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Hyperion Racing
Engine Design Report
Formula Student India
The making of the Engine system of the HRT-01 was split into the following phases:
Selection of the Engine
Designing of the intake and Exhaust systems
Manufacturing of the intake and Exhaust systems
Engine Assembly
Initial Testing
Cooling System Design
Powertronic ECU tuning
Final Testing
Technical Specifications
Royal Enfield 500
KTM Duke 390
Engine Displacement (cc)
499 cc
373.2 cc
Engine Type
4 stroke
4 stroke
Number of cylinders
Gross weight
62 kg
90 kg
Max Power
27.2 bhp @ 5250
43.5 bhp @ 9000 RPM
Max Torque
41.3 Nm @ 4000
35 Nm @ 7250 RPM
Fuel type
Compression Ratio
8.5 : 1
12.9 : 1
Engine Cooling System
Air cooling system
Liquid cooling system, continuous
circulation of cooling liquid with water
85,000 INR
1,90,000 INR
Engine Selection
Two Engines were taken into consideration, Royal Enfield 500 EFI and KTM Duke 390.
Being a first year team we opted Single Cylinder Engine for simple package of the
Reasons for choosing the Royal Enfield 500 EFI
1. Lighter in weight compared to oil and water cooled engines
2. Single Cylinder Air cooled engines, for a first year team, less complicated
compared to multi cylinder water/oil cooled engines.
3. More torque available in the lower RPM range.
4. Service centers and spare parts abundantly available.
5. Experienced engine tuners, which was the main reason in going for engine
Engine Specification Sheet
Ignition System
Digital Electronic Ignition
Wet, multi-plate
5 Speed Constant Mesh
Wet sump
Engine Oil
15 W 50 API, SL Grade JASO MA
Engine oil currently used
Motul 3000 4T Plus 15W50 with API SM,
Engine oil capacity
2.5 litres
Fuel Supply
Keihin Electronic Fuel Injection
Engine Start
Engine modification process
The engine cylinder diameter was increased from 84mm to 90mm, thus increasing
the engine cubic capacity from 500cc to 572.6cc. The cylinder head was also ground to
ensure the piston would not strike the head. Hence the combustion chamber volume
comes to roughly 576cc.
Engine components: The new piston used the engine is manufactured by the
company JE pistons, and is used in the Yamaha XT 500 engines.
Piston specifications
0.340 kg
Gudgeon pin diameter
System Goals
1. To design and fabricate an intake and exhaust systems for a modified Royal Enfield
EFI engine, displacement of 576cc.
2. Must be light in weight but should withstand engine vibrations.
3. Using the 20mm restrictor as a venturi and to increase air flow to the engine.
4. Manufacture the intake system under 185 Euros (INR 15,000).
5. Obtain peak torque at 2000 RPM for acceleration.
Software tools used:
Solid Works Student Edition 2014, Ansys 14, Ricardo Wave, Lotus Engine Simulation.
Selection of intake components:
Selection of air filter
The air filters considered were K&N, cosworth and Piper cross due to availability of
models and the air filter chosen is the Piper Cross PK-186 model.
Filter area
78mm diameter x95mm length.
Filter material volume
π x (78-75)2 x 95mm = 2686.06 mm3
Selection of throttle body
The throttle body used is the stock Royal Enfield 500 EFI throttle body, manufactured by
Keihin, Japan. Butterfly valve with cable actuation. Butterfly valve diameter 32mm.
Throttle body length 75mm.
Throttle body options:
The other option considered for the throttle body was that of the Hyundai Santro. Cable
actuated with double return spring. The butterfly valve diameter is 42mm. However, it
was not chosen because
1. It had considerably higher weight.
2. The stock wiring harness, ECU and sensor system of the Enfield 500 EFI was being
3. All necessary sensors for the intake system are available at the required location on
the stock throttle body.
Royal Enfield 500 EFI throttle body specifications
Inlet diameter
Butterfly Valve diameter
Total length
Throttle Position Sensor, Manifold Air Pressure Sensor
Sleeving the throttle body
To match the diameter of the air filter and throttle body, a sleeve has been attached on
the throttle body of ID 48mm and OD 50mm.
The operation was carried out as air filters with an inner diameter of 48 mm was not
Design of Restrictor
1. Subsonic flow through restrictor.
2. Minimum back pressure through the restrictor.
3. The design calculations and flow simulation were done to achieve maximum mass flow
into the combustion chamber for the working RPM range of 4500-5500.
Analysis tools:
Done on Fluent software.
