StrokeOrNot.pdf

SUMMARY

This white paper presents a mathematical analysis of the piston dynamics of three

popular versions of the Mitsubishi 4G63 engine, the stock 2.0L, the 2.1L destroked

version with an 88mm crankshaft in a 4G64 block, and the stroker with a 100 mm

crankshaft in a 4G63 block. Where applicable, charts are included to show the

differences between the versions at different RPMÓs or different crank angles.

The conventional wisdom that strokers make more torque but the 2.0L will rev higher is

explained with hard calculations of such factors as piston side loading friction and

tension on the rods. The 2.3L stroker has the same side loading friction at 7150 RPM as

the 2.0L at 8000 RPM.

The conventional wisdom that the vibration from removing balance shafts is less than the

effect of mismatched piston weights is challenged and explained with a mathematical

analysis. A 2.3L stroker has the same harmonic imbalance at 7040 RPM as the 2.0L at

8000 RPM.

The effect of the stroker geometry on camshaft selection is examined and supported with

charts of common aftermarket 4G63 cams. The analysis shows that stroker engines are

more tolerant of aggressive cams than the stock engine. The intake velocity of a stroker

at 7000 RPM is the same as a 2.0L at 8000 RPM. Peak piston velocity of a stroker at

7390 RPM is the same as a 2.0L at 8000 RPM.

INTRODUCTION

After spending too many hours researching how to make my 1998 AWD Talon even

better than new including reading many tuner posts in the DSM forums I decided to

create this document as a payback to the DSM community.

The scope of this document is limited to the differences between common versions of the

Mitsubishi 4G63 engine. The calculations are directed toward answering the question

Ðshould I stroke my 4G63 or notÑ.

All equations used in this document are documented in Appendix A. The charts are print

outs from an Excel project. The Excel file is available as described in Appendix A.

This document was drafted by Maurice Garoutte for the use of the DSM community and

is not copyrighted. This document ended up longer and more technical than first

planned but for readers who want more please follow the references.

Disclaimer

THIS DOCUMENT IS FOR THE ENTERTAINMENT AND POSSIBLE

EDIFICATION OF THE DSM COMMUNITY ONLY. NO 4G63 ENGINES WERE

HARMED FOR THE PRODUCTION OF THIS DOCUMENT. DONÓT TRY THIS AT

HOME. THE USE OR ABUSE OF THE INFORMATION HAS NO WARRANTY

EITHER EXPRESS OR IMPLIED. THE AUTHORS LIBILITY FOR THE CONTENT

OF THIS DOCUMENT SHALL NOT EXCEED THE PAYMENT FOR THE

DOCUMENT, NOTA, ZERO BUCKS. IF YOUR 4G63 THROWS CHUNKS AT

10,000 RPM AFTER READING THIS, DONÓT COME CRYING TO ME. YOUR

MILAGE MAY VARY. THE OPINIONS EXPRESSED HERE MAY NOT

REPRESENT THE OPINION OF THE MANAGEMENT. MANAGEMENT?

TABLE OF CONTENTS

SUMMARY ........................................................................................................................ 1

INTRODUCTION............................................................................................................... 2

Disclaimer ....................................................................................................................... 2

TABLE OF CONTENTS .................................................................................................... 3

LIST OF FIGURES............................................................................................................. 4

POWER vs. TORQUE ........................................................................................................ 5

Intake limitations............................................................................................................. 5

Bigger Valves Needs Bigger Bore .................................................................................. 7

Conversion of Pressure to Torque ................................................................................... 7

Boost is Good .................................................................................................................. 9

Heat of Compression ....................................................................................................... 9

RPM LIMITATIONS OF STROKERS ............................................................................ 11

Piston Speed .................................................................................................................. 11

Rod Tension .................................................................................................................. 13

Friction Losses .............................................................................................................. 15

WHATS AN ÐIDEALÑ ROD RATIO............................................................................... 20

STROKERS AND ENGINE BALANCE ......................................................................... 22

Imbalance in Pounds ..................................................................................................... 22

Imbalance from Mismatched Parts................................................................................ 23

STROKE AND CAM SELECTION................................................................................. 26

Displacement ................................................................................................................. 26

Piston Velocity .............................................................................................................. 27

Rod Ratio and Piston Velocity ...................................................................................... 28

Longer Stroke and Lower Rod Ratio ............................................................................ 30

Effective Compression Ratio ........................................................................................ 31

Effect of Cam Profile on ECR................................................................................... 32

Effect of Rod Ratio on ECR...................................................................................... 33

Rod Ratio and Stroke Effect on Overlap................................................................... 34

ROD RATIO STROKERS AND ROD SELECTION ...................................................... 36

STROKERÓS AND PISTON SELECTION...................................................................... 37

ROD RATIO AND IGNITION TIMING ......................................................................... 39

HARMONIC BALANCE OF IN LINE FOURS .............................................................. 41

CONCLUSIONS ............................................................................................................... 44

2.3L Stroker Pros........................................................................................................... 44

