Just two quick questions. one, i have a .494 lift cam...will running 1.8 rockers cause valve clearance problems on a factory 73 block and pistons with earlier heads? second, will factory valve springs from pre 73 hold up fine to that kind of lift? thanks a lot.

 

460's are almost immune to piston-to-valve clearance problems. With that being said, you should always check your piston to valve clearance when installing a larger than factory cam. As far as the valve springs, I seriously doubt they will hold up. One question, is the cam rated at .494 lift? Is that calculated using the standard 1.73:1 or with your 1.8:1 rockers? I do know that Cobra Jet springs were only meant to be used up to about .510 lift. Stockers probably quite a bit less. The way you need to check them is to find out what the cam manufacturer recommends for a seat pressure, then take your spring and compress it until it gives you that pressure (that's where you'll have to shim it up to on the head when your done) Measure that height. Then compress the spring until the coils bind. Measure that height. Add 0.060 to that then subtract that number from the number you got for your seat height. The answer will be your maximum safe lift with those springs. If the springs will handle the desired lift, you should then check the open pressure to make sure that it is, at least, close to the cam manufacturer's rec's. A good machine shop can do all of those things for you anyway. I'll say it again, I doubt very seriously that stock springs will hold up to that lift (not for very long anyway) especially with 1.8:1 rockers. Those are even harder on the valve train as they snap everything open and closed faster than standard ratio rockers. Why pay $350 for high ratio roller rockers, yet not want to spend the $75-100 for good springs???? My $0.02.

JJ

 

why do you need to run 1.8 rockers? are you running a high end or a bracket motor? your not going to notice in my opinion any really noticable diference. should have saved the extra cash for other parts. C.J. .......

 

well, i havnt gotten the rockers yet. i figured i would wait around and see if i could find anything used. (im not spending 350 on them). but anyway, the thought behind getting them was that my cam has a relatively low lift to it (.494") and using 1.8 rockers would be like having a cam with ~.514" of lift. i know thats not a huge difference, but every bit helps. i just figured that since im wanting to get full rollers anyway, why not get a little more lift out of them too? also, i could use a set that was "meant" for a bbc right? ive seen the 1.8 ratios for them a lot cheaper and i cant see running into any problems using them over a set meant for a bbf. any other thoughts on the 1.8's guys?

 

I run 1.85:1 Harland sharps and they work great. I called them up and for an extra 30.00 they will build you whatever you want. And I run cj springs, used from ebay.

I also use them to get more lift on a smaller duration cam. Nice idle, but still flows good to 5200 RPM. The truck pulls nice in stock class with this set up.