My car came with an Apexi intake with no cold air feeding into it, and the stock intake ducting all pushing fresh air into the intercooler. The opening for the stock airbox has been sealed off.

I recently got my hands on part of an OEM intake which would allow me to re-divert some air towards the cones. However, this would mean;

a) letting the air split between the intercooler and the intake
b) the air going to the intakes wouldn't be 'sealed'; it would just blow in the vicinity.

The car has intake, DP, hi flo cat, 3"catback, stock twins, with a PFC. Would doing this be beneficial or not in your opinion? If I do this, I'd likely modify the box so the air would flow directly on the cones.


current setup


OEM intake section considered

Underside of the OEM box; would mod the exhaust side to flow more directly on the cones.

Opinions appreciated.

 

Put the stock airbox or aftermarket equivalent or v mount. The intakes are causing more harm than good right now

 

You could open up halfway. Or let the rubber piece flap. so it opens up gradually with speed increase.

So at low speed ,or idle, the inter-cooker it getting most of the air flow in (such as it would be).


Of course if it starts to mooo, perhaps pursue a different strategy.

 

Nay.
If you intend to retain the stock IC then the best bang for your buck IMO would be to source the last component… a stock air box. THEN do a cheap-bastard mod to have that stock airbox source fresh air from the nose and NOT scavenge it from the IC duct.

Then get rid of that open intake. Even with your proposed mod, it will just continue to source hot under-hood air while reducing pressure in front of the stock intercooler. And you’ll need to get everything out of that stock IC you can.

 

First off, the "this intake isn't making more power" is bunk. Proof -

https://www.rx7club.com/3rd-generati.../#post12098745

Also every FD I've ever put an intake on has made noticeable seat of the pants power, especially up top.

Smart move is to leave the stock IC duct as it is with the airbox hole capped up. Bare minimum fab some sort of aluminum or something heat shield to isolate the intake from the radiator fans and duct some fresh air up to the intakes from between the radiator and frame rail.

At the end of the day the stock IC is so small and crappy that even a dedicated cold air setup isn't going to help much, it will heat soak like crazy.

Dale

 

I think we’re basically on the same page as far as suggestions to the OP. But I’m not convinced that the dyno results in that link for an open, under-hood intake translate all that well to real-world street use. I doubt it’s “bunk” on the street under most conditions.

 

I think the general rule for intakes, regarding the desire for cold air (which is good), and to lower restriction (also good), is:

"Cold air is good, more air is better."

Which is to say, don't restrict the intake to make it exclusively "cold", but get as much cold as possible.

 

Agree…to a point. Probably really relevant to single turbos. But the curves for ambient air vs. heated under hood air (less volume but ambient, vs more volume but heated) has to cross at some point.
But on his car I just wouldn’t mess with an open intake.

Probably not what the OP was looking for but a good conversation anyway.

 

Please explain "cheap Bastard" mod to OEM air box.

 

The cheapest mod I hear here is my opening flap idea.

At WOT the intakes get the most air. At not-wot the intercooler.

 

I read a study done with all the intakes... I have a Pettit so I wanted to compare. Although the Pettit is still open it resulted in more power due to less restrictions. I modded mine a little which I believe helps a lot.
I don't see how you can mod this one too much though.

I mean damn it is sucking air straight from the rad..... wth

 

The stock intake is a restriction, period. The size of the inlet is too small. Filter size is OK. This was common in cars of that era, the stock airboxes just had crap designs.

If you ever seen an RX-8 stock airbox Mazda learned big time over the years. HUGE intake, straight shot of cold air from the front bumper, giant snorkel, and the filter size is no kidding about TWICE an FD's filter all for a car making 220-ish to the wheels.

Making a good effort to bring in cold air and shield the intake from hot air is worth it. Turbo cars have the intercooler doing a lot of the heavy lifting with intake air temp drops, the turbos add a TON of heat to the air as its compressed.

BTW, the "cheap bastard" airbox mod is basically opening up the snorkel in the airbox to something larger and feeding it colder air. AdamC I think pioneered that, search on the forum to find more about it.

For my part, I HATE dealing with the stock air box. It's crazy in the way, a pain to install and remove, and the clips on the side love to snap off on you.

