& polishing the 305 Cylinder Heads
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!
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
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.
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.
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.
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
||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
||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
||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
If you have comments
or suggestions, email me at firstname.lastname@example.org