Say you take some unmachined heads and try to maybe do a little porting and polishing and stuff like that. Is there really anything you can do to heads that can be very detrimental to performance? Obviously if it looks visually bad it's not going to be well performance-wise (uneven polishing would probably make bad swirl right?), but are there other things to make sure you don't do that can be easily overlooked and really damage a head so that you'd have to basically get a new one or it would make the performance worse than before?

Winter break is coming up and I would maybe like to take my stock heads off and toy with them a bit and see what happens, but want to learn from others' mistakes first ;) I'm not sure what casting I have on my heads but they're the stock ones for a '71 350 and have 76cc combustion chambers and the triangle casting...so no matter what I do I probably won't get much performance out of it. But, hey, it's a good learning experience graemlins/thumbsup.gif

there are all kinds of books out there that you could read through to help through this. If your doing this at home for the first time, your goal should NOT be to open the ports up.
I would try to concentrate on the pockets of the heads(keep away from the seat area, mark with dye or a marker), the floor of the ports, combustion chambers. try to smooth things, instead of trying to make the ports larger. graemlins/thumbsup.gif

As long as you're NOT using carbide cutters, you'll be OK. Carbides remove alot of metal fast. Just be sure you do not nick the valve seats even a LITTLE bit or you must re-do the valve seat on that cyl. Don't worry about polishing especially on the intake port. Does nothing and can actually HURT performance if the intake is perfectly shiny. Narrow the guides but don't shorten them, smooth out any rough edges and pay attention to the valve bowl and short turn radius. Just smooth 'em. You should be OK as long as you don't go hogging things out without a flowbench to verify your work.

Randy

it would be a good idea to insert some old valves in the head to protect the seats while you work around them.don't bother grinding on the floor(bottom)of the ports because all the flow is up higher near the roof.when slimming the valve guide bosses be careful not to slip and nick the guide.also,if you do any work on the roof to improve swirl don't dig too deep or you'll risk punching through.when i ported my 462's i bought a cheap set of white xmas tree lights and ran a bulb down each valve guide.they worked great lighting up the ports so i could see what i was doing!one more thing,it doesn't do any good to enlarge the port openings at the entrance to the head.there is very little to be gained from that area.most of your target areas are in the valve bowls.good luck and just remember to be conservative with your grinding,it doesn't take much to gain more flow.

Guys got any tricks to protect the seats while grinding?

Originally posted by AllGoNoShow:
Guys got any tricks to protect the seats while grinding? Yes, become very familiar with your grinder before you go anywhere close to the seats. (nothing works better than a steady hand IMO) I like using a Dremel with the flex shaft because it is very easy to control, although the bits for the Dremmel are a little expensive. If you use a Dremel make sure you use one with the variable speed feature and slow it down a bunch --- electric grinders spin pretty fast.

In fact, a good place to practice is at the opening of the port by shaving a little off the pushrod bump. This can be a limiting spot on stock heads IMO, but only if the rest of the port flows very well.

After you get a little better at the throat of the port work on smoothing the roof and sides of the port all the way into the bowl. Don't polish (no need to go smoother than 80 grit) though and leave the floor of the port alone. Don't go deep here or try to remove significant material or you may find water jacket like others suggested.

Then work on narrowing the valve guide boss and the bottom of the bowl. By now you should be getting pretty good with your grinder.

The last thing you should do is blend the bowl into the seat. Don't actually get into the seat, stop a little short of the first machined cut (if you are brave and confident blend the bowl into the bottom seat cut). I like using a 80 grit drum for this area and I remove any casting flash and get rid of any bumps or ridges.

You can really pick up a lot of flow if you do it like I suggest above, but it is a LOT of work. Another way to pick up even more flow is by getting a good Serdi 3 angle valve job when you are done porting. Good valves with a 30* back-cut will add more flow yet.

PS. If your heads have a triangle on them you may have a set of 041 heads. They were used through about 1970 and are fairly thick castings.