Well the Gonkulator doesnt have too much experience with the GMC (nor do I!) so I dont trust it here as much as on the "Nova 6" or some others. But here goes. I couldnt totally match your car but after some reasonable fiddling, and assuming its a bit out of tune (or I might just be too optimistic on the intake design) I Gonkulated to
Torq 289 at 3500
Powr 248 at 5400
2.26
9.84 at 71.9
15.29 at 89.6
I couldnt see how to get 15.90 and have all the others match up so I left it there. Note those are "SAE gross" figures. NET flywheel is about 200nhp as noted already.
Before heating up the cam, I tried a hard launch and shifting at 6000 in stead of 5500. Easy for me to say, the computer wont throw a rod- and this is more fair to the bigger cam. So the 220-220 cam Gonkulated to:
2.06
9.44 at 71.7
14.86 at 89.5
So I then changed duration from 220-220 to 250-250 to compare:
Torq 285 at 4100
Powr 261 at 5900
2.09
9.42 at 72.7
14.77 at 90.7
I wouldnt put up with that wild duration for a carlength!
I then Gonkulated a 235-235 cam
Torq 287 at 3800
Powr 255 at 5600
2.07
9.42 at 72.3
14.80 at 90.2
To me it doesnt seem worth the bother if your current cam is doing good.
Thoughts based on what I've read about the GMC:
* OF course a good tune, timing and carbs. I used that Weber on my Pinto, great carb but I did fiddle with jets and air bleeds a lot.
* Is your rocker ratio really as advertised, Ive heard that is something to check from other threads
* What about swapping intakes/carbs instead, a lot easier than cams. Maybe the Nicson triple noted in Fisher's book, or a 4bbl if somebody makes one. Likely pretty easy to re-sell em after a few timeslips.
* Maybe collector length too although the Gonkulator liked your current setup a lot.
Sounds like a cool combo anyway.
