Cold Air Box...Worth It?
 

I work in a sheetmetal shop in the Air Force, so making this would be no problem for me. But I am wondering...what is the point? Please help me clear my head on this, but this is what I think.

So if you build a cold air box, the filter is enclosed with only the stock air snorkel...so yea..YAY COLD AIR...but how much air is really delivered from the snorkel. If I wanted to have a snorkel going to a box I would have just left the stock box. I think, although I'm probably wrong...But dont I get a hell of a lot more air just having the cone filter out there in the open? Sure it may not be cold, but isnt it still better? Or is a little cold air better than more warm air? And then what about not building a box, just leaving it out in the open, and buying the headlight cover scoops from fc3s.org?

Please tell me your opinions. Thanks.

1988 RX-7 SE

Well going to a different intake if for more filter area over stock. but with a cone you get no protection from the hot air in the engine bay. With a box around it you keep more heat out of that area. but to get cool air in there you need to have an inlet/snorkle/anything a duct that goes out to get air from the outside. I am trying to make a system like this but I need to master carbon Fiber first. :(
I don't think metal for it is good since metal gets very hot I think maybe some heat resistant plastic or composit would be better and some wrap would also help.

Santiago

Re: Cold Air Box...Worth It?
 

The stock snorkel is absolutely useless unless it's attached to a totally sealed airbox like the stock one. The idea is it make a heat shield that completely seperates the pod filter from the rest of the engine bay (should be easy for you) and then make a new duct that is fed cold air from the front of the car. I consider 3" a minimum size for this duct. I don't like those headlight scoops because they're simply not big enough.
If you do a search of the 2nd Gen section you should find several threads on how people ran their ducts. Unfortunately most of the good ways require the cutting of metal andthe relocation of some stuff, but it's worth it.
It is absolutely worth ensuring that no engine bay air enters the filter. Underbonnet temperatures can get very high (I've seen over 150degF) and that considerably reduces the engine's efficiency.

The reason you want to replace the stock airbox is not because the airbox is restrictive, but because the filter is.

That said, a cold air box will have a definite positive effect off the line. If you're bored, go ahead and make one. There is a hole in the passenger inner fender that is perfect to take air from instead of using the stock snorkel...But if you expect mad HP increases (yo), then don't bother.

Sorry, but this is completely wrong. The actual filter in an airbox causes a tiny fraction of the resistance of the intake system. I've seen this proven in testing of many different types of cars and airboxes, and the result is always the same. The filter will typically cause a pressure drop of ~1inH2O (0.04psi). The shape and size of the airbox's entry and exit is where the restriction lies, and the FC airbox design is quite bad in this respect.

The FC airbox has so many square edges, but I have seen the same increase in replacing the paper filter as I have seen adding a cone. However, your numbers are undoubtably more accurate then mine since I have done no formal testing on the airbox design. If you say it's bad, then I have to agree.

This is a good article in intake modification from Autospeed. The they've done several articles like this on different cars (this is the only free one) and the filter always shows ~1inH2O presure drop.

http://www.autospeed.com/A_0779/page1.html

Note the configuration of the FC's airbox (inlet on top section, outlet on bottom section) means we can't do what's been done here. Otherwise I'd prefer to keep the airbox and modify if for better flow.

So does having a cone intake with no cold air box leave you worse off than leaving the stock box with drop in or still better, but just not as good as it could be if you had the cold air box?

The power gain from from reduced restriction is partially offset by the power loss from sucking hot air. The hotter the air the bigger the loss.

The other problem is the higher risk of detonation. The hotter the air, the higher the risk.

So basically if you just put a cone filter in, you're making matters worse..

So if you put a cone filter in... make a cold air box?


Correct me if I'm wrong prrs.

Re: Cold Air Box...Worth It?
 

You better make me one, or I am calling your supervisor....:)

Jarrett

Re: Cold Air Box...Worth It?
 

Hell yeah, I love taking full advantage of the material and skillz given to me by uncle sam!:patriot:

Better yet make a cold air box right in front of the passenger fender, where the washer bottle is and make so ducting that goes to the brake ducts or the front of rad duct

Re: Cold Air Box...Worth It?
 

