LT1-LT4 Modifications 1993-97 Gen II Small Block V8

what is a safe CR to go with for a boosted application?

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Old Aug 19, 2005 | 02:19 PM
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Default Need some input for FI.

93 LT1 396 going w/ a AT1 D1 or D1SC 12psi max. Desired CR 8.5:1 or 9.1 w/ the piston? Cam choice 233/242 .569/.576 115 LSA. Main area of concern is I don't know the CC on the heads and they were milled 10/1000th. So would it be wise to just go 8.5:1 to be on the safe side?

LT1 heads are 2.00/1.56
Flow chart reads w/ a 190 port volume
Int / Exh
136 132.7
182.4 159
202.3 162.5
220.6 169.2
237.2 175.8
263.7 189.1
270.4 194.1

Could I still use my 918 springs the above cam w/ out a problem? What kind of numbers could I expect to see? Thanks for any input or advice.
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Old Aug 20, 2005 | 04:24 AM
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Question No help from FI section. Need a answer please.

Stk LT1 heads are 54cc. My heads were milled 10/1000th and have 190 port volume. 2.00/1.56 for valves

Since I don't know the CC on my heads what is a safe CR to go w/ for a boosted application? I want 9.1 but it may be higher since I don't know the CC on the head so to be safe would 8.5:1 be the smartest choice to go with?

Thanks.
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Old Aug 20, 2005 | 05:00 AM
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Yes the stock LT1 chambers run around 54cc. For a 23 degree type sbc head a rule of thumb is that every 0.007" straight milled equals 1 cc. So your chamber now should measure around 53cc.
If you know your deck height, gasket thickness and desired CR you should be able to calculate piston dish volume.
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Old Aug 20, 2005 | 08:26 AM
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Thanks SSS! Deck height is zero. Shooting for a .039 head gasket but may go .040 instead since I don't know the height after it being compressed.
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Old Aug 20, 2005 | 02:29 PM
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That calls for a big piston dish something between 25-30 cc for a target CR of 9-9.5.
There is a CR calculator as well some other usfull calculators here:
http://www.camaroz28.com/calcs/index.shtml
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Old Aug 20, 2005 | 05:20 PM
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Originally Posted by sssalah
That calls for a big piston dish something between 25-30 cc for a target CR of 9-9.5.
There is a CR calculator as well some other usfull calculators here:
http://www.camaroz28.com/calcs/index.shtml
Ross pistons just said the same thing. For 9.1cr about a -30cc. Thanks for the help.
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Old Aug 20, 2005 | 09:01 PM
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I thought stock chambers were 58 cc?
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Old Aug 20, 2005 | 09:09 PM
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NM. I don't know where I got 58cc but I always thought that for some reason. Hmm, learn something new everyday.
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I'm pretty sure the LT1 head is 58cc and the LT4 head is 54CC. Either way you will need about -30 dished pistons.
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Old Aug 21, 2005 | 02:06 AM
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Originally Posted by SRZ
Stk LT1 heads are 54cc. My heads were milled 10/1000th and have 190 port volume. 2.00/1.56 for valves

Since I don't know the CC on my heads what is a safe CR to go w/ for a boosted application? I want 9.1 but it may be higher since I don't know the CC on the head so to be safe would 8.5:1 be the smartest choice to go with?

Thanks.
Stock LT4 heads are 54 cc. Stock LT1 heads are 58 cc heads. I figure with your heads milled that much you have between a 56-57 cc combustion chamber now.
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Old Aug 21, 2005 | 07:57 AM
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Originally Posted by METALBEAST
Stock LT4 heads are 54 cc. Stock LT1 heads are 58 cc heads. I figure with your heads milled that much you have between a 56-57 cc combustion chamber now.
Thank you METALBEAST. I've decided a -31cc piston and .039 gasket. Gives me a little room to play with.
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