04/23/2009Reviewer: Professor KT Rhee | Author: Simon Tang

Internal Combustion Engines

Engine Simulation Project

The purpose of this project is to utilize engine simulation software to produce simulated horsepower and torque data for a given engine. By changing the engine properties and parts within the simulation software, the user is able to manipulate the power that he/she desires without having to physically work on an engine. This software can be very useful to any automotive or motorcycle hobbyist, both amateur and professional racers and industries, companies that study and test engine designs and perform engine analysis, students, and anyone with a general interest in engines.

Table of Contents Page

Introduction 1

Objective 1

Theory 1-3

Apparatus & Instrumentation 3

Procedure 3

Results & Discussion 3-6

Conclusion 6-7

References 8

Sample Calculations & Derivations

9

Appendices 10-20

Introduction

The engine that will be used for simulation is the Nissan VQ35DE that powers the 2003 Nissan 350Z (Z33). The stock engine produces 287 hp at 6200 rpm and 274 lb-ft of torque at 4200 rpm. This automobile has been very successful in many different professional racing series such as FIA GT4 and Japan’s Super GT. Due to its rear wheel drive layout and high torque at low rpm it is also an extremely popular vehicle that is used in an automobile sport called Drifting. This car and engine is very tunable and is capable of producing 760 hp and 713 lb-ft of torque to the wheels when stroked and bored to 4.2L equipped with a twin turbo for daily street driving.

Objective

The goal is to gain the most

horsepower per cost ratio (HP$

¿. This

engine will go through three different setups of tuning: Naturally Aspirated, Turbocharged, and Supercharged with real world parts. This simulation is performed as a parts test for my own personal automobile that will be classified and insured as a collector’s vehicle which, by law, does not have to pass emission tests and cannot be driven over 3,000 miles a year. This vehicle will also be used for autocross, track, and time attack racing so it must be easily repairable and be able to withstand high stresses for long periods of time while at the same time producing lots of horsepower.

Theory

In order to make horsepower in a spark-ignition-engine, which the VQ35DE is, the main goal is to be able to fit more fuel and air mixture into the cylinders of the

engine. This is also known as increasing volumetric efficiency. The more the fuel and air mixture can fit into an engine’s cylinder the more powerful the combustion is creating more horsepower and torque. This can be achieved through many different methods.

Engine Block Bore:By increasing the engine bore you are increasing the size of the cylinders of the engine block. By doing this more air and fuel is able to fit in the cylinders which results in more horsepower.

Engine Cylinder Head Valve Diameter:By increasing the diameter of the intake valve you are allowing more air and fuel to be introduced into the cylinders which results in more horsepower. However, the more air and fuel mixture that is combusted means that more exhaust gases are formed. In order to get rid of this larger amount of exhaust gases a larger exhaust valve diameter is needed. If only the intake diameter is increased, the left over exhaust gases will mix with the fresh mixture of air and fuel that was introduced by the larger intake diameter and will actually result in a less gain of horsepower. So when tuning the engine cylinder head it is best to increase both the intake and exhaust valves at the same time by the same amount so that the more fuel and air introduced for combustion can also be fully expelled by the exhaust.

Camshafts:By changing the camshafts that have higher lift for the intake and exhaust valves you are allowing more volumes of air and fuel mixture into your cylinders as well as expelling larger volumes of exhaust gases. By installing camshafts with longer duration time for the intake and exhaust valves you are increasing the amount of time for the air

and fuel mixture to enter the cylinder as well as leave.

Air Intake:By adding an air intake, the engine will be able to allow more air into the cylinders. There are also different types of air intakes such as short ram air intakes, which are close to the intake manifold, and cold air intakes, which usually extrudes toward the bottom of the engine bay because cold air is denser than hot air. The colder the air that is introduced to the fuel and air mixer the denser it is allowing more of the mixture to fit in the cylinders.

Exhaust:Having a larger exhaust will allow for more of the combusted gases to be expelled so that more fresh mixture can be introduced to the engine cylinders.

High Compression Ratio:By increasing the compression ratio the fuel and air is better mixed and the pressure increases, which also increases the temperature allowing for more power to be extracted by the combustion. High compression can be achieved through different methods; an example would be changing the piston shape and geometry. High compression ratios are used for those who wish to gain naturally aspirated power. When using high compression ratios the octane rating must be higher in order to eliminate pre-detonation determined by the fuel that is used.

