360 Head and valvetrain requirements/recommendations

[PA Dodger]

The engine: typical low compression 1974 360 that was freshened up years ago by previous owner. The cam was a small "purple cam" .429/.444 lift. Street Dominator intake. Nothing major, just a mild streeter. Now it's time to bump up the fun factor without going overboard. I already have a game plan for this engine but I need a few final answers.

I'm looking at two different cams. One has .475/.494. The other has .494/.513. My question is-where do you typically need to move to adjustable rockers in relation to cam lift and valve train geometry? I have a 340 with a cam at .485 that runs fine with the stock arms. I have a 470 BB stroker that got the adjustable rockers with a cam at .550+ lift. Is there a general opinion on when you run into valvetrain issues with stock arms?

The heads are the original '74 small valve 360 heads. I have a nice set of X heads with the 2.02 intake valves. Do the X heads offer much advantage over the heads that are on this engine? I understand the benefits of aftermarket aluminum heads but I'm looking for an apples to apples comparison.

Thanks
Dan 

[Chryco Psycho]

there are a few things to look at here , when you get close to .520 lift you may need to trim the valve guides for clearance & different seals  watch the piston to valve distance too  , but if you have stock pistons they should not be close . what are the spring load requirements for the cam  , excessive pressure can be a problem for stock rockers but a set of the 273 iron rockers would work well or similar Crane pieces .
 The X heads offer larger valves but are not a significant improvement  , a set of 308 swirl heads could net you 40 hp though .

[PA Dodger]

I was comparing cam between Hughes Whiplash cams and Lunati VooDoo cams. Hughes recommends adjustable rockers for cams that are nearly identical to the Lunati cams that don't specify adjustable rockers. I am looking at the 10200702 or 10200703 cams that you recommended in a different post. CR is 9.0:1 with valve reliefs so that isn't an issue.

I was debating on the 587s that are on the engine or the X heads on the shelf but if the 308s are that much better I might try to find a set.

Thanks Chryco   

[moper]

The reason some cams need adjustable rockers even with lower lifts are the lifters. Some are designed to have very little and specific preload that non-adjustable might have a problem getting with a set of 16 identical pushrods. At some point he spring pressures will begin to flex the rockers, or punch the pushrods through them. But I've run some decent sized cams on stamped before. The issue is the lifters. If it were me, I'd follow the cam manufacturers recommendations to the letter as far as spring pressures and rocker designs. There may be some power differences between those two cams but there's also the cost difference of what else you have to do to run them.

[PA Dodger]

I guess I missed that thought process. I always looked at it from a geometry concern with rocker tip to valve stem contact pattern and rocker arm to spring interference being the driving factors. I didn't think rocker arm flex or puncturing became an issue until cams go into upper .500s-.600s lift range with the needed spring pressures to keep the valves operating optimally.   

But I've run some decent sized cams on stamped before. The issue is the lifters. If it were me, I'd follow the cam manufacturers recommendations to the letter as far as spring pressures and rocker designs.

I have run bigger cams with stock rockers also with no problems. I like to make an informed decision on what is needed and what is "required" just to sell more product. If it's needed it will be there. The cams I'm looking at seem pretty average with average spring pressures.   

[Chryco Psycho]

lift is not the factor here , ramp speed & spring load are the issue a fast ramp cam can require much more spring load to keep everything stable even with lower lifts

[moper]

With a shaft type rocker system there is no effect on geometry with either rockers (beyond manufacturers' design differences), or pushrods. Geometry is set by the valve job itself. In regard to flex and springs... Take your average 280/.480 hydraulic with single w/dampener and stock rockers & stock shaft and turn it over by hand while watching the shaft and rockers closely. They move around a lot.