Originally Posted by
Turbocharged400sbc
inertia is a *****. GN guys have played with this issue since the early days of the UIM power plates, meant to provide flow restriction for more even air distribution to all cylinders. early SI 3800's have a "ski jump" at the end of the TB adaptor where the air enters the plenum. this was changed in later SI production to the more modern low plenum wrapover runner (early are alum, later plastic) manifold design that was eventually applied across the whole range of GM V type engines due to cheapness of molding/die casting. everything is a result of compromises.....no compromise gives you the larger/harder to package Lehmann style intakes and the nearly perfectly even air/fuel distribution.....most modern high performance boosted engines use a variation of it...modified usually for easier injection molding of a plastic unit.
the whole engine is too short, to save $ and weight, GM circumcised an extra inch off the deck height it means a horrible rod stroke ratio, which means ****ty high rpm cylinder filling and drop in pumping efficiency. readup on rod/stroke ratio and youll see why indycar/high reving engines run a near 2:1 rod/ stroke ratio while our L67 has a horrible 1.5:1
a hybrid SI/SII would allow for a 1.96:1 ratio....and even then the offset journal crank would make me leery of going over 7k
07-18-2018
