High Speed Vibrometry for

Valve Tracking + Piston Rockin

NASCAR Race Engines

Stephen JonesMenard Competition Technologies

Presentation Plan

• Introduction • NASCAR Engines• Research + Development using Lasers

(a) Valve Tracking(b) Piston Rock

• Conclusions• Questions

Leafield Technical Centre, Oxfordshire

Engine supplier for the Caparo T1

V8 90° 3.5 litre (Ex-IRL race engine) 580 BHP @10500 RPM 420 Nm @9000 RPM

Power-to-weight >1000 BHP/ton (Bugatti Veyron = 529 BHP/ton !)

Engine supplier to Superleague FormulaV12 60° 4.2 litre All-new design

750+ BHP @12000 RPM 530 Nm @9500 RPMOne-make race series due to start in Aug’08

NASCAR Engine Research + DevelopmentChevrolet V8 90° 358 cu in (5.87 litre)

775 BHP @ 9000 RPM 680 Nm @ 7250 RPMOval Speedway race series in USA

NASCAR engines• 3 Race series - CUP, Busch and Truck• 4 Base-engines - Chevrolet, Ford, Dodge, Toyota• V8 configuration (358 Cu in, 5.87 litre)• Cast iron Block • Single camshaft, Push-rod actuated valve-train• 2 valve combustion chambers• Single carburettor (No electronic fuel injection)• Fixed ignition angle + mechanical distributor• Speed limited to ≈ 9500 RPM by fixed gear ratios• Closely regulated by NASCAR officials

Paul Menard #15 Chevrolet ImpalaNASCAR NEXTEL CUP series – Rookie season 2007

Under the hood…

Engine out

Engine dressing at the circuit

Engine Testing on an MCT dynamometer.

MCT have four steady-state engine test cells.This engine is undergoing crankshaft torsional development testing.

Engine Build Shop @ MCT

Cylinder head off

Bare Crankcase – Chevrolet SB2 ‘small-block’ (circa 1955 !)

Rig Testing• MCT Test facility includes a ‘Spintron’ motoring test rig.

Used for component + system Investigation and Durability testing

• Sensors fitted for valve-tracking :-- Shaft encoder (BEI 720 pulses/rev) - Polytec twin-laser system

HSV-700 Sensor Heads (x2)HSV-800 Laser Units (x2)HSV-2002 Controller

• Standard Spintron single-laser system replaced because :-Twin-lasers cancel out rig vibrationImproved resolution (Polytec = 10.24μm ; Spintron = 20μm)

Spintron Test RigFor running steady-state or programmed test cycles.

Cylinder 5 ‘windowed’ to allow laser access

Spintron Control RoomSpintron software ; Vibsoft 4.1

(Can suffer ‘processor overload’ while simultaneously controlling the Spintron + collecting Polytec Data)

Valve Tracking Objectives

• Investigate Inlet + Exhaust Valve behaviour across the engine speedrange (3000 to 9600 RPM).

• Standard sign-off test for any new valve-train component.

• Ensure that lofting (@ peak lift) is kept below 0.040” to avoid :Valve-to-piston contact → Engine failureDeep valve pockets in piston crowns → Performance lossCamshaft damage → Engine failure

• Ensure that bounce (@ valve closing) does not occur to avoid :Valve or valve-seat damage → Engine failure

• Verify a Simpac valve-train computer model. (Interaction of Mass, Inertia, Stiffness, Natural frequency)

Valve-train Components• Valve• Springs (Inner + Outer)

• Top Retainer (Spring Top)• Collets• Shim (Lash Cap)

• Rocker• Pushrod• Tappet (Lifter, Follower)

Flat = CUP spec.Roller = Busch + Truck spec.

