yup....thats right......we're talkin' 16+ second combos!!

you guys have all seen them at the track.
its often a fairly nice looking resto-type muscle car with maybe a different carb and a mild cam.
a full bodied car, that looks basically stock, with an unhappy first-time-ive-ever-been-to-the-track-with-my-car owner, who was sure it should be running a couple of seconds quicker than it is.
that perplexed look on the owners face as he stares at the 16.XX or even 17.XX on his time slip tells the whole story.

so, the question is......how do you take a car that would have run at least mid-15's with a fairly used up 100% sock 440, with the 12" converter and 3.23 gears.....then rebuild the motor, upgrade the cam and a few other trinkets....and slow it down one second plus???

well my friends......i have a set of 906's in my shop now that go a looooong way to answering that question.

a customer of mine has a 1969 440 car thats getting restored.
the car was purchased as a project, and came with a freshly machined 440 that was supposedly ready for assembly.
well, when the parts get back to the shop and inspected, its discovered the engine parts had been sitting around in a damp environment for a while, and will need some clean-up before being put into service.
the heads got sent to me for a once over.

now, keep in mind had these parts not gotten rusty from sitting around....there is every chance they would have been put into service as-is.

this set of heads had hardened exhaust seats installed, all new guides, all new valves, valve job, flat milled, and new MP 933 springs.
seems harmless enough, right? i mean....how bad could they be?

well....after i got them apart and gave them a look over i knew they werent going to be the hot ticket for making power.
not necessarily a big problem, since this is basically just a stock type rebuild for a restoration.
as long as they arent too much worse that an OE head, they'd be fine.

some things were done that just didnt even make sense.
like....all the seats had two thick coats of red Dykem(lay-out dye) on them......but no seat touch up done after the application of dye.....so why was it even there???(Dykem as a seat protectant??)
the new valves also had a nice coat of Dykem all over them, but they had been refaced afterward.

the seats had been cut with a cutting system(as opposed to stones), and several of the exhaust seats had some severe chatter.
when the grooved iron guides were installed(probably my least favorite replacement guide), they spot facted the entire original guide boss on top of the head off, and just left the 1/2" replacement guide hanging out in the breeze.
not really a "problem" per se, but i found the seal arrangement amusing. the OE positive style intake seals now had nothing to grab on, so they were now umbrella seals.
the new guides were also left at the OE height, so trimming would have been necessary with many cam choices.

after disassembly, i brushed the assembly lube(paste type moly cam lube) from the guides to check the fit, which felt okay.
when you do this stuff day in and day out, you get where you can tell if there is an obvious seat alignment issue without even breaking out any tools.
these exibited those trends, so i stuck a pilot in the guide and kissed a few seats with a stone to see how the contact pattern looked.
the exhaust barely even touched on one side, and the intake hit maybe 1/3 of the way around.

okay, so the seat runout is not good.....and the intake seats have been sunk into the chambers about .030 or more, without a relief cut made into the chamber, so the valve is essentially sitting in a little pocket with a sharp vertical edge all around it.
thats not gonna be good for flow.

originally i wasnt even going to flow them....but these seemed extraordinarly bad......so on the bench it went.
the exhaust seats were the std size listed in the catalog for these heads, which leaves a noticable step under the insert.
while this looks like its going to kill the flow......it surprisingly doesnt really seem to have much effect, and in fact, this exhaust port was actually better at high lifts than an untouched low milage 906 head i have at the shop.

so, how bad was the flow as they came to me?

lift----I/E
.100--42.4/45.3(not a typo....int was less than ex @.100 )
.200--96.8/86.4
.300-153.8/125.0
.400-199.7/146.6
.450-211.2/152.9
.500-217.0/158.8
.550-222.7/162.6
.600-228.5/164.3
.650-232.3/165.1

after i took it off the bench and reviewed the numbers i called the customer to tell him these heads had lowered the bar for 906 head flow.
the flow from .450 or so and down was horrible.
once the valve was well clear of the seat, you can see the port itself wasnt that bad for a stock head, breaking 230cfm.
but with a cam that would likely be under .500 lift for this application......the area under the curve was quite a bit worse than an untouched OE head.

you'd like to think that when you got your stuff back from the machine shop that it wasnt worse than it was when you brought it there.

since its rarely the case when its just operator error when things look this bad(its usually a combination of operator error and worn out equipment), i didnt trust the new valves that had been refaced to have no(or very little) runout.....and when i chucked a few up in the valve grinder, my suspicions were confirmed.
bring the valve up to the wheel.....and you get that hit and miss sound of a few thou of runout.....but salvageable at least.

i took some pics of these jewels.....dont know how they came out, and the camera is at the shop, but i'll try and post a few pics tomorrow.

so.....imagine the entire build done with the same machining practices, the same attention to detail as these heads....and the picture gets clearer on how you make a 14-15 second factory muscle car into a 16-17 second weakling, fearing every Neon or Civic with a fart can in their neighborhood.