NewbVetteGuy

Can anyone help me understand why head intake airflow #'s are always lower than exhaust airflow numbers and exactly what that means?

Let's say a head's exhaust airflow at 0.500" lift is 150 CFM, but it's intake exhaust airflow statistic at 0.500" lift is 200 CFM --isn't the ACTUAL airflow just restricted to 150 CFM as the exhaust becomes a huge bottle neck? (Assuming a single lobe cam and rollers / rockers that are the same ratio)

Or is it ok and expected that exhaust airflow is less because a lot of what's coming into the engine is being burnt up by combustion so there's just a lot less that needs to go out the exhaust side?

If so, what's the "ideal" ratio of intake vs. exhaust airflow?



Practical application time:


My perspective heads' airflow numbers look like below; would I benefit from a dual lobe cam that has a longer duration on the exhaust, assuming that I have removed all exhaust restrictions?


http://www.high-performance-engines....p/sbc64185.htm
Lift CFM Lift CFM
0.200 130 0.200 107
0.300 195 0.300 142
0.400 240 0.400 172
0.500 260 0.500 187
0.600 265 0.600 196
0.700 270 0.700 203
0.800 272 0.800 207



Adam

gerry72

Exhaust gas is hot and has energy. There is also considerable pressure in the cylinder when the exhaust valve opens. Intake airflow has only atmospheric pressure to move air into the cylinder.

NewbVetteGuy

Well, that's kinda embarrassingly simple and obvious now that you've said it.


Thanks
Adam

cv67

Your perrecntages look fine theres a std out there somewhere
like mine a little closer together. Cam accordingly

Know most go bonanza over flowZ its just a guide.
air moves in pulses with certain characterisitics in an engine
On a bench its steady so.....
Fun seing what ya got though.

Boy if i was good with writing software I could cash in.