561's came on 97 LT1 f-bodies. I know this for a fact as this was the casting # from my 97LT1. I have heard they are also on some Impalla SS LT1's but its totally unfounded and I cannot confirm this from my experience. A GM tech that does work for my engine builder said they came on 97 TA's and some of the last #'s of the 96's that were produced.

We had a pair of LT1 heads from a 95 Z28 in the shop and decided to do some flow bench testing on both pairs to find which ones would be better. The 561 castings heads had a 3% better flow ratio across the board (method= intake/exhaust=%) The 561s flow slightly better by as little as 1 CFM @ .100 lift up to 5 CFM @ .550 lift on the intake side. IT is not much, but the noticable gain was on the exhaust side. @ .550 lift we noted a 9CFM difference in favor of the 561's. They were also lighter and you could see where the material from the roof, floor, and shortside were thinner and all unneccessary metal from inbetween the intake runners was also removed from the casting process. Which meant that of you ported them you were limited even more then pre 561 castings heads. This is why we chose non 561's because there is more potential.

Hope this helps

 

Well guess what? as if I didn't have bad enough luck, my brand new CSI water pump fell apart. It was going to take like a week to get a new one but they told jordon how to fix it, so he did. then we finally got it running, and the motor freaking fried. Don't know exactly why, or what happened, but I was driving for like 10 minutes, and the oil pressure went to 0 and the car died. There is metal shavings all in the motor now. I am in the process of learning how to take a motor out of the car as we speak. I have gotten so tired of all of this. This is the 2nd motor in 8 months! I barely have enough saved up to fix the car, but I may just end up getting rid of it for something more reliable. Hopefully I can have one ounce of good luck with this car, and nothing else will go wrong, but for some reason I highly doubt it. I will let you all know how it goes.

 

That's no good. Unexpected motor builds are no fun when you have to dig out your pennies to make it happen. Good luck with it!