Comp Cams XR280r thoughts to given combo
The car is 68 Dart, TKX 5 speed trans, 3:55 gears 25.6 inch tire stock rear tubs.
The car is going to be mostly street with very occasional strip.
Nice trans choice.
That cam may power-peak around 5400, but the curve will be fairly wide and so you might want to shift it at say 6000.
You didn't specify which TKX you bought; the 3.27 low or the 2.87low box.
Since you are using 3.55s;
my guess is the 3.27 low.
in which case 6000 will be ~39mph in First, 65 in Second..... with tires spinning all the way.
But if the 2.87 box then; 6000 will be 45/68... and tires still spinning all the way.
So since traction will be your number one problem, I'll guess it won't much matter what cam you put into it. Just make sure that it is big enough so that the Ica is late enough, so that your pressure is low enough to NOT put your engine into detonation ...... which with alloy heads at 10.23 Scr, should be easy enough to do,
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On the flipside; You could install a smaller cam, to drive the pressure up even higher, to maximize your low-rpm torque, so that you can roast the tires yet further, which at your very low cruise rpm in overdrive, means fantastic fuel-economy.
Depending on which box you have, the overdrive ratios available are;
.68/.72/.81..
Your cruise rpms at 65mph are expected to be; 2060/2181/2454 (depending on the ratio).
That XR 280R will not like to rev too slow on the hiway.
Why?
Cuz of the large amount of overlap, the very short power-extraction duration, and your possibly less than ideal EFFECTIVE DCR of 7.84 (at 1000ft elevation).
But, I don't think fuel economy was on your mind when you built a 451, lol.
Furthermore, I don't think you want a smaller cam with more pressure, cuz your pressure is already more than adequate.
I think the 280, for me, would be a pretty good choice. As for me; If I had the .68overdrive;
I would install that 280 at 2* advanced instead of the usual 4*. That would trade away 2* of compression duration which the 451 doesn't need in street trim, to get 2 extra degrees of power-extraction, which would work better in overdrive. In first and second gear, I doubt you would notice the ~3.5psi pressure loss.
In all likelihood, this combo will make better fuel mileage at 2400 than at 2100. Some combos are like that.......