Design specifications:
The restrictor profile was decided keeping in mind ease of manufacturing. Straight profile
was chosen. Parabolic profile is difficult to manufacture and requires more precision in
Since the intake design was completely changed, a parabolic profile was difficult to
refine. Also Fused Deposition Modelling does not provide a good surface finish. Hence
the straight profile was chosen.
Selection of Nozzle and Diffuser diameters
1. Nozzle diameter: Same as the diameter of the throttle body, 33mm.
2. Diffuser diameter: Iterations were carried out on Fluent to decide the diffuser diameter
to achieve minimum pressure drop across the restrictor geometry.
3. Nozzle and diffuser taper angles: The taper angles were iterated to achieve the best
combination of least pressure drop, subsonic flow and less turbulence.
Boundary Conditions
1. For choking condition at the restrictor, the Mach number will be 1. Hence, the mass
flow rate under a choked flow condition would be defined by the following formula:
Here, C = 0.62(assumed), A = 314.159mm2 (for d = 20mm), K = 1.4 (for air), ρ = 1.8768
kg/m3, P = 1.89 bar
The mass flow rate is calculated to be 0.065 kg/s.
2. Calculation for maximum mass flow through the engine
Using the equation m = density * cross sectional area of runner* velocity of air
m = 1.2* 0.001089 * 340 = 0.35 kg/s
3. To find a suitable length of the nozzle and diameter of the diffuser end, iterations were
carried out on Fluent for steady state conditions. The objective was to achieve minimum
turbulence and overall pressure loss.
Steady state analysis using Fluent
Steady state analysis was carried out to gauge the effects of change of geometry on
velocity, pressure and turbulence.
Dimensions: Total length, 183mm
Nozzle diameter: 33mm
Nozzle taper angle: 8.2 degrees
Restrictor diameter: 20mm
Diffuser diameter: 27mm
Diffuser taper angle: 1.8 degrees
Analysis Results
Pressure at inlet:
1.06 bar
Pressure at outlet:
1.01 bar
Inferences: Steady state iterations do not give accurate results. It is not possible to
obtain proper velocity and pressure results. Hence the existing geometry was subjected
to transient simulations using CFX to obtain realistic results.
Calculation of runner length
Selection of Length for the Intake Runners
The calculation for the length of the tuned intake runners is based upon the duration
between two events of the intake valve’s operation: the first being the closing of the
intake valve, and the second being the re-opening of the intake valve on the next cycle.
Therefore, considering the RPM and how an increasing RPM will suggest a reducing
time period for the wave to reflect, a range of values is calculated for the lengths of
runners required to achieve the effect of reflecting the higher-pressure air onto the intake
valves as they open.
The track is geared towards the low end powerful and nimble race car as can be
depicted from the track description. With average speeds in the endurance race between
48 km/hr to 57 km/hr and top speeds of approximately 105 km/hr the engine spends
most of its time in the lower region of its power band. As a result an RPM level of 4500
was chosen as the most suitable for intake tuning. The main design calculations were in
relation to plenum volume, runner length and runner diameter.
Governing Equation
Considering the following notations:
Effective Cam Duration
Optimal Intake Runner Length
Reflective Value= 8th, 10th, 12th
Runner Diameter (in Inches) = 1.299in = 33mm
Pressure Wave Speed (1100-1300 for hot air intake) = 1100 ft/s (Assumed)
Cubic Inch Displacement of Engine
35.1496 in 3
Volumetric Efficiency
80% (Assumed)
Velocity (Mean piston speed) =51.673ft/s
The following formulae are used to calculate required runner length and diameter:
Here we have used the measured intake valve opening duration which is 30+180+60 =
270 degrees
The runner diameter selected was based on the constraint that the intake runner
diameter of the Enfield engine is 33mm. Hence the diameter obtained from the
above formula has not been considered.
Calculating length for the 10th reflective
Similarly for the 8th reflective value the runner length is obtained to be 7.448in
= 189.1mm and
For the 12th reflective value it is 4.756in = 120.8mm
Selection of runner length
Due to availability of space, the 8 th reflective was chosen, with the runner length of
Selection of Volume and Shape of the Plenum
The main principle is to choose the right volume of the manifold as well as the resonator
resonating at an engine speed at where the boost of the torque is desired; it is also
necessary to experiment with the tuned pipe length to reach the optimum results. Hence
various shapes were experimented with keeping in mind choked flow, turbulence and
mass flow rate at the runner exit.
