Best Flowing Head
It has also been said that all
Olds BB or SB heads as a group will flow within 5% of each other. Unless
you are turning over 6500 rpm, your heads probably won't be the
Best Flowing BB Head
The '67-69 C (#394548) heads are reputed to flow the best. Pretty much
goes without saying that big-valve heads ought to flow better than comparable
units with smaller valves. Bigger valves may diminish low-rpm performance
and throttle response.
All Olds big block heads have the same mounting holes, port sizes, etc., and thus
are interchangeable. Even the combustion chambers are equal at 80cc, plus
or minus a little. Olds achieved different compression ratios by using
pistons with different size dishes in the top. Some W-30 heads were rumored
to have been factory-milled for a smaller combustion chamber. When in doubt,
measure (CC the head).
Best Flowing SB Head
Dick Miller claims that #5 heads flow the best bone stock and untouched.
[ Thanks to Chris Witt, Mark Prince, Chris Urban, Bob Barry for this information ]
Hardended Valve Seats
Before 1971, all Oldsmobile street engines require lead.
An engine uses lead for valve seat protection and octane boosting. GM states
in the 1971 Owner's Manuals that all 1971 GM engines can safely use
unleaded fuel. You might want to consider that 100,000 miles on an unopened
engine wasn't a common occurance back then.
The lead (actually tetraethyl), when burnt in the
combustion process is deposited on the valve seat. This cushions the
softer metal of the pre 1971 heads. Without the lead the harder
valve slams into the unprotected seat and will cause seat recession. This
leads to burnt valves. Heads with soft seats are A - F. Heads with hard
seats are G - K. Although some Ks might have the soft seats. I'll have
to defer on 350 heads.
To distinguish the hardened valve seat heads from the earlier, non-hardened
seat heads, Olds cast a small capital-letter "A" along with the larger
casting number/letter. This letter is smaller, and down to the right from
the main casting number/letter; hence, it is designated by the lower-case
"a", even though it is cast as a capital "A" (also to distinguish it from
the later 307's #7A head, where the capital A is the same size as the 7).
Heads with the small a designation are guaranteed to be hardened
seat heads. Such as Ca, Da, Ga and also Ka and J heads. The J is
the exception due to being a smog head from 73-76. Other heads (such as E
and F) are rumored to have hard seats, but only your budget, gut feelings,
and eventually the heads will know for sure.
I guess since the A is more of a revision code, and not really part of the
casting number/letter (unlike the 3A, 4A, 5A and 7A heads on the '77 and
later cars), the '72 heads are called "#7" heads officially.
Heads without hard seats will go about 60,000 miles on unleaded gas. In a car
that will see a lot of driving, you will need the hardend seats installed.
Valve recession is apparently not a big problem for street-driven cars.
Though the lead is gone, there are additives in gasoline today that perform
much of the same lubricating function. The
only time you absolutely need hard seats are on an engine that is not going
to be apart for a longer duration than that. All these shops that insist on
hard seats do so because they sell/install them.
Almost any machine shop can install the hardened valve seats. This in conjunction
with a 3 angle valve job. Also an octane boost will
help. I have only found one octane boost that earns my seal of approval.
It is called Lead Supreme 130. It will formulate today's pump gas into
yesterday's Rocket fuel. Contact: Stone oil co. area code 912-489-2896. They
will ship UPS. 1 ounce of this stuff per gal. can increase octane 2 points.
Use a fuel additive that contains lead if (1) your heads are pre 1971,
(2) your compresion ratio exceeds 10.1, (3) you have no catylitic converters,
and (4) you rev past 3 grand regularly.
Today's thicker head gaskets [0.045" vs. 0.025"] place the
head about 0.020" farther from the cam,
which lowers the compression about ¼ point and takes that much out of
the lifter plunger preload. If you have an engine apart, have the heads
milled for the combustion chamber volume that your calculations indicate
for the desired compression ratio.
A note for people that use leaded aditives for their fuel.
- It will destroy the useful aspects of the catalitic converter.
- When leaded additives were commonplace in the refineries, the
people that handled the lead material did so with extreme caution, and took
- It is considered a poison with extreme toxicity.
