- Dan's Performance Page

  Porting & polishing the 305 Cylinder Heads
  October 7th 2000:

Project update. I've finally run the car at the dragstrip. After some tuning sessions, the car's final run was 14.049 seconds at 100.82 MPH. All from a 133,000 mile 305 shortblock! The engine pulls linearly past 6100 RPM, and I shifted at 6000 RPM. The bottom-end torque is almost identical to the original engine configuration, so I managed only 2.08 60-foot time. Still, the engine has managed to push the 3550 pound car to nearly 101 MPH! This was sufficient to catch (and pass) several stock LT1 Trans Ams and Z28s. These cylinder heads seem to flow extremely well. I have, to date, put 31 passes on the car this year with not one single problem. The computer has not set a single trouble code, either!

February 28th:
I've finished modifying the combustion chamber. I guess you could say I have stepped upon the "slippery slope" of head modifications that amateurs like myself are not supposed to go. I just couldn't live with the valve shrouding so I went ahead and made a slight change to the chamber. Anyway, since no one struck me with lightning, and I didn't break through into any water jackets, I think I'll be okay. Maybe I ought to get these things flow-tested just to see if my efforts pay off. I have added a picture of the modification below.

I have added a new set of valve springs to the heads. The original springs had100 pounds of seat pressure, but only had a rate of about 200 lbs/inch. This means that the spring pressure at full lift would be about 200 pounds. Comp Cams recommends the SK981-16 spring, which has a rate of 384 lbs/inch. Quite a difference! So, I bought new springs and learned to set them up.

  Dec 29th: I've finished purchasing most of the components for the engine buildup. The major component is the Comp Cams Extreme Energy grind. Its the XE262H, which is a 214/224 duration @ .050", .462/.470" lift cam. I figure that it ought to yield the potential of 275 HP in the 305 and be good to about 6000 RPM. Parts arrive before New Year's day. I should begin the teardown next week.

December 29th, 1999 through Feb 14th 2000: The cylinder heads are back home after being sent out to the shop. I had them re-grind both the intake and exhaust valves as there was NO three-angle valve face on the exhaust. The intake valves were probably okay, but with all the abrasive work I didn't want to take a chance on a screwed-up valve seat.  I had them mill the heads to clean up the surface as well as fix a slight warpage problem. All up, it was about $200 in machine work.

Feb 14th: I discovered that the valvesprings that came with the heads are insufficient for the cam. They experience bind at .510" of lift. Remove .050" for safety margin and you get less than .470" of total lift. So, it looks like the "good internet deal" wasn't: About the only thing special about them were the 1.94" intake valves, which look marginally shrouded anyway.

  Click here to see the 305 HO Project notes.


Here's the stock ports. Bad exhaust seat, no porting anywhere. Lots of heavy carbon deposits. The intake port is clean, but the inside radius is quite sharp.
  Here's the first pass on the ports. I've polished the combustion chamber around the exhaust port to help reduce carbon buildup and detonation problems. I've relieved around the exhaust valve to help unshroud it at lower lifts. The exhaust port is fully polished. The inside radius has been made larger to reduce turbulence. The intake bowl used to have some sharp steps from the maching process. It sure looks nice; no sharp radii anywhere.
  Here's the eighth intake port that I did. Look at the difference in the intake guide! I'm going back and re-doing the other seven to look like this.This picture has different lighting, and the ports are full of grinding material. The chamber is not yet polished. 
  Here's the shot of the polished exhaust ports. They shine like chrome. Hopefully this will help retain heat in the exhaust gases as well as reduce carbon buildup. In addition to the polishing of the exhaust ports, I have match-ported the intake ports to a FelPro intake gasket. 
  November 22nd: As soon as I am done typing this, I am going out to the garage to finish the match-porting of the cylinder head. Take a look at this before / after shot of the intake tract. The intake is occluded with some very rough casting flash in every port! I'm match-porting to a Felpro gasket set, as is my TPI intake. I'll actually be using a good dual-plane intake first, and run-in the valve train with the L69 Quadrajet.
  Here's the cylinder head combustion chamber after the valves are installed. Notice the area around the 1.94" intake valve: It's a very tight fit! I don't suppose there is some shrouding here? I'll be making a template of the cylinder wall and will transfer the contour to the head. If there is enough clearance, I might grind open the area around the valve, then resurface the heads (again) to regain the lost compression.
  What happens when an engineer gets a grinder? An irresitable urge to grind stuff. Voila! A modified combustion chamber! This modification required the use of a 30,000 RPM Dotco die grinder with 1/8 inch collet and a 1/8" conical carbide burr. It was very, very tight, and I didn't want to nick the valves. Whoops! The Grind-o-meter just logged 30 hours of grinding time on these cylinder heads! I wonder if they will flow any better or not?
  What kinds of tools did I use?
Sears Craftsman 6 HP 33 gal 240VAC compressor
Ingersol-Rand Cyclone 25000 RPM air grinder
Various conical carbide bits
Various flapper wheels, sandpaper rolls on mandrels
Various stones, shaped into cones with a diamond block
Standard Abrasives porting kit to start. I have since supplemented my supplies from a tool shop.
  How do you cc a head?? Here's my first attempt: A 60cc syringe, an angle finder, an old sparkplug to plug the hole, and some air tool oil. A piece of 6 x 6 inch plexiglass with a single hole in it, and some silicone grease to make the seal. It didn't work well enough so I am back to the drawing board. The air pressure forced oil out the hole and I spilled probably 1 cc or so. I DID figure out that the heads were between 57 and 60 cc. Big duh! Want to see the heads on the engine? Click here.

If you have comments or suggestions, email me at