Port & Runner Math

[grumpyvette]

read this, BUT keep in mind it does little good to have killer head flow numbers if the intake manifold flows less or if the exhaust is restricting flow, and heads that flow killer numbers at .700 lift, and are designed to feed a 427 displacement at 7500rpm, DON,T do you much good if the CAM you sellected has a .520 lift AND ONLY SPIN THE ENGINE TO 6000RPM, obviously each choice you make in components effects the results

 

http://www.tmossporting.com/tabid/1805/Default.aspx

 

BTW.

ITS A COMON MISCONCEPTION,THAT YOU MEASURE PORT CROSS SECTION AT THE PORT ENTERANCE,BUT ITS NOT the port area at the enterance , you need to use in the calcs, ITS the MINIMAL port cross section at the SMALLEST point in the port, usually near the pushrod area.

LIKE a funnel, its not the largest part of the opening but the smallest thats the restriction to flow

 

SO HOW do you MEASURE THEN??

 

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=5649

 

 

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2D900014&N=700+115&autoview=sku

 

USE THIS

 

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

 

 

 

http://users.erols.com/srweiss/tablehdc.htm

 

http://www.malcams.com/legacy/misc/headflow.htm

 

 

here’s a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes

(measured at the smallest part of the ports)

...........................sq inches........port cc

edelbrock performer rpm ....1.43.............170

vortec......................1.66.............170

tfs195......................1.93.............195

afr 180.....................1.93.............180

afr 195.....................1.98.............195

afr 210.....................2.05.............210

dart pro 200................2.06.............200

dart pro 215................2.14.............215

brodix track 1 .............2.30.............221

dart pro 1 230..............2.40.............230

edelbrock 23 high port .....2.53.............238

edelbrock 18 deg............2.71.............266

tfs 18 deg..................2.80.............250

 

Potential HP based on Airflow (Hot Rod, Jun '99, p74):

Airflow at 28" of water x 0.257 x number of cylinders = potential HP

or required airflow based on HP:

HP / 0.257 / cylinders = required airflow

[SuperKid]

Great information. Thanks!

[z383z]

I am sure it is all relevant to the rpm range you want to be making power and I am aware what cross sectional area is more important for making Tq. than intake cc's but I was wondering how important intake runner length is in comparison to intake cc's and cross sectional area in keeping air velocity.

[grumpyvette]

runner LENGTH and CROSS SECTION plus PLENUM VOLUME (if there is a plenum)effects the intake harmonics and how effectively you can ram tune the intake runner charge to fill the cylinders, and don,t forget exhaust scavaging , compression ratio and cam timing, and valve curtain area,and drive train gearing must match the intended combos effective operational power band

 

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

 

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

 

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

 

http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html

[Kevin Shasteen]

I am sure it is all relevant to the rpm range you want to be making power and I am aware what cross sectional area is more important for making Tq. than intake cc's but I was wondering how important intake runner length is in comparison to intake cc's and cross sectional area in keeping air velocity.

 

I love this comment. The answer, as I see it and have pondered, as the epitomy of a properly packaged engine.

 

As my understanding goes, you cant simply take one aspect of an engine component and say it is the most important nor can you take one useful auto math equation and claim it too is the deciding factor that determines all others.

 

However, with that in mind, the three relative dictates if you will, that determine maximum output for whatever level of performance an engine builder desires, are: 1) Displacement, 2) Peak Power Output, 3) Peak RPM

 

As a caveat the performance engine is multidimensional. Three dimensional to be exact regarding these three primary functions. Most enthusiasts, myself for many years only see the engine as one dimensional. For me, and I cant claim this is the right approach for everyone, but once I understood what variables affect (control) these functions then everything else made perfect sense.

 

So, for more understanding of these three dimensions, for me at least, and how they control the behavior of any engine, I put them into relationships, such as:

 

1) The Dynamic to Static Compression Ratio; as this relationship determines if the engine will be ran on pump gas, race gas, or a combination of the two. This relationship is further evidence of how detonation prone your engine is or isnt within the category of performance you have chose to run in.

 

2) Compression Wave Dynamics; as this determines the peak rpm potential your engine will rev up to if the secondary engine component parameters match the primary engine component parameters. This relationship determines the length of you intake runners from the air horn of the carb or throttle body all the way to the intake valve.

 

3) Peak Power Intensity; which is controled by the Volumetric, Mechanical, and Thermal Efficiencies of the engine..,

 

As tuners we cant always be as adept as a rocket scientist, even tho we try, as most of the variables in engne performance intangibles are taken care of by the mfg's. But we can make good use of the control mechanisms left up to each one of us through our limited understanding of those components the mfg's have produced for our pleasure.

 

To give an answer regarding which is more important, intake runner length or the cross sectional sq.in. of the cylinder head's intake. Well, once again - they are both important.

 

Have you ever heard the reference to different performace engines as:

1) Phase 1 engine

2) Phase 2 engine

3) Phase 3 engine

4) Phase 4 engine

5) Phase 5 engine

 

Each of these different levels of engines carry with them different engine component parameters. As you dive into analyzing the differences of each engine you will find that each increase from the lower to the higher phase engine will include, higher SCR, Longer Duration Cam w/higher lift lobes, Larger Intake/Exhast Ports that breathe better, Higher Peak RPMs, and a less life expectancy.

 

To minimize these differences so as to understand the differences between each category; the components of each category could be labeled mild, moderate, or maximum. Keeping in mind that mild, moderate, or maximum is only relative once you have factored Displacement, Power Intesity, and Peak RPMs into the equation. There in lies the symbiotic relationship of the engine as at first glance it appears we are having a circular discussion; but we are not.

 

Without these three categories, you have no relavancy as to what mild, moderate, or maximum is. To help understand the phase 1-5 vernacular we could give a generic classification as Peppy Street Engine, H/O Engine, Street/Strip Engine, Moderate Race, or Maximum Race.

 

Learn to recognize patterns within each progressive build and what equations go into the Dynamic to Static Compression Relationship, Compression Wave Dynamics (not much out there on this subject), and Peak RPM.

 

The Cylinder Displacement to Intake Port Volume will determine the VE within the category of performance you have chosen to operate in, while the DCR to SCR relationship determines race gas or pump gas for a detonation free engine within the level of performance you have chosen, and the Camshaft Profile determines where in the rpm range you wish the peak powers to surface.

 

I'm sure all this makes things clear as mud and twice as confusing(?).

 

Kevin,

(Yea,Still an Inliner)

[grumpyvette]

I think that can be summed up as

YOU NEED TOO,

MAXIMIZE THE CYLINDERS VOLUMETRIC EFFICIENCY, FOR THE DISPLACEMENT,RPM RANGE & COMPRESSION RATIO

 

and realize that factors like the stroke and valve curtain area effects the compromizes that need to be made in sellecting components

 

the basics in performance limits are related to how fast you can effectively fill and burn a full or nearly full cylinder of fuel air mix and at what rpm band you can maintain BOTH that fully filled cylinders pressure curve effectively producing thrust on the piston, and the cylinder scavaging/and filling. at some point the time available just starts to become so short that the cylinder can,t effectively be fully recharged, remember at 1000rpm the cylinder fills and fires 8.3 times a second, at 7000rpm, thats 58 times a second and its hard to get a fully charged cylinder in that time frame with some component choices