Custom Pre-80's Cold Air Intake

[Sellick]

Alright, as most of you know, us early year guys got the short end of the stick in this area and don't have a lot of good options for CAI. I've been wanting to custom make one for awhile and decided that this Christmas, while I'm visiting the parents, I'll pull the trigger on the project. (Dad has the tools needed)

So the plan is to build an adapter that connects to the AFM similar to what another user on here, bfurches, did.




I'm not entirely a fan of how this then just puts the filter right next to the warm block. I'd like to be able to run piping to wherever I feel works best for getting cold air to the filter.

So the plan is to have a circular inlet on the adaptor so I can run some piping wherever I want.
Now I need to figure out how big to make that circle. I believe on the post 80 cars the inlet to the AFM is 2 3/4". With the plate in the pre 80 cars' AFM being larger than the post 80, would I want a larger inlet to the AFM? Something like 3"? I'm waiting to get the dimensions of the rectangular inlet to figure out the area of it, then figure I'll make a circular inlet on the adaptor that is the same area as the rectangular inlet on the AFM.
(lose anyone yet? )
So if anyone already knows my dimensions for me so that I don't need to do the math, please speak up!

Let me know if you guys have any advice or if I'm missing anything!
Thanks guys

[Layne]

Cool, I like the idea. Personally I would use a 3" pipe and enter the afm at an angle rather than an elbow going straight into it. Just try to keep it smooth and the area roughly the same all the way through. Then ideally you would make a cold air box around the filter like JRcook and Shauer have.

[Sellick]

Layne, like the idea of the angle into it, more direct airflow towards the plate. Wouldn't have thought of that.

Is there any negative to making the diameter of the pipe slightly too big? Is back pressure possible?

And is there anyone here who has run their air filter down low, behind their front air dam? Pics?

[epmedia]

Slightly too big on the piping is not going to effect anyting, except for absorbing more heat/cold from it's surroundings.

You may even want to consider some insulated ducting, and keep the filter mounted the way it was intended.
Also consider "rain", ie: will the air filter be subjected to water?

Just another option to consider, I never tried one on an e21 before. Robert

[Layne]

Bigger is better, don't worry about it. Mounting the filter low is extremely bad. Every day dozens of morons do that and destroy their engines by sucking up water. It can't get any better than behind the headlight inside a box.

[epmedia]

Bigger is better, don't worry about it. Mounting the filter low is extremely bad. Every day dozens of morons do that and destroy their engines by sucking up water. It can't get any better than behind the headlight inside a box.

Thanks Layne, I dumped the low part on my reply. It contradicted my thought of "rain", in a way - didn't it .

Robert

[Sellick]

Yeah, there is the rain issue, but I'm in so cal. Today was the first day it's rained in about 7 months and didn't drive anyway. haha I understand the fact that it can be a bad idea (in some locations more than others) but can't it also be a good idea?

[epmedia]

Yeah, there is the rain issue, but I'm in so cal. Today was the first day it's rained in about 7 months and didn't drive anyway. haha I understand the fact that it can be a bad idea (in some locations more than others) but can't it also be a good idea?

I would try and do an easy swap from rainy days, to dry days.
Like just loosening a hose clamp, and spinning that sucker around 180 degrees. Or rig two flaps on intake ducting; one flap for dry days, and the other flap for rainy days - that would be cool . It's either that or doing what Layne mentioned about a box and headlight area.

Ponder on that while you lay in bed tonight - see if it's possible.

Btw: I'm also thinking that the designed mounting of that filter (without a shield),
may also be subjected to water - I dunno though...

Robert

[Sellick]

There's an idea, or just taking the piping off so the filter sits directly on the adaptor on rainy days. Although, having a box behind a headlight does look to be the best idea for these cars... Just like to look at all the options.

[epmedia]

There's an idea, or just taking the piping off so the filter sits directly on the adaptor on rainy days. Although, having a box behind a headlight does look to be the best idea for these cars... Just like to look at all the options.

I just edited my previous post:
"Btw: I'm also thinking that the designed mounting of that filter (without a shield),
may also be subjected to water - I dunno though..."

[Layne]

but can't it also be a good idea?

No. It's moronic (probably why so many morons do it). You can't predict when you're going to be forced to drive through a puddle.

Explain why you think this would be better than behind the headlight.

[Sellick]

As far as I can tell, I said "having a box behind a headlight does look to be the best idea for these cars" which is the opposite of me thinking that lower is better than behind the headlight.

But, for the sake of argument Layne, hot air rises and the lowest point of the engine bay is going to be the coolest. Having it directly behind the vents in the air dam provide the ram air effect, same as the headlight, and it's in a cooler spot. (Honda forums were not my source for this info)

My plan is to run it behind headlight with a heat shield, but I'm still going to ask for other ideas.

[epmedia]

The designed location of your filter does not get that hot (it's away from the radiator, and lots of airspace below it). And to bennefit from cool air in the headlight area, you would probably have to relocate the battery to the trunk. I still feel that the original design of your filter is probably the most feasable alternative with a shield or ducting of some sort (to protect from water splashes), unless you're ready to make it a big project (Ie: removing a headlight for some ram-air effect).

