So, I am putting a pport back together, and I am considering leaving the exhaust sleeves out. What would be the negative impact of this? I had a 12abp and it had no exhaust sleeves......
I also plan on running nitrous through this engine. Lots of nitrous. Lots.

 

Turbulent gas flow.

 

If you port it properly and fab up a ring that inserts into the end of the housing where the lip of the sleeve goes on the outside, you can get some pretty nice flow. If you just leave the sleeve out and do nothing else, it's going to suck pretty hard. You don't have anything to worry about when it comes to heat transfer to the aluminum. It'll be fine.