Warm air intake, how warm can you go?

[zman]

I am interesting in modifing my intake to get more milage by going warm.

I am wondering what would be a good temperature range with 87 octane fuel, and with 92 octane?

Also what FE gains can be achived by warm air intake?

[Daox]

It differs between engine. You'll have to test to see what temp your engine likes.

[Wonderboy]

I just made a HAI for my car and I'm seeing positive results. It's hard to tell what impact the aero mods have because I installed everything at the same time, but I did a little A A B (no time for another A) test yesterday and today on the highway, and it seems like the unscientific results were a 3mpg avg. increase. I saw IA temperatures up to about 140F, which worried me a little until I saw that my engine temp gauge in the cluster looked the same as it always does. More quantitative results to follow.

My understanding before I tried this was that trying can't really hurt, its more about how your ECU will handle hot air. Depending on how it does your FE will remain the same or increase. Don't quote me on this, but please correct me if you know more than I do.

[cfg83]

zman -

For my 1999 Saturn S-Series, the upper limit seems to be 179 degrees F. This was documented by lovemysan. I think the hottest I have ever been is 166 degrees F. I like it below 150 degrees F so that I don't have to think about it.

Currently I am running with 91 octane to avoid the risk of ping/knock. However, when I ran 87 octane during the height of the gas prices, I never noticed any problems. However, my HAI configuration was probably topping out at 135 degrees F at that time.

CarloSW2

[zman]

Wonderboy with 140 degree air you definitly have warm air intake.

Can you tell me how are you measuring the inlet air temperature, and where did you rout your intake to get the warm air?

[Wonderboy]

I linked to a thread about my car in my previous post. There are pictures there of where I routed the intake. I am just reading intake air temp from my SGII. I would expect mine to get a little more than "warm" (wherever the temperature threshold is) because my highway run was only about 6 miles... it will probably rise above 140 on substantial (hour long?) highway trips... then again maybe not. More results are yet to come.

@cfg83: Could you explain the risk of knock/ping involved with using regular octane gas? Should I consider using 91?

[cfg83]

Wonderboy -

Originally Posted by Wonderboy

I linked to a thread about my car in my previous post. There are pictures there of where I routed the intake. I am just reading intake air temp from my SGII. I would expect mine to get a little more than "warm" (wherever the temperature threshold is) because my highway run was only about 6 miles... it will probably rise above 140 on substantial (hour long?) highway trips... then again maybe not. More results are yet to come.

@cfg83: Could you explain the risk of knock/ping involved with using regular octane gas? Should I consider using 91?

There area others that can explain it better than me. I think that we are safe because we are not driving under heavy load (high RPM), we are "featherfoots", so to speak.

Here are some quotes from RH77 :

Fuel Grades - Post #9

Originally Posted by RH77

When I had my HAI (160F) I used premium to prevent detonation, but the cost-benefit was off. Now, intake temps are 100-120F with full advanced timing and no ping with near-full load (some knocking at high RPM, so I don't go there much).

The TSX "requires premium", but runs just fine on regular. The savings add up. FE is the same too. There's a bit of stumble from time-to-time at 6k RPM with VTEC, but again, very rarely used.

Long live 87!

RH77

Cold air VS Warm Air Intakes - what's the difference? - Post #5

Originally Posted by RH77

I have a brief response -- incomplete answer.

From the shop manual on my vehicle, the engine is intended to run richer at intake temperatures below a certain figure (I forget the exact number, let's say 60F). Warm air is needed to satisfy this requirement, especially in Winter.

Beyond that, I've determined with repeated testing that my engine operates most efficiently with IATs at 90-100F. Beyond 120-130F, it starts to dump-in more fuel to compensate for pre-ignition, and fools with the timing. So that temp above the maximum requirement of ambient up to at least ~90F yielded around a 15% increase when I first tested it 2 years ago (the abstract is floating around somewhere -- I think there was a cold-air intake on the car before). FE drops when colder air is introduced, even at ~70F, which is well within the requirements of the sensor/ECU closed-loop management. You may find terms of HAI and WAI (hot and warm air intakes).

How it works -- not exactly certain. A couple years ago I did quite a bit of testing with different temps and found the "sweet spot" for my car. There's still quite a bit of discussion on the topic and the term "pumping losses" can best be explained by someone with more Physics knowledge than I have.

My advice? Experiment yourself with different temps -- and stay as Scientific and consistent as possible. See if you can obtain info on IATs and the vehicle ECU's compensation from a shop manual or enthusiast website. BTW, what kind of vehicle do you have?

Let us know if you test and come to some conclusions.

RH77

CarloSW2

[TestDrive]

Originally Posted by Wonderboy

Could you explain the risk of knock/ping involved with using regular octane gas? Should I consider using 91?

In the case of your '98 Civic EX, if pinging begins to occur it will immediately be detected by the anti-knock sensor (think they became common about same time as ODBII was introduced) and the ECU will automatically adjust ignition timing to avoid knock/ping. If that's the case you'd get somewhat better mpg with 91 octane, but whether the improvement would be justified by the increase in price is doubtful.

[99LeCouch]

I saw temperatures in the 140's with my OEM intake today. This was tooling around town all day, lots of low-speed driving and stopping at lights. Plenty of time to heat-soak the OEM intake components. The PCM was pulling fuel like crazy, based on the really negative long-term fuel trims. The trims started back down as the air temp decreased as the car got moving again.