View Single Post
snowman snowman is offline
Banned from Pelican
 
snowman's Avatar
 
Join Date: Feb 2003
Location: So California
Posts: 3,787
Quote:
Originally posted by sammyg2
the VE on my engine is around 140% from 3500 to around 4500 where it climbs a little to probably around 150%, then starts to drop down a little at 6000 rom, falls off to around 120% at 7000
Real engines don't need turbos or superchargers.

Anything over 100% VE is generated by some kind of "supercharging" the engine. Without an actual supercharger this is done by taking advantage of tuned ports and the fact that the engine is a pulsed system, ie the power is generated by relatively short bursts of power. If you look up the waveshape of a math function called sin x/x in the frequency (rpm) domain you will see a big hump in the center with symetrical decaying sine waves on each side. Every time a cylinder fires you get one of these things. If you carefully line up adjacent pulses you can use the mini pulses to add or subtract from the main pulse. This is what tuning and headers take advantage of. The mini pulses stuff more air in and help suck more exhaust out. but only over a narrow rpm range.
I beleive the maximum that can be done is about 120% and then only at ONE exact RPM. Thats my basic understanding of what goes on. An automotive engineer may be able to add to this and present a more precise or correct explanation.

By using extreemly sophisticated math one can broaden the usefull RPM range, reshape the pulse ect. But there is a very finite limit to what can be done without help from a turbo or external supercharger. The trick is also not to hurt performance, which is very very easy to do.
Jack

Last edited by snowman; 12-30-2004 at 03:24 PM..
Old 12-30-2004, 02:58 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)