Engine Block Stroke:This idea is the same as the higher compression ratio; by increasing the rod length the stroke is increased.

Forced Induction Turbo:A turbo is essentially a compressor that is powered by a turbine that is driven by the

exhaust gases of the engine. This forces more air into the engine cylinders and can be controlled by the user through a computer or boost controller. The problem with a turbo is that it takes time for the compressor to work, so the power will come in at midrange to high end rpm. Today’s technology has decreased the amount of time so much that it almost unnoticeable. A turbo must be used with a low compression ratio setup or else the engine could fail due to extremely high stress from the great amount of the air and fuel mixture as well as pre-detonation determined by the type of fuel being used. Since the car will be using regular pump gas, by having a large amount of the mixture being greatly compressed the temperature and pressure increase and can lead to pre-detonation which will damage the engine internals.

Forced Induction Supercharger:A supercharger is theoretically the same as a turbocharger. However, instead of having a turbine being driven by the exhaust gases, the compressor is driven by the engine’s drive belt. This acts as a catch-22 in which it needs power to make power, while the turbocharger makes power by using the waste that is produced by the engine. However, the advantage of a supercharger is that there is no turbine that needs to charge up to make the compressor work, instead the engine experiences an instant power increase.

ECU Tuning:By tuning the engine’s computer, the user is able to change the fuel and air ratio. The richer the fuel is the more the air is utilized creating more power. However, in DynoSim, the fuel and air ratio is kept the same and cannot be manipulated, but for real world application this must be tuned in order to gain the maximum performance from an engine.

There are many other ways of gaining horsepower that don’t necessary deal with tuning the engine, such as decreasing the amount of friction that is transferred to the vehicle’s wheels. These will not be simulated; due to the limits of the program the horsepower and torque curves are only to represent the power that is made by the engine and not actual horsepower that is going to the wheels which is most important in the real world. Finally when building a real world engine for racing, the engine should be built fully from the ground up and not to be replaced with parts as one is able to buy them. All the parts should be bought and installed before the engine even runs.

Apparatus & Instrumentation

- PC installed with Windows 95/98/2000/ME/NT/XP/Vista

- ProRacingSim’s DynoSim Software

Procedure

1. Open the DynoSim program.2. Enter the parameters of the stock engine into the program using the vehicle’s service manual or online resources.3. Once the horsepower and torque curves match the data of the stock engine save the engine data.4. After saving the data, change the stock parameters to manipulate the horsepower and torque until the desired values are reached.5. Once this is done save again and repeat this process until the user has collected all data that he/she needs.

Results & Discussion

Stock Engine:

The first thing to do was to achieve the same horsepower and torque as the stock engine, which is 287 hp @ 6200 rpm and 274 lb-ft of torque. The engine specifications were taken from a 2003 Nissan 350Z service manual [1] and were inputted as 6 cylinders, 95.5 mm bore, 81.40 mm stroke, 1.770 rod ratio, 37.00 mm intake valve diameter, 31.00 mm exhaust valve diameter, 10.3:1 compression ratio, 9.52 mm intake lift, 9.52 mm exhaust lift, and the valve timing is entered with the data that was given in figure A1 in the appendix, which resulted in the data given by figure A2. After entering all of this data into the program, the Air Flow data must be manipulated as well to match the horsepower ratings. The exact air flow is not given anywhere and may be kept confidential for companies only, but can be mocked up with time and patience. After manipulating the air flow data the results were almost an exact match to the stock engine. A rating of 287 hp was achieved at 6500 rpm and a torque of 272 lb-ft was achieved from 4500 rpm to 5000 rpm, figure A3 and A4 show the graph and data for the stock engine.

General Tuning:After the stock engine was achieved the next test was to see what should be tuned first. When tuning an engine the owner of the vehicle would like to waste as little money as possible so when buying new parts, these parts are meant to stay in the engine and not to be changed. In this case, general tuning that will work for the naturally aspirated, turbocharged, or supercharged engine should be considered first. The first thing to work on should be boring the cylinder heads to increase the valve diameter for the intake and exhaust. This usually costs about $500.00 when the owner of the car disassembled the entire engine and ships it to a company with the proper equipment that does cylinder head work. After the valve

