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

Difference in Head Casting #'s?

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Old Aug 10, 2009 | 12:05 PM
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Z28Camaro30Ann's Avatar
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Default Difference in Head Casting #'s?
What is the difference between LT1 561 Heads, and LT1 643 Heads? Just curious for my own knowledge...
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Old Aug 10, 2009 | 12:10 PM
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643 are thinner castings and do not have alot of material for major porting
374s are better for porting..i want to say the 561s and the 643 in the same boat but not 100% on that
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Old Aug 10, 2009 | 12:12 PM
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is that the only difference? portability?
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Old Aug 10, 2009 | 12:24 PM
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the 643 AND the 374 have more meat for porting, the 561 are on the later models and are not as portable
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Old Aug 10, 2009 | 12:26 PM
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Originally Posted by JB_97ws6TA
the 643 AND the 374 have more meat for porting, the 561 are on the later models and are not as portable
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Old Aug 10, 2009 | 12:58 PM
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cool, thanks guys!
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Old Aug 10, 2009 | 03:40 PM
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Check AI's website and you'll see they recommend the 643s for porting due to more meat in the castings.

Jake

West Point ROCKS!
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Old Aug 10, 2009 | 03:41 PM
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Originally Posted by wrd1972
^^^+1.
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Old Aug 10, 2009 | 03:44 PM
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Also, stock 561's flow about 10 cfm less than the other castings.
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Old Aug 10, 2009 | 04:07 PM
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Cool, thanks for the input! Now I know lol
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Old Aug 17, 2009 | 05:28 PM
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Mine are 643s
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Old Aug 18, 2009 | 10:54 AM
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643 heads rule ..
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Old Aug 18, 2009 | 12:24 PM
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I have the undesirable 561 castings that I had Lloyd port. I purchased 374's from a member here to have ported but he or she sold me some junk heads. Anyhow, Lloyd told me that they make about 5-8hp less when ported but it was nothing to worry about. Well they put my car into the 11's so I can't complain at all but yes the other castings are better for porting.
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Old Aug 18, 2009 | 02:20 PM
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Thats why I bought my castings from Lloyd instead of shipping him mine.
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Old Aug 18, 2009 | 02:44 PM
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I thought the shipping was going to kill me, i even considered driving them there myself but it was only $20 Maybe because he is only 6-8 hours away. And AC i cant wait to get mine back from him hopefully next week. LOL you should have yours together before me still
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Old Aug 18, 2009 | 03:53 PM
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I hope to get alot done tonight & I hope to have it back in the car this weekend.
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