99 L29 454 build

BeXtreme said:

No, that's not how that works. You can see from the data that the Temperature isn't even remaining constant, you are actually pumping heat into the air the entire way into the cylinder. Also, technically pressure isn't dropping. You are actually increasing the pressure in the manifold from idle to full throttle. At no point is the pressure in the manifold less than the pressure in the ambient atmosphere, so you are technically taking air at a set pressure and volume(atmospheric) and dropping the pressure while raising the temperature. n and R are also constant because you aren't adding fuel or changing the gas composition, so the only thing that can happen to make it balance out is for the volume to increase.

This whole thing has actually got me thinking about a manifold based intercooler like they have been running on the supercharged LS motors. I wonder how rough it would be to modify one to go in between the upper and lower manifold and what the actual effect on drivability would be... maybe a fun experiment for the future, since I have plenty of room in the squarebody for it.

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The only reason you're increasing air temperature is because everything around it is hot. I was speaking purely to the single point of P=VT. Hell the reduced velocity may just add the heat right back in too.

Supercharged111 said:

The only reason you're increasing air temperature is because everything around it is hot. I was speaking purely to the single point of P=VT. Hell the reduced velocity may just add the heat right back in too.

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I think you are fundamentally misunderstanding how all of this works.

The entire area is hotter than ambient air. You are always going to be adding heat to the system without an intercooler or atomizing fuel.

Velocity is not a part of the ideal gas law.

The only reason pressure is dropping, is because volume is increasing past the throttle blade due to the engine pumping air through it and the throttle blade acting as a limiter. The equation PV=nRT means that the Pressure and Volume would have an inverse relationship(which it does). As volume after the throttle blade is increased, the pressure decreases. Since combustion is occurring that is adding heat into the surroundings, you are also adding temperature into the system.. which means you are actually doing this P=T/V. So as the charge temperature increases, you are actually creating less of a pressure difference and sucking in less air.

BeXtreme said:

I think you are fundamentally misunderstanding how all of this works.

The entire area is hotter than ambient air. You are always going to be adding heat to the system without an intercooler or atomizing fuel.

Velocity is not a part of the ideal gas law.

The only reason pressure is dropping, is because volume is increasing past the throttle blade due to the engine pumping air through it and the throttle blade acting as a limiter. The equation PV=nRT means that the Pressure and Volume would have an inverse relationship(which it does). As volume after the throttle blade is increased, the pressure decreases. Since combustion is occurring that is adding heat into the surroundings, you are also adding temperature into the system.. which means you are actually doing this P=T/V. So as the charge temperature increases, you are actually creating less of a pressure difference and sucking in less air.

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?? Volume isn't changing. Pressure is. Let's say you cruise at 50kpa and ambient is 95kpa. Pressure in the intake manifold is less than outside of it. It's one of many things influencing the overall temperature of the air charge. I never said it was the dominant factor.

Not sure how this plays into the discussion other than IAT and air/fuel density but I'm planning to run a '87 454 TB with the TB to spread bore adapter that GM used back then. I'm guessing that adapter was plumbed into one of the heater hoses as it has water passages through it. When I was cleaning it up I thought that running the low side A/C line through it would cool the air/fuel charge as it passes through that adapter. Not that I'm going to do it, just a thought.

Supercharged111 said:

?? Volume isn't changing. Pressure is. Let's say you cruise at 50kpa and ambient is 95kpa. Pressure in the intake manifold is less than outside of it. It's one of many things influencing the overall temperature of the air charge. I never said it was the dominant factor.

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Volume isn't changing? How do you think an engine works?

That piston moving down in the cylinder while the intake valve is open and the exhaust valve is closed is increasing the volume of the area after the throttle blade. This change in volume is what drives the pressure down(creates vacuum). When the throttle blade is fully open(at full throttle) and there isn't enough restriction in the intake tract to restrict the flow of ambient air rushing in, the pressure difference will equalize fast enough with the ambient air that you will not be able to measure it, but it is still happening. This is the entire fundamental premise of an engine, you are increasing the volume in the intake to draw in the air/fuel mixture as the ambient air tries to equalize the pressure drop that results from such an increase in volume. The same thing happens with the exhaust, but in reverse. As the piston moves up, volume is decreased and therefore pressure increases. When the exhaust valve is open, the higher pressure inside the cylinder tries to equalize with the ambient pressure and flows out the exhaust.

BeXtreme said:

Volume isn't changing? How do you think an engine works?

That piston moving down in the cylinder while the intake valve is open and the exhaust valve is closed is increasing the volume of the area after the throttle blade. This change in volume is what drives the pressure down(creates vacuum). When the throttle blade is fully open(at full throttle) and there isn't enough restriction in the intake tract to restrict the flow of ambient air rushing in, the pressure difference will equalize fast enough with the ambient air that you will not be able to measure it, but it is still happening. This is the entire fundamental premise of an engine, you are increasing the volume in the intake to draw in the air/fuel mixture as the ambient air tries to equalize the pressure drop that results from such an increase in volume. The same thing happens with the exhaust, but in reverse. As the piston moves up, volume is decreased and therefore pressure increases. When the exhaust valve is open, the higher pressure inside the cylinder tries to equalize with the ambient pressure and flows out the exhaust.

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Dude you're taking this 9 layers deeper than my comment, forget I said anything at all.

Can you guys talk some more intelligensia about this intake air cooler sandwich design?

Extreme, the pressure in the manifold is almost always less than ambient. The vacuum level is typically about 15 inches at idle to 24 inches when coasting down. (29 inches is absolute vacuum). The only time manifold pressure approaches atmospheric is at wot when air flows in with minimum restriction. Even then you will usually see 1-2 inches minimum vac, which rises again as air consumption increases with rpm, due to other restrictions, like the air filter box or the MAF sensor beginning to limit the flow.

Scottm said:

Extreme, the pressure in the manifold is almost always less than ambient. The vacuum level is typically about 15 inches at idle to 24 inches when coasting down. (29 inches is absolute vacuum). The only time manifold pressure approaches atmospheric is at wot when air flows in with minimum restriction. Even then you will usually see 1-2 inches minimum vac, which rises again as air consumption increases with rpm, due to other restrictions, like the air filter box or the MAF sensor beginning to limit the flow.

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Yeah... that's what I said... in detail... two posts above yours. The less restriction you give the intake manifold to the outside air, the less vacuum you will see at WOT.

29 inches isn't necessarily absolute vacuum. That is a gauge measurement that would show close to absolute vacuum depending on your altitude and the current weather conditions. If you want to know what the actual absolute vacuum reading would be for your specific location and time, go to an airport and read the current ATIS. They will give a BARO reading that tells you what the current atmospheric pressure is at compared to absolute zero. It can be a wide variety of pressure between ~26-31 depending on weather, altitude, temperature, etc...

Standard atmosphere is the pressure of the atmosphere, at sea level, at a specific temperature(I think it is 15 degrees C) and with 0 relative humidity. It is an arbitrary number and is given as ~29.92 in-hg. In Siberia, the sea level pressure has been recorded as high as 32in-hg and near the equator it has been recorded near 26in-hg. Most vacuum gauges are going to be reading the vacuum in relation to the atmosphere that the gauge is in. A MAP sensor in the intake manifold is measuring Manifold ABSOLUTE pressure, which means it is measuring the pressure it is seeing in relation to absolute zero pressure(or as close as they can get it), not ambient pressure. So for a MAP sensor, you would be able to tell it has minimal restriction if it is close to reading the pressure reported by your closest weather station at WOT. For a vacuum gauge, you would actually just need it to show 0-1 in-hg at WOT