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Discussion Starter #1
I have asked before about the Co2 Intercooler sprayers and have gotten the response that I thought I would, The cooler air after the MAF will mess with the Rich/Lean conditions as also confusing sending units. There is a company that puts out a intake adaptor that mounts before the MAF. I assume this will alleviate the problems of the cold air not being read by the MAF. They use a streamlined radiator if the intake tube to cool the intake air, I have seen a writeup that showed a sustained blast of Co2 dropped the intake air by 40+ degrees. Has anyone seen this or heard of it? Any opinions? Looks like a great safe Nitrous alternative, or even a good way to cool the intake down during those hot track days. This is the link to the company
http://www.designengineering.com/products.asp?m=sp&pid=4 . If anyone knows of a vendor from here that sells this or knows about it , it would be great to hear about it.
 

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Not confused

A CO2 intercooler sprayers will not "confuse the sensors" !!!.

Cooling the air after the MAF sensor will not change your mixture. The MAF measures "all the air that passes through it" If you put 20 lbs of air / min through the MAF, it will read the same if the air is 90 deg F or 30 deg F.

The only way the CO2 chillers alter mixture is if you run out of fuel injector capacity. If you run your fuel injectors static due to the higher air flow you will go lean but the problem is NOT the CO2 chiller it is having inadequate fuel injectors.

On cars with short ram underhood air intakes topmount intercooler chillers can effect fuel air mixtures if some of the coolant (nitrous or CO2) gets pulled into the intake. In that case the nitrous will make it lean out, and the CO2 will cause a noticable drop in power and rich condition.

Just make sure you have enough fuel injector capacity and you should be good to go.

Larry
 

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Thinking Man's Engine
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There is a map sensor at the throttle body, so yes temperature fluctuations will affect the pressure

Using the simplest equation:
PV=nRT
(air is technically not an ideal gas, but many times in fluid dynamics, we let air become an ideal gas, just for simplicity).

if you let Volume and the number of Moles of air (IIRC what n is) is constant, and R is a gas constant...Pressure is proportional to temperature.

Using the CO2, as it evaporates it carries a lot of heat out of the intercooler, so the temperature drop may be considerable enough that the injectors cannot compensate.
 

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MAP and MAF

The manifold pressure does not matter regarding the fuel air ratio. The ECU controls the fuel based on the MAF air flow at the intake. Boost does not = air density.

If you put 20 pounds a minute of air into one end of a pipe 20 pounds a minute of air MUST come out the other end ;)

It does not matter whether it is at 18 psi and 100 deg F ro 14 psi and -40 deg F it is still the same amount of air.


so the temperature drop may be considerable enough that the injectors cannot compensate.
same as I stated above, you can run out of injectors if your stupid and do not upgrade when you need to.

Larry
 

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Thinking Man's Engine
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Re: MAP and MAF

hotrod said:

It does not matter whether it is at 18 psi and 100 deg F ro 14 psi and -40 deg F it is still the same amount of air.
It's still the same amount in terms of number of molecules.

It is different in the volume.

If the intake temperature does not matter....what's the point of an intercooler?

Take out your intercooler and see if it makes a difference. I bet it will.
 

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just the basics

Your missing the whole point. All the air that goes past the MAF MUST go through the engine. If the same number of air molecules take up less space ( when cooled significantly) more of them fit in the cylinder in each intake stroke, which makes more power.

The pressure of the air is not the important number, mass flow is what determines how much fuel you can burn.

You can gain air density by either cooling the air or increasing the pressure. Just because the manifold pressure drops when you super cool the intake charge does not necessarily mean you lose power. If the cooling more than makes up for the loss in pressure due to increased VE from the high density, reduction in likelyhood of detonation due to the lower charge air temp, ability of the ECU to run more effective ignition timing.

Manifold boost pressure is only useful when comparing two engines that have similar manifold air temperatures. As mentioned above in the perfect gas law, ---- If constant volume P1/P2 = T1/T2.

You have an intercooler precisely because temperature of the air charge is just as important as its pressure. You loose pressure as the air passes through the intercooler but it more than makes up for the pressure loss due to the cooling and the resulting improvements in the engines operating environment.

If you super cool the intercooler with nitrous or CO2 you will see a pressure drop due to the cooling but if you compute the actual air density in the manifold it will be higher than it would have been at the higher temperatures and pressures that existed without the super cooling spray system.

