M35x Attempted Solution for Simple Intake Heat Shield

[picoman]

I have the Stillen Z-tube, Z1 intake couplers (stock ones were cracked), a 2005 G35 MAF housing, and a G35 Pop-charger with heat shield.
I wasn't anticipating the heat shield fitting correctly but figured it was worth the gamble. It doesn't fit at all. I wanted to avoid fabricating a sheetmetal heat shield. I have done it before on other cars but to do it nicely and do it right takes some time and talent and i'm not ready to give that a whirl yet.
Part of the reason I wanted to replace the stock airbox is that like some other M35's ive seen, the airbox halves start separating and it opens up a gap for unfiltered air to be pulled in. I also enjoy induction noises more than exhaust noises and need something like some induction noise to keep my inner child alive since selling my BMW

with the JWT filter and no heat shield, the IATs at idle while sitting in traffic can reach into the 140F range and take about 1/2 mile to drop back to 20-25 degrees above ambient. Once you start rolling and have 140F intake air, even with 93 octane I heard some ping under heavy acceleration. A first for me in this car.

I decided to do an experiment and split the stock airbox in half to make use of the factory air inlet points.

Its a very humid and muggy 89F with 80% relative humidity.

Engine temp is 190F, AC is on, engine covers are in place (even though not shown in the photos), cruising between 40-50 mph for 2 miles to bring things to equilibrium.





With no heat shield, the intake temperature is between 20-25F above ambient.
With the front half of the airbox utilizing the factory air inlet ducting, much to my surprise the intake temperature is a few degrees hotter, coming in at a solid 25F above ambient.

Obviously there is space around the filter that hot air is getting in. I suppose an auxiliary shield to work in accordance with the front half of the stock airbox could be a next attempt.
I want to keep things as reversible as possible. The airbox can be siliconed back together (which should give better filtration since the seams wouldn't be separating anymore)

The one thing I did notice is that while stopped in traffic, the IAT was 20F lower than before. I did not do any sort of formal test on idle IAT temperatures, but with the front half of the airbox attached it took much longer for the IAT to get up to 120F while stopped, and only got up to about 120F. Without the front of the airbox in place it was hitting 133F within a short amount of time.


I dont have much of an explanation for this. I anticipate leaving it this way and coming up with a shield that can compliment what the airbox is trying to do and try it out again.

Feel free to share heat shield solutions and ideas. Im not chasing every last HP for racing or anything, but as an Engineer, I have a little bit of OCD and like to know that things are somewhat optimized.

[Ilya]

Way to go!

[EdBwoy]

A few thoughts and maybe questions too. Do you know which sensor exactly your air temperature readings are coming from?
How about the engine temperature?

This is the way I understood your experimental results, please correct me where I am wrong.
While stopped in traffic:
1. The presence of the front shield Will make the highest reading lower than without any shield
2. It takes much longer to actually register a temperature rise with the shield than without

While in motion:
1. Having the heat shield actually makes the intake air hotter than without a heat shield
2. How fast would you say the temperature rises with/without?

I'd be very curious how these readings compare with the OEM setup.

One big thing I see is that as much as the front half-shield is in place, air still comes from the path of least resistance. Around the shield, hence the hotter engine bay in this case.
The second factor is that the shield is a sort of barricade that will slow the rise of the temperature, but likewise is a trap that keeps the hotter air in there longer. Even when you're in motion, the heat isn't really being pulled out. The rad fan actually pulls heat from the coolant and sends it there. (Have you by chance kept track of how the coolant temperature trends with your experiments? Is this what you've been checking?)

[picoman]

The intake temperature sensor is part of the MAF sensor. The air temperature the engine actually sees will be a little higher since the intake manifold will warm it slightly, but for reasons of mass flow calculations the sensor needs to be in the MAF housing. Speed density systems like on Hondas and most FI applications usually have the intake temp sensor in the manifold.

Engine temperature comes from the coolant temperature sensor. Both readings come from the OBD2 data logs.
Coolant temperature rise/fluctuation was minimal, ~5 degrees F. A more accurate way to keep track of temperature is if there was an EGT sensor since coolant has a high thermal inertia and the exhaust gas temperature can rise significantly within a given 10 degree F span of coolant temperature and the exhaust heat is the most significant heat source under the hood.

The questions you have are also questions that I have. FWIW, the stock airbox on my Toyota Sienna keeps the temperature 7-10F above ambient while driving and the rise while idling is very slow and low in magnitude. I will update if I play around with it some more.

