Date: Thu, 30 Oct 2003 09:44:50 -0500
From: echristley@nc.rr.com
Subject: Re: [FlyRotary] Re: Intake manifold
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Reply-to: echristley@nc.rr.com
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> So why do I need primarys and secondarys with different lengths 
> that screw up DIE and generally make life more difficult?
> There must be more to this than meets the eye ... Jim S.

I'm just going off of what I've been told myself, but I think that the most direct answer to what you're asking is, "'Cause Mazda wasn't worried about you when they were making design decisions for their car engine."

They made decisions about port size and placement that are somewhat problematic for someone who wants to run the engine up to a specific, and rather high, RPM and get maximum performance at that point...sacrificing performance at a lot of lower RPM points in the exchange.  The differing runner lengths are necessary to counteract the earlier decision that were, literally, cast in iron (or aluminum, I forget which).