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Old 03-05-2013, 12:43 PM   #44
chasbmw
Beastly Adventurer
 
Joined: Feb 2006
Location: Bath Uk
Oddometer: 1,745
Quote:
Originally Posted by supershaft View Post
Not my experience at all. My airbox experiments had the same results regardless of whether or not I had a 32mm Bing or a 38mm Dellorto. A 308 cam or a 336 cam. Stock mufflers or Staintune Sports. Going from one small/one large to two larges horns killed my midrange. No horns killed it worse. A variety of shortened horns and holes in the top like the picture above all did my midrange NO good. It ran by far the best with the one small/one large stock top. Just about perfect in fact. On a dyno and off.

Then everything changed when I raised my CR to a calculated 10.0:1, dual plugged and remapped the ignition curve, went from 42 to 44mm intake valves, and really changed my port shapes. The same above experiments didn't hurt my midrange so much and got me gains on top. A few more tests and I am now running no top at all and my stock velocity stacks are shortened so the the bell mouths are just inside of the box. I have got super strong midrange with a setup that before would have killed it! It all depends.
I trust that you will contribute your dyno charts to the debate
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Charles
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1971 Commando Fastback
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