: Northstar Air Consumption.



Ranger
10-25-07, 09:31 PM
The PCM being cooled by intake air has always made me wonder what kind of air flow it has. So I pose this question to you math wizes. What is the CFM of intake air flow of the Northstar at 2000 RPM (70 MPH on an LD8)?
Here is what I came up with.
280 CI = 35 CI per cylinder.
Intake on every other rotation would mean 35x1000=35000 CI. per cylinder X 8 cylinders = 28000 CI converted to CF = 16.2 cubic feet per min.
Did I do that right? :hmm:

EDIT:
Got an answer from the other board (you guys are slow). Apparently I was off a decimal point. 162.1 CFM. That is a little better cooling.

Submariner409
10-25-07, 11:07 PM
:thumbsup: Yep....Around 162 cfm at 2k. Only a fraction of that at normal cruise or idle. For a real eye-opener calculate it for 6,300 rpm and figure the size "carb" a 280 would need.......(about 535 cfm, max)-blows the big throttlebody folks away.......

Now you know why a 350hp 327c.i. Chevy used a 585 cfm squarebore vacuum secondary Holley. (Bigger is better.......right?)

Not that any of this has a thing to do with cooling the PCM, and if you look at the air box there's no way air circulates around the PCM. My take on it is that its a convenient place to put the PCM to avoid unnecessary tinkerers.

Ranger
10-25-07, 11:23 PM
True, but the PCM is in a box with 162 CFM air flow so there is a pretty good air exchange which will help it shed much more heat than under the dash.

thu
10-27-07, 04:20 PM
Yes, that makes a lot of sense. It gets pretty hot under the dash during the summer. I guess it also gets hot in there during the winter with the cabin heat cranked up. Not the friendliest environment for electronics.

Submariner409
10-27-07, 06:30 PM
You're staring at this through a computer and monitor, right? Depending on your memory, processor, and video card those cutesy fans in there get rid of more heat than you want to know.

Most processor type electronics run at scary internal temperatures.

dkozloski
10-28-07, 02:16 AM
You're staring at this through a computer and monitor, right? Depending on your memory, processor, and video card those cutesy fans in there get rid of more heat than you want to know.

Most processor type electronics run at scary internal temperatures.
When the SR-71 was at cruising speed the coolest part of the aircraft was the interior walls of the cockpit and that was 180deg.F. Nearly everything else including the electronics and the hydraulic oil was at 400F or hotter. The only place to sink heat was to use the fuel in the tanks. Everything else was just plain hot. As Kelly Johnson said, not only were the Russians unable to duplicate the aircraft. They were unable to duplicate any system in the aircraft. When it was time to inflight refuel, the aircraft was brought down in altitude from 80,000ft.+ to the altitude of the tanker and slowed down to cool it. When the refueling was completed the airdraft returned to cruising speed and altitude. Because of the slowing and cooling requirement all long flights boiled down to an average speed of a little over 2050MPH. At Mach 3 and 80,000ft. the total drag of the aircraft was 12,000lbs. There were 33,000 lbs of thrust available per engine. When Kelly Johnson was asked about setting higher records he said, "There's more under the hood".
An old friend of mine that was in the "Blackbird program" for many years said that when a plane was rotated from Kadena AFB in Okinawa to Beale AFB in California it sent a departure message when it left Kadena. When my friend saw the plane arrive at Beale he worked the math backwards and realized the plane had to have averaged 4500MPH for the trip. So much for officially released performance figures.