cold air intake

[ghostrider5778]

okay y is air intake so good wouldn't it be better to have more fuel in the cylinder so that went it gets ignited the piston would have a higher rpm or in other cases nitrous, i can see how that make the car have higher rpm. what exactly does air intake do and how do u get higher hp from it? cut me some slack i dont no that much

[MattyG]

Cold air particles are denser (packed more tightly together) than air particles at a higher temperatures.

This means there is more oxygen in the cylinder when the sparkplug fires = bigger explosion = more power.

[texan]

It's also very important to note here that more fuel does not necessarily mean more power. The rate at which fuel burns (and therefore the total heat given off from the reaction) is highly dependent upon it's ratio of fuel to air molecules, and specifically that more fuel to air than about 14:1 mix slows the burn significantly. Leaner mixtures (to a point) actually burn hotter and faster than rucher mixtures.

[Steel]

Originally posted by texan
It's also very important to note here that more fuel does not necessarily mean more power. The rate at which fuel burns (and therefore the total heat given off from the reaction) is highly dependent upon it's ratio of fuel to air molecules, and specifically that more fuel to air than about 14:1 mix slows the burn significantly. Leaner mixtures (to a point) actually burn hotter and faster than rucher mixtures.

exactly. And if it wasnt for the heat, cars WOULD be burning a lot leaner than they do. Except it's hard to drive a car when her pistons are melting

[sciguyjim]

Ghostrider,
People install cold air intakes to suck in air from outside the car rather than taking the hot air under the hood which is what you might get if you simply mount an open air filter under there. A 10°F rise in air temp makes about a 3% drop in oxygen density so there isn't as much oxygen to burn all the fuel efficiently. The actual temps of air under the hood are much more than 10° above the outside air temp so the reduction in power due to the hot air is probably closer to 12%!

P.S. Since you're relatively new to this, I'm just wondering if you understand the proper relationship between octane ratings and power? Many people still don't understand this correctly so I thought I could explain it before you got too far along. To free up forum space, contact me via email if interested at [email protected]

[BluStori]

i heard something about cold air intakes arnt good cuz if they get wet it will mess up the internals of ur engine?

[texan]

It's called hydrolock, and will only happen if the filter is submerged underwater and the engine is running (and running above idle). If significant amounts of water enter the combustion chamber, when the piston comes to TDC and tries to compress the uncompressible fluid something will break. Hydrolock is a very rare occurance, but if you are truly worried about it just do what the factories do, place the filter in an airbox underhood and run a pipe from there to outside the engine bay.

[enginerd]

You would have to drive the car into a lake for hydrolock to happen. Cold air intakes aren't going to pump water into the engine. Besides, you would need a lot of water to go into the engine.

[SaabJohan]

One problem which is much more likely to happend is misscalculation by the airmassmeter if your car have one. When you change the intake this can cause turbulent flow around the airmassmeter, and since airmassmeters can easily be fooled the result will be an engine which isn't running like it should.

[texan]

Originally posted by SaabJohan
One problem which is much more likely to happend is misscalculation by the airmassmeter if your car have one. When you change the intake this can cause turbulent flow around the airmassmeter, and since airmassmeters can easily be fooled the result will be an engine which isn't running like it should.

To be fair though, this is a lot less likely than it used to be. More and more MAF systems use multiple wires and average the results to obtain reliable data, and virtually all have fine mesh screens to break up incoming air which might be flow biased to minimize false readings. As time passes, very few systems are still suceptible to innacurate readings from minor alterations in intake design.

[SaabJohan]

Actually there is still problems with airmassmeters, and sometimes an open air filter is enough to get problems. Also, some have got their massmeters to break by just replace the airfilters.
Airmassmeters are usually not used in racing since they are so easily fooled.

[texan]

Originally posted by SaabJohan
Actually there is still problems with airmassmeters, and sometimes an open air filter is enough to get problems. Also, some have got their massmeters to break by just replace the airfilters.
Airmassmeters are usually not used in racing since they are so easily fooled.

