intake flow requirement of 3.0?

[MotoSook]

Can someone provide some numbers? I need to verify some numbers. IN particular the per cylinder flow.

[Tim Walsh]

do you need CFM numbers or something else? I have a spreadsheet that can tell you what the required port sizes are or how fast the gases are flowing depending on cam and port size.

[MotoSook]

You have e-mail.

[Wayne 962]

Yes, are you talking about air supply numbers, or CFM of stock engines? It depends upon the characteristics of your engine as well. A stock 3.0 will require much less air than a high-revving, race motor with high-lift cams, etc...

-Wayne

[MotoSook]

Wayne,

How about a stock 3.0 intake CFM. Ultimately does it come down to optimal intake volocity at desired peak?

[jluetjen]

Souk;
Are you still running the stock CIS? Just stock there are 2 data points with the two different versions of the heads -- early with 39 mm intake ports and then the later ones with the 32 mm intake ports. I haven't seen anything that would suggest that either engine performed significantly different then the other. It would most likely be safe to assume that the results would be the same for any points between those two extremes too.

The other thing to consider is what else is in the intake path? Specifically the CIS system. If that is the gating feature, then port measurements won't be particularly meaningful for peak airflow. I'm not aware of anyone posting airflow data through the CIS system, so that is one big unknown. On the other hand, it may be beneficial in CIS engines to have smaller intake ports since that will keep the air speed up in spite of the slight vacuum that I believe is created by the CIS air meter. Note that this is a suspicion of mine, but I haven't played around with CIS systems enough to test this theory. It should be pretty easy to check by hooking a vacuum guage up to the plenum (downstream of the air meter) and drive up and down the highway and see what happens. Keeping the intake air speed above a certain value most likely helps keep fuel suspended in the ports and promotes better mixing once the air-fuel mixture enters the cylinder, both of which promote combustion quality and as a result torque.

Anyway, while I think that Tim's spreadsheet is pretty accurate for carb'd or MFI'd engines (we've compared notes), I'm not sure about how valid it would be for an engine running with CIS. Something to consider.

[Bill Verburg]

At 100% volumetric efficiency a 3 liter will process 344cfm @6500rpm

[MotoSook]

Tim, John and Bill:

Thank you for your responses. I feel better about my numbers now.

Tim and John: I'll send some questions on your work via e-mail.


Thanks guys. This is good stuff!

[Wayne 962]

The CIS system is not known for its performance, however, it's also not terribly known for bad flow numbers. The path that the air must take winds itself around the system, which doesn't create good airflow, however, there's not much you can do about it. The Carrera Motronic runners are well known for being uneven, and can be modified via an extrude-hone process that evens them out a bit. I think that if you worked on the CIS system, you would be frustrated by the fact that the airflow restrictions come more from the sensor plate than the runners themselves...

-Wayne