If
you recall, the last time we took project �67 to the track, it was the maiden
voyage for the new 331 stroker engine.
That day turned out to be very encouraging, as we cam home with a 11.87 ET at
117 mph. Since then we've only made six more passes on the new motor -bringing
us to a grand total of 10 passes so far.
We knew that there was more in
the motor, especially considering the 1.59 60fts, but we were weary of the stock
28 spline 8� axles. We had already snapped one with the previous motor, and on
a test drive shortly after installing the 331, we found twisted splines on the
drive side axle. It became readily apparent that we had to address the issue of
axle strength. Unfortunately the 8� Ford differential is limited physically to
a 28 spline axle, unlike it�s 9� big brother which can accommodate up to 40 splines.
Round 2 Nevertheless we put it on out to-do list to research
the options. In the meanwhile we were dying to get to another track session. We
made our way to a test and tune, and got fired up about the prospects of dialing
in carb jetting and timing. The first pass showed promise. Launching the car at
an axle-sparing 2500rpm, we had 1.7 60ft and still ran 12.00 @ 118. With plenty
of traction coming in the way of ET Drags, we figured the next run would show
a nice high 11 sec timeslip if we raised the launch rpm to 3000.
The next
run started off in the right direction. A 1.62 sixty-foot time flashed up on the
board. The 1-2 shift was nailed, and then it was over� the nose of the car dived
down, and the engine acted as if it hit the rev limiter. The run was over, and
now the question was what broke. A quick glance at the gauges indicated no problems
with oil pressure or water. However the engine was at a constant sputter, not
wanting to rev past 1500. I limped the car off the return road and back in to
the pits.
My initial feeling was that something in the ignition system
failed. Perhaps the MSD box or distributor decided to go out. However after checking
for spark at all eight cylinders, and pulling and inspecting the distributor,
no glaring problems were noticed. Next step was to suspect a broken valve spring.
Pulling the valve covers revealed the problem � a broken rocker arm stud on the
# 7 exhaust valve. Who would have ever expected a 7/16� rocker arm stud to break?
Not us� hence we didn�t bring a spare. In fact judging by the fact that no one
at the track seemed to have a spare stud, we concluded this was a rare event and
perhaps we just had a bad stud to begin with. After rigging up the stud so that
it would work, we drove the car home �gingerly, keeping rpms below 2000 rpm the
entire way. The stud would be replaced, and we�d cross our fingers that this wouldn�t
occur again. After all, a stud girdle is an option, but realistically a hydraulic
roller cam with .550 lift should not warrant one.
Round 3 In
the mean time we came to a decision on our axle issue. Rather than spend the $1000
or so it would require to build a full 9� rear end, we decided to push our luck
and order a set of hardened 28 spline axles. After
doing some research, we opted for a set of Dutchman 28 spline axles. Dutchman
gave us fair warning that for the level of power we�re making, we should really
be using a 31 spline 9� rear-end. They stated that their 28 spline hardened axle
would be about 25% stronger than stock. We figured that since we weren�t shearing
this things upon every launch, that 25% should provide an adequate margin of safety.
In general axles for race use should have a 200% margin of safety per axle� i.e.
an engine making 400 ft.lbs. of torque, with a 4.11 rear gear and 3.35 first gear
is making 5500 ft.lbs. to the axles (or 2250 ft.lbs. per axle) and thus should
use an axle capable of handling 5,500 ft.lbs. (a 31 spline hardened axle can generally
handle 6400 ft.lbs. of torque, a 35 spline can handle 9600 ft.lbs.)
The
following weekend we headed back up to the track. The Dutchman axles installed
as easy as advertised, and looked like being capable of handling some serious
launches. The three passes we�d make that day would prove our hunch correct. Our
best pass would be a 11.72 @ 118.8 with an outstanding 1.56 60ft. This is a car
using stock 4-leaf springs, eight year old Monroe replacement shocks, and $99
under-ride traction bars. We�re dumping the Spec Stage 3 clutch at 4500 rpm, and
the car handles it like its pulling out of the car wash on a Sunday afternoon.
It launches so smooth that it�s hard to believe the short times that flash up
on the score board.
With less than a dozen passes on the new motor, and
each pass getting subsequently faster, we're indeed very pleased with the results
of the 331. What is more impressive is that the motor is very streetable -offering
nearly 12 mpg on the 120 mile round-trip drive to and from the race track.
The
next steps call for some chassis dyno time to nail in the timing and fuel tuning,
and then let our resident hot shoe Victor Silva pilot the car -if history is any
indicator, his talents should put the car smack in the middle of the 11's. F/M
We
decided to postpone a full 9" rear end buildup for now. These 28 spline hardened
axles from Dutchman should give us 20-25% more strength.
We've
snapped a stock axle at the splines, and this one that came out looked as if it
was headed down the same path. The Dutchman axle on the left is visually beefier
at the splined end.
We
ordered the axles with studs and bearing pressed on, making for a "plug and
play" installation.
We
spent a few more bucks to have the flanges drilled and tapped for 1.5" long
studs (NHRA tracks typically require rear wheel studs stick out past the lug nut
end.)
With
the drum off we removed the axle retaining flange nuts.
A
drum can make for a quick and easy axle puller: Flip the drum around and attach
a few lug nuts loosely and yank.
Slide
the old axle out. Now's the time to replace axles seals if they are leaking.
Slide
the new axle right in. We were impressed with how the Dutchman axles fit perfectly
per our measurements taken over the phone. No surprises or fitment issues to deal
with.
Install
the supplied retaining plate and it's off to the track for some abuse!
distributor,
no glaring problems were noticed. Next step was to suspect a broken valve spring.
Pulling the valve covers revealed the problem � a broken rocker arm stud on the
# 7 exhaust valve. Who would have ever expected a 7/16� rocker arm stud to break?
Not us� hence we didn�t bring a spare. In fact judging by the fact that no one
at the track seemed to have a spare stud, we concluded this was a rare event and
perhaps we just had a bad stud to begin with. After rigging up the stud so that
it would work, we drove the car home �gingerly, keeping rpms below 2000 rpm the
entire way. The stud would be replaced, and we�d cross our fingers that this wouldn�t
occur again. After all, a stud girdle is an option, but realistically a hydraulic
roller cam with .550 lift should not warrant one. 
After
doing some research, we opted for a set of Dutchman 28 spline axles. Dutchman
gave us fair warning that for the level of power we�re making, we should really
be using a 31 spline 9� rear-end. They stated that their 28 spline hardened axle
would be about 25% stronger than stock. We figured that since we weren�t shearing
this things upon every launch, that 25% should provide an adequate margin of safety.
In general axles for race use should have a 200% margin of safety per axle� i.e.
an engine making 400 ft.lbs. of torque, with a 4.11 rear gear and 3.35 first gear
is making 5500 ft.lbs. to the axles (or 2250 ft.lbs. per axle) and thus should
use an axle capable of handling 5,500 ft.lbs. (a 31 spline hardened axle can generally
handle 6400 ft.lbs. of torque, a 35 spline can handle 9600 ft.lbs.)