Dale

 

Appreciate all the advice, and the Banzai thread was an eye opener as that is real measured gains on a similar spec'd car pre HKS twin power.

My intercooler is a Koyo. Basically same performance as a stocker?

I'm kind of torn here. From all the data seems it best to leave the intake as is and work on some shielding instead. I love the intake sound to be honest, and would only go to the stock airbox if it was definitely more beneficial than the cones.

To throw a wrench into the recipe; if I were to upgrade the intercooler, say an SMIC, would allowing the cold air to feed both the intercooler and the intake (albeit not sealed on the intake) become a good play?

 

I often wonder if that was on purpose to restrict air flow and make it easier to control boost with the primitive systems circa early 1990s...

 

I have come across some curious pieces for the S6. One, a delete cover for the right side oil cooler opening. Two, fog light delete covers (not to be confused with the the semi-circular gap covers for the normal fog light set up. Both of these pieces seem to be restricting access for outside air through the fascia. Was the purspose to somehow force air through the remaining opening?

I assume these would have been standard pieces for certain base models. However, they seem to be commonly MIA.,

 

Agreed, I think that's just half the reason. The engineers also needed to meet a required fuel economy number for sales. Restricting the intake decreased power substantially, therefore keeping the MPG's comparable to other 90's sports cars. The sad reality is, the whole car was designed that way. Which is why power comes so easily with mods. Just removing the plastic intake bridge piece helps out tremendously. I wish I had back to back runs on a dyno with the bridge piece on and then off. With the bridge piece installed, my primary intake hose would collapse in on itself. When I removed the plastic bridge piece, the hose wouldn't collapse. Really shows how much vacuum is created in the intake with the bridge piece installed. It also means the turbos are working hard just to breathe.

As for the original post, shielding would be best bet, or the stock airbox mod.

 

The intercooler you posted pictures of is the stock intercooler. You aren't talking about a radiator? Koyo makes the most popular RX-7 aftermarket radiator.

I would stick with your intake and add some shielding and maybe a duct, you will be good there.

Upgraded SMIC's typically have their own duct that doesn't connect to the intake. It's generally best to let each get their own fresh air. The IC duct is CRUCIAL to an intercooler performing well, without it you just add dangerous amounts of heat, it has to be force fed cool air.

Dale

 

I had an up close and personal look at HRain's intercooler tonight. II definitely says Manufactored by Koyo Manufacturing. It also bore the version number N3A1.

Maybe all of our intercoolers (if stock) where made by Koyo?

 

Most likely. There are a number of Japanese companies that make OEM parts - our brake master cylinder was made by Tokico, calipers by Sumitomo, AC parts by Nippondenso, etc. I'm sure Koyo made the stock IC for Mazda.

Regardless it's still a stock IC and not up to the job .

Dale

 

I have about 15 discarded intercooler. Any hope in making these into double-wides that would fit in?

 

That's a lot of time, money, and effort that would probably be best spent with another option.

Dale

 

I am one for not removing stock airboxes on a car due to less filtration and higher intake temps. I really think intakes on most cars are for looks and sounds, rather than performance, BUT...
Ditto what Dale said... I know OP's question is whether or not his intake is hurting performance due to heat. I have seen this argument a lot, where people will say stock airbox or PFS airbox or nothing. Yes those may be better for having cool intake temps, but it does not do much after the hot turbos, compress the hot air and make it even hotter and send it to the dinky little tin box Mazda called an intercooler.

I think there is something to be said about having an intake that is easier to remove and work on the car. The stock airbox is the biggest pain and limits the size intercooler you can run. You are better off upgrading the intercooler and adding meth than farting around with a clunky airbox.

 

Thanks all. I'll do an IC upgrade in the future as time allows. A second oil cooler is in the garage waiting to go on first.

 

I am bit bewildered by the comment that removing a stock airbox is a pain. Compared to what?

 

It’s not. At least I don’t remember having much of a problem with it. The plastic “loops” did have a tendency to break with age and heat. 10mm captured screws were easy. And with the stock IC, if you opened the bottom aka ‘cheap bastard’, I don’t think it was the restriction in the system. It did take air away from the face if the IC, but when moving at moderate speed pressure there was probably kept at acceptable levels given its size.