Sorry if this has been answered before but I couldn’t find anything. I now have everything for this engine except the cam and I keep getting varying numbers on the lift of the stock Vortec heads. I’m gonna be running it with a rpm performer intake and a Holley 670 street avenger. I was hoping someone could help me out with cam choice, I don’t want anything to crazy, just a mild street cam that can Get everything I can out of the engine while still being reliable. Also should I swap the stock springs to get more life out of them? I will but I’m not sure how much of a difference it would make. If upping it to say .500 would make a HUGE difference I’m definitely down to do it.

 

In stock condition, the stock retainer, on the stock valves, hit the stock valve guide, at a valve opening of somewhere between .460" and .480", on at least one valve, on most stock L31 heads.

Interference on ONE valve is enough to trash a motor. Do ya feel lucky today? Well DO YA?

Did I say "stock" enough times? Did I give any hint as to how vague and indeterminate and how random this is? It's not like, at .465" everything is cool, but at .4655", the anti-matter meets the matter in the reactor core and the entire known (and unknown) universe melts down into a micro black hole in your driveway leaving only Mustangs.

Meanwhile, the stock (there's that horrible word again) valve springs that come on those heads are only barely adequate to control the valves when BRAND NEW, and if they have ANY miles on them AT ALL, can't even manage that much. You MUST change them, NO MATTER WHAT, if you replace the cam. Or really, even if you DON'T, since they're so CRAPPY.

The trick then is, use LS6 springs such as these https://www.texas-speed.com/p-9573-g...laced-ls6.aspx with the Comp "adapter" retainers https://www.summitracing.com/parts/cca-787-16 and of course new keepers; and shim them to 1.800" installed height if possible, or at least, 1.750" if all will allow that.

I'd suggest this cam. https://www.summitracing.com/parts/cca-08-422-8 But of course, ONLY IF you do the above parts choices.

 

so essentially I might as well up the lift a little since I need to change the springs anyway?

 

You don't "up the lift", as such. What you do is, up the CLEARANCE.

The root cause of The Problem is, the valve guide on those heads, is [donaldtrump]YYYYYYYYUUUUUUUUUUJJJJJJJJJJJJJJJJJE. Very, very, very, yyyuuuuuujjjjjje.[/donaldtrump]. As the valve opens more and more, the retainer gets closer and closer to the top of the guide, which is a giant chunk of casting; when the valve opening reaches the point at which the retainer hits the guide, the whole valve train binds up, and either parts bend, or break, or wear, any/all of which will shed metal chips into the engine interior, which causes catastrophic total FAILURE, as in SCRAP METAL. All it takes is a few too many .001"s to throw your motor in the trash.

What you do to work around this WITHOUT $$$$$$$, is to use thinner parts (retainers), so that the bottom of the retainer doesn't crash into the top of the valve guide. Butt, NO traditional small block Chevy retainers, are any different, really, from the L31 ones, in that regard. The solution is the LS motor "adapter" retainers, which require LS springs (which are altogether better in every way than SBC springs ANYWAY), all of which are VASTLY superior to the old 1950s stuff we've all been struggling with all the last half century or more. (yes I've been in this hobby for a length of time comparable to centuries... I used to talk in terms of decades, but that was 20 yrs ago or more) By using those thinner retainers, you dodge the expense of machining the guides or anything else, which then allows you to use appropriate cams that create reasonable lifts, WITHOUT the big $$$$$ we all used to have to put out.

Think in terms of HP per $$$. The mantra is and will always be: speed costs, how fast do you want to spend? This is one of those FEW techniques that allow you to short-circuit that truism. YOU can go faster than your $$$$ would seem to make possible otherwise, if you're smart about it.

 

If you have a Mexican casting, no real reason to go over 0.450 lift. The absolute garbage Mexican castings port stall around 0.450 and actually decrease in intake flow as the valve lifts higher than 0.450. The Mexican castings seem to crack more easily as well.

 

So these springs are a direct drop-in? No cutting of the cylinder head spring seat, or the guide for diameter or of course height with those retainers?

As I remember reading about these retainers, the only potential drawback is that they "can" create an interference problem with tabs on the self-guided rockers at the valve tip end, possibly contacting that new retainer? Something to be checked for I guess?

 

Yes

Never heard of any such but it never hurts to check

That doesn't mean that having a cam with a bit more lift than that can't be advantageous. After all, the valves spend VERY LITTLE of their time at max lift, or even very close to it.

And of course there always remains the problem of the exhaust ports, which are the same sucky crappy things as on any other stock SBC heads. The intake ports might be better - ALOT better in fact - but the exhaust side needs all the help it can get.

 

Find a stock L98 cam if you want a lil better than the stock offering and youre still at only 415-430 lift or so. Preferably the GM #049 cam. 207-213 duration.

 

Everything said so for has been great!

The original Springs have to go...
The original Rockers have to go.

Neither are meant for higher lifts.

 

Wait...what? I was thinking of running mine. While I like the idea of full rollers, I keep reading about them being noisy, which is not appealing to me. What wrong with the stockers in a mild engine?

 

Depends on how much Lift...

What are your Camshaft Specifications (Cam-Card if you have it)?

 

 

That old Crane cam is almost a dead clone copy of this one https://www.summitracing.com/parts/sum-1103/ which itself is a dead clone of a design that came out over 50 yrs ago when there were no valve springs available. Just cut onto a roller core. Still the same 1970 "Stage 2" profile.

Not that that's "bad", as such, or that it's a "bad" cam; just, as a species, we've learned a thing or 2 about how to do things better since then. Not to mention, lots of external conditions - speed limits on roads, available fuel, other cars, driver expectations, fuel cost... - have changed a bit.

The XR cam is close to 20 yrs newer. Still not "cutting edge", which to a certain point, is unavoidable, since we ARE talking about the SBC which itself is almost 70 yrs old (nearly ¾ of a CENTURY); it was introduced LONG BEFORE I ever saw a color TV, or a car with AC; but still. Nice to take advantage of whatever learning and adaptation one can, as the moving finger writes on.

It makes less than zero sense to retain the stock stamped rubber rockers whenever pretending to "upgrade" the valve train. They're a weeeeek point in just a totally stock (929 for example) application, let alone anything "better".