an engines Torque peak is almost always very closely related to the point in the rpm curve where the most effective/efficient cylinder fill, cylinder fill is related to both intake port cross sectional area and exhaust scavenging,efficiency, and is limited by port stall, and cam duration in relation to displacement, compression and valve train stability, ...all factors are easily calculated
links below
THINK THROUGH YOUR OPTIONS AND THE COMPLETE COMBO,
I see guys have long discussions about things like the difference in port cross sectional area or the best connecting rod length, to use, no one factor is going to make your engine totally dominate the competition, its a combo of small almost insignificant individual component choices being made and a good deal of time and effort taken during the assembly and clearancing work, that stack up to give you or prevent you from maximizing the engines performance.
you may not even think about factors like polishing crank journals, or valve train geometry or intake runner cross sectioinal area or length ,or intake runner port matching or surface finish, but the combined effects of your choices and components selected do mater!
look guys I think a good deal of this discussion is missing the point here, Ive built well over 150 engines in the last 45 years, (I lost cound decades ago)
but I can assure you that longer rods and the easily verifyable slight increase in dwell time, the longer rods produce will be totally meaningless UNLESS, you design the engine for and select components too take full advantage of the minor increase, by carefully calculating the REQUIRED compression ratio,fuel octane required,all the factors related to the cam timing,(duration,lift, LCA) you calculate and build and install, and tune the engine for , a matched exhaust header scavenging (header primairy length and diameter plus collector design) and the intake runner length and cross sectional area, to maximize the cylinder scavenging effects, plus you match the fuel/air ratio, and ignition advance curve, to maximize that longer dwell times potential advantage.
the valve seat throat area as a percentage of the intake valve diameter effects the port flow rate, yes the port cross section and angle also effect flow rates and larger valves and larger throat areas with less restriction obviously have some potentially lower flow restriction.
SO HOW do you MEASURE THEN??
lets do a bit of math, and keep in mind that a correctly designed header and exhaust system, if matched to the correct cam timing can significantly increase the engines potential power/rpm band
port cross sectional area can be measured and the stall speed , accurately calculated, as can the required matching header configuration, and cam timing, yeah! it takes some reading but the infos readily available
just a bit of info on intake gaskets sizes to match port cross sectional areas
Calculating the valve curtain area
The following equation mathematically defines the available flow area for any given valve diameter and lift value:
Area = valve diameter x 0.98 x 3.14 x valve lift
Where 3.14 = pi (π)
For a typical 2.02-inch intake valve at .500-inch lift, it calculates as follows:
Area = 2.02 x 0.98 x 3.14 x 0.500 = 3.107 square inches
SO lets do a bit of math
a cylinder head with a 2.02' intake valve and a cam with a .450 lift at the valve with a 1.5:1 rocker will in theory produce a valve curtain area of 2.79 sq inches, swapping to a 1.6:1 ratio increases the lift to .480 lift 2.98 sq inches, increasing the available port flow potential at least in theory by about 6%, but keep in mind the port can only flow at full valve lift for the limited time the valve remains at full lift and if the narrowest section of the port cross sectional areas less that the valve curtain area that not the valve restricts flow
USE THE CALCULATORS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/
http://www.hotrod.com/articles/choosing-the-right-camshaft/
http://garage.grumpysperformance.com/index.php?threads/bits-of-383-info.38/
if you were to look at a performance big block chevy cylinder head your largest standard intake valve size is either a 2.19" or in a few cases the larger 2.3" valves
a bit of math shows that you won,t reach the max potential flow until valve lift reaches or slightly exceeds about .575-.600 inches of lift with a big block chevy
and a bit more math suggests a minimum of 4.2 square inches of port cross sectional area would be about ideal to match that potential flow,
if you built a 496 BBC stroker that 4.2 SQ inch port would max out at about 6000 rpm and would be best matched with a single plane intake and a cam with a tight 105-106 LSA
http://www.wallaceracing.com/Calculators.htm
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=5649
useful RELATED INFO you might want to read
http://www.wallaceracing.com/runnertorquecalc.php
http://www.pontiacracing.net/js_header_length1.htm
http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/
http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/
http://garage.grumpysperformance.com/index.php?threads/calculating-ideal-port-size.624/
http://garage.grumpysperformance.com/index.php?threads/sellecting-cylinder-heads.796/
http://garage.grumpysperformance.co...ting-a-port-size-and-intake-for-nitrous.4930/
http://garage.grumpysperformance.com/index.php?threads/semi-fool-proof-cam-sellection.82/
http://garage.grumpysperformance.co...velocity-heads-tuned-intake-turbulence.12998/
http://garage.grumpysperformance.com/index.php?threads/calculating-header-design.185/