Hey guys I have the modified Vortec heads from SDPC and I have a XE-274 cam with the stock 1.5 self aligning rockers. Now I was thinking about putting a bigger cam in but this whole motor only has like 2000 miles on it so I am just going to see what I can get out of what I have. Now would the 1.6 rollor rockers make any difference or not really? also would I have to do any other machine work to the heads to put them on or would they pop right on?? thanks guysand any special ones you might suggest woudl be cool..

 

I'm using harland sharp 1.6 roller rockers on my vortec heads from sdpc. You will most likely need to get taller valve covers.

It will give you just as much gain as a cam with slightly larger lift would, assuming you already have roller rockers anyway. There is most likely a mathematical formula out there to figure out how much your lift will increase but i don't know what it is. Just be sure that your lift dosn't go over the limit for the valve springs. If you have the same heads i have from sdpc i guess you have the valve springs that are good to .525" lift.

 

Generally speaking, and this is only a guesstimate but still very close, a 1.5 to 1.6 rocker change will increase lift by .030 and duration another couple of degrees.

 

Just take the lift with the 1.5 rockers and multiply it by 1.067 to get the lift with 1.6 rockers.

 

ok guys well I used that little formula you got there and its gonna come out being .522 and.519, Now on the SDPC website it says that the springs are good till .525 lift, I planned on putting on some beter ones anyways and I was thinking about them new beehive ones cause I heard with them your can give more lift without touchin the guide. Anyways my question is does anyone know if my heads are clearenced enough for my to put on the 1.6's cause I think it woudl boost my power quit a bit because thats alot more cam. thanks guys

 

I would not use a spring that's "rated" to .525", with a cam/rocker setup that makes .522". Do you know how accurately your springs' installed height is set? Do you know how little margin for error .003" is? Do you have the tools to set up, or even to check, valve springs to that level of precision?

Besides, those are GM springs, notorious for being inadequate for any serious use.

The springs don't have anything to do with whether the retainer hits the guide. The only things that affect that, are the valve stem length, the retainer and the guide. You have stock length valves, not longer ones such as we use in heads to allow more lift; so you're stuck with the stock retainer/guide situation, plus whatever clearancing SDPC did to them.

The "beehive" springs are probably the best way to go. Get rid of the stock-configuration springs, and especially the stock springs you have now. As a general rule, .500" is as much lift as you want to put on ANY 1.25" diameter springs found on this planet, including GM's with their overly optimistic "rating". The stock XE274, with its .487"/.490" lift is already within a sheet of paper, of exceeding the ABSOLUTE MAXIMUM "rating" of every 1.25" valve spring in existence except GM's and K-Motion's.... the very 2 brands that are most widely known to fail catastrophically when used anywhere near their "ratings". Hmmmm....... maybe the laws of physics apply equally to everybody.... ya think? Note also that NONE of the actual cam mfrs., i.e. the people who will warranty your cam if you follow their recommendations (Comp, Crane, Luanti, Isky, etc. etc.etc.), spec a 1.25" spring for above .500" lift. Only people who don't have to warranty anything give them a higher "spec". There's a clue in there somewhere.

You will find very little difference in going from 1.5 rockers to 1.6s. Think about it; you'd be opening the valve about .020" or so more by going to the higher ratio, right? and that's what, the thickness of a business card or thereabouts? that won't boost your power "quite a bit", or even, really noticeably, in all likelihood.

Now if your 1.5s are stock and you change to anything of better construction than those in ANY ratio, you will see a HUGE gain; but that's from removing the rubber piece and installing something that consistently transfers the push rod movement to the valve. If you already had good quality (NOT stamped sheet metal) rockers on it, you won't see much at all. So, any real gain you see, will be from stepping up from the usual inconsistent 1.38 - 1.44 ratio (stock ones average around 1.42, with wide variations in both directions, mostly you get occasional ones with far less) that you have now, to something that gives the design ratio, on every valve, with no errors.

If you have a 350 and a XE274, you have enough cam already. More duration won't help; and in all likelihood, the valve lift isn't your engine's flow limit either, and therefore increasing the valve lift won't increase total flow aka power to any significant extent. Get yourself a set of 1.5 roller rockers, preferably steel; or at least roller tips. The Comp 1412 would be good for not too much $$$, or their 1302 if you want to go full roller. That however will also require taller valve covers. I would not recommend aluminum rockers from anyone, for a street-driven motor. If you use the 1412s, add a jam nut on top of the rocker nut; having had that exact cam and those rockers before, I can tell you, they WILL back off otherwise.

 

Hrm, maybe I should get some new springs. I'm running sdpc vortec heads with the same valves that are supposedly good to .525" and the LT4 hot cam that with 1.6 rockers has .525" lift. What happens with inadequate springs, valve float?

 

Yes, valve float; which is not what you'd think, i.e. the valves being "tossed" off into space as the cam passes through peak lift, rather, it's the valves bouncing off the seat at the time they close..... deadly to exhaust valves, as that's how they contact pistons. They're supposed to close just as the piston reaches TDC and the intake valve opens; but instead, they hit the seat, bounce, and the piston comes up and smacks them. Instant death to something.

Also, excessive force on the parts at peak lift, due to the vibrations set up in the spring causing the coils to smack into each other. (go hit a spring with a hammer sometime and watch what happens, that's a good representation of a valve spring under operating conditions) That force wipes cam lobes, bends push rods, wears rocker *****, pulls pull-out studs out, etc.

Also, excessive heat build-up in the spring itself, which causes rapid failure. Think about what a spring is: it's a coil of wire, that bends every time it operates, right? So, for another real-world simulation of a day in the life of a valve spring, go take a coat hanger, and bend it back and forth until it breaks, and immediately feel the ends of it at the break; when you get through cursing me, you'll understand yet another dynamic of valve springs a little better. One of the absolute worst things that can happen to a motor is for a valve spring to break while at speed, which of course allows the valve to drop into the cylinder with the engine at high RPMs. Words cannot adequately describe the devastation that will happen. Let's just say, valve fragments are incompressible; but something has to give when they must be compressed in order for the crank to continue to turn. Usually the piston gets shattered, or the connecting rod bends, or sometimes they'll put holes in cylinder walls, etc. In short, things that make a good set of valve springs look real cheap by comparison.