|Preface: All of you hardcore carburetor racers
take notes. The results in these articles were obtained using a stock, 92
hydraulic roller camshaft. Try to match them with a carbed intake and this
cam and you will be disappointed. Read on for the explanation.
When we last reported on
Green Machine II, our trusty, green pony was running 13.3s-13.4s
in the quarter mile at 102mph. We had hoped to push closer to the 12s
with the stock heads/intake/cam combo. Maybe even crack that 13.00 barrier.
The truth is that the day the 13.39 was run was a cold, dry day in February
and the track conditions were perfect. Try as hard as this author might,
the best ET would stand. Once summer weather set in it was apparent that
the quest for lower timeslips would be on hold until either the weather
changed or more power was added to the equation. And if you are reading
this you already know which option was more attractive. Besides, drag racers
arent known for their patience.
Trickflow Twisted Wedge heads were procured
used, with mild port work. Originally set up for pedestal mount rockers,
we had TFS convert them to stud mount.
A peak behind the curtain in the last article revealed a set of used
and refreshed Trick Flow Twisted Wedge heads waiting in the garage. We
had discussed putting the stock intake on top of those heads and seeing
how much power would increase. While doing research for that install and
the article to follow we came across two very interesting facts. First,
the stock lower intake is the biggest restriction in the airflow path
in a stock 5.0. Take a look at the flow numbers for the stock intake and
you see that runners #1 and #5 barely hit 120cfm at 28 of water.
The stock E7TE heads will flow between 150 and 160cfm straight from the
factory. This did not bode well for the proposed head swap. Second, we
found a nicely ported Cobra intake for sale locally. Lets look at
why this is such a big part of making power on the 5.0.
Ford debuted the computer controlled, fuel injected 5.0 Mustang in 1986.
Two things made this 302 cubic inch motor produce torque like it was 352
cubic inches. One- the hydraulic roller cam that debuted in 1985 allowed
for more aggressive ramp rates on the cam lobes since the roller lifters
could follow the lobes where a flat tappet cam could not. The valves are
opened sooner, and stay open longer than a flat tappet cam with the same
total duration numbers. The flat tappet lobes look like eggs where the
roller lobes are more square. The second part of the big, flat torque
curve puzzle is the long runner EFI intake. With the advent of sequential
fuel injection delivered right at the head, Ford engineers could design
an intake without worrying about keeping fuel in aerosol suspension as
it moves thru the runners. And boy, did they come up with a great design.
By using computer modeling an optimum length was found that would promote
lots of torque from idle to 5000rpm. The length of the runners exceeded
anything seen on a production automobile. The runners were tuned
to take advantage of the natural resonance of a pipe. Each time an intake
valve slams shut it sends a pressure pulse back up the runner. If the
runner is long enough the pulse will hit its natural resonance point
which acts like a wall- and the pulse will be reflected back towards the
valve. This happens multiple times for each valve closure, with pulses
traveling up and back several times. Each single circuit is called an
effect. The 5.0 intake is tuned so that one of these effects
(3rd or maybe 4th effect) coincides with the valve opening and increases
the amount of air entering the cylinder- a mini supercharger. By turning
the intake sideways Ford engineers found they could fit this long runner
intake under a stock hood. So, with the cam and intake dramatically improving
volumetric efficiency and the fuel injection maintaining a perfect (close
to it) tune, the short stroke small displacement V8 acts like a long stroke
big displacement V8. Now that the stock intake was working so well with
the stock heads, how do you support better heads? Enter the GT40 and Cobra
intakes from the formerly named Ford Motorsport. Bigger runners and plenums
to allow more flow, yet retaining the tuned runner length. Even these
two pieces could benefit from more engineering as the aftermarket heads
kept upping the flow and velocity antes. So, lets see what has been
done to improve on Fords performance intake.
Don't look for a Cobra intake of this caliber
in your Summit catalog. This came off a supercharged application,
hence the extensive porting, enlarged plenum, and note the additional
injector bosses in the top photos. This intake flows 25-30% better
than an "as-cast" Cobra intake. It goes to show that new
parts aren't always better.
As you can see from the pictures this was not a simple port match job.
