bump for a great thread !

 

Alright so im a newbie to the rotary and RX7's so please bare with me here. What would stop a guy from cutting out the whole underside of the airbox? As long as it seals against the filter theres nothin under the filter of any importance is there? That would give a nice BIG open filter element to flow through and with the factory ducting being modified a little it should get plenty of air.

Am i right here guys?
Thanks

 

There's no advantage to doing that since (if you look at the pics) you will see that cool air can only enter the gap next to the radiator.

Plus if you have original plastic/rubber parts you'll find they tend to disintegrate if you start poking them. The hose couplers on the stock air box in particular like to go snap crackle pop on an old air box.

Personally I think one of the best things you can do for your car (and your sanity) is get rid of every rubber hose and piece of plastic in the engine bay and replace them with metallic pipes/tubing.

 

The main reason for having an airbox, is to keep hot air away from the filter(s). That's why they are called cold air intakes. If you simply cut a hole in the bottom of the airbox, you will allow hot air in. My shield channels cool air into the intake from the front, and the underside of the car.

 

So the disadvantage is that youre gonna get some warmer air in the intake. But if the bottom is open it would flow more air correct? I mean, the stock inlet hole is awful small... And i dont mean to cut any of the nipples off the box, just the bottom where there is nothing.

It would expose the filter to a much larger surface area for the intake, but suck warmer air in return, correct? Obviously your duct is an improvement for a cold air intake, but for sheer air flow my theory would work yes?

 

I think the flow restriction will move to the turbo inlet pipes at some point. Increasing the area of the air box opening beyond that point wouldn't improve flow and it would be at the expense of inlet air temps. Roughly speaking, I would guess that is an area a little more than the total of the turbo intakes.

Opening the bottom as in Adam's mod makes a very efficient path and if the original "snorkel" is maintained, I don't think the stock turbos work too hard for air. That is evident in my car by a boost spike after making the mod.

Fundamentally, your idea doesn't seem too different from open filters as on many intakes but with a single elelment.

 

I just did this mod with making my own heat shield. Use my soldering iron with a cutting tip to remove the piece then sanded it down smooth.

I still have a stock air filter (K&N drop in is on the way) but I could really tell a difference. After warming the car up pulling out of my neighborhood in 1st gear I got the rear end loose at only about 1/2 throttle. That didn't happen before so easily!

I'm seeing about 10psi in 1st gear, 10.5psi in 2nd gear, 11psi in 3rd gear, and 12psi in 4th gear. Car is definitely quicker. I monitored AFRs on my wideband and they are well within the safety range (I also have AI). Sound increase isn't as loud as I expected and much more modest.

I would really recommend people do this! Well worth the limited amount of time it takes to complete.

 

Yes, it will provide more (hot) air with just the hole there. If you are going to spend the time to modify your airbox, why not do it right? Making the shield is not that difficult. PM me for info.

 

After searching I have not seen too many dyno results with this mod. Most that I see are around 300whp. Is there anybody out there pushing 350whp+ with this mod?

 

Most of the higher HP cars have bigger intercoolers. The stock airbox is pretty big, so it limits the size of intercooler that will fit in the remaining space.

 

Thanks for responding Adam. The previous owner of my FD did this mod but he closed the stock intake opening portion. I just found this out recently and removed it. It’s now sucking cold air from the bottom and hot air from the front. I'm missing the piece that hooks to the duct to suck in cold air from the front of the car. Man, after removing the restriction on the stock opening, my car pulls so much harder, even though it’s sucking in hot radiator as well! It feels like 15 or 20 more hp!

After talking to someone who has experience tuning, he says the stock box, modded or not is still restrictive. (Not to knock your product) I am really debating whether to upgrade to a better flowing intake system, even if it sucks in hot air. But if I could find people running this mod and still be able to push around 350whp, which is my goal, then I'll just stick with it. I don't know anybody yet though. Most people that are pushing high horsepower from the twins are using a hot air intake or M2 style intake. I have also heard of people running 400whp with a Greddy smic which is what I have also. I'm not sure if its the intercooler or the air box that will hold back the power. Would you happen to know anyone running high power numbers with the cheap bastard air box mod?

 

Also, a good portion of the volume in the top of the airbox is taken by an enclosure for noise muffling. This restricts the path after the filter. Take a look and you will see what I mean. Notice how close it sits to the filter. You can cut this out to improve air flow.

[IMG]https://www.rx7club.com/attachment.php?attachmentid=387117&stc=1&d=1273523 444[IMG/]

[IMG]https://www.rx7club.com/attachment.php?attachmentid=387118&stc=1&d=1273523 444[IMG/]

- Sandro

 

I think I'll try that. ^

 

Sheldawg,

A properly modified stock airbox will flow better than ANY other cold air intake. With 2 sources of cool air (front oem intake duct and modified underside opening), there is virtually zero restriction for airflow. The stock airbox houses a huge filter (K&N replacement). You simply cannot do better than that.

Your Greddy intercooler will be the limiting intake temp factor, not the airbox. That being said, I can't see any reason you couldn't run 400 rwhp with it. It just won't cool the intake charge as well as a bigger intercooler.

Sandro,

Very interesting modification to the inside of the box. Any feelings on gains from doing this?

 

wow I can't believe this thread is still alive LOL

 

No feelings yet Adam... I have been doing this to make room for a WI "rail"...another of my always-late-never-finished projects...

- Sandro

 

Did you notice if it was louder? I did something similar with my RX-8 air box, it definitely got louder, but I didn’t really feel any power gain. From the looks of it should flow better, while using more of the surface area of the filter.

I’m sold, I’m going to stick with the cheap bastard air box. I’ll post dyno results after I get my tune…..

 

Cannot answer that either...for the same reason... I have not installed this gutted box yet.

But expect I could hardly hear any noticeable difference since I am cat-less.

- Sandro

 

I'm a little late to the party, since it just did this modification today.
The only slight variation is that I added foam around the cutout on the airbox.

My mods are DP and this one.
The car definitely has more pickup.
The 'growl/moo' will take some getting used to.

Great mod!

 

---> https://www.rx7club.com/showthread.p...&highlight=moo

 

Glad to hear it is in and running well. Congrats

I prefer to think of the noise as a low growl. I haven't even noticed it years. You will probably only hear it at very low speeds. I wouldn't/didn't bother to try and get rid of it, and I am one of those guys that doesn't like extra noise coming from my car.

 

I know the pettit tkd shield costs more but does it not function in the same manner?

 

of course you cant use the stock intake box with it but just wondering how this would compare to the Pettit intake system

 

The pettit cold air intake is not a cold air intake IMO. While it's shield does keep hot radiator air from directly entering the intake filters, it still relies on hot under hood air to feed the intake. This includes hot air radiating directly off the engine and turbos.

There are no aftermarket intakes that can provide as much cool as as a properly modified stock airbox. NONE!!!

 

Yep. This mod is very functional.

It's less obvious from the pics, but CBI shield creates an air channel from the front nose between the radiator and the frame of the car. If you close any gaps with foam, air has no choice but to get rammed up into your airbox!

Thumbs up to Adam!