The volume of the plenum was calculated based on the thumb rule of it being 1.5 times
the cylinder volume. Taking into consideration manufacturing inaccuracies, the plenum
volume was taken as 1.6 times the cylinder volume. Accordingly the plenum volume is
576cc x 1.6 = 922 cc
The shape of the plenum was chosen after much iterations on Ansys Workbench.
Various shapes were rejected due to insufficient mass flow rate, excess eddy generation,
and energy loss. Two primary shapes were considered. One being the usual onion
shaped air box commonly seen in FSAE events. The other one was a trial on a tapered
air box so as to check for higher pressure generation.
All flow analysis was done using Ansys Workbench 14.5
Analysis of plenum
The earlier designs that were chosen for the plenum was the conventional onion shape.
However these were rejected due to:
1. Not meeting the requirements of the surface envelope.
2. Insufficient mass flow through the plenum.
3. Improper restrictor design.
Iterations of onion shaped plenum
Iteration 1
Restrictor dimensions:
Nozzle diameter
Nozzle taper angle 16 degrees
Diffuser diameter
Diffuser taper angle 2.4 degrees
Total length
Plenum volume
Runner diameter
Iteration 2
Restrictor dimensions:
Throttle diameter
Nozzle taper angle
16 degrees
Diffuser diameter
Diffuser taper angle 2.4 degrees
Total length
Plenum volume
Runner diameter
Runner length
Inferences: The onion shape design failed because
1. The plenum did not hold in enough air.
2. The restrictor geometry caused choked flow and generated supersonic velocities
which was highly undesirable.
Due to availability of space between the engine and the roll hoop bracing, and also due
to obstruction from the head restraint it was decided to completely redesign the plenum
as a side intake profile.
Iterations of tapered cylinder plenum
Iteration 1: Inwards taper
Restrictor and plenum dimensions:
Nozzle diameter
Nozzle taper angle
8.7 degrees
Diffuser diameter
Diffuser taper angle 1.85 degrees
Total length
Plenum volume
Runner diameter
Runner length
Peak velocity at restrictor: 367.7 m/s
Peak pressure at plenum entry: 1.309 bar
Peak pressure at plenum exit: 0.8114 bar
1. Incorrect orientation of restrictor with respect to runner preventing reduction of velocity
in plenum. Causing turbulence and less flow into runner
2. Due to the orientation of the restrictor, the pressure generated at the plenum entrance
is high.
3. Also due to the inwards taper of the plenum, the pressure gradient inside the plenum is
uneven, hence air keeps swirling inside the plenum. This leads to loss of energy and
mass flow rate in the runner was greatly reduced.
Iteration 2: Outward tapered cylinder
To eliminate the above issues, the taper angle was inverted so that the taper increased
towards the runner.
Restrictor and plenum dimensions:
Nozzle diameter
Nozzle taper angle
8.2 degrees
Diffuser diameter
Diffuser taper angle 1.8 degrees
Total length
Plenum volume
Runner diameter
Peak velocity at restrictor: 432.7 m/s
Peak pressure at plenum entry: 1.172 bar
Peak pressure at plenum exit: 0.75 bar
1. Pressure gradient and air flow inside the plenum has improved.
2. Mass flow into the runner has increased to 0.142 kg/s
3. Pressure at plenum exit reduced.
1. The above design is much easier to manufacture compared to the Onion shaped
plenum design.
2. Reduced restrictor length means reduced bending stresses on the intake flanges.
Hence chances of failure are reduced.
Hence the above design was chosen for manufacturing.
The final design is as follows:
Manufacturing process options
Material selection:
Molding or casting
Hand molding using
glass fiber resins
Rapid prototyping, using
Fused Deposition
Owing to the complete redesign of the intake system layout, and the expense of creating
a mould, Rapid Prototyping method was chosen for manufacturing the intake system.
Rapid Prototyping specifications:
Rapid prototyping process
Fused Deposition Modelling
Material thickness
Modelling material used:
ABS plastic
Support material used:
ABS plastic
Machining time:
22 hrs
Manufacturing cost:
185 Euros (15000 INR)
Coating applied:
Yes, on outer surface, to eliminate porosity
Adhesive used:
Fevikwik 203 and Araldite for sealing flanges
Exhaust System
The exhaust system is built around rules and regulations formulated by FSAE
organisation and quoted in FSAE rulebook which are as follows:
1. The exhaust must be routed so that the driver is not subjected to fumes at any speed
considering the draft of the car.
