Cold Air Box Advice?

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Daryl Smith
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Cold Air Box Advice?

Post by Daryl Smith »

I am going to have to build a cold air box for the throttle bodies I am going to use, something I've never done, and don't seem to be able to find specifics of material thickness to use, and how to build/seal the 'top' when installed.....Advice appreciated....

Box is going to be a 15 1/2" long oval, 4 1/2" wide, and 4 1/2" tall. Just enough clearance around the engine bay. Inside there will be 7/8" clearance to all sides of the velocity stacks and about 1 1/2" above stacks. Would have liked more side clearance, but, there isn't room. I am going to bring the air into the top side of the box with a 3" diameter 45 degree bend cut/welded in.

What thickness material would you recommend for the bottom, sides and top?
Assuming aluminum construction, my expectation is that the base should be thicker, possibly the 'top' also...
Pic of cardboard model:
ITB Air Box Model (Small).jpg
Thanks,
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FergO2k
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Re: Cold Air Box Advice?

Post by FergO2k »

.090 thick sheet stock should be plenty, the suction isn't going to be that much, and should only be temporary when going to WOT.

I like to start with ballpark weights (as I have ended up looking foolish when not thinking of that early enough), and at the dimensions you have, .090 thick sheet stock will weigh 1.06 lbs, which sounds right. You might be able to use .060 stock. The large flat wall is the weakest area, so if you find it bowing in, you can go back and add a rib in the middle of each wall. (.060 thk = .71 lbs)

You won't have the wall and lid moving independently, so you don't need a bulb seal (like a "P" or a "d", or most anything with an O)
Something more like an "n" where the legs sliding/sealing over your aluminum walls, as the suction will pull the lid toward the upstanding wall.
The theme is "make the applied pressure improve your seal", don't try to with stand the pressure. And that way you only have to snug the lid bolts, which leaves the seal more relaxed at rest, and then it will last longer.
most industrial metal supply houses have an "off-cut" bin out front that they just sell by the pound.
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Re: Cold Air Box Advice?

Post by redroadster »

Can't find a.modifiable salvage yard plastic box,? alum. Gets hot quick , are you going to bring in air from in front of the radiator?
after 15-20 mph the CFM of air passing the eng bay is so larger it's basically moot
This mod is talked of quite a bit in factory training courses as ?
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Re: Cold Air Box Advice?

Post by Daryl Smith »

Thanks,
I had picked up some used K&N filter housings for DCOE's to modify, but, with the time involved I could have the airbox and better breathing as the filters would have been right up against the velocity stacks. I would have preferred more clearance (1" - 1.25"), but the engine bay is too tight.

red,
Yeah....nothing close that I could find or think of that could be modified to work, not plastic, or anything I could find on the internet for a dual carb setup...I did spend a fair amount of time looking at different setups, both factory and homemade.
"This mod is talked of quite a bit in factory training courses as ?"
I don't know about any training courses, but, most (all?) factory cars/trucks now have cold air intakes. It makes a difference.
I think I'll be running a filter down near the bottom left side of the radiator, in the engine bay....that way I don't have to move/cut anything else.

Ferg,
Thanks, some good info there. Air intake will be 3" so I don't expect much suction.
Ordering materials Friday, will have to start making a jig to bend the ends.....
Base will be .090" as I have to thread a temp sensor into it, rest will be .0625"

Will post finished picture when it's done.
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Re: Cold Air Box Advice?

Post by redroadster »

Yeah plastic ones , it gives slight hp increase at low speeds one reason they do is the mass METER, off the block heat & to keep it a bit out of the way of the radiator flow so a long tube is needed for that
one trouble with ramming air down the tube it causes buffeting which impeeds air flow, it needs to be sucked in , per japan engineering.
But a digital temp sensor under hood will drop to very near air temp at 20 mph
Mitsu training had a video on the after market air intake ,vs stock and problem s with it

At Mitsu in the mid 90s I took over high perf trouble shooting from the senior tech , because he was in Ill health .we were the designated dealer to do it in our area
The other one gaught caught over 100 mph doing it .
Our test was a nearby highway entrance ramp , so steep you couldn't walk up it about 400 ft .we stopped at the bottom just before the grade , and you'd floor it get to high rev in 3rd at the top ...a new 3000gt VR4 would be going 70 @ the top a bit less on turbo Eclipse
So many modified engine of those came in and claimed 100 200 more hp, but the test track don't lie they get to 57 & 51 mph
$ 4-6 k and it's way slower


I'm not miss typing the fuxxxcken auto protect is shit
Last edited by redroadster on Mon Mar 08, 2021 3:20 pm, edited 3 times in total.
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Re: Cold Air Box Advice?

