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Yes. The 996 cup and 997 cup head ports are somewhat close in size. All R (meaning R, RS and RSR) intake manifolds are somewhat close and have much bigger openings than any of the cup ports. The R exhaust is much larger also.
If you decide the next step might be to use R heads, you should know that the valve angle is different than the cup and the cup cam boxes don't fit or work.
Yes, the 6 throttle intakes bolt up to the 997 cup heads. The ports will need to be opened up considerably to be matched.
Isn't that going to disrupt the airflow to the designed choke area of the port unless you completely redesign the port to work with the larger throttle bodies?
Yes. The 996 cup and 997 cup head ports are somewhat close in size. All R (meaning R, RS and RSR) intake manifolds are somewhat close and have much bigger openings than any of the cup ports. The R exhaust is much larger also.
If you decide the next step might be to use R heads, you should know that the valve angle is different than the cup and the cup cam boxes don't fit or work.
Thanks for the info - I actually have the R motor complete, but just exploring different options for the rebuild...
Yes, you're correct. However, sometimes you do strange things to get what you need. For instance, I'm building a ground effects 914-6 with GT3 RSR everything. It's going to take alot of developing to get the aero package working well. I may build what looks like an RSR motor that uses cup heads and cam boxes so the RSR exhaust and plumbing is set up but it lasts 150 hours while I'm tuning chassis, tunnels and everything else that goes wrong with a new car like this. Then I replace the motor with a full on RSR motor. Simple as that!
I did some checking and it appears that 996 Cup, 996 GT3 Street, and 996 RSR heads all share the same valve angles. Which model deviates from the rest?
I made the valve angle comment based on observations of my engine parts, not actual measurements (might be wrong, but.....). The cams are spaced the same in cup and R cam boxes, the boxes definitely don't interchange, the R intake valve is much larger and the R exhaust valve is smaller than the cup valves. They are spaced differently in the chamber so I guessed that the angle is different.
mklaskin,
I've been considering doing a build thread regarding the car. I'm not normally inclined to do things like that but this is intended to be a fun club car so I might. I have all the major parts I can aquire and I'm in the design phase now while I finsh a few major projects that are in front of the race car build effort. I hope to start fab work in April or May. Trevor Harris (Frisbee Can-Am, Shadow F1, Nissan GTP, Gurney Eagle Chf. Engr) and I (lots of similar stuff Chf. Engr.) am collaborating together on this. I will be the one who gets to wreck (I mean race) it after building. It's going to be at least 120" WB and around 80" wide with F and R diffusers running as a closed top car in SCCA super pro and NASA Super unlimited. The car will be cut off at the front spindle (bulkhead) and at the rear window. The rest will be tube frame so it won't be PCA legal unless they want to have pitty on us and take our entry money. It should end up looking like a Toyota GTP Gurney Mk III with a 914 roof and sails etc.
Sorry for the divergence; back to normally programmed viewing
Digging up this old thread as it's the only one regarding 996 / 997 Cup heads
Just noticed after cleaning, i have 997 Cup (3.6) Cylinder heads on my 2004 996 Cup.
If all was done correctly which it looks. Is there an advantage over the 996 Cup heads and if so what ?
Minimal, if any advantage. Per PCA here, it is considered a legal change because 996 heads are either NLA or really hard to get.
Here is PCA Rule, - which seems to answer your question indirectly.
GTC3 cars may use the following 997 parts for an engine rebuild, however, the existing 996 intake runners may not be
modified to match the 997 larger intake port: 997‐104‐016‐92 cylinder heads, 997‐105‐039‐91 camshaft housing 1‐3,
997‐105‐040‐91 camshaft housing 4‐6, 996‐105‐236‐97 Intake camshaft
01-09-2010, 11:20 AM
Yes. The 996 cup and 997 cup head ports are somewhat close in size. All R (meaning R, RS and RSR) intake manifolds are somewhat close and have much bigger openings than any of the cup ports. The R exhaust is much larger also.
Sorry for the divergence; back to normally programmed viewing
