Experimenting with Intake Air Temp. Request for comments.
 

I'd like to do a little experimenting with the goal of lowering Intake Air Temperature with minimal modifications to the stock setup. This is not an attempt to increase HP or MPG (although it should help both, if successful), only to get IATs down to a reasonable level, to avoid having the ECU pull timing. Please make suggestions.

Any permanent mods should be easy to perform by an intermediate DIYer with "standard" home shop tools. Any temporary mods (eg, thermocouples) should be easy to put back to stock condition. I have ordered replacements for the filter boxes and ducts, so they can be modified extensively if need be.

I need to install some thermocouples to get a baseline and measure results. Measuring engine compartment temp shouldn't be difficult, but I'm not sure how to go about measuring the the temp of the air in or near the intake manifold.
At first glance, it looks like drilling a hole in the duct, just before it enters the manifold, would be easiest. Does anyone know of an easily un-doable way to get a t/c inside the manifold?

After getting some baseline readings, I plan to install some insulation on the filter box and ducts. Any suggestions on type of insulation to use? I'm thinking something that is flexible, less than 1" thick, and having a reflective outer cover would work best. Maybe something like an exhaust blanket, only lighter weight. Tentative budget for insulation is $25-50 per side.

From there, I may explore extending the filter box inlets to an area of cooler air. Depends on how well the insulation works.

Hints, tips, and suggestions are welcomed.

PS: Yes, this is another of my obsessive projects - much like trying to figure out what causes the occasional pause when starting. :)

Most excellent tip. Thanks. :tiphat:

That's a mod that I might implement as part of "extending the filter box inlets to an area of cooler air". It appears that most of the mods involved can be returned to factory condition easily; that's a plus.

So in my experience (hundreds of hours of logging on the street, on the dyno, on the track, on the strip, autocrossing) the number 1 heat buildup causing factor is the radiator.

When the car is not in motion, the radiator heats the air behind the bumper cover up to 30-40 degrees over ambient.

With metal intakes, even if you have aggressive insulation (like me) it still ends up heating up the interior of the pipe, leading to eventual heat soak.

Plumbing the intake snorkels through the bumper to the outside air would be the only truly effective treatment for this phenomenon, by my reckoning.

Thanks for the input. Some form of CAI is phase two.

Once you get "normal" air flow, about how long does it take to cool insulated metal tubes back down? Seconds? Minutes? Do you know if the stock plastic tubes would cool down faster or slower?

This I am curious about, as being boosted I generate more heat both from the engine and other moving parts.
Intake piping coating:
-Silver heat shield
-Gold heat shield
-Black coating (like GTM has done on a few FI cars)

Are any of these good at separating the heat away from the piping and keeping it cool? Is one better than another?

Depends entirely on ambient temp and how long the car sat and sucked in heated air. Sitting in traffic, I'd see 160+ degree air and it didn't matter how much I drove after that, unless I was doing WOT pulls one after another, temps would never get back down to ambient (100ish), they'd just hover around 130.

Plastic doesn't conduct heat worth a damn, even if they do heat up, they won't transfer much of that heat into the air in normal use. Again, if you're idling for a long time, it'll heat, but I'd expect your temps to return to something like 'normal' relatively quickly.

So, generally speaking:

Shiny = Reflects IR
Black = Absorbs IR

Gold is one of the best reflectors for IR, 'swhy satellites and whatnot are covered in it and why DEI's radiant heat protectant products are all gold.

If the major heat sources in the engine bay are already shielded, I could see why they'd use black.

GTM shields their manifolds (and perhaps turbines?) already, so radiant heat is less of an issue, so they'd run black because that will help move heat out of the hotter charge air into the cooler ambient air. It's all relative and all comes down to heat gradients. Heat moves from one place to another, if you understand what I mean.

Think of the Light/Dark paradigm, darkness is the absence of light, cold is the absence of heat.

So yeah, tangents aside, they'd use black so that heat is transferred through the charge pipe into the atmosphere rather than hanging out in the charge air and going into the engine.

Every little bit helps!