Post by greydog »

Alloy will be almost as important as thickness.
1100 will be softest, then 3003 followed by 5052. These bend easily with little spring back.
6061, 6063 and 7075 are hea t treated so strong but more difficult to form.
Extrusions like bars, shapes and tubes are often different alloy than sheet and not all will weld easily to each other.

If it's all welded construction, I'd use 3003 or 5052.
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Re: Cold Air Box Advice?

Post by Mike Unger »

This issue with aluminum is it's a great heat conductor. I made a cold air box for my S2000 race car and used carbon fiber with a foam core to have some insulation properties. My 2 cents. It has two chambers and a foam filter element between them.
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Re: Cold Air Box Advice?

Post by Alvin »

Here is a box I've seen on an R16:
Image
Image
Image

Another consideration: shielding the carbs/manifold from the hot exhaust, shown by Robert P:
Image

I've seen this approach on many vintage racing roadsters as well. It "looks" more effective than a air intake box. :D
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Re: Cold Air Box Advice?

Post by CSP311 »

As redroadster points to, no point having cooler air coming in and gaining power, if how the air is delivered to the trumpets/carbs is disrupted, and that power is lost. You after all spent $$ on your trumpets which have been designed to work in a set way.

Have a look at some other Nissan period airboxes, there was plenty of time and Yen spent on their design back then. Look at a z432, even the likes of a stock 260z/510 uses baffles so the air is distrubuted around the box, not just "slamming" into the front trumpet and then gets disrupted for the others.
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Re: Cold Air Box Advice?

Post by spl310 »

Why not something like this? It may work out better:

https://www.ebay.com/itm/1967-Alfa-Rome ... SwAuVgPVd-
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Re: Cold Air Box Advice?

Post by Gregs672000 »

That's a really nice box, especially for the money. The only bummer is no velocity stacks. I tried numerous air box designs, ultimately deciding to route cooler, filtered air to the intake via a tube much like the air box on the 1600 Alvin posted, but no longer using a box. Wth the EFI system now I can now monitor air intake temps with a sensor inside one of the filters. When I'm running again I will see what happens to that temp just out of curiosity.
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Re: Cold Air Box Advice?

Post by Daryl Smith »

Greydog,
Thanks, local shop only has 5052, so that's what it will be.

Mike,
2 chambers?
No carbon fiber for this one.

Alvin,
Saw that 1600 one. Problem is I need 4 1/2" for enough clearance over the stacks, and there won't be enough clearance between the stacks and inner fender to slide that deep a box in. Thanks.

CSP,
Trumpets came with the throttle bodies (2 sets of throttle bodies, one set of trumpets - $200 Can.). No room to bring air in on the fenderwell side, so I will bring it in on the 'top' or hood side into the base of the trumpets, don't know if that will have any detrimental effects, but, doing my best to have it balanced over as much of the box as I can.
To be clear, there are NO stock/afermarket boxes that will fit. I have to build or modify. I have spent a good amount of time searching and see nothing that can be easily modified. Even got a freebee K&N dual 3 1/2" setup from Carl and after sandblasting and cleaning up realized by the time I'm done modifying them to work, I can build a better box...at least, I think I can...ymmv.

SPL310,
You got me thinking on that one...only way I can think to make something like that to work would be to have the top and side come off together to give access to the trumpets, making it much more complicated....Air intake will be similar tho, but, coming in from the top front, not the top side
Last edited by Daryl Smith on Mon Mar 08, 2021 1:18 pm, edited 1 time in total.
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Re: Cold Air Box Advice?

Post by Daryl Smith »

Pictures...
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Re: Cold Air Box Advice?

Post by Mike Unger »

Daryl Smith wrote: Mon Mar 08, 2021 1:03 pm
Mike,
2 chambers?
No carbon fiber for this one.
My cold airbox is for a plenum intake not ITBs but you get the idea of two chambers. Cold air is rammed into the bottom chamber of this insulated box from an intake low and in the front of the car and it goes through the filter before going into the velocity stack. You could do something similar on the top of your box with a sandwiched filter so you have better flow into the box from the front of the car and the filter helps to diffuse the air before the intakes.
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Re: Cold Air Box Advice?

Post by CSP311 »

Hi Daryl,
Yes, I realize nothing "off the shelf", but then again I think most aren't quite cutting it design wise.

I know this is forced induction, but the idea is the same, my friend has an HKS surge tank on his 240z (not the link below, just a google search) but this has the air coming in the side ( I know you don't have room) and the air then has to go through a baffle with 6 holes cut in (for each cylinder).

The 260z and the Japnese market cars running the L20, both have air entering the inside of the air box from the bottom. The 260z has front and bottom, whilst the L20 is just the bottom. Air evenly distrubuted and the velocity reduced. Carbs don't want pressure.

Got to think outside the (air) box.

https://catuned.com/devil-in-the-detail ... atsun-240z

Here are my trumpets I plan to use, as I know you guys like that sort of stuff.
20210309_173507.jpg
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