So I was just watching this video on a K20 with what looks like Kinsler Itb's make 352/ 238 or something close to that, And the Itb's were a top feed injector injector setup with secondary injects. The one guy was saying that the secondary injector's help creat a cooling effect on the intake and that if you notice it becomes chilly.

My question is how does that happen?

Could it be the fuel they were running which was Q16 i think having something to do with the air causing the fuel to chill when atomized?

I understand that having a top feed injector setup on Itb's helps atomize the fuel the best and gives it a straighter flow path into the head then into the combustion chamber.


Anyways here's the link to the video

http://www.youtube.com/watch?v=OIxdR...mbedded#at=278

 

All it means is that, the fuel, when sprayed into the TB neck, absorbs heat from the air around it, giving it a cooling effect. This is nothing new. Older carburated cars had "wet" intake manifolds because the air and fuel mixtures traveled through them entirely which helped cool them. Most fuel injected manifolds are "dry" and only draw air thorugh them. This can be bad when the car gets heat soaked from sitting on the line etc which can cause inconsistent ET's. Placing the injectors that far up like that helps top end performance but isn't usually practical on the street since it usually hurts low speed/RPM performance.

 

yeah i know its not pratical on the street as there's a good chance of something getting sucked in without being able to run filters.

that makes sence that the fuel helps absorb the heat, I don't know why I didn't think about that.

Another question why is it that say on a b16 intake manifold that they don't place the injector's up higher on the runners to help have that effect and atomize the fuel better?
Or is it cause it wouldn't make any difference and that it is better to place them closer to the head?

 

oem's design the system to meet goals for drivability, emissions, fuel mileage.
moving the injectors further up the track would start to compromise things like idle and drivability. your best bet is staged injectors....first set as close to the back of the valve as possible for idle and light load bring on the second stage thats further up the track as engine load increases.

 

x2

To expand a little on the emissions, OEM's spend buckets of money on fuel injection technology to allow all fuel injected to be burned. If you place the injector further from the combustion chamber, there will ultimately be fuel deposited on the ports/intake runners. This is a big no-no for OEM's.

The cooling effect is due to the Latent Heat of the fuel. When fuel changes phase from liquid to vapor, it absorbs energy in the process. That energy is in the form of heat. So it is removing heat (cooling) the air charge.

Ethanol has about 3 times the Latent Heat than regular gasoline, so its phase change has an even greater cooling effect on the air charge.

 

To the OP: Wiki 'latent heat of vaporization'.

Any liquid that changes state to a vapor absorbs heat. The latent heat of fusion is the main reason ice makes things cold (absorbs heat due to change from solid to liquid). Any transition between states will either absorb or release heat, depending on the direction of the transition.

 

to expand the , detailed answers


.... also the farther the injectors are the more time/area it has to atomize and mix well with the air , giving more potential for power

on the other hand
some mass produced oem cars are meant to spray/squirt fuel from their injectors
when the valves are shut... as cooling method for the valves which also helps splash/atomize the fuel

which is why most are either direct or close to valve injection

 

Not completely true. If you place them to far up the runner you could allow more time for the atomized fuel to fall out of suspension. This could cause fuel dropplets to collect on the bottom of the runner and pool. Causing unmonitored spuratic increases of fuel to drop into the cumbustion chamber.

 

You can still run a filter if you put your whole setup inside an airbox and filter the box. I have heard its good for ~10hp up top, difficult to say.

The best location IMO is right behind the throttle plate, where the plate is as close to the opening as possible. This gives more time but the turbulence caused by the throttle helps with low rpm and still allows you to idle normal.

one reason for the top feed on some setups is for the effect of sharing fuel, apparently.

 

http://www.youtube.com/watch?v=m27xXVgg1nc

 

yes i agree....


but who would go for top feed super hero set up LOL
and idle all day?


my thoughts were : theyre usually reserved for high rpm use or if primary use was WOT

thats also why we see ITB's with 8 injector set ups
using the oem location for most of the idle/part throttle use etc
and WOT mostly on the stand off's

 

piratemcfred actually further expanded wat i meant on my post


forgot to read that bfor posting LOL

 

Thank you for the clarification.