I'm bored, this won't happen till next summer, but thought I'd ask now. I will be adding a comp 268XE cam, Stealth intake along with around 2800 stall TC.


The heads I have now have 1.94/1.5 valves, I've been told they're decent heads just need some porting. Should I go with 2.02/1.6 valves, as this car is no longer a daily driver. I would like it to be reliable though. What all is involved if I go with bigger valves?

 

depends on what heads they are...

post a casting #, maybe aomebody could make an educated guess

Some heads flow so bad, the bigger valves wouldn't be noticed (kind of like putting a 1" fitting on your 1/2" garden hose); other castings have very little metal between the valves, and will crack right there; others work great.

 

Installing those valve sizes in your heads will require recutting the valve seats to the larger diameters. Depending on the heads, you may want to have the seats induction hardened after machining. If the heads are aluminum (or any other material that includes a hardened seat insert) you may be able to forgo the hardening step.

Of course, if you enlarge the valves is would only be reasonable to enlarge the valve bowls as well. A larger diameter valve alone does present more perimeter for flow improvement (like the theory of having multiple valves per cylinder), but you might as well have the port capacity for good flow at higher RPMs.

Once the bowls are opened, you should also cut down the valve guide bosses that intrude into the bowl area, and blend the larger bowls back into the ports. Eliminating the large, intrusive humps of material that the factory calls a short side radius would be another important step to improved flow.

Polishing the exhaust ports and chambers can help reduce heat gain in the head and prevent the formation of deposits.

And any time you perform any head work, the rocker studs should be replaced with threaded ones - don't even bother pinning them, since the studs themselves are weaker and will work the roll pins loose.

If you're going to a more aggressive cam profile and ramp (XE268), you'll need far better than factory springs to maintain any valve compliance with the lobe, so you may have to machine for those as well.

Other than that, it's really pretty straightforward.

 

I see from your sig that you have a GM engine. It probably has the 993 castings. The GM engines come with the thicker non-emission castings that lend themselves to performance well. They are worth putting the effort into, just not the money, when you consider how much you are looking at for the machine work, valves, springs, retainers, seals etc. Just get yourself some AFR's and be done with it. You could sell the heads you have to offset some of the cost. Vortec heads would be cheaper initially, but still need machining to accept higher lifts and need an expensive vortec intake.