Originally Posted by Rx7carl' post='847219' date='Nov 29 2006, 06:55 PM

I would tend agree with you in theory, but...........

Well I ran some tests using different spacers on an RX-3 mainfold (Indpendent runners). Open plenum spacer made the best power up top (5k up) but lost considerable amount below that. The IR spacer was great till about 5K then felt weak (probably flow limited as the primary ports on a 12A stink for flow). The dual plenum was the best compromise (at least for street use). Very small loss at low to mid range, and decent top end (probably from the good flowing secondaries "borrowing some of the primary intake charge through the channels, at least thats my theory after flowbenching stock irons). I agree that the channels should hurt VE at low rpms (probably responsible for the small power loss), but it seems the best compromise for a street engine. This was all on a 1st gen, 12A, stock port, RB SP exhaust, Sterlingcarb. Stopwatch, g-tech and butt dyno.



Bottom line to me is that whatever works best for the application is what should be used. Theory is all well and good but we're limited by what Mazda has already engineered so we have to work around that, so compromise is the best we can reasonably achieve, unless you want to get into custom fabbed parts, which most of us dont have the resources to do.