"Which
turbo?" That's the question we get right, the first time, every working
day as we consult with performance enthusiasts and racers. Here's the short
answer.
The
selection of the best turbocharger for the job boils down to three questions.
Give
us realistic, accurate answers to the above and we'll put you where you want to
be. We'll ensure the best results, save you time and money if you think through
certain decisions and criteria. In other words, to build a faster car you need a
plan. First you must decide on the intended use of the car: mainly street
driving or racing only?
A
race car is highly specialized. The goal is the ultimate horsepower within a
narrow RPM range. But the trade-off is lousy power at low engine speeds. A
street car, on the other hand, needs low-end response. If you're honest, you'll
see that a street car can spend 90% to 95% of its time at 4000 rpm or less. This
means a well-designed "driver" must pull strongly from idle.
What's
very often missed by beginners who wake up and declare, "I'm going to build
a fast car!" is that a properly engineered 300 hp street car will
outperform a 600-hp race car on public streets and highways under normal driving
conditions.
Other
issues that need to be addressed include:
Just
remember that our specialty is providing the air. Fuel, ignition, exhaust,
cooling, electronic engine control mapping, etc. are the responsibilities of the
vehicle builder. What you get when you select a Turbonetics turbocharger and
accessories is our knowledge and expertise in providing more airflow to the
engine. In the vast majority of cases, we know what works for any given
application. Our tech and sales department have highly specialized computer
programs and flow maps to aid in the selection of your turbocharger. We don't
buy into the one-size-fits-all mindset. That's why we don't have any completed
turbochargers on shelves. Virtually every unit we sell is customized and
blueprinted for your specific vehicle and application.
Note: This section is intended to
provide general turbocharger sizing information, not solutions to specific
turbocharger- engine-vehicle combinations. Typically, an optimized turbocharger
match is the result of combined engine dynamometer testing and installed vehicle
performance evaluation. Often compromises must be made to arrive at a match
yielding satisfactory response, power, and fuel economy in a retrofit or special
application. Estimated engine air flow requirements at varying RPM are plotted
in Figure 1 for typical 5 psi and 10 psi boost levels, and in figure 2 for 10
psi and 15 psi (Intercooled, typical modern 4 valve/cyl. engine, or race
ported 2 valve engine.) To determine air flow for a given size engine at
maximum engine speed, read upward in Figure 1 or figure 2, to the appropriate
boost and speed line. Engine air flow requirement is read directly by projecting
the boost-speed point horizontally to the left.
Engine air flow requirements can be used directly in
establishing an operating line on an appropriate compressor map. Refer to pages
18 - 23. Compressor pressure ratios corresponding to boost levels of 5 psi and
10 psi are 1.34 and 1.68, (1.68 and 2.02 in figure 2) respectively. Select a
compressor such that the engine torque peak operating point is near to the
compressor peak efficiency island as possible while maintaining the engine rated
speed point in the compressor 60% or higher efficiency region. In the case of
larger displacement engines with high RPM capability, it will usually be
necessary to use two turbochargers to provide adequate air for the desired
airflow / boost conditions. To determine operating points on a compressor map
for a twin turbocharger arrangement, divide the total air flow found in Figure 2
in half, and select a map that will satisfy those conditions.
Do not attempt to establish an operating point in an area
on a compressor map to the left of the surge line. This is an area characterized
by unstable operation and violent flow reversal, potentially resulting in
turbocharger failure. Turbine selection and a method of boost control for spark
ignited engines must also be considered for a successful turbocharger match.
Most turbochargers described in this catalog are not equipped with a wastegate
or other device to bleed off excess exhaust energy when a desired boost is
attained. Turbonetics, Inc. offers the DELTAGATE Mark II and the RACEGATE
wastegate in several configurations to satisfy most applications.
Turbine selection is a variable based on intended use,
weight, and desired response. Turbine power available to drive the compressor
can be varied in two ways: 1) the Area to Radius (A/R) ratio of the turbine
housing can be changed to alter turbine inlet pressure; and 2) the turbine wheel
trim can be specified to effect an increase or decrease in turbine pressure for
a given turbine housing A/R. (See data sheets for available turbine trim and
housing information.) Initial recommendations for normal single turbocharger
applications (assuming a controlled boost of 10 psi or less) may be selected as
shown in the following table:
ENGINE DISPLACEMENT |
COMPRESSOR TRIM |
TURBINE TRIM |
TURBINE HSG |
60-100 CID |
T3-50 Trim |
T3 Standard |
.36/.48 |
100-150 CID |
T3-Super 60 |
T3 Standard |
.48/.63 |
150-200 CID |
T3-Super 60 |
T3 Standard |
.63/.82 |
200-250 CID |
T4-S3 Trim |
T4 O Trim |
.58/.69 |
250-300 CID |
T4-V1 Trim |
T4 P Trim |
.69/.81 |
300-350 CID |
T4-V1 Trim |
T4 P Trim |
.81/.96 |
350-400 CID |
T4-H3 Trim |
T4 P Trim |
.96/1.30 |
400-450 CID |
T4-H3 Trim |
T4 P Trim |
1.30 |
High
speed engines, heavy vehicle loading, special purpose vehicles, and applications
requiring multiple turbochargers will require turbine configurations based on
specific requirements and may vary considerably from above recommendations.
Contact a Toysport turbo specialist for specific recommendations.
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