1. SUPERCHARGING TRs for the road
BOOST
ATM
Peter Cobbold
TR Register
International Weekend
Malvern, August 2015

2. Inspiration for Supercharging
<<<
2.6litres, 260bhp,
on 'petrol'
VSCC meetings are the place to see supercharged engines

3. DIY design using Wade RO34 blower TR Action 1998

4. Supercharging : plan of talk
Supercharged TRs
Boost, pressure ratio
Heat and density ratio, torque gain
Knock, RON, compression ratio
Carburettor or Injection+Intercooler
Engine requirements: mixture, cam, spark
Fitting a Blower: DIY or kit
Driving

5. Boost for Torque
BOOST
ATM
“ A supercharger is a device for making the small engine burn as much fuel as the large engine, thus enabling it to supply a great deal more torque than is available normally from the small motor.” Eldred Norman

6. Eldred Norman 1954. First TR2 in South Australia, supercharged
“ Supercharge ” book is on-line:

7. Eldred Norman
“In 1954, driving a supercharged Triumph TR2, I finished 4th in the Australian Grand Prix. On this car I used a “boost’ of 12lbs. The supercharger was a G.M. 271 Roots type unit operating at 1.1 times engine speed.”

8. Supercharging for the road

9. ....towing a trailer with two 44-gallon drums of methanol racing fuel.
Eldred drove the TR miles from Adelaide to Southport, Brisbane, Queensland....
....towing a trailer with two 44-gallon drums of methanol racing fuel.
Winning the Brightways Trophy and Cords Piston Ring Trophy support races on the morning of the Australian Grand Prix gained him entry into the main race, in which he came fourth.
One of Eldred’s race-mates, (later Sir) Jack Brabham, had to retire his Cooper T26 after only one lap,.....”

10. Supercharged TR2, 1954
1957: Dr Coombs installed an Arnott supercharger .
1978: Fitted Shorrock C142B bought from A.R.Allard.
Present owner Duncan Ravenscroft will be in the arena with
SAF 424 tomorrow morning.

11. Alan Allard

12. Alan Allard
“A maximum power increase of 25-35% and a similar torque increase is all that is necessary to give a substantial performance boost without impairing reliability or necessitating extensive internal engine modifications this can be achieved with a modest boost of from 4-7psi ”

13. TR3. Moss Eaton and Opcon Autorotor
< ROOTS Blower
LYSHOLM Screw Compressor

14. TR4
JUDSON sliding vane compressor
Moss Eaton kit

15. TR6 Austin Branson Eaton M62 Vespertini USA head, 7.75:1 2” SU
Machining by Bradbury Engineering
“The car is transformed. In it’s atmospherically inducted form, it was a waste of time trying to exceed 3,000 rpm – it simply wouldn’t breath. Now, the engine just pulls, and revs to levels I didn’t think it could! Wonderful ! “

16. TR John Jervis
“The pickup is pretty much instantaneous, and the engine extremely tractable, to the point that I was ignoring changing gear for hills I would normally drop down a ratio.”
Moss Eaton M62
Standard boost kit.
DIY fitted to CP-series
9.5:1 compression
Cold air intake.

17. TR6 Chris Orson
Eaton M62 Moss kit Professionally fitted

18. TR7 Mike Warnes Own design and build
Eaton M45 ex Merc200 Drive: 2.75:1
5psi boost at 1500rpm 10psi at 3400rpm psi at 5000rpm
8.5 Comp Ratio USA-spec pistons
Megasquirt port injection
Cold air intake.
“ I have the rev limiter set to as the engine is not balanced its probably done about 10,000 miles on the road and seems quite reliable.”

19. Mike Warnes' TR7 Mike is at IWE with the S/c TR7
– in the Arena Event and Trials car section

20. Boost, Volumetric Efficiency, Pressure Ratio
Supercharging
Supercharged TRs
Boost, Volumetric Efficiency, Pressure Ratio
Heat and density, torque gain
Knock, RON, compression ratio
Carb or Injection+Intercooler
Engine requirements: cam, spark
Fitting a Blower: DIY or kit

21. Positive displacement: Roots “blower” - no internal compression
BOOST
Atm.
With carb at wide open throttle, blower pumps more mixture than engine can consume at atmospheric pressure.
Upon flooring the throttle from cruise boost will rise fully in approx 0.1sec.
DRIVE RATIO
from
PULLEY
DIAMETERs

22. Positive displacement: Roots “blower” - no internal compression
BOOST
Atm.
With carb at wide open throttle, blower pumps more mixture than engine can consume at atmospheric pressure.
Upon flooring the throttle from cruise boost will rise fully in approx 0.1sec.
DRIVE RATIO
from
PULLEY
DIAMETERs