2.3L Stroker Cons ......................................................................................................... 44

Summary of Calculations .............................................................................................. 45

RECOMMENDATIONS .................................................................................................. 46

REFERENCES.................................................................................................................. 47

APPENDIX A Î FORMULA USED IN CHARTS .......................................................... 51

APPENDIX C - DEFINITIONS ....................................................................................... 55

LIST OF FIGURES

Figure 1 Hemispherical Combustion Chamber................................................................... 5

Figure 2 4G63 Combustion Chamber ................................................................................. 6

Figure 3 Leverage on the Crankshaft .................................................................................. 7

Figure 4 Cylinder Pressure to Torque Conversion.............................................................. 8

Figure 5 V-1710 Allison Engine ......................................................................................... 9

Figure 6 Piston Velocity at 8000 RPM ............................................................................. 11

Figure 7 Peak Piston Acceleration 4G63 Versions ........................................................... 12

Figure 8 Rod Failure in Tension ....................................................................................... 13

Figure 9 Gratuitous Image................................................................................................. 13

Figure 10 Rod Failure in Compression ............................................................................ 13

Figure 11 Force on Rods by Crank Angle......................................................................... 14

Figure 12 Peak Force on Rods by RPM............................................................................ 15

Figure 13 Side Load Friction Components Î 2.0L............................................................ 17

Figure 14 Side Load Friction by RPM .............................................................................. 18

Figure 15 Side Load Friction Components Î 2.3L............................................................ 19

Figure 16 Piston Acceleration 4 Rod Angles .................................................................... 20

Figure 17 Piston Acceleration 4 Rod Ratios ..................................................................... 21

Figure 18 Piston Acceleration 4G63 Versions .................................................................. 22

Figure 19 Harmonic Imbalance 4G63 Versions................................................................ 23

Figure 20 Balance Forces for 2.0L 8000 RPM ................................................................. 24

Figure 21 Balance Forces for Stroker 8000 RPM ............................................................. 24

Figure 22 Balance Forces for Stroker 4000 RPM ............................................................. 25

Figure 23 Displacement vs. Crank Angle ......................................................................... 27

Figure 24 Piston Velocity 4G63 Versions ........................................................................ 28

Figure 25 Peak Piston Velocity vs. Rod Ratio .................................................................. 29

Figure 26 Mid Stroke vs. Rod Ratio ................................................................................ 30

Figure 27 Piston Velocities 3 Rod Ratios and Stroker..................................................... 31

Figure 28 Cam Timing and ECR ...................................................................................... 32

Figure 29 Rod Ratio and ECR........................................................................................... 33

Figure 30 Valve Overlap 4G63 Versions .......................................................................... 34

Figure 31 Torque Conversion at Max Pressure................................................................. 40

Figure 32 Piston Acceleration at 8000 RPM..................................................................... 41

Figure 33 Harmonic Imbalance 4G63 Versions................................................................ 42

Figure 34 Mitsubishi Silent Shafts .................................................................................... 42

POWER vs. TORQUE

A quick search finds 1300 pages on dsmtuners.com site with the words stroker OR 2.3L

AND torque. That topic is a thoroughly beaten, very dead horse. Without reading all

of those pages, itÓs clear that the conventional wisdom is that the stroker makes more low

end/mid range torque but not necessarily more power. That old saw is pretty much true

and this paper is focused on the differences in the two versions, not on which is ÐbetterÑ.

The next section of this paper is concerned with

the RPM limitations of the stroker. Before

getting into the limitations of the stroker version

of the 4G63, the horsepower limitations of the

4G63 are examined here. This is pretty much

basic engine theory so feel free to skip to the next section.

This is pretty much basic engine

theory so feel free to skip to the

next section.

Intake limitations

The 4G63 is a strong engine capable of handling much more horsepower than the factory

spec. Regardless of how strong the parts, engines making power just from air and

gasoline are limited by how much air can get into the combustion chamber. Boost is

good. A charge with two bar of boost can burn twice as much fuel as one bar.

For any boost level the limit of how much air can

enter the combustion chamber is limited by the

intake tract and the size of the intake valves. Back

when the author put a 1951 hemi engine in a 1948

Plymouth coupe the hemispherical combustion

chamber was state-of-the-art in car engines. See

figure 1 at right. Back in 1951 those were some

really big valves, angling the valves in from each

side allowed bigger valves while a center mounted

plug improved flame propagation.

Figure 1 Hemispherical Combustion

Chamber

Bigger valves are a good thing because we canÓt just make the air go faster. When air

flow reaches mach one (equal to the local speed of sound) the flow is ÐchokedÑ

increasing the pressure drop across the valve just puts more energy in shock waves but

the air flow does not increase. According to the Mechanical Engineers Handbook (19)

engines have the best volumetric efficiency with a mach index of 0.45 to 0.5. While a

mach index of 1 is a hard wall, the choking effect from high mach flow starts about 0.6.

Above a mach index of 0.6 the volumetric efficiency of any engines falls off rapidly.

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