Grumpy, can you explane??

[grumpyvette]

yes the larger valve has a lot to do with it but one of the things that the DD-2000 program does not show is that the flow numbers are derived useing just the cylinder head on a flow bench while the larger 215cc head really flows quite a bit better than the 200cc head at almost every lift when an intake and headers are attached in an engine with moveing pistons and valves like in a real engine because most airflow in an intake port is along the roof of the port to the far side of the valve not evenly across the intire ports area, the larger valve and port gives the airflow more room to straiten the flow as the valve changes lifts and remember that valve is moveing open and closed 30-70 times a second in a running engine where that airflow must pulse into the cylinder but air flow rateings are taken with the valve locked at a set lift (something that NEVER HAPPENDS in a real engine) remember at 6000rpm that valve is only open for about 230-250 degs out of the 720 deg cycle, thats a time frame of about 1/3 of the cycle time and the valve is expected to flow air into the cylinder 3000 times a minute or ever 1/50th of a second for only about 13 thousands of a second, I could get into pulse harmonics but look here, the presure waves move at several cyclic rates, some as fast as the speed of sound (roughly 900ft per second) and since the valve itself is also moveing flow bench data taken with a stationary valve is only a EXTREMELY POOR way to judge port flow.

 

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

 

http://www.grapeaperacing.com/GrapeApeRacing/tech/intakehelmholtz.cfm

 

http://www.grapeaperacing.com/GrapeApeRacing/tech/intaketuned.cfm

 

let me put that another way , you know those toll booths you go through on the turnpike? well the end one is usually about 2 feet wider and 8 ft taller for trucks right, well that air in the intake averages better than 350ft per second in the port thats 238mph, if you had to go through that toll booth at 238mph which bay would you think would be easier to drive through at 238 mph , the narrow one or the slightly wider one??

[utvolman99]

Well, I guess that makes sence. I do understand that logically the larger ports should flow more. At the same time it is not clear to me why the static state flow testing would not be a good predictor of the dynamic flow characteristics. I would see the variables as time, valve lift and valve size? Oh well, your the man and I trust your information.

[grumpyvette]

btw

http://www.kendrick-auto.com/dart_cs_iron_eagle_215.htm

 

these are the flow numbers with a minor port job

[utvolman99]

I am using the Iron Eagle 215cc heads (per your suggestion) and have a question. I was looking at the flow numbers for these heads compared to the 200cc heads. For the lift cam I will be using (xe268 or xe274) it would seem the 200s flow much better. The thing is when I plug the flow date into Desk Top Dyno 2000 I get almost identical numbers?? Here is the flow data from Dart.

 

215cc Iron Eagle Heads

Lift CFM

0.200 127

0.300 178

0.400 216

0.500 249

0.550 264

0.600 268

 

200cc Iron Eagle Heads

Lift CFM

0.200 129

0.300 185

0.400 229

0.500 261

0.550 252

0.600 252

 

The data I'm using for the simulation is as follows

 

350 ci

short tube headers

single plane intake

750 carb

10:1 compression ratio

cam lift of 477/480

 

Does this have anything to do with the fact that the 215s have 2.055 intake valves and the 200s have 2.02s? I suppose its possible that the DTD #s are just wrong??