23. Pressure - old and new units
Atmospheric pressure is:
14.7 psi
1 Bar kPa ; 101 N/m2 ;1013 millibars ; inch Hg
(at sea level)
psig 'gauge' is what we measure above atmospheric.
psia 'absolute' is gauge plus atmospheric

24. Boost vs. rpm curves

25. Mike Warnes' TR7 Boost psig vs. Crank rpm

26. Allard: “A maximum power increase of 25-35%. can be achieved with
Allard: “A maximum power increase of 25-35% can be achieved with psi ”
BOOST
Atm. 14.7
7psi boost is % above atmospheric pressure
......So why not 50% more power ?

27. Heat and density Supercharging Supercharged TRs
Boost, Volumetric Efficiencies
Heat and density
Knock, RON, compression ratio
Carb or Injection+Intercooler
Engine requirements: cam, spark
Fitting a Blower: DIY or kit
Driving
More boost !!!

28. Compressing a gas always heats it.
BOOST is HOT
BOOST
Atm.
Compressing a gas always heats it.

29. Some of the pressure rise is due to the mixture being hot.
BOOST is HOT
BOOST
Atm.
Some of the pressure rise is due to the mixture being hot.

30. And hot gas is less dense
BOOST is HOT
BOOST
Atm.
And hot gas is less dense

31. Density rises less than pressure
So a 50% rise in pressure does not give a 50% rise in density.
The 'pressure ratio' always exceeds the 'density ratio'
And torque follows density.

32. Blowers heat gas more than compressors
The 'worse' the compressor the hotter the gas.
<< This is “ADIABATIC Efficiency “
AE of Roots ca 50%
Eaton ca 65%
Twin screw ca 70%
Why?....turbulence

33. “Adiabatic Efficiency” for Eaton M62 can be found from factory data
AE is read off the map contour
AE is 66% for 7psi boost and air flow rate for TR6.(arrowed)
Good.
Knowing AE we can get Density Ratio

34. Density ratio for pressure ratio=1.48
On the 66% AE line, Pressure Ratio of corresponds to Density Ratio=1.3

35. Answer 7psi boost is a Pressure Ratio of: (14.7 + 7 ) / 14.7 = 1.48
( ) / = 1.48
BUT the blower heats the mixture and its density drops to a Density Ratio of 1.3
Which gives 30% increase in torque.

36. Hot Boost to Torque Take home message:
7psi boost from an Eaton M62 blower on a TR6 will deliver ca 30% more torque.
Approximately !

37. Knock, RON, compression ratio
Supercharging
Supercharged TRs
Boost, Volumetric Efficiencies
Heat and density, torque gain
Knock, RON, compression ratio
Carb or Injection+Intercooler
Engine requirements: cam, spark
Fitting a Blower: DIY or kit
Driving

38. KNOCK is explosion of the 'endgas'

39. Knock is the major limitation to boost -promoted by high cylinder pressure and temperature
In-cylinder pressure during combustion:

40. 'Knock' =detonation Ways to reduce knock: Lower the compression ratio.
Use high octane petrol, or alcohols.
Retard spark at high boost : ' boost retard '
Use very rich mixture, which burns slower.
Lower temperature of boosted gas by: water injection, intercooling ( but not with 'wet' blower), rich mixture.
'Tin ears' – stethoscope -to detect knock

41. Heavy knock is destructive of pistons, often followed by preignition
BUT, on the positive side, when knock is prevented >>>>>

42. Eldred Norman:
“Off all the forces operating in an engine the pressure on the piston is by far the least. This pressure could be doubled and it would still not represent 10% of the stresses at work.
Moreover, one of the greatest forces, centrifugal force....is two and a quarter times as great at r.p.m. as it is at 4000.
From this it can be seen that supercharging is much easier on the motor than increasing the r.p.m. by improving the breathing.”

