As of 7-6-19 we have a small supply of these castings in-stock and ready for finish work with our high quality components and craftsmanship. These castings have not been available since Fall of 2018, and when current supplies are gone we do not know when they’ll be available again.
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.
We purchased our first pair back in 2017. They had a grab bag of minor imperfections, but overall weren’t bad. Subsequent casting runs have seen solid improvements. As of July 2019 the latest batch has addressed most of these issues.
2017-2018 we prepped fifteen pairs of these heads. Every pair received thermal coatings to the combustion chambers and exhaust ports. So far we have heard nothing but positive feedback on performance and reliability. But the sample size is small and not a lot of time has passed. I will say that one of our customers has been using a pair with excellent results on his heads on a 914 prepped for Chumpcar endurance racing. His feedback has added to my confidence.
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 centers and register centers as well as chamber floor heights were all spot on.
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. The AA supplied fly-cut surface finish is okay, but a random check of the heights 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 and respond nicely to our bespoke performance valve seat profile, provided good flow balance for oversize intake valves. 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 several areas of these castings that would benefit from more material. But that goes back to the fact that these are in most ways true factory-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 recommend the application of thermal coatings to the chambers and exhaust ports. This is also in line with our current position for all air-cooled heads, so this recommendation on its face is not a condemnation of the castings. Heat is the enemy of all air-cooled heads and perhaps more so for these, we just don’t know.