There's actually more adjustment with the 4 spring (you have 8 weight levers to work with.)
I like the 4 spring for the animal engine in the adult classes. Set up with blue springs @.225" and 1 bolt in every other weight lever. This makes for a softer engagement that handles the torque of a BP'd animal engine using slicks on a low/no bite dry slick dirt track. You can use the 4 spring for blue plate too - you'll just need to add more weights to the levers.
Generally, the 6 spring "hits" harder when it engages, but you can open up the air gap some on the 4 spring and get that same "feel" if that's what you want. Personally, I think that a softer engagement also helps under-powered restrictor plate classes too by not pulling the engine out of it's torque curve (which can happen in the real small/beginner plate classes.) For blue plate animal, I don't think you'll see much difference in performance in either 4 or 6 spring as long as they are set up correctly.
I'm kind of surprised that the company that you purchased the clutch from didn't already have it set up for your class/engine application. That's the most important thing about a clutch -- that it is set up properly.
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Brian Carlson
Carlson Racing Engines
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