diameter has been bored the valve seats need to be replaced, which costs about $300.00 for custom machined valve seats. Finally the actual intake and exhaust valves need to be installed as well. The ones that will be bought will be the Brian Crower Stainless Steel Valves [2] with a diameter of 38 mm for the intake and 32 mm for the exhaust. This is a 1 mm increase in diameter from the stock valves and will cost about $600.00. The data is shown in figure B1 which shows a power gain of 6 hp. After boring the cylinder head the next step would be to increase the lift and lift time for both the exhaust and intake valves. To do this a camshaft with higher profiles will be needed. For this we will try three different camshafts to see the difference in performance. The first one will be a Brian Crower High Performance/Race Camshaft [2], which is about $1,100.00, has an intake and exhaust lift of 10.82 mm, and has an intake and exhaust lift duration of 264°. The data by this camshaft is shown in figure B2 which shows a power gain of 52 hp. The next will be a Brian Crower Race Camshaft [2], which is also about $1,100.00, has an intake and exhaust lift of 11.66 mm and an intake and exhaust lift duration of 272°. Even though this is the same price as the Performance/Race Camshaft it actually needs an additional Brian Crower Spring Kit [2], which is about $500.00 due to the faster speeds. The data by this camshaft is shown in figure B3 which shows a power gain of 59 hp. The final camshaft will be a Cosworth ZK2 VQ35 Camshaft [3], which is about $1,400.00, has an intake and exhaust lift of 10.65 mm, and an intake and exhaust lift duration of 270°. This also requires a Spring Kit, but from Cosworth which costs around $500.00 as well. The data by this camshaft is shown in figure B4, which shows a power gain of 55 hp. The powers of all three camshafts are compared in figure B5 which shows that the Brian

Crower Racing Camshafts [2] produces the highest performance gains. This camshaft costs less than the Cosworth ZK2 VQ35 Camshaft [3], but will be more expensive than the Brian Crower High Performance/Race Camshaft [2] because it requires the Brian Crower Spring Kit [2]. The performances of all three camshafts are closely related. If the buyer did not care for maximum performance, the best choice would be to get the Brian Crower High Performance/Race Camshaft [2]; it is a lot of power for the cheapest price. However, for maximum potential and power the best would be to get the Brian Crower Race Camshaft [2], which gives you a tiny bit more power than the Cosworth ZK2 VQ35 Camshaft [3] and will is also cheaper. One should also consider when building up a complete engine to buy stronger engine components such as the Cosworth Cylinder Head Studs [3] as well as the Cosworth High Performance Head Gasket [3]. The cost of the general tuning will be:

Part PriceCustom Valve Seats $300.00 Cylinder Head Bore $500.00 Brian Crower Valve Stems $600.00 Brian Crower Spring Kit $500.00 Brian Crower Race Cams $1,100.00 Cosworth Head Gasket $250.00 Cosworth Head Stud Set $500.00 Total $3,750.00

Naturally Aspirated Tuning:After the General Tuning has been performed the next step is to figure out what engine setup would fit best for best power gains. For naturally aspirated engines, the goal is to have as much cold air and fuel mixture in the cylinders as possible while the mixture gets compressed without reaching pre-detonation. First we can install a generic air intake; the price is usually

around $400.00 and the data is shown in figure C1 which shows a 2 hp gain. Next is to be able to exhaust all of the combusted gases by installing a generic open exhaust, which is usually around $1200.00 and the data is shown in figure C2 which shows a 53 hp gain. Next would be adding a higher compression ratio. The Cosworth 11:1 High Compression Piston Kit [3] with a 96 mm engine bore that costs about $1,500 is tested and the data is shown in figure C3 which shows a power gain of 156 hp. The Brian Crower 11:1 High Compression 4.1 L Stroker Kit [2] with a 100 mm bore, 86.4 mm stroke, and about $5,000 is also tested and the data is shown in figure C4 which shows a power gain of 168 hp. Also the block must be shipped out to a company that is capable of boring engine blocks. This usually costs about $500.00. The comparison for both the Brian Crower 11.1 High Compression 4.1 L Stroker kit [2] and Cosworth 11:1 High Compression Piston Kit [3] with the added intake, exhaust, and general tuning are shown in figure C5. In figure C5 we see that there is immense power gain by doing these modifications. The Brian Crower 11.1 High Compression 4.1 L Stroker kit [2] wins by just 12hp at 455 hp @ 7500 rpm. However, the cost is a lot greater. The cost for the Cosworth 11:1 High Compression Piston Kit [3] plus the other parts as:

