I have a set of GMPP production vortecs, and the lock groove on the exhaust valve stem is .030" lower then the one on the intake. Is this typical for stock valves, or is this just something they did to get by with the weenie little stock springs they put on the heads?

 

That would gain you spring pressure on the exhaust side. Generally camshafts are ground with more duration and lift on the exhaust side. This would help them compensate rather than running two different springs.

 

I figured that was the intent of locating the lock lower was to provide additional spring pressure. Question is, is this typical for stock and stock type exhaust valves? Id prefer to have the retainer at the same height as the intake valves so I can just shim them as needed, and have my max lift be .500" rather then .470".

 

Have you checked installed height, and have you considered how much that will change spring pressure?

 

I haven't checked the installed height yet. Need to get a spring mic. Either way, Id still like to replace the exhaust valves if the aftermarket ones have the groove located higher up the stem.

 

There are aftermarket valves with .100" greater installed height. I would invest first in a vise mounted spring pressure tester and an ISH checker. You may find out that the spring pocket on theses heads is .030" lower on the exhaust side and that a taller valve will greatly comprimise spring pressure.

 

Is it typical for the exhaust lock groove location to be lower on an exhaust valve stem then the intake valve stem? Thats my main concern. If the aftermarket ones have the retainer at teh same height as the intake, then I'll pick those up and take it from there. That way at least I wont have to worry about having too low of an installed height on teh exhaust side. Im not looking for exact precision since Im running a mild flat tappet, but I would like to at least have things kosher prior to putting the heads back on.

 

I'll jump in here and say, YES, I have run into stock heads quite a few times like that. I'll add..... DON'T assume the groove is lower down. It might be exactly where it needs to be to get the same spring installed height as the intakes. It could be the extra length is actually on the tip above the groove.

I have no idea WHY the factory sometimes does it like this, but they do.

 

Also if your having a valve job done your machinist should verify and set ISH to your specifications. Again i would ask the manufacturer for the required open pressure, closed pressure, and pressure attained per inch. Check the pressure of your springs in a vise with the tool at the ISH your shooting for, see if its acceptable, then tighten the vise up until your at max lift, then check your pressure, again does it meet the requirements. Then insert take it another .060" and make sure the coilds aren't binding. You may also want to check the spings constant. Watch how much the pressure changes when you compress the valve .100".

I just told my machinist "They reccomend these springs and retainers at an installed height of 1.7 inches "

 

I checked with a dial gauge. The retainer is definatly lower then the intake from what i could see. Also, I measured the spring pockets and the exhaust also appears to be deeper. Its odd that they did it like this. They list the heads as being good for .450". Id have to check the retainers to be sure, but it appears that they may only be good for .420" of lift in stock form. I guess I could just say f it, install them as is, shimming as necessary to get the desired pressures, and accept the max lift of .470". I just get the feeling that a year or so from now I'll be saying "man, I really wish I set these up for more when I had the chance..."

As far as the springs go, Ill be using comp cams beehives, which I have the listed specs for. Unless their QC is way off, I should be able to set the installed height and have some fair idea of what the seat and open pressures will be, no?

 

yeah thats how i went about mine, but.... what camshaft do you plan to run and what do the manufacturers of the camshaft say?

 

Its an isky 262/270 now, .435/.445 208/216 @.05. I was hoping to run 1.6 ratio rockers with it since I decided to pull the heads for screw-in studs, but I may just stick with the standard 1.5 ratio rockers given teh limits on teh exhaust side. Isky recommends the use of their 205-D springs with .030" of shim over the recommended install height of 1.7" if I recall. I think that worked out to around 115 seat with 255 lbs open with the recommended 205's plus shims. Im basically going to just shoot for that neighborhood that with my comp-cams springs.

 

Heres teh timing card: http://www.iskycams.com/timingchart....g_chart_id=757. The listed open pressure is fairly generic and the same listed for all the cams using that 205-D spring.