Tom 400 CFI

Is there a formula for figuring optimal port/runner cross sectional area, based on displacement and desired RPM? In other words, I know the bore and stroke. I know the RPM I want the engine to make max torque at. With that info, and I figure the best runner area?

Thanks.

-Tom

Vader

I'm sure there has been an attempt at a formula of some sorts. I've never encountered one. To my simplistic way of thinking, it's as much an art as a science. The VE of any given engine will determine the volumetric needs, and that is affected by chamber design, valve position and design, valve timing, RPM, and various other factors including the intake design. Presuming a "perfect" intake, one might extract a given runner area (cross sectional) for a given pressure drop. Unfortunately, there are dynamic forces within the intake runners themselves which affect the overall flow. That was one of the original intents of the CFI (and TPI, and most other intakes).

As a result, both conventional fluid flow dynamics and sonic wave/pressure theories are involved. How they will overlap with any particular combination is your question. Search for theories about the "Mesh Method" as described by Roland Benson. His texts may have some helpful information.

One crude, incomplete formula is as follows: Peak torque rpm = (cross section area x 88200)/cylinder volume.

Tom 400 CFI

Thanks a bunch Vader. This will help me w/my current project.

-Tom

Streetiron85

This is interesting reading, if nothing else.
http://www.circletrack.com/techartic...458/index.html

grumpyvette

"Is there a relationship between plenum volume
and runner length or can runner length be changed
moderately without requiring a complementary
change to plenum volume?"

yes! IT CAN!
but theres other factors
your forgetting
port cross section
port taper
valve size
COMPRESSION,ratio
CAM TIMING,
EXHAUST SCAVAGING,
exhaust back-pressure
ROD LENGTH,
DISPLACEMENT
throttle body flow
ignition timing
bore to stroke ratio
intended rpm range
rear gear ratio
flame front
and a few more




http://victorylibrary.com/mopar/intake-tech-c.htm

http://victorylibrary.com/mopar/cam-tech-c.htm

http://www.rbracing-rsr.com/runnertorquecalc.html


http://www.bgsoflex.com/intakeln.html

http://headerdesign.com/extras/engin...take_Manifolds

http://www.digitalcorvettes.com/foru...light=designed


http://www.team-integra.net/sections...?ArticleID=466

http://turbonation.com/intake.htm

http://www.wallaceracing.com/runnertorquecalc.php

http://www.mercurycapri.com/technica...intake/pt.html



ever wonder WHY intakes are designed with runners shaped like they are?
you might want to read this info