Generic Air Intake $300.00

Generic Exhaust$1,200.0

0 Engine Block Bore $500.00

Cosworth Forged Piston Kit$1,500.0

0

Total$3,500.0

0

Brian Crower 11.1 High Compression 4.1 L Stroker kit [2]

Generic Air Intake $300.00 Generic Exhaust $1,200.00 Engine Block Bore $500.00 Brian Crower 4.1L Stroker Kit $5,000.00  Total $7,000.00

The HP$ ratio for the Cosworth setup is

0.126 and for the Brian Crower setup is 0.065, which is almost half of the Cosworth setup. The best way to go for the naturally aspirated setup would be the Cosworth setup. However, when going for maximum performance when money is not an option, then the Brian Crower setup would be the choice.

Forced Induction:The simulation program is unable to compute twin turbo setups, which most turbo kits for the VQ35DE are made to be, so instead the Air Power Systems Single Turbo Kit [4] which is about $7000.00 that uses a Garrett GT3582R Compressor is compared with a Vortech V2 Supercharger Kit [5] which is about $6000.00. Before testing the power of these kits, it is important to see how having low compression ratio on a stock engine can degrade its performance. The Cosworth 8.8:1 Low Compression Piston Kit [3] with a 96 mm engine bore and about $1,500 is tested on a stock engine and the data is shown in figure D1 which shows a power loss of 24 hp. It is very important to build an engine from beginning to end or else you could have various performance drops as like this. Next is testing whether the Vortech V2 Supercharger Kit [5] or the Air Power Systems Single Turbo Kit [4] is better on the stock engine. From the graph in figure D2, the winner is clearly the supercharger, it makes more horsepower and costs less on the stock engine. The Vortech V2 Supercharger Kit [5] gives about 369 hp @ 7500 rpm and 343 lb-ft of torque at 4500

rpm, while the Air Power Systems Single Turbo Kit [4] gives about 355 hp @ 6500 rpm and 336 lb-ft of torque @ 4500 rpm. The max psi level is about 8 psi of boost because the VQ35DE is naturally at a high compression ratio of 10.3 and cannot handle more boost than that or else the engine will fail. The calculations for the boost and flow for turbochargers and superchargers are in the Sample Calculation section. So for someone who wants to just buy bolt on power, the supercharger is the way to go. However, what will happen if there is more volumetric efficiency by testing both the supercharger and the turbo in low compression settings? After the general tuning has been completed, a comparison between the Brian Crower 8.8:1 Low Compression 4.1 L Stroker kit [2] equipped with both the Vortech V2 Supercharger Kit [5] and the Air Power Systems Single Turbo Kit [4] is up against the the Cosworth 8.8:1 Low Compression Piston Kit [3] also equipped with both types of forced induction kits is performed. The comparison is shown in figure D3 and is clear that the turbocharger has a lot more potential than the supercharger when building the engine fully. The turbocharged engine with either the stroker kit or bore kit has a lot more power than supercharger kit with the stroker or bore kit. In this case the turbocharger is chosen for maximum performance. The maximum hp for the Air Power Systems Single Turbo Kit [4] combined with the Cosworth 8.8:1 Low Compression Piston Kit [3] is 737 hp @ 7500 rpm and 629 lb-ft torque @ 5500 rpm which costs:

APS Turbocharger Kit $7,000.00 Engine Block Bore $500.00 Cosworth Forged Piston Kit $1,500.00 Total $9,000.00

This yields a HP$ ratio of 0.08, while the

turbo kit combined with the Brian Crower 8.8:1 Low Compression 4.1 L Stroker kit [2] is 761 hp @ 6500 rpm and 724 lb-ft of torque @ 5000 rpm which costs:

APS Turbocharger Kit $7,000.00 Engine Block Bore $500.00 Brian Crower 4.1L Stroker Kit $5,000.00 Total $12,500.00

This yields a HP$ ratio of 0.06. The

Cosworth 8.8:1 Low Compression Piston Kit [3] combined with the Air Power Systems Single Turbo Kit [4] is the best buy, but the Brian Crower 8.8:1 Low Compression 4.1 L Stroker kit [2] combined with the turbocharger is the best for maximum power and also the gain in torque is a huge compared to the Cosworth setup which can be useful.

