SCR questions
09-09-2006, 02:54 PM
#1
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SCR questions I am about to replace my factory heads with a set of CNC ported ones that have been milled .018. I`m also going to use .042 head gaskets. My motor is a stock 01 LS1. They are 853 heads with a factory 66.67 CC size.
Bore: 3.98
Stroke: 3.662
Head gasket: .042
Deck Height: .007
PTV: 0
CCV: 63.67
With a positive deck height of .007 I get 10.77 CR, but with a -.007 I get 11.15 CR. Way more compression than I wanted. I was looking for around 10.6 to 10.7. Are you suppose to plug in a positive deck height number or negative number? Also, how much of a difference in compression would it be to polish the cast off of the CC`s on the heads? They still have the casting in them other than the valves being deshrouded.
Bore: 3.98
Stroke: 3.662
Head gasket: .042
Deck Height: .007
PTV: 0
CCV: 63.67
With a positive deck height of .007 I get 10.77 CR, but with a -.007 I get 11.15 CR. Way more compression than I wanted. I was looking for around 10.6 to 10.7. Are you suppose to plug in a positive deck height number or negative number? Also, how much of a difference in compression would it be to polish the cast off of the CC`s on the heads? They still have the casting in them other than the valves being deshrouded.
09-09-2006, 08:15 PM
#3
The number should be a -.007 since that is how far they come out of the hole. Your SCR may or may not be OK. It will depend on how soon the intake valve closes on the cam you put in (DCR). If you are getting a decent sized cam it shouldn't be a problem and you may even want more compression.
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09-10-2006, 06:18 PM
#10
Must be a slow weekend for responses.
If you are using the stock block, rods & pistons and heads with 63.67 CCV heads I get 11.05 SCR. Your DCR with that cam will be 8.38 - 8.67 depending on how much advance it has. This is using Piano Prodigy's spreadsheet. I don't know how much advance they usually grind in. If you can get 93 octane gas you will be just fine either way. On 91 octane gas the higher DCR could be problematic depending on temperature, humidity & altitude.
This info is just from what I have gathered reading stuff on this site. As for me I am planning on changing my cam and head gasket to get a DCR of 8.4 - 8.6 and see how it goes. Then, if that goes well I plan on getting a set of heads and taking the DCR up another .2 and see what happens. I can only get 91 octane around here but I am also at 4000 feet and the corrected altitude is always quite a bit higher so I feel pretty safe.
Which head gasket are you using to get a .042 thickness? I might need something like that.
BTW I think the stock bore is 3.9 and the stock stroke is 3.622. You listed different numbers which could be why you are getting a higher SCR.
If you are using the stock block, rods & pistons and heads with 63.67 CCV heads I get 11.05 SCR. Your DCR with that cam will be 8.38 - 8.67 depending on how much advance it has. This is using Piano Prodigy's spreadsheet. I don't know how much advance they usually grind in. If you can get 93 octane gas you will be just fine either way. On 91 octane gas the higher DCR could be problematic depending on temperature, humidity & altitude.
This info is just from what I have gathered reading stuff on this site. As for me I am planning on changing my cam and head gasket to get a DCR of 8.4 - 8.6 and see how it goes. Then, if that goes well I plan on getting a set of heads and taking the DCR up another .2 and see what happens. I can only get 91 octane around here but I am also at 4000 feet and the corrected altitude is always quite a bit higher so I feel pretty safe.
Which head gasket are you using to get a .042 thickness? I might need something like that.
BTW I think the stock bore is 3.9 and the stock stroke is 3.622. You listed different numbers which could be why you are getting a higher SCR.
09-10-2006, 07:25 PM
#12
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The .042 gasket is the Mr. Gasket composite gaskets they have out now. I corrected the numbers you gave me and still got 11 SCR compression. I don`t know how to figure DCR, so that is why I haven`t done that. Also, I don`t know the full specs on the cam, so guess I can`t do it anyway. I can get 93 octane around here, but it seems some gas stations cheat us. I remember an old truck I had with a chip that was tuned for 93 only gas and filling up at several different gas stations and I got major pinging in the engine. I think I`m going to polish my CC`s on my heads to drop compression a bit. Think that will reduce it much or not?
09-10-2006, 08:05 PM
#13
You can get the SCR/DCR calculator I was using here: http://www.alantripp.com/VE%20Calcul...y%20Lookup.xls (you'll need excel). Different calculators have minor variations in how they come out, shouldn't be more than .05 though.
If you can get what is supposed to be 93 octane then I'd bet you'll be just fine especially if there is no advance ground into the cam. These engines handle the higher compression pretty well. Like Ferocity02 was saying, if you have problems you can back the timing off a bit.
I wouldn't think the polishing would reduce the compression too much but it depends on how much material you take off. If you are really worried about the compression (you shouldn't be) then get a thicker head gasket.
If you can get what is supposed to be 93 octane then I'd bet you'll be just fine especially if there is no advance ground into the cam. These engines handle the higher compression pretty well. Like Ferocity02 was saying, if you have problems you can back the timing off a bit.
I wouldn't think the polishing would reduce the compression too much but it depends on how much material you take off. If you are really worried about the compression (you shouldn't be) then get a thicker head gasket.