- If you use this material, wear thick rubber gloves,
good eye protection and a respirator face masks at a very minimum.
Do not come into physical contact at all.
Remember when gasoline was 'red.' The red was an aniline dye added for
anti-knock (relative octaine boost) purposes. It too is harmful to C.C.s.
I don't have a problem with my 10.25:1 455 in the Cutlass
(back when I mixed 92 unleaded with 89 leaded), and
even now I don't have a problem running my '69 Toro's 10.25:1 455 on 92 or
93 octane unleaded.
I did have a problem with part-throttle pinging, and even backing the timing
way down was not enough to cure it. I bought an adjustable Crane vacuum
advance unit, followed the tuning advice (it also includes springs and a
vacuum advance limiter), and have no pinging on even the hottest of days
lugging it up a hill at part throttle, with the initial advance set at the
factory 8' BTDC. It seemed that the problem was the excessive vacuum advance
under part-throttle load; with the Crane kit, I could tune the spark curve
to reduce the advance under those conditions, but keep it at just under
pinging in all other places. Highly recommended.
I have mine set at the factory 12' initial advance with 34'-36' total on my
455 with 10.5:1. I don't have any pinging or knocking at any rpm or load.
I am using straight pump unleaded Chevron Super Supreme 94 Octane gas. It
is the only gas station in Canada that has a 94 Octane fuel. If I use a 92
or 91 Octane then I do get pinging. I have all the stock components under
the hood (for now). I did purchase a MSD Adjustabe timing control (I have
yet to install it) to use so that when I do travel to areas that don't have
94 Octane gas, then I can just turn the little dial and retard the timing by
up to 15'. I have seen it work and would also highly recommended them (ie.
either the Crane or MSD system).
Most of the time I go out to the local airport, purchase
about 10 gallons of av-gas, and run a 2:20 (2gal av-gas:20 gal super
unleaded), and my 10.25:1 350 runs fine at just about any timing setting.
VP Racing Fuel says that octane does not matter as much as the blend
of the fuel does. It is all a matter of how well an engine can burn the
fuel. They sell a leaded and un-leaded racing gas for stock engines,
they sell gas for NHRA Pro Stock racers, and everthing in between. If
you tried to run their highest grade stuff in your street car, it most
likely would not run at all. Your stock engine does not make enough
I used to run a 50-50 mix of unleaded premium and VP Red
(the lowest grade of leaded) in my Fairlane with great results. I have
also ran brand X racing fuel with the same mix ratio in my Olds with
great results. I thought I had Sunoco 260 in the tank again, just like
the old days. I have a friend that runs 3-4 gallons of racing gas with
a tank full of premium in his GTOs. He reports smoother running and
driveability. I would seek out a racing fuel supplier and shy away from
aviation fuel. VP is headquartered in Dallas, Texas and has bulk
plants all over the U.S.
When I tried Lead Supreme 130 I found
that I could put my timing almost anywhere I wanted it. LS 130 uses the
same additives the oil companies used in the good old days. This
includes tetraethyl and toulene. One ounce per gal. will raise 93 octane
gas to 95 octane. You can custom blend to your own octane needs.
To raise the octane 1 point
(of course I am speaking of R+M/2 method) from 93 to 94 one gallon of
LS 130 will yield 214 gals of treated gas. This will really only protect
valves and CRs of 9.5:1. To raise octane 2 points add 1 ounce per gallon
this will make 129 gals.
to get 4 points add 4 ounces per gallon this will make 32.5 gals.
For racin' 1 gallon of LS 130 to 9 gals of super unleaded will raise
octane 8 points.
One gallon of LS 130 is about $18.00 less S/H.
|Product ||Comments |
| 104+ ||Good stuff. Car pings a little 90% effective. |
| Bartyls Lead additive and Octane booster. ||80% effective |
| Snap Octane booster. ||Save your money. |
| Trick Octane booster. ||Haven't tried it yet. |
| Stp Octane booster. ||75% effective. |
[ Thanks to Bob Barry, Nick DiGiovanni, Stephen Hoover, Cliff Feiler,
Dave Wyatt, Danny, Chris Sparks
for this information
Do any head porting before you do the valve job; one nick of the
valve seat (and if you work from that side of the port, you will nick the
seat) and you've got to do it over anyway.
