Factory intercooler duct mod DIY
 

I purchased my FD with a rather unique configuration; it had aftermarket intakes and a stock intercooler with no shroud. So the inlet air was hot, and the intercooler was constantly heat soaking with no chance of cooling down. Pretty much a recipe for disaster. Upon further investigation, I discovered the factory intercooler duct was removed because the aftermarket radiator wouldn’t allow clearance around the AC drier portion of the ducting...

Therefore, I was faced with a few options:

A. Continue running the heat soaking time bomb
B. Buy an aftermarket intercooler setup
C. Fabricate my own intercooler duct

Fortunately the factory duct was engineered very well. With some time and modification, I was able to produce a rather functional component as outlined below.

As depicted in the first picture, the course of action was to remove the AC drier housing and fill both holes.
https://cimg8.ibsrv.net/gimg/www.rx7...18db8c085.jpeg

After removing the drier shroud with a cutting disc, I used a dremel and block sander to true up the mating surfaces being patched.
https://cimg0.ibsrv.net/gimg/www.rx7...0239b5e79.jpeg

Once the mating surfaces were ready, I made a template out of cardboard then transferred it to plastic. The material used was from an old deployment tough box I had laying around, but suitable plastic can be found at Home Depot or various craft/hardware stores.
https://cimg4.ibsrv.net/gimg/www.rx7...280078bc2.jpeg

The patch material was adhered with plastic weld, then some of the fine gaps were filled with CA. After that, I finished shaping the components by sanding, then lightly scuffed the entire box for paint.
https://cimg3.ibsrv.net/gimg/www.rx7...a5190a5a5.jpeg

Next, I sprayed the duct with Dupli-Color primer followed by a semi-gloss black engine paint to withstand the extreme heat above the radiator. After that, I added foam tape to the factory locations, replaced the hardware and push pins, and cleaned up the mounting brackets with a wire brush bit.
https://cimg7.ibsrv.net/gimg/www.rx7...9713707f0.jpeg

Lastly is the finished product installed on the car.
https://cimg8.ibsrv.net/gimg/www.rx7...a3e029f94.jpeg

I know this mod is unconventional and not suitable for everyone. However, I was racking my brain and researching for months trying to find a solution to my unique problem. There are no aftermarket ducts available for the factory intercooler, and I didn't feel like upgrading when the factory unit worked just fine. I've seen threads about fabricating an entirely new duct out of sheet metal, but this approach certainly requires less guess work as the part was already designed for this vehicle. As for results, the intercooler temp is substantially lower than it was without a shroud. Anyway, hope this helps!

Excellent job! I've done similar mods to the stock duct, such as blocking off the hole up top or blocking off the hole going to the battery box. Really like how you painted it up, looks nice.

I think that the stock duct can be improved greatly by modding it like this. I think that extending the front of the duct so it can grab more air could help as well.

Next step would be doing something to block the hot air the intakes see and getting some sort of ducting to get fresh air to them.

Dale

Great job. That will definitely make an improvement. I did something similar with fiberglass a ways back. You can also extend the forward lower edge of the IC duct to gather more air from the bumper, if you haven't already.

Nice, but seems like a lot of effort on a marginally effecient SMIC. And the hot air intake doesn't help

Are you able to read/log your IATs?

Very cool, I need to do this as well.

Thanks Dale! It was a lot of work but I'm happy with how it turned out. I agree, the intakes are definitely next on the list. I've been toying around with ideas, but I'll probably just go with a different setup entirely. I was never too fond of these in the first place.

Thank you! I haven't tried yet, but that's a great idea for sure.

I have a stock management system, so unfortunately I'm unable to log temps. Although empirically, the intercooler temp dropped substantially when compared to the previous setup. I agree it's a lot of work for a marginal intercooler, but I'm trying to keep the car mostly stock and this was a huge improvement from how I got it lol.

The wheel is reinvented 25 years later.
It does help even with hot air intake with the stock IC.
Originally air is lost to cool the battery and into the stock air filter box.
In 1st and 2nd gear hot air could actually flow backwards through the stock IC system sometimes.

I posted this 25 years ago, and Mazda finally discovered this back around 1997/1999 when it blew some engines on the track.
Then they made the intake get its air from above the radiator on the right side just as the IC gets its air from above on the left side.
This I also posted 25 years ago.