Also note that we are talking about two different things here. Radiant heat can be shielded against, convective heat can only be handled by replacing that heated air with fresh, cool air or by insulating what you want to protect.

This is why I have my intakes wrapped in both header wrap (for insulation) and DEI reflect-a-gold for radiant protection. (I have un-wrapped headers at present, they heat everything up, on the list for this season to get those taken care of)

Wow. This got long, quick.

I messed around with my stock filter boxes a while back for a similar reason. I documented most of it here: Lets cut our stock intakes to pieces

This isn't exactly what you're going for, but it might give you some more ideas. I'm probably going to add Modshack's mod to this eventually.

From what I've seen, the stock airbox intake temp is approx 10 degrees F hotter than ambient air temp while moving down the highway at speed. There's a lot of room for improvement here.

As far as measurement, any OBD2 device hooked into your android phone will be able to give you the car's intake temp. Cross-reference that with the ambient air temp from the trip computer and you're good to go.

That should come in very handy when I get to phase two. Great DIY. Repped.

I'm getting about 6°F difference between the ambient temp sensor and the IAT reading in cool weather (40-50°F) at highway speeds and 9-11°F when the outside temps rise.

I have a ScanGaugeII that I use to monitor IAT, but, I think that comes from the MAFs (if I'm wrong, please correct me) and I'd prefer to get a reading closer to (or inside) the manifold. I may end up using IAT if getting a t/c in there is too difficult.


Thanks to all for the info and suggestions. Keep 'em coming. This is going a lot better than my "pause on start" thread. :)

I expect to have the spare parts in tomorrow or Monday. I am trying to track down a small t/c that can be inserted into the ducts or manifold (I have an industrial panel meter and an inverter already).

At present, my plan is to get some engine compartment temp measurements, do some baseline measurements of the air in the tubes/manifold, insulate, take more readings. If all is going well at that point, I'll try some homebrew CAI.

Thanks again for all the help.

Yes it was, but lots of good info. Thanks.

what about swapping radiator fans? if there are stronger fans pulling in more cooler air from outside of the car, wouldnt that cool the radiator down a bit more, thus making cooler intake temps? i dont think it would lower it by much but it should help in theory

Great idea. Thanks!

It's one of the things on my list of things to investigate someday. But I was thinking of fans as primarily a water and oil temp solution.
It certainly sounds like a good theory. Maybe I need to change my thinking. :)

For now, I'm trying to keep any permanent mods to a minimum and as cheap as possible, so new fans may have to wait for phase three. I'm shooting for lower air temps on general principles, not any HP/MPG gains.

I was going to track down some insulation today, but Real Life intruded. I've been posting between chores. I have new front brake rotors now - got some mud in the grooves in one of the pads and it was starting to eat up one of the rotors. Replaced the other rotor "just because".

that sucks but i like the way you think, did you go to slotted rotors or stick with stock?

aside from that maybe even an oil cooler might help cut down radiator temps as well, cooler oil means cooler coolant in radiator which means cooler temps, again that is just a theory based off logic

also you might be able to modify the air box itself and relocate it to behind the wheel wells or something, that should allow the box itself to suck in cool air at all times even when not moving but im not sure how temps would be at the MAF or even the pipes before the MAF, heck you might be able to do that with some flexible plumbing hoses from home depot or something and a few hose clamps and scrap metal to use as brackets

Stock, but not Nissan. My "suspension guy" said he would get as good or better than OEM and I trust him. I do some occasional spirited driving, but seldom hard on the brakes. Defensive driving FTW.

Maybe. But the heat from the oil cooler is right in front of the radiator. When stopped, I don't think there would be any improvement without relocating the filter box inlet location (eg, using tubing as above). Something to look at during phase two.

Great idea, but waayyyy beyond the scope of this project. I'm hoping to limit heat gain from the engine compartment and then I'll probably do one of the CAI DIYs above (depending on how well insulation works). An oil cooler is a possibility much later on.


Wow! Lots of great input. Thanks. Now I need to get some insulation, find a thermocouple, and figure out the best place to locate the t/c. No rest for the wicked.