If you are really concerned with maximizing flow, just follow the standard
porting techniques for Olds heads (remove E.G.R. or A.I.R. bump, teardrop the
valve guide, port-match the intake and exhaust ports and manifolds).
The Olds head can gain about 80% of its total potential flow by matching
ports on intake and exhaust side (yes grind out those headers),
removing E.G.R. hump in the exhaust port, clean up of the bowl area behind
the valve seat, and tear dropping, or at least narrowing the valve guides.
The metal around the valve guide is round from
the factory, and you grind it so that it is shaped more like a teardrop,
with the skinny end pointing away from the valve.
The intake runner of the head should stay rough to help the fuel
atomization. Smoothing the surfaces til they are smooth and shiny will
cause fuel puddling and reduce atomization.
When looking at an Olds head exhaust port you will notice the EGR hump on the
roof of the port just inside (header side). This hump when ground out so that
its flush with the surrounding area will net a gain of approx 30% on the
exhaust flow. Also blend it into the roof of the port. There is also a kind of depression next to the AIR boss (it wasn't used for EGR, though it may
have had that effect) that you will need to blend in to the rest of the port
roof as well.
To port match, you scribe the outline of the port from the gasket on
the surface of both the head and the manifold, and then grind the
entire port up and out to that point.
Just short of all out porting is to have the heads bowl
ported to a distance of about 1" just down from the valve seat and blended
into the port runners the basic idea is to try to get the bowl area to about
75% of the valve diameter.
This one mod alone will increase power better than any dual
pattern camshaft would (when you attribute the increase to the dual
pattern and not the camshaft profile). Larger valves can be cut into any head.
Unless your cam is really wild,
however, and you're turning 6000+rpm, just removing the EGR bumps,
tear dropping the valve guides and smoothing out the transition from the
valve seat to the port will be sufficient. No sense in trying to increase
port volume or such.
Make sure that the shop you take the heads to will actually do a three angle
Have the intake and exhaust valves back cut on the back side of the valve
(called back cutting the valve).
Also try to have the back sides of the valves polished or smoothed out.
Have the center exhaust
port divider welded up and then milled flush with the rest of the exhaust
gasket seating surface.
Needless to say, you should also completely wash out the head after porting
it; metal particles and shavings will be everywhere after your porting job!
Any further porting should be left to someone with more experience, as
flow can be just as easily reduced as increased.
Mondello offers an entire kit (~$70), with the cartridge rolls and the
carbide burrs you would need. You can pick up seperate pieces if you
run out, but the whole package will end up costing more if purchased
seperately. Go with the Mondello kit, unless you find a good
cheaper source for everything.
The carbide burrs are like rotary files on the end of a shank, and you use
them to remove material; they come in a few different shapes, such as round
and almond-shaped, as well as triangular. I found myself using the round one
most often (wore it out, in fact, on one set of heads).
The cartridge rolls are just strips of sandpaper rolled-up like a jelly
roll, which screw on to the end of a shank; as you use up the abrasive, that
bit of the roll breaks loose, revealing new abrasive underneath (I didn't
know this, and got concerned when bits of these things started flying off
the tool at 22,000rpm!) They don't really remove much material, and you'd go
through a lot of them if you tried to port a head with them alone. You use
them for final polishing and blending, and perhaps to even out the surface.
[ Thanks to Chris Witt, Tom Lentz, Robert Whitaker, Mark Prince, Chris Urban,
Cliff Feiler, Danny, Bob Barry, Tony, others for this information ]
Manifold Crossover Passage
Some W-30 heads have only one center exhaust port open to the intake
manifold heat crossover. This is called "blocked heat crossover."
