THE PREMISE
Making noise with exhaust cutouts is big
fun, but is there really a power gain? No
matter how well constructed an exhaust
system is, it still restricts flow with piping,
bends, mufflers, and sometimes catalytic
converters. The old-school solution is
exhaust cutouts. Like a fork in the road of
the exhaust, the cutouts empty the gases
after headers but before the rest of the
exhaust system. The original cutouts were
made with simple block-off plates that
were unbolted after climbing under the car.
The new-school answer is electronically
activated cutouts using butterfly valves, and
Quick Time Performance (QTP) sells the
highest quality ones we've seen. They can
even be opened with a wireless key fob.
The pipe is lying in the front flange, and we
tilted it around so it faced upward away from
the ground before tack-welding it.
THE STUFF
A local friend, Mick Batson, from Yucaipa,
California, threw us the keys to his '67 GTO
with the original 400ci Pontiac V8. According
to Mick, the Pontiac has some extensive
head work, a Crane hydraulic cam with
214/222 duration and 0.537/0.560 lift, an
800-cfm Edelbrock Thunder Series carb,
and Doug's Headers long-tube headers.
The base-level QTP cutouts are polished
stainless steel pipes that come with bolt-on
block-off plates; they are available in pipe
diameters of 2-1/4, 2-1/2, 3, 3-1/2, and 4 inches.
We chose the 3-inch (PN QTP-10300),
which retail for $46.55 each at Summit
Racing. The electronically operated, stainless
steel butterfly valves bolt in where
a normal block-off plate would go, and
they come either round or low-profile
oval. We opted for the circular ones (PN
QTP-QTEC-60) that retail for $323.00 a
pair at Summit. That adds up to $416.10,
which is also the price for the complete kit
with two cutout pipes and two valves (PN
QTP-QTEC60CP). We also used the addon
wireless remote kit (PN QTP-10900;
$71.25). It comes with a controller and two
remote control fobs.
The installation was simple. We bought a
set of flanges and bolted them to the header.
The cutout is a straight weld-in, which
might be easier and cheaper for most. The
electric motor is big, but turning the pipe
just a little before tack-welding it in allowed
for plenty of room. We ran the protected
wires up the framerails and firewall into a
wireless signal receiver, which is a 3x2x1-
inch box that mounts under the dash. It also
comes with a toggle switch we could have
put in the same location if we didn't use the
wireless function.
The 400 needed to breathe, although the
exhaust system wasn't very restrictive to
begin with. The GTO's exhaust used Doug's
long-tube 1-3/4-inch primary headers into
3-inch cross-pipes into two 2-1/2-inch Pype's
Streetpro Mufflers with 2-1/2-inch pipes
past the mufflers that exit behind the rear
bumper.
The stainless steel cutouts are the bestlooking
pieces of this exhaust. They make for
easy welding and a sharp-looking finished
product.
THE TEST
We put some street miles on the ol' Goat
with the exhaust both open and closed
before sending it to Swanson Performance
(Torrance, California) for dyno pulls. After
working out the kinks, we produced two
identical, back-to-back pulls with the cutouts
closed and then three with them fully
open. Each run was made from around
3,400 rpm until just shy of 6,000 rpm,
where power began to drop off. No tuning
or adjustments were made to the car.
RESULTS
The baseline numbers were 291 rwhp and
309 lb-ft. After opening the cutouts, we
saw 297 peak rwhp and 318 lb-ft. The peak
power came in 200 rpm lower than when
the cutouts were closed. The performance
gain is not enough to notice in the seat of
the pants.
On the street, the cutouts delivered big
grins. Our kit came with a wireless key fob
that never left our hands while driving.
When fully open, the exhaust occasionally
popped and sounded too loud, but when
we opened the cutouts just 3/4 of the way,
they sounded great. The Crane Cam is tiny,
but with the cutouts open it sounded like a
monster.
CONCLUSIONS
For a street/strip car, the cutouts were great.
Sound when you wanted it, a quiet cabin
when you didn't. The electronic butterflies
are expensive but give you the ability to
open them a certain amount to tune the
sound, and you won't ruin your jeans climbing
under the car to unscrew them.
Perhaps the power gain from the cutouts
would be bigger with a more restrictive
exhaust system, or on a newer car with catalytic
converters.
As for the QTP kit itself, the electric motors do not automatically stop, which
allows for opening only partially to tune,
but if you run the electric motor past fully
open or fully closed (which is easy to do),
you can hurt the life of the QTP motor. The
remote trigger was a little finicky and didn't
always work, but the kit comes with a standard
toggle switch, and we couldn't really
find a reason to stand away from the car
and open them anyway.
Our tech center manager, Grant Peterson,
helped us install the cutouts, and the job
only took an afternoon to finish. It can be
done without a lift, but it’s nice to have one
for jobs like this.
BOTTOM LINE
For pure performance, you're better off
spending your money somewhere else,
but for a street-driven car, these cutouts
help you go from timid to aggressive at
the flip of a switch.