43. Carb or Injection+Intercooler
Supercharging
Supercharged TRs
Boost, volumetric efficiencies, pressure ratio
Heat and density ratio, torque gain
Knock, RON, compression ratio
Carb or Injection+Intercooler
Engine requirements: cam, spark
Fitting a Blower: DIY or kit
Driving

44. Intercooling allows more boost without knock
Intercooler not allowed with carb feeding a 'wet blower' - severe explosion risk from inlet backfire
Thermal inertia usually allows ca.15 sec continuous boosted operation.
Intercooling needs fuel injection after intercooler.
Lean injector can melt piston silently by preignition
Below ca.6psi boost pressure lost in intercooler can exceed density gained by cooling.
- Simplicity versus Complexity Old v. New

45. Engine requirements: Comp Ratio, RON, mixture, cam, spark
Supercharging
Supercharged TRs
Boost, volumetric efficiencies, pressure ratio
Heat and density ratio, torque gain
Knock, RON, compression ratio
Carb or Injection+Intercooler
Engine requirements: Comp Ratio, RON, mixture, cam, spark
Fitting a Blower: DIY or kit
Driving

46. Compression ratio rises with boost
Allard rule: “3.7psi boost raises CR by one ratio”
(Tables of CReff vs Boost on web are WRONG )
Stock TR6: “on 97RON...no knock at CR=10.5:1”
So, for a stock 9.5:1 head, ca 4psi boost is OK before remedial measures might be needed
TR6 USA heads Comp Ratio 8.5 or 7.75 allow more boost on 97RON.
eg 8.5:1 head and 97RON allows ca 8psi boost
>>>>>>>>> APPROXIMATELY !!

47. Fuelling, mixture High octane fuel: 97 RON or more. Bottle boosters.
RON required ? > Complex (Rises with higher charge density, low humidity, less exhaust carry-over...etc). So not predictable.
Always rich under boost: AFR 12 to 10.5
Never run lean under boost: preignition risk
Cold air intake

48. One 2” SU carburettor can meter petrol for a supercharged engine of 200hp
Tuning- how ? Fluid mechanics: operating-limits-of-an-su-carburettor-2/
testing soon.

49. Camshaft Standard is best. High overlap wastes boost.
Can retard cam a few degrees to allow more exhaust flow
Possibly more exhaust valve lift
Avoid thin exhaust valve seats to keep conduction of heat as high as possible

50. Ignition: boost retard
Eldred Norman: “ As a rough rule the spark is retarded by about three degrees crankshaft for each unit the Comp Ratio is raised ”
Allard : “ 3.7psi = 1 CReff increase “
So, for TR6 with geometric Comp Ratio of 9.5: retard 3 crank deg at 4psi, another 3deg at 8psi But always check for knock !!
=======
Higher boost can need higher HT but 'iridium' wire plugs reduce need to raise HT, can keep stock coil.

51. Tuning aids Boost/vacuum gauge Mixture:
Air Fuel Ratio by wideband 'UEGO' exhaust sensor
SU piston lift camera
Intake temperature: thermocouple probe
Timing strobe light
( camera to monitor vacuum advance, boost retard, on the road )
'Tin ears' stethoscope to listen for knock

52. Fitting a blower: DIY-build or Kit?
bolt-on, works out of box
M62 is new.
DIY fitting OK
quick
ca £3.5K
DIY
ebay Eaton M62 (£250 )
ebay Eaton M45 (£175 )
design, plans, models, fabrication: £??? - unless acquire basic DIY machining expertise
time..lots.
help ? professional expertise in VSCC,but at a cost ....
Later....modify to push limits: more boost, flowed head, cam, Water injection but learn the principles first !!!

53. David Vizard on Allard-Wade RO20 supercharged Capri V6
“One could maintain high cruising speeds yet still not have any boost one could be travelling at 100mph on small throttle openings and then suddenly give the car full throttle. The boost gauge would rip round to 4psi boost and the car would immediately roar off as if 100mph had been snail's pace”
“ It retains the docility needed for Granny shopping.”
“In London traffic..its docility and road manners are almost beyond criticism, especially so if you are used to high performance cars which do have a degree of caminess”

54. For the last word...... Eldred Norman:
““ ANY car can be supercharged. If yours seems difficult, just sit down and think. Once you have got it properly supercharged you'll realise that all other forms of 'hotting up' are only a shadow of the real thing.””

55. Thank you. Peter Cobbold pcobbold@fireflyuk
Thank you. Peter Cobbold To be archived on blog: “SuperTRarged” - via the forum

57. Moss Eaton M62 kit for TR6: calculated boost
Based upon Eaton M62 data and guesstimated TR6 VE 80% at rpm
Pressure Ratio
Engine air consumption at 3000rpm: (2.5/2) x 0.8 x 3000 = 3000 litres per min.
Blower air intake at 3000rpm = 150cfm = 4250litres per min
Hence pressure ratio= 4250/3000 = 1.42
Boost from pressure ratio
So boost = (pressure ratio x atmospheric pressure) – atmospheric pressure
which is (1.42 x 14.7) – 14.7 = 6.1psi.
Predicted boost for the standard kit.
6psi is the same as Moss’ sales information.
Source:

58. Eaton on Mercedes

59. Eaton superchargers