joepaluch wrote:
Bad things can result. Nothing terminal, but it is a pain.
Bad, as in it doesn't always real well? That's not so bad. Actually these car idle very well with this stuff removed. And again, it's an issue for people that have updated/backdated electronics without changing the wiring harness. Additionally, there are 4 hose end to secure and although they usually fail closed, it could fail open causing a massive vacuum leak. I just think it is subjective.
dmdirks wrote:
...so it's not really an apples-to-apples comparison.
Yeah but with a spec series, are goal is to make apples and oranges all taste like bananas.
dmdirks wrote:
I'm not sure we can isolate the ports in the 6R head as the cause for your power drop-off at high rpm.
Agreed, there are lots of variables even going down to how tight the production tolerances for Porsche were. If we get enough data, we can start to develop trends. Eric's motor may be a statistical anomaly. We won't know until we get more data. I do feel that my assessment of the 6R head is pretty spot on--high torque, low peak hp, increasing A/F in the upper RPM. What I can't tell you is if this explains everything or how significant the differences with the 6R head should or could be. Everything I know about the performance of the 6R head is anecdotal.
dmdirks wrote:
BJ- may I ask how were the volumes of the ports measured? If this was done with the valves installed, different valve types and seat heights will affect this measurement.
I did the comparison using a complete 6R and 8R head. Only one of each was measured, so it's not a much of a sampling. I used the simplest and most repeatable method I could come up with using the tools I had for the job--which were none. I used a syringe to fill the ports with water tracking the mls added. I did this 5 times per port and averaged the results. Each head was secured at the same angle with the port opening parallel to the ground. I confirmed this with an electronic level. All ports and readings were within 2 ml, so I think the process was very repeatable. (1 ml = 1 cc)
Additionally, I spoke with Mike Lindsay a couple of weeks ago when looking for a replacement head for a customer. Mike confirmed that there is a significant difference. They have measured the port volume on tons of these heads over the years. Mike said they won't even accept a 6R head as a core because they are so inferior to the 8R.
Again, I don't know how this translates into real world performance numbers. We could be talking 2 hp or 10 hp. Until more data is collected, we just won't know.
The right way to find out would be to spend a day on an engine dyno testing the same motor with both heads. I'm not sure any of us has the time or resources to make this happen, though.
