will a ported plenum that was made for siamesed runners 1)work on a stock setup? 2)add any additional power gains of any sort? Just wonderin cuz I know a dude that's sellin one for 50 bucks or so. He decided he wanted to use a diff engine and wants to get rid of it. Its intended for a 58mm TB and SLP runners but he said it would work fine on a stock setup. What do u guys think??

 

Yes it will work fine with a stock runner setup. Who knows if you'd gain any power with it.

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1991 Camaro Z28
350 L98 w/ T56 (originally 305 LB9 w/ T5)
318 RWHP, 419 RWTQ
12.803 @ 108.50 MPH (1.932 60')
Member: SoCal F-Bodies
ThirdGen 4-Life!

 

Yes it will work. You'll have some flow issues at the runner openings but not any worse than what was there in the first place.

As for the 58mm throttle body opening, its not an issue. Your 48mm will bolt up and you wont see any problems. Consider the lowly carburator that sits on a single plane manifold: It usually just dumps into a big hole called a central plenum. Your plenum also has a big hole and your 48mm will dump the fresh air in just fine. The modified plenum simply has a wider hole is all. Airflow isnt laminar at the throttle plates anyway. It's quite turbulent so the plenum inlet isnt very critical in terms of shape and smoothness. You just have to clear out the restrictions is all...