[brewski]

Goal: Strong 455 engine for pump gas as a daily driver.
Novice at engine building.
Have a 455 short block rebuilt to standard specs at .30 over by a reputable shop.
96cc 7k3 heads just rebuilt by same shop.
Comp Cam 268H
Need to select rocker studs, rockers and pushrods.
What height for BBC 7/16 screw in studs?
How beneficial are the roller rockers to this application?
Stick with 1.5 or go to 1.65? Is there a concern with hitting flat top Sealed Power pistons?
Is there a standard set of pushrods for this combo, or do I need to use an adjustable to get the size figured out?

[Will]

Not a big fan of your cam choice. Very narrow powerband, concentrated lower in the RPM range, will be all done by 4800. That cam also wants an excellent flowing exhaust and installing headers is going to be a mild pain given the lack of end bolt holes on the 7K3 heads. The upside is you'll be able to smoke the tires all the way around the block and it'll idle like a pussycat, so if that's what you're after, I'll shut up.

I'd run the 1.65s on that cam since it's so small. In fact, I'd buy the Harland Sharp 1.65s since they're actually 1.72 ratio. Make sure the pushrod holes in your heads have been modified for the higher ratio rockers. No worries about valve to piston clearance with that cam, even with high ratio rockers.

Are their choices for the BBC rocker studs from ARP? Hmmm. Do you have a stock stud to measure? Get whatever's closest to that.

It's always a good idea to check your valvetrain geometry. Milling the block and heads, using an aftermarket cam and rockers, valve jobs changing the depth of the seats in the heads, etc. etc. can all have an effect on the geometry. It's likely a stock length pushrod would work fine, but no guarantees so the only way to make sure is to check it.

[brewski]

Thanks Will. I told the engine guy I was wanting a daily driver and let him pick the cam. I can't afford to race, so good street manners and making lots of smoke will be fine! Thanks for the input.

[dmac]

Make sure you have enough spring for the extra lift if you go with 1.65 rockers. Most aftermarket cams already have more lift than stock cams, and adding 10% more lift with 1.65 rockers could give more lift then your springs can handle. Every part affects every other part, so select carefully. You do have the option of 1.6 ratio rockers, which won't add as much as the 1.72 ratio, maybe enough difference to keep you from having major problems.

[Will]

Good point, I overlooked that.

Crower 68404-16 springs will install at stock height with stock retainers and will provide plenty of clearance for even the 1.72 ratio rockers.

Be sure to check retainer to valve guide/valve seal clearance too.

[brewski]

Thanks DMAC, Will. As I stated in the initial posting, I'm new at engine building. The real builder already installed the cam in the block and the valves/springs in the heads. Heads are set up as stock. So I guess my best bet would be to go with the stock 1.5 ratio. For my schooling, what are the variables that lead to spring selection?

[Will]

Cam lift and intended RPM range combined with the aggressiveness of the lobe profile will determine the kinds of pressures you want on the seat and open. Available installed height will determine whether you can even get springs that will work.

When running big cams, especially rollers, you need to go to a taller spring in order to get enough clearance for the lift and have adequate pressure to control the valves. To do this you will need to do one or more of the following: Use longer valves, machine the spring seats in the heads, use offset retainers or locks.

For most hydraulic cams we're pretty lucky that Crower makes a nice spring that works at the installed height and can handle lifts up to about .550" or so as long as the RPM range is kept under 6000 and the lobes aren't super agressive.

Stock springs are questionable at any lift over .450". Some people have gotten away with as much as .470" lift with them but if I was running a cam with .450" or more lift I'd be checking the coil bind clearances very carefully. You don't have to actually reach coil bind to break things. As the spring gets close to coil bind, say within .020" or less the pressure will spike up plus the harmonics (the coils of the spring oscillating) will drive up spring pressures even further. Ideally you want to stay at LEAST .050" away from coil bind, preferably .080" or so.

Also, be sure to check coil bind height with the retainers you will actually be using installed on the spring. The inner step on the retainer can cause the inner spring to coil bind before the outer spring will. It will also increase the measured spring pressure some because it compresses the inner spring a little bit more than the outer.

I don't have the most recent Comp catalog in front of me but I'd be asking the engine builder whether he checked spring pressures and coil bind height and see what he says if that cam has over .450" lift.

[brewski]

Thanks Will. I should probably go stock for now. If I need something more in the future, I will rethink the cam and the associated valvetrain.