[Hasbro]

Originally Posted by aerohead

I'm no engine guy.I've read a bunch of stuff.I think the root of your question comes down to the one-size-fits-all conundrum.If you go for low end,you loose top end.The transient regimes an engine is asked to operate within,seems to require trade-offs somewhere.You may have read of variable-length intake runners,which switch between two separate intake manifolds,depending upon a prompt from some fly-by-wire gizmo.It's an attempt to deliver "both worlds".I think economics constrains the engine designer,as the bottom line is always in sharp focus,and everyone does the best they can within the budget constraints for a particular model.I'm still focussed on load reduction and trying to keep the engine I've got in it's "sweet-spot." I may get under the hood one day,however my confidence in out-smarting a powerplant engineer, for performance and driveability in the real world is weak at best.For the rpm band modern engines perform at during cruise,I think the volumetric efficiency is good overall.You might want to think in terms of maintaining the best brake-specific-fuel-consumption(BSFC)for your existing setup as your target.Engines are a lot like algebra.Whatever you do to one side of the equation,you've got to do the the other.Engines are really complicated.I'll shut up.No doubt other,better qualified members will jump in on this one.If you've got access to a dyno,you'll be in a position to know about mods in a controlled environment.Short of that,it's going to take a lot of patience and time to figure out what your changes are doing.Best to you on the project.

My 04 Civic Si has the same i-vtec motor as the RSX except the RSX has a different dual intake runner. While the Si has a higher hp. top end of 160 vs. 155, the RSX has 141 ft-lb of torque vs. 132. All the "tuners" want the Si's manifold...