Dynamic Compression Ratio
Thread Starter
Bud2
Joined: Jul 2005
Posts: 1,237
Likes: 4
From: Warrnambool Victoria
I just went onto Cometic's site. Maybe I'm just plain stupid but I couldn't find a gasket there that was over .040. Put in the stock number and it came back with nothing.....
I dunno, I'm gonna have a cup of tea and a laydown.
Bud.
I dunno, I'm gonna have a cup of tea and a laydown.
Bud.
Safety Car
Joined: May 2003
Posts: 4,797
Likes: 239
From: Ocean Township NJ
My flat topped pistons have 5cc in the valve reliefs and are 0.012 down in the hole. The piston ring height is .2236, 0.003 piston to bore clearance. 65cc AFR heads. 6 inch Scatt rods. The Felpro 1003 gasket is 0.041 after torqued. The HR cam is Lunati lobe separation of 106, advertised duration of 290, IV closes at 41.5 (@.050 lift). What have I left out??? Anyway, I've had results of DCR of 8.83, 10.34, 8.92, 8.46.
I thought this was maths. If I'm using the same figures why am I getting different answers?
So, am I in the poo?
Bud.
Oh, forgot to say the bore is 4.030 and the stroke is 3.75. It's a 383.
I thought this was maths. If I'm using the same figures why am I getting different answers?
So, am I in the poo?
Bud.
Oh, forgot to say the bore is 4.030 and the stroke is 3.75. It's a 383.
Your SCR (static compression ratio) is 10.598:1.
You must use "advertised" duration for valve events when calculating dynamic compression ratio (DCR). Based on the info you provide, it looks like your cam is the Lunati 60112. You can not use 0.050" valve timing events, and so, 41.5 degrees is way out of line. Lunati uses actual durations at .006" valve lift (SAE J604D) to figure advertised durations. Using this information, along with the recommended installation timing (4 degrees advanced with a 110 LCA, 106 ICL and 114 ECL) and 282 degrees advertised intake duration, the intake closing event is as follows:
IVC = ICL + [intake duration/2] - 180 = 106 + 141 - 180 = 67 ABDC
Using this, along with a 3.75" stroke and a 6" con rod yields a 2.86" dynamic stroke and a 8.32:1 DCR, which is excellent.
Congratulations on a well thought out build!
Now go to sleep and don't change anything.
Last edited by 65tripleblack; May 10, 2012 at 10:38 PM.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
.010 will not make difference unless it is way off to begin with.
I still think the compression is a little high....but the DCR numbers support
it.
I never built them that high for two reasons:
1)You will never miss the power.
2)You can run garbage if you can't find the good stuff in a pinch.
Your call......will run fine either way.
Jebby
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Thread Starter
Bud2
Joined: Jul 2005
Posts: 1,237
Likes: 4
From: Warrnambool Victoria
[QUOTE=65tripleblack;1580781466]Your SCR (static compression ratio) is 10.598:1.
You must use "advertised" duration for valve events when calculating dynamic compression ratio (DCR). Based on the info you provide, it looks like your cam is the Lunati 60112. You can not use 0.050" valve timing events, and so, 41.5 degrees is way out of line. Lunati uses actual durations at .006" valve lift (SAE J604D) to figure advertised durations. Using this information, along with the recommended installation timing (4 degrees advanced with a 110 LCA, 106 ICL and 114 ECL) and 282 degrees advertised intake duration, the intake closing event is as follows:
IVC = ICL + [intake duration/2] - 180 = 106 + 141 - 180 = 67 ABDC
Using this, along with a 3.75" stroke and a 6" con rod yields a 2.86" dynamic stroke and a 8.32:1 DCR, which is excellent.
Well... My cam card indicates its the #50199 and they note the timing figures are at .050". Lobe center line of 102. Now that's not exactly what you said - so am I still in the poo without the .051 gasket?
Bud.
You must use "advertised" duration for valve events when calculating dynamic compression ratio (DCR). Based on the info you provide, it looks like your cam is the Lunati 60112. You can not use 0.050" valve timing events, and so, 41.5 degrees is way out of line. Lunati uses actual durations at .006" valve lift (SAE J604D) to figure advertised durations. Using this information, along with the recommended installation timing (4 degrees advanced with a 110 LCA, 106 ICL and 114 ECL) and 282 degrees advertised intake duration, the intake closing event is as follows:
IVC = ICL + [intake duration/2] - 180 = 106 + 141 - 180 = 67 ABDC
Using this, along with a 3.75" stroke and a 6" con rod yields a 2.86" dynamic stroke and a 8.32:1 DCR, which is excellent.
Well... My cam card indicates its the #50199 and they note the timing figures are at .050". Lobe center line of 102. Now that's not exactly what you said - so am I still in the poo without the .051 gasket?
Bud.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
[QUOTE=Bud2;1580781876]
50199 is a generic custom grind code......most likely someone was smart and
had this ground on a .990 base circle.
This is necessary with a 3.750 stroke crank....so it will not contact the rod bolts.
I crossed your duration specs as it jibes with what Tripleblack says.....
The DCR is measured like TB said with advertised duration @ .006
You should be fine.
So yes...go to sleep
Sorry to get you stirred up earlier......
Jebby
Your SCR (static compression ratio) is 10.598:1.
You must use "advertised" duration for valve events when calculating dynamic compression ratio (DCR). Based on the info you provide, it looks like your cam is the Lunati 60112. You can not use 0.050" valve timing events, and so, 41.5 degrees is way out of line. Lunati uses actual durations at .006" valve lift (SAE J604D) to figure advertised durations. Using this information, along with the recommended installation timing (4 degrees advanced with a 110 LCA, 106 ICL and 114 ECL) and 282 degrees advertised intake duration, the intake closing event is as follows:
IVC = ICL + [intake duration/2] - 180 = 106 + 141 - 180 = 67 ABDC
Using this, along with a 3.75" stroke and a 6" con rod yields a 2.86" dynamic stroke and a 8.32:1 DCR, which is excellent.
Well... My cam card indicates its the #50199 and they note the timing figures are at .050". Lobe center line of 102. Now that's not exactly what you said - so am I still in the poo without the .051 gasket?
Bud.
You must use "advertised" duration for valve events when calculating dynamic compression ratio (DCR). Based on the info you provide, it looks like your cam is the Lunati 60112. You can not use 0.050" valve timing events, and so, 41.5 degrees is way out of line. Lunati uses actual durations at .006" valve lift (SAE J604D) to figure advertised durations. Using this information, along with the recommended installation timing (4 degrees advanced with a 110 LCA, 106 ICL and 114 ECL) and 282 degrees advertised intake duration, the intake closing event is as follows:
IVC = ICL + [intake duration/2] - 180 = 106 + 141 - 180 = 67 ABDC
Using this, along with a 3.75" stroke and a 6" con rod yields a 2.86" dynamic stroke and a 8.32:1 DCR, which is excellent.
Well... My cam card indicates its the #50199 and they note the timing figures are at .050". Lobe center line of 102. Now that's not exactly what you said - so am I still in the poo without the .051 gasket?
Bud.
had this ground on a .990 base circle.
This is necessary with a 3.750 stroke crank....so it will not contact the rod bolts.
I crossed your duration specs as it jibes with what Tripleblack says.....
The DCR is measured like TB said with advertised duration @ .006
You should be fine.
So yes...go to sleep
Sorry to get you stirred up earlier......
Jebby
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