If you can stick your finger from the intake heat crossover passage into
both valve pocket areas of the center exhaust ports, it's not blocked;
if your finger can access only ONE exhaust valve, that is blocked. Blocked
is better, for performance. For similar performance gains, more mundane
heads can have this crossover blocked with molten metal, etc., or a stainless
steel shim can be placed over that heat passage when the intake manifold
Blocking Manifold Heat Crossover Passages
I advise against using stainless steel shims to block the manifold heat
crossover passages. I used to use my just-removed intake "bathtub"
as a source for clean stainless, since anything much thicker would affect
the manifold sealing. This works well for an engine that is torn down frequently
(once per year). Beyond that, the steel starts to deteriorate (gets warped
and thins out). I had one of these plates break up and a dime size hole
appeared when a piece broke off. Thankfully, the fragment that came loose
slid downward and was trapped harmlessly between the shim and the manifold;
could have been quite damaging if it had been ingested.
I saved up my pennies and put about a pound of Mondello's zinc aluminum
alloy in each head. Best money I ever spent. I did this myself, with a
handy lab furnace at work. You can use a small cast iron skillet to hold
the alloy, and one hell of a good potholder to hold the skillet. Helpful
hint: install two old (unwanted) exhaust valves in the center ports with
springs to hold them tightly shut. I used an 18 inch piece of 2x4 and bolted
over the exhaust crossover outlets (where the intake manifold usually is),
countersinking the bolt heads to ensure the head would stand on edge in
a stable (read SAFE) manner. Next, you should pour the molten metal (in
the port outlet where the exhaust manifilod normally goes) at a good pace
so that it hardens as one piece and not in layers. A few gentle raps with
a rubber mallet, as you pour, by a second person will help displace any
On another set of heads, I did not use the exhaust valves, so I was only
able to fill up the ports until the alloy ran out of the exhaust valve
pockets. No harm was done to the valve seats. Because the alloy had a pretty
high surface tension, I did not get optimal filling of the entire passage.
The top of the alloy cooled in a dome shape which was not tightly in contact
with the walls of the port.
While the passage was certainly completely blocked, there was not alot
of alloy that projected into the port area for optimal porting of the long
side of the runner. Of course, a completely blocked passage is bettter
than no block at all, and I was able to shape the pockets pretty well with
my trusty CP die grinder and assortment of carbide burrs. I recommend filling
the passages right up over the valve stems. This will ensure that enought
molten material will contact the walls of the passage for smooth porting.
This should provide more than enough meat for port work. I would rather
have too much since it ports out quickly with the die grinder.
The alloy seems like very durable stuff, but ports with the same ease
as cast iron. To date, I have had no problems with durability. On a cool
evening, in conjuction with the OAI hood, the car feels massive. After
a good highway cruise, you can put your hand on the intake with no discomfort
from heat! The car will take longer to warm up and may stumble a bit when
you stop at the off ramp after a cruise on the highway. If you want smooth
idle all the time, better buy a road turtle with EFI. For the boulevard
cruiser, blocking off the passages won't provide as great of a benefit,
since normal heat soak will eventually warm the manifold to the same temp
as the rest of the engine. It's the passage of air and evaporation of the
fuel (i.e. high speed cruising) that cools off the intake. I used to cruise
the highways for a while, then get on the boulevard within a few miuntes.
[ Thanks to Scott Mullen for this information ]
Joe Mondello does not advise the use oversize exhaust valves
when hardened exhaust valve seats are being installed in a head. The use
of 1.71" exhaust valves w/hardened seat inserts and a 2.07"
intake can result in intrusion of the hardened seat insert into the intake
seat area. I asked him about this because I had already done exactly what
was not recommended. After about 20,000 miles, I have had no problems,
but a very small portion of my intake seat is very close to the insert.
I think the risk is worth it, since I wanted it all (big valves and the
durability of hardened seats).
[ Thanks to Scott Mullen for this information ]
Rocker Arm Ratio
All Olds heads use rockers with a 1.6:1 ratio. By a mathematical coincidence,
this is also the ratio between movement at the rocker pedestal and the
movement of the pushrod. That is, if there is 0.030" clearance under
the rocker pedestal with zero valvetrain lash and zero lifter plunger depression,
then there will be 0.048" [0.030*1.6] of lifter plunger preload when
that rocker is tightened down.
