Hot Air Intake ....failure....
 

There is no place for failure stories here, but they are as valuable as success stories. How else are we to know what doesn't work? T

I put a hot air intake on my 2010 Subaru Outback. The method was to use an automotive heater core... a fairly large one from a full size pickup. The heater core was mounted beneath the air cleaner by cutting the intake resonator or whatever it is called, that Teed off beneath the air cleaner housing on the dirty side, and bonding the core to the cut end. The inner fender needed to be removed to do this. I then installed a butterfly valve where hose that is supposed to bring fresh air from the grill goes..(which I removed). Initially this was an automotive throttle body, but I found it too restrictive, resulting in an inability to reduce the intake air temp below about 130F. I then removed that, and built a large aluminum flap that was hinged. This was operated by a vacuum cylinder built from a Clippard air cyliinder, but with a spring installed inside it. I played with spring tension to try to achieve a useful result of high temp at high vacuum, and low temp at low vacuum... it sort of worked to a degree, but I was never able to tune it to work the way I wanted it to. I then rigged a vacuum switch which was adjustable, with the idea of having two settings..... a low power high temp setting, and a high power low temp setting. The switch worked the same cylinder, but with a light spring, and vacuum from a reserve tank with a check valve. I was able to get temps ranging from about 10 deg above ambient to about 145 - 150 F.
It all worked quite well in the final iteration.........but it gained me no appreciable mileage. My observations are subjective, based on scangauge readings while on long trips of many hundreds of miles

One could say the whole thing was a colossal waste of time.... I don't look at it that way. I look at it as a learning experience that may save someone else from following the same path.

The only way I can up the mileage on this car is by manually driving, as opposed to cruise control. A absolutely hate the CVT transmission! I'm a standard transmission guy, and even with an automatic, I can resort to pulse and glide or allowing the car to lose speed on the up hill and use Georgia Overdrive on the down side. These CVTs will not tolerate being put back into gear when moving at any speed, so I only coast when coming up to a stop.

I still feel that a hot air intake can gain mileage by increasing effective cylinder pressure at low throttle settings, mimicking a higher compression engine. Essentially throttling with heat, which eliminates some throttle drag, and the fuel should burn more efficiently. Unfortunately the programming on this ECU, I suspect makes compensations that cancel out any gains. Some of that is in engine timing.

The 2010 Subaru is a fairly heavy car, and my normal driving strategies give me about a 30 mpg year round average over all. I do no "city driving" to speak of except when visiting relatives, and then I piss all the other jack rabbits off by conserving momentum so I don't have to stop.... they just do not get it that roaring from light to light and sitting at idle waiting for it gains no time and costs gas... "citiots". Rush Rush Rush, and never gain anything.

H.W.

It didn't help even in the Montana winters?

That’s what mine is mainly for, gets to operating temp faster pulling air off the ca


My guess on something like a Subaru it probably runs richer at higher intake temps given the motors propensity to blow head gaskets.
On a car like a Subaru I would be careful not to let anything get too hot given it’s reputation.


Good learning experience but yeah if he already has the thing I would keep it on for winter use

Very little........ plugging in or parking indoors helps more.

What is "Georgia Overdrive"? That's a new one to me.

You must not be from Georgia.... ;-) .... but neither am I. It refers to kicking a truck into neutral and coasting down a hill.... "Put 'er in Georgia overdrive travel'in special air mail".....

H.W.

Ha ha! I'll be sure and use that from now on. (I'm from Washington state originally. All of our driving idioms are derogatory toward California).

I think part of the problem is that using coolant isn't necessarily 'waste' heat. You're not going to gain anything in warm up if you're taking heat out of the coolant with another heat exchanger.

Longer warm ups could negate any gains from a WAI on trips up to ~10miles - keeping in mind that a hypermiled car take a long time to warm up at the best of times.

My newer cars are designed to run with the thermostat only partially open. The radiator is barely warm after a drive even on the hottest of days.

The latest 1960s-early 1970s emissions controls were predicated on an intake manifold floor temp of 115F.

Though no real effort beyond minimal was incorporated, I chased the second half of the equation to get cool fuel. This was with a big block Chrysler where I changed the coolant thermostat from 185F (stock) to 195F.

I installed an electric fuel pump and vacuum-regulated fuel pressure regulator.

The spreadbore carburetor was mounted atop an insulated 4-hole spacer. Etc.

The genuine advantage of EFI is only in two areas; initial warm-up and altitude calibration. The other problems remain.

You may not have “failed” so much as chosen to stop prior to success.

I drew hot air per the OEM exhaust manifold shield (re-designed). Your hot air source may simply be TOO hot.

My hot air intake was controlled by a thermostat. It mixed hot & cold air after warmup. Under full throttle, the low vacuum closed off the hot air portion.

FE was about the transitions the carburetor saw. As they work off of pressure differentials, all sorts of temptations about internal air cleaner airflow presented themselves.

One must resist temptation to remain pure (ha!)

Under cruise conditions where terrain varies (not even hills) the need for warm air decreases as a function of distance. During de-cel, it rises. So, THE TRANSITIONS in terms of engine vacuum were what I used as a gauge against rpm (engine load). Messing with the APT (adjustable part throttle) mixture was how I found smoothness (for a given load & road).

The “hot air” was more of a backdrop. Not the constant once moving. Come to a stoplight, or maybe extended idling, it was predominant.

I could see where NO LOAD and high heat would be counterproductive while moving down the road. And could be overwhelming while idling. Total engine vacuum was how these emission-devices worked to regulate engine intake air temperatures.

It was the introduction of EGR that made those cars balky. The air temp regulation plus hotter coolant really was an improvement (generally speaking).

The exhaust manifold shield drew cold air over a very long cast iron surface. After expansion the only time those manifolds were radiating TOO MUCH heat was in an extended mountain ascent with trailer in tow. Flipping the air cleaner lid @solved@ that problem.

So my thought is that your intake may be restricted to too much hot air at all times versus engine draw. A heat exchanger is practically PUMPING hot air.

And how to measure effectiveness is still against a constant: use of cruise control, and a speed setting which allows one to avoid lane-change while en-route. The WAI is always going to show better results in city driving. It’s no real trick to get good MPG highway. Steady-State.

Load your car to GVWR by using a CAT SCALE and then re-test after fighting how to get closest to 105-115F intake temp.

Testing an otherwise empty car is a conceit around here. Means nothing, as Interstates ARE DESIGNED to reduce engine load. Until you EMPHASIZE transitions (vacuum) against the terrain, winds, etc, highway mpg improvements are going to be slight.

As before, cruise control-only. A constant constant
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My grandpa said the georgia overdrive line when I coasted in neutral with him in the car. Never heard it before that. I just figured it was just him saying "state" overdrive, but I guess it really is a thing.

I also tried a warm air intake in my car, I used dryer vent to suck air off the front pre-cat. It got the temperature up, but the car must monitor the intake temperature and assume the engine bay temperature is too hot, so it runs the fan constantly. No boost in mileage for me.. :(
The vent hose also was too small (3"?), when I took it off it felt like the car had another 40 horsepower.