Irrespective of Other individuals claim of the 20HP or more maximize- on modified heads alone, this is simply unattainable devoid of camshaft or pistons adjusted. Toyota has casted and machined all their 4 valve heads to really close and accurate tolerances for Avenue (and rally) use. from A further forum https://4age20vblacktop26936.link4blogs.com/48894604/toyota-4a-ge-no-further-a-mystery