2. The exhaust outlet(s) must not extend more than 45 cm (17.7 inches) behind the
centreline of the rear axle, and shall be no more than 60 cm (23.6 inches) above the
3. Any exhaust components (headers, mufflers, etc.) that protrude from the side of the
body in front of the main roll hoop must be shielded to prevent contact by persons
approaching the car or a driver exiting the car.
4. The maximum permitted sound level is 110 dBA, fast weighting.
1. Exhaust runner length
Exhaust runner length is determined by maximum scavenging that can be attained at an
rpm. Since our engine of Royal Enfield Motorcycles has rpm range up to 5500. Thus the
exhaust runner is designed at 4000 rpm.
The crank angle for which the exhaust valve remains closed is 430°. Thus it takes time
for which the exhaust valve remains closed is 0.0179s. Temperature of exhaust gas as
per Lotus simulation is 600 degree celsius. Speed of sound at that temperature is
calculated as 590m/s. Hence runner length is L given by:
L = (speed of sound × time for which exhaust valve remain closed) ÷ ( 2 × number of
L= (590×0.0179) ÷ (2×5)
L= 1.05 metres
Thus the exhaust runner length is 105mm. Thus the noise pressure waves are reflected
5 times from the runner back to the valves. For longer stroke single cylinder engine,
considerable scavenging can be obtained by 5 reflections at 4000rpm.
2. Muffler Design
The Muffler Was designed following ASHRAE Technical Committee Rule 2.6 for Heat and
Sound vibrations.
Step-1: Unsilenced noise level (UNL)
Modelling on Lotus was done to obtain unsilenced noise at the exhaust outlet as
shown in the figure given below
As per the above simulation in Lotus Engine simulation software, the unsilenced noise
level obtained is 120dB.
By actual running of engine without the muffler the exhaust noise was found to be
Step-2: Calculate exhaust noise criteria
ENC=RNC – 10 (dB) where,
ENC = Exhaust Noise Criteria
RNC = Required Noise Criteria = 110 dB as per rule no. IC3.3
ENC = 110 − 10 = 100 dB
Step-3: Calculate Insertion Loss (IL)
IL = UNL – ENC + 5
IL = 120 − 100 + 5 = 25 dB
25dB noise attenuation is required for muffler design.
Step-4: Cylinder Firing Rate (CFR)
CFR = RPM / 120 for a 4-stroke Engine at 5500rpm
CFR= 45.83
Step-5: Engine Firing Rate (EFR)
EFR = n × CFR where, n = no. of cylinders.
EFR = 1 × 45.83 = 45.83
Step-6: Chamber Length Selection using ASHRAE Technical Committee Rule No. 2.6
Since insertion loss was 25dB, Residential grade of mufflers was chosen
Residential Grade:
IL = 20 to 30 dB
Body/Pipe = 2 to 2.5
Length/Pipe = 6 to 10
Silencer inlet pipe diameter (d) = 38mm
∴ Silencer Length (L) = (6 × 38) ≤L ≤ 10 × 38
= 228mm ≤ L ≤ 380mm
∴ Body Diameter(S) = 2 × 38 ≤ � ≤ 2.5 × 38
= 76mm ≤ � ≤ 95mm
Thus higher values are taken, so L = 380mm and S = 95mm
To allow for manufacturing and welding errors, etc body diameter is increased by 5mm
and length to 10mm.
Step-7: Selection of insulation material
Glass wool of density 130kg/m was selected having maximum service temperature of
750° C.
3. Design of Perforated pipe
For perforation, 60°staggered type is selected to obtain higher noise
Transparency Index (TI):
It is given by the following equation
TI= (n×d)/ (t×a2) where,
n = number of perforations per sq in;
d = perforation diameter (in);
t = sheet thickness (in);
a = shortest distance between holes (in);
a = b - d, where b = on-centre hole spacing (in);
For attenuation of frequencies less than 2000Hz, TI should be less than 6000
Thus taking standard values as hole diameter (d) = 3.5mm, b = 10mm TI was obtained
1.12, which is much lesser than 6000.
Assembly of the exhaust Muffler:
Intake, Exhaust Modelling in Ricardo Wave:
Noise Test results on Ricardo Wave
Inclination on Intake Valve Flow Characteristics of a Single Cylinder Engine using
ParticleImage Velocimetry”, World Academy of Science, Engineering and Technology 68
2. Ceviz M.A and Akın M., “Design of a new SI engine intake manifold with variable
length of plenum” ELSEVIER JOURNAL, (2009).
3. Design of a single cylinder intake system – Ladislav Adiamek, University of Brno
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