AZGASSER

This is a technical question for the engine pros. What is the air flow in the factory intake. CFM will work. I am working on the physics of heat transfer through the intakes and underhood temp. Just a little light math for a Sat morning. My contention is the CFM flow through the intake and the relative insulating properties of the hard plastic intakes is that the transfer is almost nothing. We do so many things to keep the temps cool that I don't think we are doing much benefit.
So far I am working with an underhood temp of 104 deg C and ambient air temp of 27 deg C. Surface area of the intake of .91 m sq. and a thickness of .003 m. My initial calculations is .24 watts of heat transfer per second.
I know this is maybe not the best place for the question but maybe some of the physic geeks out there can help with this.

atljar

I'm not a physicist.. . But I do know that cfm doesn't exist without a force to create air movement and I have spent a fair amount of time around flow benches. In other words, the intake has no airflow unless the engine is sucking air through it. (duh)

In the aftermarket, the relatively small ports of heads are normally tested at 25 or 28" of h2o, which is the amount of suction pulling air through the heads.

Bigger things like carbs or air filters or intake tubes are normally tested at a much lower " mercury rating, like 1.5 or 3". Sometimes 10"h2o. . A flow bench simply doesn't have a big enough vacuum on it to suck any harder to get to the 28"h2o mark.

The tested Cfm of any item, at a higher vacuum test point, is going to be higher.

So with that said, the first thing you need to know how much suction force is in the intake tube from the engine. Of course this will vary with mods, temperature, rpm etc etc . Then you need to be sure the cfm numbers you're using in your calculations match the "h2o of suction that the engine is producing under certain conditions

The other option would be to use Maf readings and go from there. To me, that's the simpler route. I don't know for sure, but I also would think mass would be what you would want to use for heat transfer calculations, not volume.
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Keppler

The maximum mass air flow for a normally aspirated engine is:

max air flow = rpm x engine displacement/2 (add the unit conversion constants)



Found this site: http://www.epi-eng.com/piston_engine...efficiency.htm

atljar

That is for volume not mass. Engine displacement times revolutions, is volume, divided by two because it's a 4 stroke engine. You can covert that to mass, but it's not perfect

Warp Factor

Using the general rule-of-thumb of 1.5 CFM per horsepower, it would be about 975 CFM at full power for a stock ZO6 engine.

AZGASSER

OK, so now we are getting somewhere. I made the following assumptions. Intake diameter is 5 inches so that give the intake area of 0.135 sq ft. If we move 975 cubic feet through a hole that size you use the equation 975/.135x60(mins in hour)x5280(ft/mile) this yields a speed of 82 MPH. That is moving. I would challenge that the air is moving so fast that any heat under the hood or even by contact of radiator hose with the intake are not going to impart any measurable heat to the air going into the engine.

Mr. Gizmo

Higgs Boson

Even more confusing is the fact that most flow benches in the racing industry measure dry air at low pressure drops, commonly 10 inches of water column (W.C.), one bore or venturi at a time. This result is multiplied by a factor to arrive at what that bore would flow at a higher vacuum (i.e. 1-1/2 or 3 inches of mercury), then that figure is multiplied (by four, in the case of a 4 barrel carburetor) to get the C.F.M. rating. This rating is usually much higher than it actually is.

http://www.candsspecialties.com/ratings.html

furthermore, compression, fueling and spark lead precision, etc are major contributors to power, not "just" airflow.

fwiw, my race car has a 327ci engine with low compression (8.5:1) and a 300 cfm carb (rules) and made 580 hp on an engine dyno. the car weighs 2900 with me in it and runs 9.80 on avg.

Warp Factor

On the Dodge, that is the rated flow of the intake system when a certain amount of test vacuum is applied, not what the engine and intake are actually flowing during operation. The engine itself would not actually be pumping that much air, regardless of what the intake system is rated at.

The stock heads on the 440 Chrysler were very restrictive. My blown bored and stroked (505 cubic inch) Chrysler wedge made peak power on the dyno at only 4600 rpm with the stock heads, because the heads were so restrictive. Power just dropped above that. The same blower and carbs on my 502 Chevy made peak power at 6500 rpm, and 200 more horsepower.

So the money spent on increasing the displacement, and putting in internals capable of spinning to 7500 rpm were kind of wasted on the Chrysler, without going to aftermarket heads.

Mr. Gizmo