Airflow over the rear trunk?

We might be on to something here! With limiter straps to keep the rear trunk lid from opening too much, we could have a fresh air supply that varies with speed! Except, of course, there is probably more air rushing out the trunk than trying to get in to feed the carbs. What is needed is a wireless pressure sensor to let us know what is really happening in there. You DCNF guys have it easy, you know the carbs are sucking in the hottest air in the engine bay (just above the exhaust manifold).
spring loaded or weighted louvers maybe, always open a little but as flow increases with speed the louvers rotate to near vertical, how about a "scoop" of sorts incorporated into the lid, with filter incorporated that when closed mates with the carb, scoop has wings with openings pointed down into the engine bay that funnels air towards the carb, it might need a louvered opening at the top, a waste gate of sorts so when going down the road a rush of cool air would surround the filter at all times, probably way more work than it's worth but fun to think about
 
Since the discussion is on air and water flow around the engine... I might need to cut off the lower level of sheet metal on the engine cover to clear my IDF's (without as of yet fitting the carbs my calculations predict a snug fit). That is once I get to that point in the resto.

Will I need to worry about rain water getting in the air filters in the off chance I ever get stuck driving in rain?

I'm picturing that my cover would end up looking like this one and these are my Redline air filters, just not on an X in the image.

X Engine Bay.jpg

Redline Filters IDF.jpg
 
K&N filters were originally developed for dirt bikes and I remember running them on my motocross bike without any issues in wet or muddy conditions (boy, this goes way back to the late 60s). I ran IDFs on my 128 but never on an X, I have a feeling you will be sorely challenged for air cleaner clearance. Whatever you end up with, you could make a rain hat to go over your filters if the engine lid has to be trimmed.
 
I have 40 IDF's on my 1500 x1/9. They do fit with 50mm tall air filters. But if they fit or not will depend on your manifold.

On the flow over the rear of the car. I have some images I generated using 2D flow simulation. I'll see if I can track them down.

Dishy
 
The trouble with drawing air from under the car is on a hot day it will be hot from the road and from air from the radiator passing underneath. Dust could also be an issue. The turbulent air above the engine cover will also be relatively hot from coming up from the engine bay. A large air filter is ideal, but not all cone filters are restrictive, it depends on the size and design. A K&N Apollo or Orion cone filter has the same surface area as a regular X1/9 1500 carby circular filter, but flow much better than the paper filter, they are also used by over half the field of the British 2 litre touring cars that develop over 250hp. ps, may not be street legal in US.
 
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IDF Sprint.jpg I have the SPRINT manifold which looks about as low profile as possible and still mount to the head at the ideal angle. I'll have to measure the Redline's height. Thanks

I'm sure ram air would be ideal for the carbs like on the Abarth but does negative air pressure act like a vacuum or just cause the carbs to suck hot engine air?
 
I would think the vacuum effect below the engine cover would be negligible to nil, it would just be drawing warm/hot air. If you can feed cool air from the existing side ducts to the air cleaners would be an advantage.
 
Since we are starting to get a little more scientific in this thread, how about establishing a baseline before we start modifying?
Measuring the intake air temp of the existing or "bad" scenarios so we have something to compare it to.
It may even show that the starting point is not as bad as we think.

I have been running K&Ns on my DCNFs and have been wanting to build/buy an air box to duct cool air in from the left scoop.
I now have decided to measure current intake temps first.
Yes, the carbs are sitting directly above the exhaust manifold, but the engine compartment is very well ventilated through the slotted engine cover. Coupled with the pronounced low pressure area above the engine cover, there should be a lot of ventilation at speed.
If you compare that to a traditional front engined car with an air intake through a hot radiator and then no exit from the engine compartment at all, the X should have much cooler intake temps even without a cold air intake.
 
Ulix, what will you use to measure air temps in the engine bay?

The Abarth 124 Stradale and Euro market 124s with twin IDFs used the "turtle back" air filter with two snouts facing forward. They were near the top of the engine compartment and a good chance the right hand snout was sucking up air from the radiator. You have to wonder how much scientific thought went into air filter pickup location back then. The other question is how much if any power are we gaining between true cool intake air and ambient engine bay air for a street car.
 
The only concern I might have with getting the air from underneath is the exhaust is right there, so it would likely be hot air.


I would pull the air up between the firewall and the engine block. Not between the engine block and the rear of the car..

Sounds like a fun experiment with a remote grill thermometer!
 
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Ed, my giant rust hole in the bottom is in the jack well so clearly that was a design feature for guys planning on using DCOEs 30 years later. Besides, my exhaust runs out through the rear grill now.
 
Carl, I installed a digital temp gauge where the instrument light rheostat once was (1300 center console).
I mounted a temp probe in the oil drain plug as an oil temp gauge.
I have a second temp probe that I would place in various locations and temporarily connect this to the gauge instead of the probe in the drain plug.

2017-04-20-PHOTO-00002121.jpg 2017-04-20-PHOTO-00002105.jpg
 
Carl, I installed a digital temp gauge where the instrument light rheostat once was (1300 center console).
I mounted a temp probe in the oil drain plug as an oil temp gauge.
I have a second temp probe that I would place in various locations and temporarily connect this to the gauge instead of the probe in the drain plug.

View attachment 7034 View attachment 7033

The only problem there is that the calibrated value range for an oil temp sender & gauge is way outside the lower window for typical ambient temps - and will likely not respond accurately or rapidly below the normal window of that sender, don't you think?

There are thermistors used specifically for ambient air temp used for climate control systems and dash displays on most (newer) cars that will have much better response time in the temp window we are looking at, but you would need a gauge calibrated to that resistance range.

I used to have a bunch of Innovate (laptop) data logging gear that I used to log ambient, engine bay and hot & coldside of the Intercooler on my old turbo setup for testing all this crap. I'll have to see if I kept any of the hardware needed to hook this all up on the X1/9.
 
Ed had mentioned to me using a wireless digital grill thermometer but I have yet to look for one.
 
This is not an oil temp setup per se.
The gauge is a generic china item.
The sensor is an industrial item sourced from a professional lab environment.
It did fine measuring the air temp in my oil pan before I filled the sump. :)
Anyway, I am only looking to determine the approximate temp difference between inside my K&N and ambient temp.
 
This is not an oil temp setup per se.
The gauge is a generic china item.
The sensor is an industrial item sourced from a professional lab environment.
It did fine measuring the air temp in my oil pan before I filled the sump. :)
Anyway, I am only looking to determine the approximate temp difference between inside my K&N and ambient temp.

I should have realized you would be using something a little more accurate & responsive than a standard oil temp probe :D
 
No, not a grill thermometer. Get a few thermistors. They put out a voltage signal that is proportional to the temperature, some even a few spots to the other side of the decimal point. You use a look up,table to convert the voltage to temperature. You can silicone them, tape them, epoxy them, whatever...into position. Very, very accurate results.
 
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