View Full Version : Do I need to spot face these screw in stud bosses for guide plates? PIC

09-27-2011, 01:48:54 PM
I have a pair of new, odd ball EQ Lightning Vortec heads. They came with screw in studs but no guide plates (or any product literature). I know on some heads that used screw in studs but no guide plates, if you want to add guide plates you need to machine the stud bosses down by the thickness of the guide plate (0.3" I think).

How can I tell if these heads are already machined for guide plates or whether I need to machine the bosses? Is there a reference dimension I can check?

Here is a pic of my actual heads

Would it really even matter since I have an adjustable valve train whether I was off by 0.3" in stud boss height? As long as the valve cover fits and I can thread the rocker nuts down far enough to obtain the proper lifter preload, does it really even matter? Thanks


09-27-2011, 03:15:16 PM
Usually, the machining is the same with or w/o guideplates IIRC, because if you don't use guideplates under the studs, usually a washer is used. I know this is true for aluminum heads anyway - iron is likely the same?

That said, those pushrod holes look awfully small for a guideplate setup.

09-27-2011, 03:16:48 PM
They are definitely not slotted so they are going to require either self aligning rockers, or guideplates. Guideplates won't affect the sweep of the pushrod vs self aligning rockers. I can certainly take some carbides and open up those holes before I get started, I see what you mean, they are small. As long as I can put the guide plates I already bought on these heads without more machine work I am happy. Thanks for the reply. I think I was thinking about needing to spot face and trim down bosses when converting push in stud heads to screw in...oops.

John Wright
09-27-2011, 03:26:55 PM
Are you sure that the guide plates are .3" thick? Just strikes me as awfully thick for some reason...I'm thinking more like an (1/8") .125" vs nearly 5/16" thick(.3")

09-27-2011, 03:27:18 PM
I had the same question of my machinist. I am adding guide plates to a set of the '88 Corvette aluminum heads, as I'm going to be running adjustable (non self-aligning) rockers. These heads already have screw in studs, but not guideplates. I was told they did not need to be remachined, just unscrew the studs and install the guideplates.

09-27-2011, 03:33:28 PM
John they appear to be .110" thick not .3" I was pulling that # out of my butt. Here was an old thread I was thinking about when I brought this up

It even includes PDQ's 900 millionth mention of 8,000 rpm 301's in it...haha

John Wright
09-27-2011, 03:41:29 PM
LOL...OK, that sounds keep in mind that they may be for .3125" pushrods. So maybe that is part of what was stuck in your mind....LOL. You're too young for this CRS stuff that plagues us old guys...LOL

09-27-2011, 03:42:56 PM
Those would have been the thickest guide plates ever, eh? Oops. You are giving me too much credit in re: CRS. I think this was a case of DNS. Don't know s....

09-27-2011, 04:19:48 PM
I don't have the same heads as you but I ran into the same issue with my patriot vortecs. Those stud bosses look a lot like how mine looked. When we mocked it up the roller tip was to far over toward the outside tip of the valve stem. We ended up having to spot face the stud bosses. All good after that was done. Just curios, how tall are the intake runners on those heads?

09-27-2011, 04:21:33 PM
I can measure later, I'm not sure. These are a 170cc vortec type intake runner so they are kind of an upgraded 906 type head from what I have read. Thanks very much for your feedback, that is interesting to know. How much did you take off the bosses? If that winds up being the case I could just use some stamped self-aligning rockers with no guide plates, but I am going to be running .490/.510" lift so I didn't know if that was getting a little aggressive for a self aligning rocker.

09-27-2011, 04:36:13 PM
We ended up taking off about .110. Guide plates measured .125. I'm running a .500 lift cam with 1.6 rockers. Just curios on the intake runner height. My patriots are listed as 185cc but the intake runners are tall. They measured 2.31 and it seems like we measured some factory runners as 2.10-2.15.

09-27-2011, 04:37:10 PM
Ok cool. I will let you know later tonight what they measure. I paid $99 each for these heads as you see them so I am all about making these work.

09-27-2011, 04:49:44 PM
WOW! Nice. I'm guessing they were bare? I thought I was doing good getting mine for $300. I bow down to you sir, and acknowledge your frugal ways.

09-27-2011, 05:26:35 PM
haha. Yeah they were new in box bare heads. $10 for the screw in studs and $75 for a set of off brand undercut stainless valves, and maybe another $50 for springs and retainers although I already had those. If you paid $300 assembled for yours you actually did better than me.

09-27-2011, 05:49:55 PM
No, mine were bare also. Just a FYI on the undercut valve stems. When I was reading the vortec sticky, I remember reading on the very first page that the GM engineer that did a lot of development, said when they tried undercut valve stems they created turbulence in the intake runner,at least that's how I took it. It's in post #9. Like I said, just a FYI.

09-27-2011, 05:50:05 PM
Where did you make such a great purchase, any others available?

09-27-2011, 05:51:09 PM
Interesting, and noted. I can change to regular valves if I need to, I may actually have some. Good info

These heads were on ebay a while ago, a shop was closing out a lot of them. I almost bought 2 pairs since they were so cheap. They are long gone.

Here are more pics of the heads. The casting quality is really nice. They were made in Australia by some company called Toowoomba Engine Products. I was just glad that even at this price I wasn't getting chinese crap.


10-27-2011, 11:39:58 PM
Just curios on the intake runner height. My patriots are listed as 185cc but the intake runners are tall. They measured 2.31 and it seems like we measured some factory runners as 2.10-2.15.

79redz, the intake runners measure 2.160" on my heads and they are listed as 170cc. Seems to be reasonable.

10-28-2011, 12:22:19 PM
very close on the height of the port like the factory heads then. you shouldn't have any problems with port mismatch like I did then. should be a fun little engine.