with more thought I ain't sure if it was magnum manis but I had kinda thought that but in any case it was regular iron & the soak time wasn't too long & what impressed me was the cross section area they gained. EDIT lookup "Acid Porting Cast Iron Manifolds" & the vid is 3 minutes & 18 seconds long to confirm you have the right one. they said 16% more volume & I tried to post the address but it would not take.