Since the heads are very similar, and the 350 has a large 4.057"
bore, you can put the 2.000" valves, and probably even the 2.072"
intakes into a SB head, but it'd probably lose some low-end throttle response
to gain some high end WOT power.
[ Thanks to Chris Witt, Tom Millard for this information ]
Stainless Steel Valves
From what I have read the cause of seat recesson is that when the
exaust valve closes a few molecules of the seat weld themselvs to the
valve. When the valve opens these are ripped off the seat and go out with
the exaust. Leaded gas helped to prevent this by forming a cushon and
lubricating the seat and valve mating area with molecules of lead. S/S
valves may help some but I don't think they would prevent it.
Stainless steels have thermal conductivities along the lines of 15 W/m k,
versus carbon steels that are aound 60 W/m k. This means that the
stainless valve will not conduct nearly as much heat to the valve seat when
they are in intimate contact as the carbon steel valve. I know that the
exhaust gases will still be rushing by the seat at the same temperatures,
but they will not be slamming against the seat, in a way providing a weak
sister of a force weld. The continual contact at much elevated temperatures
will result in earlier wear. How much, I don't know. Always ask a guy with
experience for that kind of info.
The conductivity is much lower in the S/S
valve, it will take on less heat than the carbon steel. It will also not
give it up as readily. the decreased thermal conductivity causes the
stainless steel valve to retain more energy in the form of heat at the stem.
This is because the rate of heat transfer to the valve guide is lower.
Basically, the S/S valve has higher heat resistant properties and is more
resistant to mechanical stresses and strains than the carbon steel valve.
Truck engines (I mean real trucks, not pickups) have used hardned
seats for years. Not even leaded fuel will save the cast iron seats when
the exaust temp gets high. A truck pulling a heavy load up a steep grade is
very hard on seats, as is a motorhome that catches a lot of wind and is
heavy too. This is because the throttle is wide open at a low rpm for a
long period of time creating very high exaust gas temp. Sometimes the
manifolds will turn cherry red. It doesn't take many miles under these
conditons to completely destroy a seat.
I have seen very few high
performance engines have seat problems even when using older heads. I
think that this is because most ot these engines are run with a richer
mixture which helps keep the exhaust gas temperature down and
they are not run under lugging
conditons. Of course they are usually driven less miles so that helps too.
If I am building heads for car that will be hot rodded I offer to put in
hard seats if they want. If the vehicle is to get a lot of highway miles
and doesn't have the factory induction hardened seats I recomend them. If it
is to pull a trailer I insist on them.
[ Thanks to Walter, Paul Brillhart for this information ]
Valve Rotators / Spring Seats
Starting with the E/F heads in 1970 came valve rotators,
which required deeper spring seats to be cut. With those
heads, you can use valve rotators, or standard retainers and stiffer, longer
reach springs suitable for very high lift cams [over 0.600" valve
lift]. Shallow spring seats do not allow valve rotators or very high valve
lift. Shallow seats can be cut deeper to suit, however. The presense of
rotators doesn't necessarily indicate hard exhaust seats.
Generally speaking, there were two intake valve sizes: standard run
of the mill engines used 2.000" valves [which also served as the small
blocks' "big valve"], and performance engines used the larger
2.072" intakes. A small, but not negligible, 3.6% difference. Generally
speaking, for heads up to and including G, the large valves have a 30 degree
face, and the 2.000" valves have a 45 degree face. Almost all heads
used 1.625" exhaust valves with a 45 degree face. Notable exception
would be the 1972 Ga heads. Aftermarket performance exhaust valves are
commonly larger than stock: 1.710" diameter. Any head can be fitted
with larger valves, this only requires grinding the seats to match, about
Various valve lengths were used by the factory, with as little as 0.005"
difference in length. Generally, the pre-'72 Toronado and 442 engines used
the same valves, while more common engines had slightly different length
valves of smaller head diameter. When a valve job is done, the valve tip
is generally ground a bit, and the valve has moved due to cutting of the
seat and face anyway, so what difference 0.005" might have once made
is probably lost. The most important thing to check is that when you assemble
the engine, you have the recommended 0.050" lifter plunger preload
[+/- 0.020" or so].