00"
Stroke - 3.62"
Piston Dish - 7cc
Combustion Chamber - 65cc
Head Gasket Bore - 4.005" *educated guess
Head Gasket Thickness - 0.040"
Piston deck height - -0.008" (out of the bore) *average for Lsx engines
This results in a SCR of 10.5:1. To reach 11:1, you would need a head with a 61cc chamber. Using the general rule for 243 heads of 1cc = 0.006 mill that works out to about a 0.025 mill.
Assuming that you have picked cams using Comp Cam lobes, we can calculate your valve events. I am assuming that there is no advance ground into these cams (i.e. ICL = LSA). Grinding advance will change the valve events.
For your 230/236, 112 cam - These are comp XE-R lobes 3725 int, 3728 ex.
IVO 27.5* BTDC
IVC 71.5* ABDC
EVO 74.5* BBDC
EVC 30.5* ATDC
ICL - 112*
For your 230/224, 111 cam - These are comp XE lobes 3718 int, 3715 ex.
IVO 30.5* BTDC
IVC 72.5* ABDC
EVO 69.5* BBDC
EVC 27.5* ATDC
ICL - 111*
Using this info to calculate your DCR gives us..... Drum roll please.....
10.5:1 SCR, 230/236 cam - 7.9:1 DCR
11.0:1 SCR, 230/236 cam - 8.25:1 DCR
10.5:1 SCR, 230/224 cam - 7.8:1 DCR
11.0:1 SCR, 230/224 cam - 8.2:1 DCR
As you can see, big durations bleed off quite a bit of compression. Everyone seems to be keyed into 8.5:1 - 8.7:1 as the magic DCR number to hit, but I if you actually sat down and figured it out ,the majority of the trucks here would be in the high 7s.