Robert

[Layne]

As far as I can tell, I said "having a box behind a headlight does look to be the best idea for these cars" which is the opposite of me thinking that lower is better than behind the headlight.

Fair enough, the other post just sounded like you really wanted to go for it.

But, for the sake of argument Layne, hot air rises and the lowest point of the engine bay is going to be the coolest. Having it directly behind the vents in the air dam provide the ram air effect, same as the headlight, and it's in a cooler spot. (Honda forums were not my source for this info)

My plan is to run it behind headlight with a heat shield, but I'm still going to ask for other ideas.

Continuing the sake of argument, it's irrelevant that hot air rises. The box should be insulated from the engine bay and ingesting outside air, the same as the low-down method would. On hot days, however the black pavement can be extremely hot, so the air nearest to it might actually be hotter. It's also significantly dirtier, you would have to clean the filter constantly. There is no ram air effect in either location unless you have a trumpet facing forward. Pretty difficult to actually do unless you abandon using a filter at all.

[shauer]

I run a K&N cone filter immediately behind the left headlight with a box fully enclosing the filter. At any speed over about 30MPH the intake air temp is the same as the ambient (outside the engine bay), even on hot summer days.

At highway speeds (70+ MPH), there is a ram air effect of between 3% and 5% due to the fully enclosed air box. Ok, the 5% was measured closer to 80+ MPH...

You should be able to do something similar with the kjet setup, especially if your battery is already relocated. The battery tray makes a nice air box mount.

- Steve

[milotrain]

On hot days, however the black pavement can be extremely hot, so the air nearest to it might actually be hotter.

It almost certainly is, that's why we see the mirage effect on hot days. Because the air just above the tarmac is hotter than the air at waist or head height.

[1980 320iS]

At highway speeds (70+ MPH), there is a ram air effect of between 3% and 5% due to the fully enclosed air box. Ok, the 5% was measured closer to 80+ MPH...

And how was this measured???

[alpina323c1]

Thanks Guys !!! good work there, very clean and tidy , love that kind of dedication to craftmanship. keep it up .

[shauer]

And how was this measured???

My claims were measured using the MAP (manifold absolute pressure) sensor and IAT (intake air temp) sensor on my Megasquirt setup.

The IAT sensor would indicate the same temperature as ambient when speed reached approx. 30 MPH. My IAT sensor is mounted in my intake plenum just before the intake runners.

The MAP sensor would indicate 103% to 105% barometric pressure at speed.

- Steve

[epmedia]

... The MAP sensor would indicate 103% to 105% barometric pressure at speed....

So, is that without removing a headlight, just the box behind the headlights?
Also, did you fab that airbox for a turbo setup? Or just through the Kjet?

Robert

[1980 320iS]

Interesting. I wouldn't have thought the there would have been enough direct "clean" airflow behind the headlamps to cause any measurable ram effect... but there's nothing like solid data to change my mind. Thanks for the info.

[Layne]

Also, did you fab that airbox for a turbo setup? Or just through the Kjet?

Robert

Steve has neither. It's EFI with 4 throttle bodies.

Interesting. I wouldn't have thought the there would have been enough direct "clean" airflow behind the headlamps to cause any measurable ram effect... but there's nothing like solid data to change my mind. Thanks for the info.

Agreed. That's impressive.

[shauer]

So, is that without removing a headlight, just the box behind the headlights?
Also, did you fab that airbox for a turbo setup? Or just through the Kjet?

Robert

Correct, just a well fitting box directly behind the headlight with the headlight still there. This was fabricated as a cold air intake for my Megasquirt EFI setup, not for use on kjet. I think you could do something very similar for kjet though. I could imagine the air duct going straight back to an elbow under the AFM.

There is a lot of air flow and a region of high pressure immediately in front of the car. Picture a 1 square foot air scoop going down the road at 70 MPH and you get the idea. This was the point Layne was making. Obviously the headlight blocks some of the air but enough makes it through to make a difference.

When running EFI, the drop in IAT was a bigger factor in performance gain than the few percent increase in MAP. Although it was fun to see a manifold pressure above 100% baro on a NA engine.

"Honest officer, I need to drive this fast to run my engine more efficiently...."

- Steve

[epmedia]

Thanks Shauer, Layne - and everybody else too.
It's really great to tread unknown territory with a "map" in-hand (haha).
I never realized enough air could flow past the headlights to make a difference.

And Shauer - the filter on your setup stays reasonably dry during rainy days too? Or just enough water induction to make it perfect on a rainy day maybe? Or not enough water to even be measurable?

Just curious, thanks! Robert

[shauer]

T
And Shauer - the filter on your setup stays reasonably dry during rainy days too? Or just enough water induction to make it perfect on a rainy day maybe? Or not enough water to even be measurable?

I have never had a problem with rain. I can't say how wet the filter gets as I have never checked it immediately after driving in the rain.

- Steve