Conclusion

In the end a choice must be made for the best engine set up. For a car that will be considered a collector’s car and that will also be raced intensely, the best way to go is the combination of the Cosworth 8.8:1 Low Compression Piston Kit [3] combined with the Air Power Systems Single Turbo Kit [4]. The total price will be:

Part PriceCustom Valve Seats $300.00 Cylinder Head Bore $500.00 Engine Block Bore $500.00 Brian Crower Valve Stems $600.00 Brian Crower Spring Kit $500.00 Brian Crower Race Cams $1,100.00 Cosworth Head Gasket $250.00 Cosworth Head Stud Set $500.00

Cosworth Forged Piston Kit $1,500.00 APS Turbocharger Kit $7,000.00 Total $12,750.00

If money was not an issue, the choice would definitely have to be the same engine setup, but combined with the Brian Crower 8.8:1 Low Compression 4.1 L Stroker kit [2]. The total price will be:

Part PriceCustom Valve Seats $300.00 Cylinder Head Bore $500.00 Engine Block Bore $500.00 Brian Crower Valve Stems $600.00 Brian Crower Spring Kit $500.00 Brian Crower Race Cams $1,100.00 Cosworth Head Gasket $250.00 Cosworth Head Stud Set $500.00 Brian Crower 4.1L Stroker Kit $5,000.00 APS Turbocharger Kit $7,000.00

Total$16,250.0

0

The turbocharger has the highest potential out of the three types of engine builds. However, most racers use naturally aspirated setups because of the response of the engine is instant, but it is proven that cars equipped with turbochargers can still be able to be as fast or even faster than naturally aspirated or supercharged cars. For my money I will be installing a turbocharger into my 350Z.

References

[1] Nissan Motor Company - 2003 Nissan 350Z Service Manual

[2] Brian Crower, Inc. - http://www.briancrower.com/

[3] Cosworth Engineering - http://www.cosworthusa.com/

[4] Air Power Systems Turbo Kits - http://www.airpowersystems.com/

[5] Vortech Supercharger Kits - http://www.vortechsuperchargers.com/

[6] Garrett Turbochargers - http://www.turbobygarrett.com/turbobygarrett/

Sample Calculations

- All of the parts and prices are listed online and can be bought through an online retailer. The price calculations were all calculated using excel.

- The turbocharger and supercharger data was compiled using a compressor map. For the Garrett GT3582R the compressor map is shown in figure E1. Learning how to read the compressor map is shown in figure E2. The Pressure Ratio is calculated by taking the total amount of boost that one wants then adding it to 14.7 psi, which is the sea level pressure, and then dividing that value

by 14.7. Pressure Ratio=Boost psi+14.7 psi

14.7 psi , so for a boost pressure of 8psi, which is the 350z

stock engine’s limit before failure, the pressure ratio is 1.55. This value is then used to read the compressor map to get the data that the program requires. However, the compressor maps are in lb/min while the program asks for cfm. In order to convert lb/min into cfm, divide lb/min by 0.069.

- The rest of the data was given by a reference source or calculated by the program automatically.

Appendix

A1 – Stock Nissan VQ35DE Valve Timing

Image From 2003 Nissan 350Z Service Manual [1] where a = 240, b = 238, c = -6, d = 64, e = 8, and f = 52

A2 – Stock Nissan VQ35DE Camshaft Timing Graph

A3 – Stock Nissan VQ35DE Graph

A4 – Stock Nissan VQ35DE Data

B1 – Cylinder Head Bore of 38mm Intake and 32mm Exhaust Valve Diameter Data

B2 – Brian Crower High Performance/Race Camshafts on Stock Engine Data

B3 – Brian Crower Race Camshafts on Stock Engine Data

B4 – Cosworth ZK2 VQ35 Camshafts on Stock Engine Data

B5 – Camshaft Comparison

C1 –Air Intake Installed on Stock VQ35DE Data

C2 –Exhaust Installed on Stock VQ35DE Data

C3 – Cosworth High Compression Piston Kit with Air Intake and Exhaust Data

C4 – Brian Crower 4.1L Stroker Kit with Air Intake and Exhaust Data

C5 – Naturally Aspirated Tuning Comparison

D1 – Stock Engine with Cosworth 8.8:1 Low Compression Piston Kit Data

D2 – Stock Engine with Forced Induction Comparison

D3 –Both Stoker Kit & Piston Kit with Forced Induction Comparison Graph

E1 – Garrett GT3582R Compressor Map

E2 – How to Read a Compressor Map