I picked up a set of '601/'801 305 heads from a GMC Vandura the other day. The '083 L98 heads that I was using cracked and I simply couldn't find another set. These will be going on my L98 350. This should boost compression somewhere around 10:1, depending on the final combustion chamber size. The heads will be cut for 1.94/1.60 valves.

I cc'd the heads before I started any work. The intake runners were 152cc and the exhaust runners were 51cc.

Thus far, I've done the following:

• Removed the majority of casting flaws (not yet complete)
• Matched the intake ports to a stock-size gasket. Basically, I just straightened the angle on the one side of the port and gently worked around the valve cover boss (these are perimeter-bolt heads).
• Slightly worked the area around the pushrod. I was afraid to break through the casting so I didn't remove too much metal.
• Slightly worked the area between the valve guide and the head bolt. Again, I was concerned with the metal thickness so I didn't do a whole lot here.
• Reshaped the valve guide bosses

I did not touch the short side radius and other similar areas. I'll do that when my machinist cuts the heads for larger valves. I also haven't done anything with the combustion chamber, such as unshrouding, shaping, or polishing. All in due time.

I'm using an electric die grinder for most of the port work and a Dremel for the bowls. I find that I have much more control with the Dremel when working the bowls, even if it does cut a little slower.

How does everything look? Are the guide bosses still too large? I'm getting more involved than the previous set that I ported (the cracked L98s), but I'm still being careful not to remove any more metal than necessary.

 

You have the right idea in working the bowl area; that is where most of the flow increase will come from. Just try and not change the shape too much as that can adversely effect swirl.

After the new seats are installed (with a 5-angle valve job) carefully blend them into the bowl.

In the chamber you can unshroud the intake the intake a little but be careful and maybe clean up the spark plug boss.

I suggest a copy of David Vizard's books on building SBCs as these have lots of good advice on hand porting SBC heads of various types.

Good luck with the project, it sounds like fun.

 

Looks very good to me, and kind of familiar too

Yes, you are doing a good job. Don't worry about making it look like something from a CNC machine. The rougher sort of finish on the intake side is what works well for mixing the air and fuel. Polish the exhaust if you like but it doesn't look too bad as it is.

The valve guide bosses are just like mine were; almost flat to the roof of the bowl on one side and just a smooth sort of bump on the outlet side.

You're gonna have a nice set of heads when you're done

 

You can remove quite a bit more material without fear of breaking through.

The area at the red arrow is important. The only result of straightening out this area as it should be is that you'll break in to the valve cover bolt hole. No problem as long as the bolt is in the hole. But that whole corner of the common wall and roof is a high flow area. I'd work it some more.
Like what GM did with the vortec head, you can straighten it out and clean it up quite a bit more. (green area and left most blue arrow)
The roof is too chunky. you don't want it polished but you don't need it chunky either. Use a broken 5/16"round rat tail file in a 3/8" drill to smooth and straighten it out. Works nice on the corner radii too. The file will leave the right texture and show you the high spots. Actually cuts the metal nicely at just the speed of a electric drill.

The roof corner at the pushrod pinch wall needs to be kept constant as it curves around and into the port.
(orange arrow) Again the rat tail file will help clean this area up. All the chunkie-ness and changes in corner radii will create a lot of turbulence and reduce flow from what it could be. When porters like Vizard refer to leaving the intake ports rough they mean about a 60-80grit finish.
This is plenty of "roughness" to keep the fuel off the walls. ("boundry layer turbulance")
Try the round rat tail file in a electric drill. I think you'll find it a nice addition to your porting tool kit.

 

Ok I have asked this question to Sitting bull already and I dont think he answered me. As u see in the pics above the height of valve guides in the bowls. I have to get a pick on here to let u see (if i can figure out how) I did not cut my valve guides down just rounded the edges and blended the guide into the port floor. They look nice... untill I see what 86blue did with his and u all praised him for it. I thought I was half way done. 1 head all done and polished. And why do the valve guides on each end of the of heads stick up in the bowl more than the other two intakes. can any one inlighted me about these







:lala:

 

Hmm, if you could post a picture it would help. What castings are you working with?

 

Well if you have bronze guides you can reduce the boss to the end of the guide. If no guides have been pressed in, I would be careful on reducing boss height.

I wouldn't take off any material on the side of the push rod but rather take off a little on the opposite wall, though this won't realy enhance flow much nor will gasket matching.

 

Thanks for clearing a few things up, guys. F-BIRD'88, I printed out your picture and I'm going to attach it to my work bench. I'll see what I can get done today and post some new pictures later on.

F-BIRD, in some other posts that I've read, you suggested raising the roof of the intake runners by 1/8" or so. I can't do this, simply because I don't have the right cutters. The longest extension that I have is about four inches, and it only works with the sanding rolls for my die grinder -- these rolls are practically a joke; even just in surface-texturing, they break apart. I know that I can buy extended-length carbide cutters, but are they really worth $50 from Summit (there are no machine tool stores around here). By not raising the floor, am I passing up a major performance option?

 

The object in pocket porting is to maintain about the same runner volume while improving flow & swirl as much as possible.

To this end you don't want to increase runner volume but rather streamline the runners and work the bowl area. You can raise the bowl roof a little as well as widen it a little to compensate for flow around the valve guide boss.

 

I spent a little more time working the intake port radii and removing some of the bumpiness inside the ports. I also worked the area around the valve cover bosses. Here's what I have right now -- some original cast metal may still be visible, but I expect it to go away when I go over the runners with 50- or 60-grit sanding rolls. The first picture shows the reworked radii on the floor of the runner, but the roof is the same way.

With the tools that I have available to me, I really can't do anything about the slight bulge on the common wall near the head bolt hole. I'm going to leave that alone on this porting job.

 

Looking good.

It looks like about all you have left is to hit it with the sanding drums and blend the seats into the bowls.

 

There are many machine tool stores in Pittsburg, just not next door to the local Walmart. Snap on Tools is one source. A Welding supply is another source.
Good carbide cutters are not cheap.
You only need one long shaft cutter to get deep in the port. I use a cylindrical shaped cutter with a rounded nose. Any extension u use with a short shaft cutter will not run at high speed. Use a speed controler for this.
( search my posts on how to build one)
I also use the rat tail file as mentioned above. You can cut it to any length(s)
You can round off the raw cut off end with a grinder so the end of the file does not gouge your work. Do not use the file in a die grinder.
Is it worth it to raise the roof? Depends on what you want out of the job. A half ditch effort will only get you half the results. The more lift the cam has the more the motor will benefit from raising the port roof. ( especialy with a single plane manifold like a Vic Jr or Stealth Ram where the runner path is relatively straight.

Any Canadians or American budds near the border looking for porting tools check this out