The trick is to get the valve open fast past it's max flow lift. On the RPMs, they will move air well to about .550, then they peak. Now, the faster it lifts, the more spring you need, and the more oil the lifter base needs to stay alive. This is splash fed, so idle time (with little windage blowing the oil around) is rough on a cam with high spring loads. I don't use the ".904" lifter profiles on my large cams for that reason. Street cars idle a lot, and I hate idle speeds over 900. You asked for numbers and like CP, I cant say for "x" you will get "y". Because I'm not building yours. If you have to run power brakes, then exceeding 245°@.050 will probably mean your brakes wont work well. CP's 240 is a solid spec and will definately make enough vacuum. As far as what you need, like CP says... more details. Engine, trans, gearing, honest usage, etc. It's only a 10% stroke increase with the 4.15, so you can over cam it if you try hard enough. You want to run enough lift so you get the valve open to that .500 number plus a little. Lash is .022, and you're running 1.6s. So take all that into account. That makes the XS274S look good to me depending on your answers to the "more info" part. That gives you about 241°@.050 and .513 lift intake, about 246°@.050 and .523 lift exh and should work with the Edelbrock supplied spring even tho Comp wants thier dual spring in there.