I wholeheartedly disagree. There are thousands of race cars which use MAF systems with success, IMO they are not nearly as sensitive as you suggest. Take a note of how many factory cars running boost use speed density systems and figure out why the other 99.9% of them instead choose MAF for air metering. Then notice how many cars retain these stock setups under race conditions and explain how they are so unreliable in both longetivity and sensing accuracy. All current production American setups use MAF, all Japanese boosted cars use MAF that I have seen, and there's very good reason for it.

[SaabJohan]

Originally posted by texan


I wholeheartedly disagree. There are thousands of race cars which use MAF systems with success, IMO they are not nearly as sensitive as you suggest. Take a note of how many factory cars running boost use speed density systems and figure out why the other 99.9% of them instead choose MAF for air metering. Then notice how many cars retain these stock setups under race conditions and explain how they are so unreliable in both longetivity and sensing accuracy. All current production American setups use MAF, all Japanese boosted cars use MAF that I have seen, and there's very good reason for it.

One reason to choose MAF instead of speed density in production cars is that if when VE change the system would easier adapt to the new conditions. Also, another reason is that just few automobilemakers build their own management systems, most of them buy systems like Bosch Motronic which use an airmassmeter for metering.
Usually airmassmeters don't fail or miscalculate if the car stays original.

But it have been found that the oscillation created by the valves in a raceengine can result in miscalculation.
In racecars you also don't want the airmassmeter to restrict the airflow. Also, some racecars use their speed to create pressure in the intake, this is also a problem if you're using MAF

Some production cars use both speed density and an airmassmeter to calculate airflow.

Just take a check en see how many aftermarket management systems which are fitted with an airmassmeter. Also, most of theese systems use peak an hold injectors and drivers, oem systems don't, and peak and hold is better.

[texan]

Originally posted by SaabJohan


One reason to choose MAF instead of speed density in production cars is that if when VE change the system would easier adapt to the new conditions. Also, another reason is that just few automobilemakers build their own management systems, most of them buy systems like Bosch Motronic which use an airmassmeter for metering.
Usually airmassmeters don't fail or miscalculate if the car stays original.

But it have been found that the oscillation created by the valves in a raceengine can result in miscalculation.
In racecars you also don't want the airmassmeter to restrict the airflow. Also, some racecars use their speed to create pressure in the intake, this is also a problem if you're using MAF

Some production cars use both speed density and an airmassmeter to calculate airflow.

Just take a check en see how many aftermarket management systems which are fitted with an airmassmeter. Also, most of theese systems use peak an hold injectors and drivers, oem systems don't, and peak and hold is better.

Look, as I said before there are thousands of cars using MAF with no problems. And that includes 1500 hp race engines. As for restriction, that is not part of the basic MAF design, it's just what some OEM's end up building. Does this look restrictive to you?


Ram air systems do not cause problems with properly designed MAF setups. If it did I don't think you'd see working and effective OEM ram air systems on vehicles with a factory MAF. I've never heard of "valve oscillation" causing metering problems, but again it doesn't seem to bother the thousands of race motors using MAF.


Ps- Off the top of my head, I can think of several OEM cars which use peak and hold rather than saturated injectors. All Mitsubishi Eclipse turbos, every Supra Turbo and TT, the old MR2 turbos, and a few older Honda setups. Peak and hold is only better in response time btw, they are also a lot more expensive and generally not beneficial to performance on any remotely stock motor. The necessary pulse timing response can be taken into account and adjusted for electronically anyways.

[SaabJohan]

After having looked more into MAF vs. Speed density I have found this:

Speed density, is more direct, fast and easy. But the problems are exhaust emissions, can need recalibration.

MAF more accurate (if it is left original). But it has downsides, easily fooled from like turbulence, system leakage and air pressure pulsations/oscillation (caused by the valves). It is also slower and more indirect.
Since you have to put an airmassmeter in the intake it's more restictive, there are large meters but compared with the speed density system it's more restrictive.

Also, today we get more and more advanced methods to help the ECU to control the engine, like in cylinder pressure sensors, ionization measurement and turbo speed sensors. This can make the speed density system more accurate.


Peak and hold is faster, and this mean more accurate. But they also need less power to be controled. Some peak and hold injectors acually give the same amount of power back as are needed to open them and hold them open when they are closed. This isn't so important in a normal car but in a racecar which sometimes only have 30 amps alternators it can be important.