Agree with the others, very nice clean job.
Also as mentioned above, it helps to keep those open intakes from sucking too much hot underhood air. If you're wanting to stay stock, at least in appearance you could also easily source a good stock airbox and talk to adamc (another member here) about a cheap-bastard intake kit. It simply sources air to the underside of the stock intake box from that gap beneath directly beneath. And is, essentially invisible when installed and I doubt you would see any performance loss.
I also got some black upholstery foam and stuffed pieces in all the little gaps around the duct inlet and radiator you can see thru the nose.

Thank you!
I couldn't agree more. The plan is to get an M2 intake or stock airbox, I'll probably post a WTB thread here shortly if nothing pops up. I contacted Adam and unfortunately he doesn't offer the kit anymore. He will however sell a template for $50, but I'm not much of a metal worker so I'm hesitant at this point :scratch:.

I went this exact route (re-ducted stock IC with cheap bastard air box) and ending up with an aftermarket intake and IC. You will eventually conclude (if you ever get a PFC and see actual temps) that the stock IC is a huge limitation on the car's performance even at stock boost levels... just as many others have for many many years.

The intake you get affects what IC you can use and vice-versa... so plan your intake and IC together, even if you're not doing them together.

Very nice work on the modified air duct!

Another forum member made his own version of the adam c cold air intake and posted plans on the forum that you could attempt for just the cost of materials: https://www.rx7club.com/3rd-generati...intake-628764/

If you decide to try to make this, I recommend first using cardboard to get everything sorted before moving to aluminum or stainless sheet. Also, I think it isn't necessary to make the full closed design, just the inside panel to block off the radiator heat and a bend to attach it to the body sheet metal.

For anybody interested in the "hot air intake" debacle, I found an outstanding OEM solution. Mazda redesigned the fresh air duct for the S8 FD, so it pulls air from behind the hood latch instead of the intercooler duct (see attached pictures). Better yet, it fits the stock airbox perfectly. This part accompanied with the Adam C mod or similar will outflow most aftermarket setups with cold air, in an OEM package. I'm a huge fan, and I managed to source a distributor from Japan at a reasonable price. There are no pictures, only a part number and Japanese writing :lol:. But I took a chance and the brand new part showed up today!

Here's the link:
https://buyee.jp/item/yahoo/shopping...arts_N3G113201

https://cimg8.ibsrv.net/gimg/www.rx7...bfe9a324f.jpeg

https://cimg1.ibsrv.net/gimg/www.rx7...64f8512454.jpg

https://cimg2.ibsrv.net/gimg/www.rx7...57a75e764f.gif

https://cimg7.ibsrv.net/gimg/www.rx7...429bd904f.jpeg

The s6 nose doesn't have a fresh air inlet like the 99 spec nose, and that duct may interfere with the airbag bracket and require trimming. It's also subject to a circuitous air path and a small inlet cross section. That said, it's an improvement on the s6 design, when accompanied by the 99 spec or similar bumper and ducting.

That's true, we don't have ram air from the front bumper opening; however, it's still pulling cool air from in front of the radiator instead of sharing the IC duct with the potential to reverse flow and heat soak. This part does present a small cross-sectional inlet area, although it's not any worse than the S6 duct. Furthermore, the Adam C mod would certainly free up some restriction. That's the only way I'd run it lol.

As for the airbag bracket, this part doesn't protrude into the bumper cavity at all, it merely sits on top of the core support. That stated, my car is a '92 and doesn't have airbags. Someone with a U.S. car would have to weigh in on the airbag bracket location relative to the core support. If the bracket doesn't extend above the top of the core support, no trimming should be necessary.

The statement that this duct will outflow good aftermarket intakes is based on what data? And if you ever want to upgrade the IC you'll be stuck with a stock size intercooler because of the huge stock airbox.

Sure... this is better than the stock 92 intake setup, but only marginally. And if you went to the trouble of doing the Cheap Bastard intake, I don't understand why one would need this in addition?

I stayed stock for a while too... until I saw the light (in the form of a PFC, datalogit, and wideband).

I recently did this mod on my 1995 that has a Pettit-style 99-spec front bumper (without the license plate opening).

The forward airbag acceleration sensor cable interferes with the air duct as it routes over the front support where the hood release mechanism is located (the sensor is bolted to the hood release latch and the support). The cable can be re-routed to pass under the support as opposed to over and retain the same attachment point for the sensor, which is what I did. No modification is needed to the airbag sensor bracket whatsoever. The sensor may create a slight restriction for airflow through the support opening, but that is a small price to pay to retaining the OEM design rigidity for the crash sensor.