A turbocharger is a constant pressure variable volume compressor. You set an output pressure with the wastegate system and it will flow as much air as it can without exceeding that pressure. If you super cool the intercooler so the pressure on the outlet side of the intercooler drops the system is capable of flowing more air at the design wastegate pressure. Assuming you are not running the turbocharger at choke flow it will try to keep the discharge pressure at the design value inspite of the greater pressure drop across the intercooler.

The intercooler cryogenic spray systems typically show about 15-20 or more hp increase in engine power on subaru engines (depending on the normal power output of the engine without the spray cooling activated)


Larry
 

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Thinking Man's Engine
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In a naturally aspirated engine, the MAF signal with the throttle position signal and some other inputs, will dictate the timing and amount of fuel.

Many GM engines, do not use a MAF, instead they use a MAP sensor. With the MAP sensor, intake pressure can be converted to a mass flow rate.

Throw a turbo and intercooler into the mix....this changes a lot of things. Mass flow rate at the MAF sensor is not necessarily the same as the after the throttle body, since there are the turbo and intercooler in the way.

How this works now is:
all the usual inputs....in particular you have the throttle position, MAF signal, MAP signal, and the wastegate signal.

At one instance...let's say you are cruising along (1), then you want to pass someone (2), and the act of passing (3)

At instance (1), you have the mass flow rate at the MAF sensor, intake air temp sensor signal (more on that later), throttle position (let's say, almost closed), and the pressure after the throttle body (in vacuum).

Instance (2), the throttle position is fully open, same MAF signal, IAT, pressure, and wastegate. The ECU is calling for -- say 14 psi of boost.

Now, with the existing inputs, now it tells the wastegate to be closed completely to allow for full boost real quick (3).

As the boost pressure goes up, the ECU will still compensate. MAP signal is converted to a new mass air flow rate, and the ECU adds the appropiate fuel/timing.

You reach full boost, 14 psi, the MAP, MAF, TPS, etc now tells the wastegate to open to bleed and maintain 14 psi, according to the MAP signal. Consequently, 14 psi of pressure has its own correlated mass flow rate.

So in the EJ25, the MAF (along with the TPS and other inputs) determines how much fuel you can burn.

on the EJ20, you need the MAP, so that it can correctly determine the new mass flow rate after the turbo and intercooler, and thus determines how much fuel you can burn.
-----------------------------------
Intake Air Temperature

The intercooler basically cools the heated air (from the turbo) back to (or close to) ambient air temperature, as measure by the intake air temperature sensor at the airbox with the MAF.

As agreed, with constant volume, cooler temperature means pressure drop.

Spraying the CO2, as soon as it evaporates, it draws out a lot of heat, so now the temperature after the intercooler can be lower than ambient air temperature, as measured by the IAT sensor.

With the pressure drop, the wastegate remains closed to compensate for the cooler temperature (to increase boost pressure to desired).

14 psi @ 70°F (ambient air temperature) has less air than 14 psi @ (say) 50°F (it can be lower). The ECU does not see the 20°F drop, it still assumes 70°F.

Now what happens is, you run the risk of leaning out, because it is not compensating for extra air you just cramped in.
 

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different cars

Your absolutely right on a car that uses a MAP system to compute air flow, unfortunately that is not the case on the WRX.

Subaru does not use MAP for that purpose, it reads the actual air flow directly from the MAF sensor voltage and a look up table. With the exceptions of possible leaks in the intake system air flow measured by the MAF will always exactly equal the airflow passing through the intake valves (I'm talking near steady state conditions here for the limiting case)

Airflow changes propagate through the intake system at near sonic speed (ie about 1100 ft / sec). There is only a few millisecond delay between when the throttle valve changes postion and the ECU detects the changed airflow demand at the MAF.

Mass flow rate at the MAF sensor is not necessarily the same as the after the throttle body, since there are the turbo and intercooler in the way.
Unless the turbo and intercooler magically create or destroy matter, the mass flow in -- must equal the mass flow out!

I think you may be focusing on minor fluctuations in flow as pressure transiants sweep through the system, and corrections for engine load computed from the MAP sensor reading.

As stated above the pressure fluctuations only last for thousandths of a second. The MAF is so sensitive it can see pressure fluctuations from turbulence in the intake system from a poorly designed intake, or back flow when the blow off valve activates. For all practical purposes, the MAF voltage follows true mass flow in real time.


As the boost pressure goes up, the ECU will still compensate. MAP signal is converted to a new mass air flow rate, and the ECU adds the appropiate fuel/timing.

on the EJ20, you need the MAP, so that it can correctly determine the new mass flow rate after the turbo and intercooler, and thus determines how much fuel you can burn.
The Subaru wrx ECU DOES NOT COMPUTE MASS AIR FLOW from the MAP --- it is not a velocity air flow system like the DSM's that infer/compute air flow from flow velocity and air density. I think you are confusing the MAP's function for triming the injector duration for changes in engine load.


