VerdeZ28

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

Whiteaw57

iTrader: (2)

that doesnt sound right at all. what is the intake valve close timing number for the cam?

VerdeZ28

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

Whiteaw57

iTrader: (2)

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

VerdeZ28

where i live, 93 octane is available, do you guys think i would be able to run this?

LSOHOLIC

iTrader: (3)

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.

PREDATOR-Z

I took your heads to be 59cc, your DCR is ~ 8.8, your SCR ~11.4:1

LSOHOLIC

iTrader: (3)

Hey Mr Predator-Z...that sounds a bit high...what did you calc as intake ABDC point ?? 66* @ .006 ??

And how did you calc it ??

Thanks....

PREDATOR-Z

IVC 68.5

I use my excel spreadsheet.

VerdeZ28

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.

Whiteaw57

iTrader: (2)

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

VerdeZ28

what exactly is optimal? and wouldent a higher DCR mean more power?

Whiteaw57

iTrader: (2)

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

PREDATOR-Z

I run my 370ci at 9 DCR with 93 octane in desert heat. Good quench and the right plugs with correct tune go a long way to facilitate things.

Whiteaw57

iTrader: (2)

^^^this is very true. There are alot of little things if you build it right and get a good tuner you can push it a little bit and get a lot in return