HEMI Technical Info

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Clutch - Drag Racing


AFT Multi Disc, Multi (18) Arm, Multi Stage, Titanium, 9 Stand,
Top Fuel , Slider, Centrifugal Clutch
( shown 10.5 and 11 inch)  aprox $10,000.00/each


Aluminum RAM 8 bolt Hemi (early flange)  2 Disc Sintered Iron,
Pedal Style, Chevy Starter Ring Gear, 6 release Arms,
6 Stand (Titanium), , Pro Mod Clutch  aprox $4,000.00/each



Flange / Crankshaft  
6 Bolt  Chrysler
most common flange slant/6 to 440

Flywheel and flexplate are located  (centered) on raised area in center of crankshaft

no bronze bushing for 4speed standard transmission input shaft , but crankshaft is machined to install a bushing

8 Bolt Chrysler
same dimensions as 6 bolt (above) with 8 bolts

Flywheel and flexplate are located (centered) on raised area in center of crankshaft

no bronze bushing for 4speed standard transmission input shaft , but crankshaft is machined to install a bushing

8 Bolt Chrysler /old style 392 hemi
( this is what all fuel / TAD/ FC/ and most promods use today)

Flywheel is located (centered) on outside of crankshaft flange center is removed like early Chryslers This is preferred because it allows for larger input shaft bearings needed on
multidisc clutches

shown with adapter ring installed to allow use of flexplate or flywheel that doesn't locate on outside of crankshaft flange. in other word converted to 8 bolt later style shown above



Flywheel Material
  cast iron, steel, aluminum, stainless steel, and titanium
Size / Diameter
from 5" to 12 inches


Disc / Floaters  
Disc 1.375 Dia
  1.750 Dia, 10  or 40 spline.


Pressure plates
( hat/ clutch/ donut/ pressure-plate )

Automotive Street/Strip  
There are 3 Basic types of pressure plates.
diaphragm-type - static pressure (center) street /strip - low pedal pressures
- Borg & Beck - static pressure (right) street/strip
- Long - static pressure and Centrifugal (left)competition / very adjustable

springs force pressure plate against discs - Springs provide all or most of locking force,centrifugal force added by arms extending out of the end of arms ncreases the force as engine RPM goes up

this example is a 2 disc, aluminum flywheel , chevy starter ring, long style cover, adjustable springs (threw holes in cover ), adj centrifugal force (by adding bolts nuts and washers to 3 arms)


In auto racing there is always exceptions
this is a diaphragm clutch with centrifugal arms added ?


Pressure plates - Slider Clutches



If it is desirable to program the clutch forces to engine RPM (Drag Racing) then reducing (or eliminating) the springs (static) and using the centrifugal weighted arms for most or all clamping forces is an option. In drag racing we call this a slider clutch . at an idle the clutch may not even provide enough force to  move the vehicle , sometimes a clutch pedal isn't needed , like an automatic/converter equipped car. Sometimes described like a snowmobile centrifugal clutch

springs force pressure plate against discs, needs a pedal to launch race car, but force primarly centrifugal


spring hold pressure plate away from discs, may not need a pedal to launch race car, but force only centrifugal

Multi Stage

Note :
- arms installed are 6 base arms same length (height from release bearing)
this makes it a single stage possibly an A fuel or Nostalgia

- arms on left can be added in empty slots on cover, or even replace base arms
this would be added to clamping force of pressure plat as release bearing is moved back by hydraulic/pneumatic clutch management system (keep in mind there will be an
imbalance if arms aren't kept equal weight - which is impossible so bye bye rear bearing)


Clutch Managment
(multi stage TF)
Fuel and clutch release bearing position - air management system
Hydraulic cylinder to control position of release bearing