I read somewhere on here that the headlight is not in a high pressure area to really allow a ram air effect. Does anyone have wind tunnel info on the car? Either way, I agree with NZ, the headlight scoops don't seem to be big enough convince me to drop $150 on them.

So I guess I'll just build the box...I got all the tools and any metal I could possible need so what the hell. Anyone got any plans or know a good site where I can read about making a box? Or see some pictures?

What do you mean by this?
Anyone got an answer?

Higher intake temps mean even higher temps during compression, which on an engine thats just about to detonate on its own, the higher temps could push it over the edge..... but an engine thats tuned with any regard to safety shouldnt have an issue with that.

It's not good to just replace the stock air system with a cone intake right on the afm and leave it sitting in the engine, since you are just going to be pulling in hot air that way... there are a few cold air box designs around, and mariah motorsports sells one, also checkpoint sells a filter relocation kit, which puts the filter right behind the front grill in the front bumper (this is what i have), but the same thing could probably be made out of parts from home depot if you want to measure everything and figure it out (wont quite flow as well though, since it probably wont have as smooth edges)

so all and all, i would either stick with the stock air system (using a drop in k&n filter instead of the paper filter), or buy / make a cold air, or filter relocation system for yourself.... otherwise its money wasted just to get a filter and slap it right on the afm

That's what I did, and it works great. I made my box out of aluminum, and used 3" PVC pipe to duct in cold air. Here's the thread:
https://www.rx7club.com/forum/showth...hreadid=181680

http://208.62.166.66/guest/pics/inta...akeholebox.jpg

I think the sucking in hot air by just putting on a cone filter is way over blown...Thats only the case while stopped at idle or moving very slow on a warm or hot day.
I have done some mods to insure additional cold air entering the area.
I have removed flash to pass lenses, (Love the look too) removed the black plastic in front of the front frame and also removed some foam insulation from where the radiator is close to where my cone filter is. I am also researching and agree with others that the pass. side brake duct inlet (Side) is a area that can bring additional (Cold) air into the filter area...
Its much improved over a stock restricted air box system...
Its very noticible at speed, but yes, stopped on a hot day in traffic, your likely to have hotter air then the stock box before moving again...

Regardless of what, the open air filter w/out a box or ducting outside of the engine bay WILL pull in hot air. It's pulling in more air yes (more filter area...greater volume) but it's still pulling in hotter air than stock. It's much worse when you're sitting still, but even when you're moving you're still pulling in hot air from under the hood. Yes there is more air flow while moving, but it's still a majority of hot air under the hood that's being pulled in. I'm not starting an argument (please don't take it that way), but as long as that filter is open air and under that hood it's still pulling in the same air as when it's not moving...which is hot air. Cool air intakes are priceless advantages and should never be overlooked as a waste of money or time.

I agree, most of the air that is under the hood most likely has come thru the front radiator / oil cooler / ac radiator, since that is the easiest way for air to get into the engine bay, and since those are going to be hot, the air after it gets thru them will be hot as well, meaning that even at speed most of the air in the engine bay is going to be hot (or at least warmer than outside air)

I will let you guys know about the results after building atommicas cold air box. Should be getting the templates very soon.

what is atommicas? Anyone else got any templates or anything I could use? I guess I'll just build one, got the time and resources.

Here is the link to atommicas write up
https://www.rx7club.com/forum/showth...hreadid=101026
He is charging $5 for the life size templates, pictures and a list of supplies and tools you will need to complete it.
Looks amazing. I just hope mine comes out looking like his. If you want to waita week or 2 I should have it completed by then and can post my results and feedback.

If you read the article I linked to you can see the sort of temp drops achieveable. I've measured the underbonnet temps in my own car and even at speed it's always considerbly higher than ambient. When stopped this shoots up much higher still.

If you've been sitting at the lights for a little while and accelerate hard when it turns green you're applying full load to an engine that's sucking in air as hot as 140degF. Apart from the noticable drop in power, that's a recipe for detonation... :eek: Those mods will be having very little effect on the temps at the air filter. Considering all the obstacles along the way very little air will be reaching the filter from the FTP lense. Air always follows the path of least resistance, so if you have no heat shield it's much easier for the air to be sucked from the engine bay.

BTW, that foam stops air from going around the radiator instead of through it. I'd put it back. ;)