I also dremeled a slot (similar to the OEM 99-spec opening) into the bumper support directly below the hood latch opening and made a small sheet aluminum deflector for the slot to direct air into the new 99-spec inlet area around the hood latch/support opening. Not sure how effective that is, but I figured it wouldn’t hurt. At the same time, I installed a cheap bastard air duct to the airbox so there should be plenty of intake air and just the action of blocking off the airbox opening should really improve airflow volume to the IC.

Now, the increased airpump noise level from the airbox mod is another matter…still searching for a perfect solution for this.

My apologies, maybe I should've been more specific with the qualifiers. In terms of a cold air intake on the twins, the Adam C mod to a stock airbox is generally considered better than most aftermarket cold air setups; adding this fresh air duct, to an already modified airbox, will provide further improvement over the S6 duct which is susceptible to reverse flow the IC. Although empirical, it's based upon tribal knowledge.

I agree that space is the huge constraint to the stock airbox, it's very limiting. But for those who want to remain relatively stock while improving flow and reducing inlet temp, the S8 duct with an Adam C mod is a great solution.

jza80:
Excellent write up, thanks for the information!

3/4" (19/20mm) OD universal silencer. You could event make something with a drill, fill material, and some pvc pipe. Or, get fancy with it. I think Pettit sells a 3/4" restrictor plug, which is how many address the issue. The M2 intake uses similar restriction to mitigate noise. It helps, a lot. But, I can still hear it putting around on the street with the windows down.

Get a rubber chair leg cap from the hardware store - I think it's 7/8" ID is what you need. Drill 3-4 small holes in it and clamp it on the ACV output pipe (the one making the moo noise).

Takes all of 5 minutes to do, costs a dollar, and does a great job. You can change the amount and size of the holes to fine-tune the sound.

Dale

Thanks guys. Following Dale's past comments on this I made a silencer by cutting an approx 1" section from a spare wooden broom handle, worked the diameter down a bit on the grinder to fit within the outlet hose, drilled 4 small holes in it and secured it in the hose with a hose clamp. This greatly reduced the airpump noise level but I can still hear it a little. I haven't experimented with it much, I am thinking that a 2-piece silencer (i.e. cut the wood dowel in half with an air gap between the sections) may work better but haven't had a chance to try out the theory. The amount of air discharged from this hose is phenomenal, even with the silencer with the tiny holes a good blast comes out. But what I am really wondering is whether the open airbox bottom is even needed with the 99-spec air guide. I mean, for sure it allows a goodly amount of air in to the airbox but for normal use would it really make any difference? That is, OEM uncut airbox w/no noise and 99-spec. I did notice about a 0.2 AFR enleanment after doing the airbox mod back-to-back with the OEM 1995 air inlet system. Haven't checked it since I changed to the 1999-spec air guide but I suspect that there is little or no difference.

I did not modify the side of that piece with the ac drier thing but I did patch up the top hole of it like you did. I have a 99 spec bumper with the 99 spec air guide and an SR motorsports intercooler, which is just a fatter stock mount. I tried this with different configurations on and off the track. I used both the Adam C and an autoexe carbon intake.

No matter how I messed with the intercooler ducting, it didn't seem to drop the intake air temps, so I just put all the stock pieces back together. The two things I noticed the biggest drop in temps was using some of that DEI gold wrap on the cold side intercooler piping and the intercooler itself, and then a feed style carbon hood. I was able to drop a good 10 degrees celsius with those two things using the Adam C mod on the stock intake box. I decided to ditch the carbon intake because it's very limiting in terms of fitment.

And of course, driving faster. My intake temps stayed nice and cool at Laguna Seca vs any sort of street driving since air was constantly being pulled in and out of the vented hood. Street driving is still hot I suspect because of the twin turbo system choking up any space under the hood and the limitations of the little SMIC. The best thing is really to just go v-mount and single turbo...I have that set up on a different car and the intake temps stay nice and cold and the car boosts very consistently.

If you had blocked off the AC dryer portion of the duct and extended the duct opening fully into the bumper to take up half the airflow you could have seen some dramatic improvment. However, the stock IC is a huge bottleneck as you know. To give you an idea of how much cooler I ran after switching to a good SMIC (M2 medium) & ducting my injector duty went from 80-ish% to near 100% at the same boost levels and ambient temp.

The performance at autocross is amazing too. While the stock IC would have highs and lows (it would cool off well in grid, but didn't control temps well during runs), the M2 is consistent. It will heat up in grid (up to maybe 50C with the radiator blowing on it), but immediately cools down during runs to 40C and stays there. The stocker just couldn't control temps during boost due to low mass and low heat exchange capability.