Enlarged SCPI Blower Top & Intercooler Evaluation Report
I recently received my long awaited Enlarged Super Coupe Performance (SCPI) Blower Top and upon
opening the box I became quite convinced this modified top is the ticket.
The enlarged top came with everything needed for a successful installation;
bolts, flange sealer, anti-seize and instructions that include, as one
might expect a splash of Bill's humor. There is nothing humorous about
this blower top however; it's serious business. The only part that is not
included is the Spanner nut wrench which can be purchased from the SCPI
The stock blower top is severely restricted where the air passage transitions
from the square top area to the round section just before the intercooler
collar nut. The reduction is 50% in this area. By comparison the raised
and enlarged blower top from the SCPI maintains nearly full cross sectional
area through this region and is smooth and aerodynamic.
I started the technical evaluation by measuring the pressure drop between
the square section of the blower top and the intercooler tube by tapping
into the castings and measuring the pressure difference with a differential
pressure gauge. The stock blower top measured 2-PSI pressure drop at 6000
RPM! This pressure drop, caused by friction, heats the incoming air causing
it to expand and reducing the available air mass. Also, because the blower
sees a higher pressure it must do more work reducing available horsepower
to the wheels. By comparison the Enlarged Blower Top from SCPI measured
less than a 1 PSI pressure drop, quite an improvement.
Part two of the evaluation was an acceleration test. The improvement
is quite remarkable. My SC with the stock exhaust and stock blower top
accelerated from 20 MPH to 55 MPH in 4.17 seconds. With the 3 1/2 inch
exhaust this time was reduce to 3.80 seconds, a .37 second improvement.
The Enlarged Blower Top from SCPI reduced this time to 3.57 seconds a
.23 second improvement! This kind of power improvement is not easy to come
by in most applications, but lucky for us this part is available from SCPI.
The enlarged blower top from the SCPI is a real power builder and a necessary
addition to any performance minded SC owner.
SC Intercooler Evaluation Report:
The Thunderbird SC sports two power making devices, a Supercharger and
an Intercooler. The idea of the supercharger is to force more air into
the engine than a normally aspirated engine could, thereby allowing more
fuel to be burnt and producing more power. The disadvantage is that air
gets hot when compressed. As hot gasses expand there are fewer air molecules
per cubic inch resulting in less air to burn fuel, hence less power produced.
This is where the intercooler comes in. The intercooler cools the supercharger's
hot gasses causing the air to become denser, burning more fuel and producing
Over the last few months I measured the air temperatures and pressures
between the supercharger and the intake manifold, this article reports
The supercharger and intercooler from Ford work quite well, but as one
might expect there is room for improvement. At a normal 60 MPH to 80 MPH
cruise the air exiting the supercharger is 160' F to 170' F when the ambient
temperature is in the mid 50's. Under full throttle I measured a maximum
temperature of 404' F at 6000 RPM! These temperatures were much higher
than expected and demonstrates the need for an intercooler. Power increases
1 % for every 1 degree F of air temperature reduction. In this case an
intercooler capable of reducing air temperature from 404' to 55' would
improve power by roughly 35%. This represents the maximum benefit one could
expect from an intercooler when running 15-PSI boost.
How good is the stock SC intercooler? See the chart below. Note; exit
air temperature measured while accelerating under full throttle.
Ambient cooling air velocity measured at various vehicle speeds is displayed
in the chart below. Note air speeds were too slow to measure, with my equipment,
when vehicle speeds were below 50 MPH.
What I learned by making these measurements. First, the intake system
including the intercooler, supercharger and intercooler tubes are heated
by the engine and are quite warm even when the engine is under Very light
loads. Between 60 MPH and 80 MPH the intercooler's exit air temperature
hovers around 100' F, even with light throttle. Around town and in stop-and-go
traffic this temperature creeps up to 112' or so with the ambient temperature
at 55'. Under full throttle this temperature is much higher. Referring
to the first chart you can see that the exit air temperature rises only
slightly as the car accelerates from 0 MPH to 50 MPH. From 50 MPH to around
80 MPH the intercooler's exit air temperature begins to rise as the intercooler's
mass continues to absorb heat. From 80 MPH and up the intercooler's exit
air temperature begins to stabilize since the vehicle speed is high enough
to force significant quantities of cooling air through the intercooler,
extracting heat from the air charge. Note that at 100 MPH there is three
times as much as air moving through the intercooler as at 60 MPH.
Next I installed the intercooler fan from the SCPI and saw a significant
improvement. With the fan running and the car parked the ambient air moving
through the intercooler has a velocity of 4.5 MPH. Although this is not
very high it is enough to make meaningful improvements. I noticed a reduction
in all temperatures throughout the system. At a 60 MPH to 80-MPH cruise
the intercooler's exit air temperature was only 67' compared to 100' without
a fan. Around town the exit air temperature with a fan rose to only 75'
compared to 112' without a fan. Also observed was a reduction of supercharger air.
Temperature from around 175 degree to 123 degree at cruise speeds. This
might seem a little odd at first but is explained by the fact the SC has
a supercharger bypass which under no boost conditions circulates air from
the intercooler back to the supercharger's intake. This cool-air cools
the supercharger and tubing.
Below is a chart showing the improvement using an intercooler fan under
full throttle acceleration.
On the average this is an improvement of about 30' that translates to
about a 3% improvement in power or about 10 HP, not bad for a $90 part.
Finally, I measured the pressure drop across the intercooler and again
found room for improvement. At full throttle and 6000 RPM I measured 3.5-PSI
drop across the intercooler, not good! The reason, the SC intercooler is
much too small, at least for high RPM operation. Spearco recommends designing
an intercooler with a pressure drop of 1-PSI or less. What this means is
the supercharger is working much harder than if the SC had a larger intercooler.
If you read 12-PSI boost on your boost gage the supercharger is really
pumping out something like 15.5-PSI ! This requires extra HP to drive the
supercharger and is part of the reason I measured temperatures from the
supercharger as high as 404 degrees. According to the numbers there is
something around 50 HP improvement possible by going to a much more efficient
and larger intercooler. I plan to design a high flow intercooler system
for my SC using a large Spearco (SCPI) intercooler. Those of you out there
who are handy and have the need for speed can do the same. Have fun!
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