Sorry to springboard off an ancient thread. SPArKy_Dave posted some pics (above) of a head build he did, including the cam specs. I am building a head for my EF XR6 wagon, including a new cam, and was looking for similar specs to Dave's cam. I want effectively a "Stage 2.5" cam - something between Crow's Stage 2 (198*/194*) and Stage 3 (210*/200*) cams. Since the demise of Wade cams and their 1673 grind (206*/198*), there is really nothing in this space. Dave's was a custom grind and I'm going to have to go custom, as well.
In deciding the exact spec, I came up with a question that no one has been able to answer so far. Why do some Falcon cams have a single pattern (same duration on intake and exhaust) and some have a split pattern (different duration intake vs exhaust)? Among the off-the-shelf Stage 1 to Stage 3 cams available, they range from 0* (single pattern, like Crow 222825) to 10* more intake duration than advance (like Crow 2222549). Interestingly, Stage 4 and hotter cams are almost all single pattern.
The conventional wisdom is that you add duration to either intake or exhaust if its flow is weak in comparison. For typical American V8s, with "wedge" heads and parallel valves, the exhaust flow tends to be poor, so cams are often specs with more exhaust duration to compensate. So, the longer intake duration of many of Falcon SOHC cams would imply that intake flow is weak and needing some help. But I don't think that's the case; the hemi head flows very well up to about 5500rpm, and even the factory induction system is not very restrictive. If I have heard any complaint about head flow, it is that the exhaust port is too restrictive. So, theoretically, the split should be the other way - longer exhaust duration. Does anyone know what actually does work best with the SOHC and why?
I have settled on an average duration of about 202* (with 114* LSA to retain decent idle with my automatic). I could go single pattern 202*/202* or a split pattern of 206*/198* (the old Wade 1673) or something in between (204*/200*?). What differences would I see? How would it affect idle quality, torque curve, exhaust sound, induction noise, fuel economy, etc?
To complete the picture: my car is my daily driver and we drive it long distances on our holidays, so I'm keeping it reasonably mild. But I also use it for DYO drag racing over the summer, so it needs to go well too. Basic specs:
- SS Inductions snorkel, 3" airbox exit, Territory induction tube, oversize 68mm throttle body, Coby headers, cat delete and Tickford 2.5” mandrel-bent exhaust, so it breaths well on both ends
- currently building a mildly-ported and deshrouded Tickford EF XR6 head with 3-angle valve grind and back-cut valves
- skimming it for 10.0-10.2:1 compression to suit the new cam and 98-octane
- vernier cam gear, so I can dial the cam in
- factory 3.45 LSD
- high-stall torque converter (2850rpm at current torque level)
- TI Performance J3 chip and tuning pack, so I can tune the ECU to the new cam and head
Any help would be much appreciated. Thanks.