It uses the MAP sensor primarily to determine engine load, not air flow.
The engine load infered by the MAP sensor value would alter fuel injection values slightly for the purposes of supressing detonation under high boost for example, but that correction is on top of the basic injection rate determined by the MAF sensor air flow rate.

The MAP is also used as a double check on the MAF. In the case that the two sensors wildly dissagree then the ECU would throw a CEL.

Page FU-6 volume 8 Mechanism and Function.

"F: MASS AIR FLOW AND INTAKE AIR TEMPERATURE SENSOR

The mass air flow and the intake air temperature sensors are integrated into a single unit. The unit is mounted on the air cleaner case and measures the amount as well as the temperature of the intake air.

The measured amount and temperature are converted into electrical signals and sent to the ECM.
The ECM uses these signals to control injection and ignition timing as well as the fuel injection amount."


What I am talking about is the limiting case that mass flow through the MAF must be equal to the Mass flow through the engine.

For a silly analogy -- If you have 20 people a minute going in the front door of a building and your not allowed to have more than 20 people in the building at one time, then you must have 20 people a minute comeing out of the building some where. If there are no leaks (ie jumping from windows) 20 people a minute must be coming out of the back door. :D

Larry
 

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Thinking Man's Engine
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YOu also forgot to mention FU-3, Pressure Sensor:

The pressure sensor is attached to the top of the throttle body, and continously sends to the engine control module (ECM) voltage signals that are proportional to the intake manifold absolute pressures. The ECM controls the fuel injection and ignition timing based on the intake manifold absolute pressure signals in addition to the other signals from many sensors and other control modules.
 

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Discussion Starter #10
The mass air flow and the intake air temperature sensors are integrated into a single unit. The unit is mounted on the air cleaner case and measures the amount as well as the temperature of the intake air.
From this I can assume it is better for the engine and A/F mixture if the engine can see a 40 degree air coming in than a 100 degree air going through the first sensor then getting supercooled before it hits the next. I just thought that the ECU had a base adjustment for what subaru thinks the intercooler would cool the air and applys it in the ecu maps. Isnt this why heat soak in the intercooler creates detonation in the engine? (The ecu thinking that a cooler air is actually coming in, thus mapping for a cool air when a much thinner hotter air is actually entering). I would just have to think that letting cool air enter from the start would be much better than changing the air from warm to cool between two sensors... That probably came out allll wrong and thus I need a beer,, Cheers.. and thanks for the input
 

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From the dead I came and to the dead I must return...

I know I am kicking corpses, but I have to get this going again, I am researching this... here's why:

The smallest intercooler which can still deliver charge air to the turbine compressor is best. It is easier to build stronger, since the panel widths are smaller, and corners are closer together. There are less fins/tubes/bars/plates, therefore there is less surface area which may be attacked by the elements (this is not very important). There is less surface and a shorter distance for air to travel and find friction, and less turbulence in it, and it will be less prone to heat soak, unless it is too small for the application.

I really want to keep my WRX (02) stock intercooler.
I polished the outside of it completely, combed and straightened every fin, ported the throttle mouth to a blade-edge at 200 grit - grain is swirled, ported the knuckles to the same qualities w/ mirror polished doglegs and IC joint.

It stands to reason that the CFM it has will not be under the requirements for at least a 300hp setup. I don't want more than that until I can get real money into the transmission to support this.

I can use a big16G and tune with it without issue.


This brings me here...

If intercooler temperature is optimally 1 degree above freezing, the CryO2 method of cooling has to be about the most effective.

I would think that by now, CryO2 would have a FAQ sheet about how to overcome tuning of A/F on the EJ series turbocharged engines... it is not a new design. The CryO2 item has been available for many years.

There is no FAQ on their website regarding our application.

Has anyone tried it who posts here?

My intention is to use the IC Spray switch included in my OEM sprayer kit, and it's pump attached to a Weapon-R billet washer tank, on a relay and valve T'ed with a CryO2 spray rail and tank. This creates the option to run water or purge-to-gas.

In Winter, IC Sprayers freeze up. They aren't very important, heat soak is gone when the cold hits, but in Spring through Fall, it's probably good for 10hp at the crank, and a healthier turbo due to lower operating temperatures.

More recent data would be appreciated, I really want to learn more about this before I start altering my IC.
 
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