While browsing my local junkyard today i came across a pair of L31 vortec heads in a 2500 Silverado, so i pulled them. Having read about these heads for awhile i realize they are decent performers "out-of-the-box". However there are lots of upgrades that get mentioned often.

My question is at what level are the following modifications actually nessesary?

-Screw in rocker studs
-Non self-aligning rockers and guideplates
-Roller Rockers

I imagine that the chosen cams lift/duration will have an effect on all of these, but i'm not really sure where the limit is. I ask because here in Calgary my local machine shop wants $300 to install screw in studs :-(

-Zander

 

Wow, you found a set of Vortec's in PNP? Not bad.

For a typical street engine, doing such changes isn't required.

Screw in rocker studs are required when used with heavy valve springs. High spring pressures can pull a pressed in stud out of the head. High pressures as in 500-600+ pounds open. Factory springs may be close to 200 pounds open.

Heads that use self aligning rockers don't have the alignment holes in the heads. To switch to rockers that will need guide plates, you need to get the rocker stud boss machined down to install guide plates. That's all the labor you're paying at the machine shop. After doing a lot of modifications to factory heads, it can be a lot cheaper to just buy aftermarket heads that have the modifications already done and will be a better casting.

Roller rockers are always a good investment. Just get the proper ones for the heads. They reduce friction.

I have a set of heads at Northwest Performance Engines getting some work done to them. New intake valves, new guides, valve grind. I'll get them back and need to install and setup my own springs. I'm guessing it will be at least $1000 worth of machine work including the price of the new valves and guides. Including the value of the heads, when they're complete and ready to install on the engine, they'll be worth about $5000.

 

Thanks, i didn't realize you were in Calgary Stephen, although now that i look a little closer at your signature pic (past your wicked Camaro) i noticed the performance parts center sign :-).

Does anyone make self-aligning roller rockers?

-Zander

[EDIT] Looks like proform is the only company that makes SA full roller rockers (according to summit). Anyone have experience with these? i usually think of proform parts as OE replacements...

 

Have those heads inspected for cracks before you put any money into them.

 

I'll have them hot-tanked and Maged, are 906 castings particularly fragile ?

-Z

 

You used the word "necessary" and of course none of it is necessary unless/until something breaks.
To better answer your question it's generally accepted that once you go over 0.500" lift and above 300 lbs of spring pressure it's a good idea to do those upgrades.

For just the machining and tapping of your heads $300 is too much. If they are providing the studs and guideplates and doing any other disassembly, assembly, and/or cleaning of the heads then it's about right.

Most stock heads with high miles will also need the valve guides and valvejob freshened up, a deck resurfacing, and new seals. If you're going to be running a high valve lift then you'll also want to have the guides and guide bosses trimmed down and if you need larger diameter valvesprings then it's also a good time to get the spring pockets machined as well.

 

As far as the rebuild costs go, the heads were $80 from the yard. New valves are fairly inexpensive (summit stainless valves go for ~$120 for all 16), valve stem seals are inexpensive as well but new valves guides worry me a little bit. given how outrageous the shop prices here are, i hope new guides aren't necessary.

If i recall correctly the permissible clearance between stem and guide is 0.001-0.002" is that correct? if so how do i go about measuring it? has anyone tried to estimate the clearance by measuring the distance the end of the valve tip moves and using trig?

if it helps at all i think the heads have 250 XXX kms on them

-Z

 

Although I rarely get out for the Friday nights because of the idiot street cars at the track, you can come and watch me during the race days. The CDRA has made arrangements with Race City to have a bunch of races this year which is the last year the track will be in operation.

Using Summit Racing's search feature, I found a bunch of listings for 7 different self aligning rockers.

http://tinyurl.com/cbtz24

 

Thanks Stephen, i definitely tried that moments ago any summit only returned the proforms. Perhaps i'm just not as skilled a summit-surfer as yourself :-)

What CDRA class are you racing in?

-Z

 

I use a hole mic but after a while you can pretty much tell by the feel.
You are correct about the clearance values. Most shops like to stay around 0.001".
You may have some bad guides but most could be refreshed by guide liners. If you're doing liners then why not consider resizing down to the 8mm valves and use the better shaped and lighter LS1 type valves?
The benefits are many. You could then use a $50 set of Z06 beehive springs with the lighter retainers and probably avoid any extra machining of the guide bosses or spring pads because of the installed height gained by switching to the new valves and retainers. You should be able to find a good used set of LS1 valves, retainers, and locks for around $50.
The seats have to be recut anyway for a valvejob and you could do some porting of the seat/bowl area yourself to open up for the larger valves.
The swap would require the guideplates though.

 

I haven't belonged to the CDRA for a number of years now. Under IHRA rules I run under Box or Electronics class (Calgary and Edmonton). NHRA it's Super Pro (Medicine Hat). The CDRA is playing around with the class structure this year because they're going to run the show. I'll fall into what they call Super Sportsman. Basically all cars that run 9.99 and quicker.

Using a throttle stop I could also run in Super Gas (Super Rod) or Super Street (Hot Rod) but I don't throttle stop race.

My BBC heads are getting all new guides and the intakes are being resized down to 5/16". The intake valves are 2.300". Exhaust are staying at 11/32"

 

My advice, is figure out what you want to do, then get prices from the machine shop. I did the same thing a while ago with SBC heads, getting them milled, valve job, ported, studs pin'd, long story short it was about 900 worth of work. In the bigger picture, for 100 bucks more, I could have bought aluminum heads from summit or jegs.

 

pin the studs

get some z28 springs

buy some roller tip rockers

remove and replace the exaust roller retainers and put intake retainers in place

valve job and check of the valve guides

slap em on and keep the lift of your cam under 500