There are 4 different Holley heads, 1.9 x 1.6-17 degree stud mount, 1.9 x 1.6 17 degree pedastal mount both of these heads are made by Brodiz for Holley, then there are the new 20 degree heads which are machined my AFR for Holley they are available in the 1.9 x 1.60 stud mount, and the 2.02 x 1,6 stud mount. I have the 2.02 20 degree heads on my car and I have the flow numbers they are a good head and have the wonderful AFR machining. I was talking with Ed Curis about these heads and he said they are good heads, but could be a little better if you take a little more of the sharp corner radius out a little more but he would pick then over a Edelbrock, or Wedge head but that was his opinion but he does favor the AFR's as the top head out right now. Make sure you know what heads you are getting I was really surprised when mine cam with 2.02 valves, I believe I was the first one to recieve the 20 degrees heads and I still haven't met or talked with any one else that has these. I have 62.1cc chambers.
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My Ride Check Out My Site 91GT, Holley SysteMAX II Kit-Heads 2.02" x 1.60",Full MAC exhaust 1-5/8" Long tubes, 2-1/2" O.R H-Pipe, 2 1/2" cat back, 12" K&N Filter, RNH PERFORMANCE Ram Air, Ron Davis Radiator, Full Suspension,3:73's, Welds, Best on new motor-12.60 @ 108, no traction 1.98