The "street heat" heads are not very common anymore. When they came out they were the #1 head on the market. I think the heads that are on the market now flow better than the TFS heads. I used a set on a 351W a long time ago and had no problems with them at all. I actually still have a set of bare cast iron "Street Heat" heads that have never been assembled or anything. I bought 2 sets about 10 yrs ago and 1 set has been sitting in my garage since.