Camshaft Lift eg. Peak = 11.7 mm (0.461”)Valve Lift eg. Peak = 20.4 mm (0.803”) Rocker-ratio = 1.75Valve speed eg. Peak = 12.0 m/s @ 9600 RPM engine speed

0

5

10

15

20

25

-100

-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

Camshaft Degrees

Lift

(mm

)

-15

-10

-5

0

5

10

15

Velo

city

(m

/s)

Twin-Lasers directed at inlet valve head and cylinder head.Retro-reflective tape used for best signal strength.

Baseline valve lift trace @ 3000 RPMA-B displacement signal displayed by Spintron software

Overlaid Valve lift trace @ 9000 RPM

Look for :- ‘Late Opening’, ‘Lofting’, ‘Harmonics’, ‘Early Closing’, ‘Valve Bounce’

Zone definitions for valve control assessment

Comparison spreadsheetDatafiles post-processed using an Excel Macro.

Deviations integrated for each of the 5 zones at 35 test speeds.

Piston Rock Objectives• Rock is significant in NASCAR race engines because :

- Large piston-to-bore clearance due to radiator blanking practice.

- Large bore diameter (4.185” = 106.3 mm)- High piston mass (NASCAR rule = 400g)

• Characterise the rock around the gudgeon pin• Determine which areas of the skirt do the most work• Use the findings to improve the skirt design

(Piston design + manufacture is part of MCT’s core business)• Investigate the effect of crankcase depression on rock

Piston-rock laser set-up(Oil contamination affected signal strength; Airlines + extraction helped)

Laser B

Laser A

Retro-reflective Tape

Extraction forOil mist (Blowby)TOP

BOTTOM

CYLS 2,4,6,8R/H BANK

CYLS 1,3,5,7L/H BANK

VIEWFROMFRONT

BB

AA

Schematic of ‘Positive-Rock’. (A-B = +ve)

NASCAR engines run a ‘large’ piston-to-bore clearance ≈ 0.010”

Piston ‘skirt’ supports the piston-rock

•FRONT

CYL 8

REACTION FORCE (BOTTOM OF SKIRT)

+VE ROCKDIRECTION

REACTION FORCE (TOP OF SKIRT)

Piston Displacement + Velocity v. Crank AngleOver one engine revolution

(Engine Speed = 9000 RPM ; Stroke = 82.55 mm ; Conn-rod length = 152.4 mm)Concern that piston speeds > ±30 m/s outside capability of HSV-2002 controller

0

10

20

30

40

50

60

70

80

90

100

0 30 60 90 120 150 180 210 240 270 300 330 360

Crank degrees

Dis

plac

emen

t (m

m)

[

Dow

n bo

re is

+ve

dire

ctio

n]

-50

-40

-30

-20

-10

0

10

20

30

40

50

Velo

city

(m/s

)

Trigger signal (From shaft encoder once per engine rev).Rock trace suffered from :

Drift and discontinuities.Blow-by oil contamination robbed signal strength± 8V signal voltage resets

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3 0.35 0.4 0.45 0.5 0.55 0.6

Time

Dis

plac

emen

t

2

2.5

3

3.5

4

4.5

Volta

ge A - B

Trigger

( Sample Frequency = 25.6 kHz ; Sample Time = 1.28 s ; No Filters )

Raw Vibsoft Data Trace

Vibsoft datafiles were exported as ASCII files and analysed in Excel.1. Cut out a ‘good’ trace between two triggers.2. Convert x-axis from time-base to crankangle-base.3. Correct the trace for drift.

Typical piston rock trace. (8500 RPM Cylinder 8)

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

0 60 120 180 240 300 360

Crank Angle (Degrees)

Roc

k (m

m)

VaccNo Vacc

110°71.0 HP- 70 mBarNo Vacc

50.4 HP- 640 mBarVacc

Power-to-drive SpintronCrankcase Depression

Conclusions• Accurate valve tracking allows us to develop a more durable valve-

train and to improve engine performance.

• Piston rock measurement allowed us to better understand piston dynamics and helped with piston skirt design.

• Results compromised by non-firing engine, ie.No combustion pressureNo combustion temperature No thermal growth

Any Questions ?