[EniGmA1987]

My idea for what to do next would be to get a 1/4" thick piece of black plastic with around 200 degree temp rating (most plastic). Drill some holes in the stock airbox housing on that left side that sticks out an inch for your mounting point. Then extend that side out towards the intake tube to block off air some more from the engine to the intake. If you get a tall enough piece of plastic you can extend it down to the frame section that runs by there so that air is mostly pulled from the wheel well area.
Which reminds me, you should have that wheel well cover removed for these types of intakes so that clean, cool air can be pulled from outside the car more easily. Our bumpers are closed off and with the wheel well covered the only place to pull air is from the direction of the engine, which will be hot air.


Some plastic pieces:
https://www.mcmaster.com/#8674K203
https://www.mcmaster.com/#9123K74


The nylon seems like a good choice since it is cheap, black to match the other housing parts, resists gasoline and refridgerants, has a proper temp rating for its location. Just use a sawzall, or a Dremel saw-max, or something similar to cut it as needed to fit nicely.

[picoman]

The idea was to keep things 100% reversible so If I do any extension, it would likely bolt to the popcharger mounting holes and act as somewhat of a backstop which, if high velocity air was coming in, that would create a high pressure region and have a slight ram effect.

I definitely agree with there not being much ambient air getting through to the engine bay on these cars. I will take a look at removing the fender plastics to see if that will leave too big of an opening or cause road grime to splash into the engine bay, otherwise I may try to find a spare fender liner and ventilate it/run an air duct to get some freshness going on.

[EniGmA1987]

If you get a spare wheel liner then you can always modify the spare by cutting out a hole in one portion of it and then epoxy down some mesh over the hole. That way you allow air to be pulled in from that section but you can prevent any medium sized rocks or other debris from getting into the engine bay still.

If you cut the hole in a semi circle instead of completely out, you may be able to modify things so that it has a sort of scoop on the wheel liner as well as it directs a portion of the air up into the intake nicely.

[Larz]

Can you actually hear induction noise from inside the car without the stock air system?

[picoman]

absolutely, Its fairly loud

[EdBwoy]

OK, great. I was curious if you were using the OEM OBD system for reading or some other method.

I can't tell exactly how significant heat soak is going to be for your system especially since it's plastic as well. And even with say metal tube, the mass flow velocity of air through the intake should render it less significant.
Disclaimer: it's been a while since I cracked open a heat transfer book. I am going off memory of common engineering principles and rules of thumb.

As far as highly reversible, minimally intrusive mods go, I would modify the filter box to accept your cone and keep taking in from the factory designed cold air intake.

I would also consider an all-OEM system (with the Ztube). There should be some change in sound, although not as noticeable with an open-to-air filter

[picoman]

I decided that there are enough M's in the junkyards and in the ghettos that I can replace the airbox readily if I want to sell the car. I also see new fender liners for around $39.I trimmed down the G35 heat shield that came with the pop-charger and drilled 2 holes in it as well as the airbox to attach it. I used some clips to attach it and finished it off with the rubber edge trim that came with it. Next time I mess with it I will run a duct down to the fender liner under the car and make some clearance on the fender side of the airbox then re-test. I think this should work out real well

[Larz]

That design is nothing short of genius. Maybe I'm being too daft, or simplistic but if you use air from anywhere inside the engine bay ... isn't that warmer than the air that used to come in from the grille? I could see using the OEM pieces and insulating the intake tubes from the air filter to the engine intake, but short of that, you're still pulling in hot engine bay air, no?

[picoman]

You are correct. With the stock air box, the only air inlet point is the front edge of the hood, so anything that has an exposed filter in the engine bay is definitely pulling in hotter air than what the stock airbox does. My thoughts about leaving the front half of the airbox is that the front edge of the hood is typically a high pressure area and you will get a little bit of forced air at the intake point which should bring some fresh air in front of the filter while helping to block some of the hot air passing through the radiator.

For me the cone filter is primarily for induction noises with an understanding that hot air is going to be pulled in.

This guy tested a short ram, a "cold air intake" and stock airbox on his S2000 with surprising results. The short ram was not as negatively affected by hot air as one would have thought.

https://www.carthrottle.com/post/engine ... m-intakes/

[picoman]

IATs today were a solid 10-12F above ambient over the course of a 30 minute drive at 40-50mph. No back to back comparison on this one but ive at least moved in the right direction