These heads produced by AAPistons are knockoffs of the 039 101 371A heads that came on pre-smog 2.0 914/4’s. They are often referred to as 3 stud heads due to the fact that they feature 3 intake manifold studs, unlike all other Type4 heads which have 4 studs. Since their release earlier this year we’ve fielded a lot of questions about these heads. Naturally I purchased a pair to investigate for myself. In this article I’ll address my observations of this single pair.
First though I feel the need to clear up some misconceptions and misinformation that have been circulating and have made their way back to me recently. First, that because my company supplies heads for Raby Aircooled Technology there is apparently an assumption flying around that Raby will be switching to these heads on his custom Type4 engines. Nothing could be further from the truth. The heads that we supply for R.A.T. are bespoke variations of our AMC based LE-200 model heads born of years of development and are engineered to work with bespoke pistons designed by Charles Navarro of L.N. Engineering. There is no plan, immediate or distant, to make a change, even if the AA heads did have as much “beef” as the AMC heads (which they don’t) to accept our unique port designs. The second misconception circulating is the notion that I’ve “signed off” on them. Let me be clear, the fact that I worked up a pair of the AA heads for testing does not serve as an endorsement of them, tacit or otherwise. While I am hopeful that these heads will prove themselves over time, it’s going to be a long time before I step forward with an actual endorsement. We have over fifteen years of development and positive experience with the Spanish AMC heads. It’s going to take a while before we develop that level of comfort with these, or any other replacement heads that might come down the pike.
Now for some analysis, keeping in mind that I have only worked with one pair so I have no idea how repeatable these will be. As knockoffs go, overall they make a pretty good visual first impression. There are some exterior details that aren’t as exquisite as the German originals, but that’s no surprise and not particularly alarming. The first thing that jumps out is that AA dispensed with the 15mm O.D. exhaust guides, opting instead for the 12mm size used on the intakes. This sits well with me, but does eliminate the option to run 9mm exhaust valve stems. Something we haven’t done for years on any but our transporter heads, so no problem there.
After a thorough visual inspection we mounted them in our CNC machine for some reverse engineering to see how they compared to our programmed specs for factory heads. Overall I was pleased with those results as valve guide bore centerlines and register centerlines as well as chamber floor heights were all spot on. We did find that the intake ports were rough as corn cobs and out of position (especially the #2 ports) relative to the manifold stud pattern which was properly positioned relative to the registers (thankfully). This means port matching, at a minimum, will be critical for good performance and even cylinder filling from cylinder to cylinder.
Once we were done reverse engineering, we CNC machined valve seat counter-bores using the same feeds and speeds with the same tooling as we use on AMC heads. The chips and machined surfaces were identical in appearance to the AMC heads and the machined dimensions were within .0002″ of what we get with the AMC’s. That tells me that they at least have similar machinability, which is encouraging regarding alloy characteristics, but hardly conclusive in predicting durability.
As for the critical features, the chambers are perfect repops and chamber volumes after our finish work measured at 58cc’s, about average for an uncut O.E. head, and were all within .5cc’s of each other, which is nicely within tolerance. On the down side the pushrod tube bores were ~.002” small, which was good since the machine work to them was very course and required honing to smooth them out so they won’t tear o-rings. The AA supplied fly-cut finish was okay, but the height from chamber to chamber varied by .0025”, which is way out of spec. Our finish work is within .0005″.
The exhaust ports are pretty much dead nuts copies of the O.E. heads but with a rough texture. After polishing and blending, flow testing results were nearly identical to an untouched German port, which is good when comparing to other O.E. T4 heads (1.7&1.8) but bad when comparing to what we get out of our AMC heads, which come from Spain with tiny ports and lots of meat around the outside of the port that allows us to carve a far superior shape, one that we’ve developed over years of testing. There’s room for some improvement, but not enough to match our proven shapes as AA chose to copy pre-smog heads, which have a lot less material around the exhaust ports. It’s also worth noting while on the subject of the exhaust ports that these heads can not be machined to accept the air-injection tubes that later California model 914/4 2.0’s came equipped with.
Unfortunately there are also several other areas of these castings that would benefit from more material. But that goes back to the fact that these are in most ways true knockoffs. Those of us who’ve been around long enough already know that the original 2.0 914 heads were lightweights and prone to cracks. IMO these castings are too faithful to the originals.
Because they are lightweight castings of an unknown alloy I sent this first pair out for thermal coatings to the chambers and exhaust ports.
My verdict is still out on these castings as far as durability goes. I don’t have a cyrstal ball so we’ll just have to wait and see. My hunch is that they are going to do at least as well as 40Y.O. castings that have been run through the ringer. That said, I’m willing to build them out with quality parts if people are interested, but I’m not willing to put a warranty on them beyond my workmanship.