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don't do it (long) Posted by KenManiac [Email]  (#392) [Profile/Gallery]
(more from KenManiac) on Sun, 19 Feb 2006 11:24:37
In Reply to: Re: Crazy idea to help decrease 2.1 head lag?, MS, Sat, 18 Feb 2006 23:23:28 Members do not see ads below this line. - Help Keep This Site Online - Signup |
don't do it. plenum volume is important for low rpm unboosted torque, as well as for cylinder filling under boost.
ideally, the runners should taper from big in the plenum to small at the head (cross section of the runners). don't make it small to big or undesirable effects will occur.
plenum volume should be 50 to 70% engine displacement. more important than volume is taper from plenum to runner. smooth and gradual is good here. radius of taper should be equal or greater than radius of runner, in a perfect world.
to reduce lag, increase CR. you're going in the right direction here. restrictions are bad, but total intake system volume is not. pressure waves move at the speed of sound. don't worry about smoothing every single bump in the manifold - much better results come from smoothing transitions - the hose to pipe junctions are an area where dramatic improvements can be made.
gasket match the head and manifolds, but leave a positive step. the intake mani port should be 1/16 to 1/8" smaller than the port in the head. ditto the exhaust port to exhaust manifold. a little anti-reversion never hurt anyone.
bigger volume, longer runners increase low end. the turbo will stuff it in on the high end. think tuba versus piccolo.
more CR, more intercooler, more boost. as far as manifold shape, those engineers do know what they're doing most of the time. an NA manifold on a turbo can be rather lovely.
(much of this info comes from Corky Bell's 'Maximum Boost'. i highly recommend it)
, Sat, 18 Feb 2006 21:48:23, Sun, 19 Feb 2006 11:24:37 <-- Viewing This Message
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