Inspite of Other people declare of a 20HP or even more raise- on modified heads by itself, this is just unachievable without the need of camshaft or pistons adjusted. Toyota has casted and machined all their 4 valve heads to very close and accurate tolerances for street (and rally) use. https://4age20vitb72580.dgbloggers.com/27137333/4a-ge-engine-for-sale-things-to-know-before-you-buy