What is the difference between LT1 561 Heads, and LT1 643 Heads? Just curious for my own knowledge...

 

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

 

is that the only difference? portability?

 

the 643 AND the 374 have more meat for porting, the 561 are on the later models and are not as portable

 

 

cool, thanks guys!

 

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!

 

^^^+1.

 

Also, stock 561's flow about 10 cfm less than the other castings.

 

Cool, thanks for the input! Now I know lol

 

Mine are 643s

 

643 heads rule ..

 

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.

 

Thats why I bought my castings from Lloyd instead of shipping him mine.

 

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

 

I hope to get alot done tonight & I hope to have it back in the car this weekend.