Thursday, June 14, 2012

Clutch Selection

The clutch decision was a big one for me and one that I didn't take lightly.  The clutch can have a huge effect on how the car drives.  My final decision was to go light to lessen the hit on the tires and let the engine rev faster for the approximately 2600lb car.  First I was going towards a 7.25" racing clutch but after seeing a lot of you tube videos with extremely jumpy, light switch like clutches and reading manufacturers recommendations to not even drive cars onto the trailer with them I got the idea that it was a little more aggressive than I want to deal with.  Dru Nichols (SicBastard on compiled some great information on moment of inertia of clutch assemblies.  For those of you not familiar with the term or the concept, moment of inertia in context of a clutch is the idea that the same weight at the same rpm has more energy the further it is placed from its axis of rotation.  A good example is a baseball on a string, a baseball on a 2 foot string rotating at 100rpm is only going about 7mph, but the same baseball on a 17 foot string at the same 100rpm is going about 60mph.  Enough about the physics and back to the clutches.

Tilton Clutch Assemblies MOI (lb-in^2)
Includes: Clutch cover with diaphragm spring, pressure plates and floater plate(s)
(add 66 MOI and 2.5# to include the button
(add 87 MOI and 3.4# to include a Sonic ultra-lightweight flexplate)

13 4.4” Tilton carbon carbon 4 disc
21.4 5.5” Tilton 1 disc cerametallic
29.4 5.5” Tilton 2 disc sintered metallic (6#)
32.2 5.5” Tilton 2 disc cerametallic
52.4 7.25” Tilton 1 disc cerametallic
76.3 7.25” Tilton 2 disc cerametallic
89.6 7.25” Tilton 3 disc sintered metallic (10.2#)
99 8.5” Tilton 1 disc cerametallic
100.2 7.25” Tilton 3 disc cerametallic
158 8.5” Tilton 2 disc cerametallic
337 9.0” Mantic street dual sprung clutch (33.8#) cool set up!
>3200 11.5"? Stock LS2 flywheel and clutch (52#)

(MOI list thanks to Dru Nichols MD)

I also put together the following list of weights without MOI with a lot of google searches for light weight clutch assemblies for the LS series engines.

McLeod RST 9-11/16 dia. w/Aluminum Flywheel 560530 (36#)-w/13.5# flywheel
McLeod Mag Force 8" dia twin Assembly (Approx 25#, Goes on the scale tomorrow)
Spec Lightweight flywheel w/Al PP Option 11-1/2 dia. (33.4#) (McLeod also offers a similar set-up if you call them)
RPS Street Twin 1/2 Carbon (40#)
RPS Street Twin Full Carbon (36#)
RPS Billet Carbon Street Twin w/Steel Flywheel (32#)
RPS Billet Carbon Street Twin w/Al Flywheel (25#)

After talking with Lee at McLeod clutch and Scott at SPD Metalworks I went with the Mag Force twin.  They put together a custom assembly based on the pin drive Mag Force, with a strap drive pressure plate, and ceramic discs.




Here's a video for an example of how I expect it to rev.