The Cobra intake had been cut open, hand ported and modified for auxiliary
fuel injectors. This type of modification was common on fast blower cars
before larger fuel injectors became readily available. The second set
of injectors would have been controlled by a boost pressure sensor and
secondary driver. While we did not need the extra fuel supply the rest
of the modifications gave us exactly what we were looking for in a reasonably
priced EFI intake. The lower intake was ported to a Fel-Pro 1250 intake
gasket, removing the biggest restrictions in the runners. The upper had
the runners smoothed without reducing the length, thus keeping that awesome
torque curve that 5.0s are known for. The last mod added pads for
mounting the injectors, and most important to us, an increase in plenum
volume. If you compare any of the aftermarket intakes designed after the
Cobra and GT40 you will find the plenums are all about twice the size
of the Ford Racing pieces plenums. While the Cobra/GT40 twins excel at
torque production they run out of breath after 5500 rpm, even on stock
displacement. Companies like Holley, Edelbrock, and Trick Flow all found
that by adding volume to the plenum allowed more rpm range without a major
tradeoff in low-rpm torque. One last fact stiffened our resolve- the ports
on the Cobras lower intake and the Twisted Wedge heads matched up
perfectly! We understood the message the gods of power were trying to
communicate thru these signs- Install the heads AND the new intake- Immediately.
Who are we to defy the horsepower deities?
While the heads were at the machine shop being surfaced and setup for
o-rings (is there boost in the future?), we decided to drop the new Cobra
intake onto the stock heads just to see the effects. The next trip to
the track gave us only a minor improvement- a 13.35 at 102.5mph. If we
waited to run in late Fall weather conditions there was probably another
1mph to be had. Of course, who wants to wait months just for a measly
1mph? Not us.
|Track Results: Cobra intake only
||Previous Best, stock intake
||Ported Cobra intake, stock heads
With the heads back from the shop and new gaskets in hand we went to
work. Out came the stock intake and heads, and after a careful cleaning
of the block, on went the new ones. The last two pieces to the puzzle
were a new 255lph fuel pump and adjustable fuel pressure regulator. By
increasing the fuel pressure we hoped to stay with the 19lb injectors.
Any more changes and the stockers will be maxed out and have to go. Many
racers report supporting a little over 300 fly wheel horse power with
the stock injectors. Time to hit the track and see if the reports were
The new GMII combo
Trick Flow Twisted Wedge heads
Ported Cobra intake
1.7 ratio rockers
Stock Mustang 5.0 HO cam
Fuel pressure set to 48psi
Timing at 18 degrees initial
Shorty headers (unequal)
76mm C&L MAFsensor
BBK 65mm throttle body
Stock h-pipe and mufflers
Unfortunately the first shot at breaking into the 12's came at a bracket
event. With only one time trial before eliminations, we did not get to
run the new combo to it's max. Still we dialed in at 12.98, with a good
feeling our first 12's was due today.
The first run would come against a late model Camaro. We left first and
had a clean launch. The Camaro played catch up. The green pony stayed
in front until the last 100 feet. With the Chevy now even and the line
coming up fast this driver knew the run was going to be faster than 12.98.
The shifts had come up so much faster than before it was obvious a breakout
was coming. So, at the last moment before the finish line I stabbed the
brakes hard and we crossed the line almost perfectly even- almost. My
instincts were on that day- Green Machine II ran a 12.981 on that 12.98
dial-in. Having to ride the brakes to prevent a breakout, the trapspeed
was a meaniningless 93 mph.
The following week we attended an actual test n tune session.
Since you can run without mufflers at test n tune we unbolted the
stock mufflers and ran thru the open, stock catalytic h-pipe. The timing
was set back to 14 degrees as a starting point for testing. The fuel pressure
was left at 48psi. The first full run was hampered by a bad bog off the
start , resulting in a poor 2.10 60 ft. and only a 13.26 ET. The good
news was the mph- 106.42. Better than the hoped for 105 and a great starting
point. A another run was made with no changes to improve the launch- thsi
time a 1.86 60 ft, yeilded a 12.97 at 106.57mph.
Dropping the fuel pressure to 45psi raised the mph to 106.91, even with
another bog on the start. With time running out we got greedy and set
the timing to 18 degrees as many other Twisted Wedge owners recommended
that for best power. This time the slicks grabbed the track with a screech
and reeled off a 1.82 60 ft, resulting in an awesome 12.81 at 106.74mph!
||Previous best, port. Cobra int. stock heads
||Ported Cobra int, TFS heads *brakes
The clean, green machine is now the fastest fuel injected 5.0 in the Fordmuscle.com
stable. The 4.7mph increase equates to more than 45hp at the flywheel.
And that is just the beginning. Wait till you see what we pick up once
the restrictive stock exhaust is replaced. We will test both an off-road
h-pipe and the Prochamber h-pipe from MAC products. Things are just starting
to get good