Dynamic comp ratio: Have I made a mistake?
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
Likes: 1
From: Pembroke pines FL
Dynamic comp ratio: Have I made a mistake? So im planning to be running a set of 243 heads milled .030" with stock thickness MLS head gaskets from texas speed. the cam im running is a comp cam 228 230 XE lobe i think the lift is .571 .573. on a 112 the bottom end will be stock.
I tried using a dynamic compression ratio calculator program and apparantly my DCR will be 10.47 if my SCR is 11-1. does this sound right? i am told that DCR should be around 8-9
I tried using a dynamic compression ratio calculator program and apparantly my DCR will be 10.47 if my SCR is 11-1. does this sound right? i am told that DCR should be around 8-9
Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
Likes: 1
From: Pembroke pines FL
I am not sure. the program I used calculates it when you enter advertised lift and duration, LSA and ICL. but im thinking that advertized lift and duration is different than lift and duration at the valve and im not sure if the 228 230 is at the valve or not
no the way you calculate DCR is all dependent on valve timing. It matters where the intake valve closes and allows the cylinder to pressurize. youll have to find your cam card and figure out the intake close abdc number which is a degree that represents where the intake valve closes after bottom dead center
Here you go....where the formula calls out .006 duration...if you don't have that advertised will work.
Formula used; (.006 duration/2) + CL - 180= Intake ABDC
After you come up the the intake closing point....use the calc. that I provided to figure you SCR and DCR. Disreguard the .050 call out in the calc. for your ABDC point. This calc. was setup for much more aggressive lobes, just plug in the number you get from the formula and it will be really close.
http://www.kb-silvolite.com/calc.php?action=comp
Just from the looks of your basic engine info, you will be fine and are probably in the DCR range of 8.1 to 8.3.
Thanks and good luck with your build.
Formula used; (.006 duration/2) + CL - 180= Intake ABDC
After you come up the the intake closing point....use the calc. that I provided to figure you SCR and DCR. Disreguard the .050 call out in the calc. for your ABDC point. This calc. was setup for much more aggressive lobes, just plug in the number you get from the formula and it will be really close.
http://www.kb-silvolite.com/calc.php?action=comp
Just from the looks of your basic engine info, you will be fine and are probably in the DCR range of 8.1 to 8.3.
Thanks and good luck with your build.
TECH Senior Member
Joined: Mar 2004
Posts: 14,620
Likes: 17
From: BFE
So im planning to be running a set of 243 heads milled .030" with stock thickness MLS head gaskets from texas speed. the cam im running is a comp cam 228 230 XE lobe i think the lift is .571 .573. on a 112 the bottom end will be stock.
I tried using a dynamic compression ratio calculator program and apparantly my DCR will be 10.47 if my SCR is 11-1. does this sound right? i am told that DCR should be around 8-9
I tried using a dynamic compression ratio calculator program and apparantly my DCR will be 10.47 if my SCR is 11-1. does this sound right? i am told that DCR should be around 8-9
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Brett Foote Thread Starter
Launching!
Joined: Nov 2008
Posts: 284
Likes: 1
From: Pembroke pines FL
So is this good? basically I'm asking since i bought all this stuff, and now is when i hear of this dynamic compression ratio concept. i want to make sure nothing goes wrong since my car has 143K miles on stock bottom end.
8.8 is a tad higher than i think is optimal. but with 93 octane and a good tuner you should be able to pull it off. Just dont let the wife drive it and put 87 in it. Saw that go bad once
yes it does but it also means youll need higher octane fuel. more compression means more power but more octane. If you get too high on compression (too high for 93 octane) then youll have detonation. detonation or knock will then lead to bad things like flaked pistons burnt valves cracked heads etc. you get my drift.
Ive seen some people get away with 8.75 to 1 if the location isnt too extremely hot and they do have 93 octane
Ive seen some people get away with 8.75 to 1 if the location isnt too extremely hot and they do have 93 octane
