Hot intake air causes the combustion chamber to run hot. That is different than making the coolant temperature hot which is mostly a function of ignition timing.

For every 10 degrees you increase IAT, you increase the octane requirements by .5.

You also increase the chance for knock which we all know kills your FE not to mention engine life.

I personally refuse to run a WAI because I don't believe the tradeoff for engine wear is worth it. Also, I have a tiny 1.5 engine, any less power would make the car a chore to drive.

I've been running 86 or 87 octane since day own of ownership of my SL2. Had the HAI on about a month and haven't heard any new noises or experienced anything of than a slight reduction in power above 150*F. To compensate, I do as directed by others, wide throttle in highest gear, seems in 3rd gear I can accelerate w/ TPS at 25% and the MPG reading dips to 20's, but in 4th I can go 50% TPS and MPG is still above 30 (speed is the biggest factor there obviously too).

For now, the HAI is my new best friend.

Before HAI the IAT was basically ambient... so I've doubled it in some cases, say from 80*F to 160*F, meaning you suggest I should put in 90 or 91 octane over 87?

Would I benefit in FE for doing so, or is it just to prevent knock/ping?

if your compression ratio is really low though, you don't even need 87 though it is the lowest that you can buy. I think you only need 93 when the compression ratio approaches 12:1 or so. I have seen cars that have a compression ratio of 9 or 8:1 so if you fall into this category, I don't see where it would be an issue. you may require a higher octane but you still may need a minimum of less than 87 which is the lowest you can buy.

this is just my understanding of it.

*edit* BTW, project84, your pics look similar to mine. are you plugging the other end of the tube though. is it some sort of check valve?

The plug that you see isn't really a plug, it's just metal flashing riveted over the hole. That is where the OEM intake air tube was which contained the IATS. Since I relocated the sensor, I got rid of the provisioning as well.

My LT1 Camaro has a compression ratio of 10.5:1 and it requires premium, anything less and it runs like poo.

I want to say the SL2's are 9.5:1

I know that my truck ('04 dakota 4.7L) is 9 even.

not sure about the car

My '93 SL2 would ping pretty fiercely in low rpm/high throttle conditions. It ran much smoother with 93 octane, for sure. It was a stick shift so I may have been lugging it a bit...

Not sure that car was considered "high compression" or not.

A technical note on comment #22 by Project84. 80*F to 160*F is not doubling the temperature. Anything having to do with thermodynamics, including ideal gas law equation, is based on absolute zero. 80*F to 16*F is really 540*K (Kelvin) to 620*K, a 15% increase.

Running a HAI may not be the best way to improve economy IMO. All I see it doing is making the IAT sensor read higher so that the fuel maps are leaned off via the temp compesation tables in the engine management system.

The better way would be to have a cold air intake and just to lean off the fuel mixture. Sometimes just turning the fuel pressure regulator down a little can achieve this.

Whilst hot air is of some benefit to making the fuel atomise better in the cylinder, depending on the where the fuel rail is positioned on the engine, if the fuel rail gets little heat then warming up the fuel can help a little.

In summary, I think only a small percentage of the fuel economy gain is from the heat. I think a majority is just from throwing less fuel into the cylinder which can be done via other methods. The main one being programable engine management systems.

For me, it's really as simple as this...

Total cost for HAI build - $14

Total saved in less than a month.... and I only drive about 700 miles per month... projected near $25.

Whether I'm getting the gain from here or there, I NEVER got above 27 in mixed driving in the 3 years of owning my SL2. I put the HAI on and WHAMO 31.xx 4 consecutive times.

My best highway mpg was 33... My new best? 46.

I'm an instantaneous kind of guy, whether the engine blows up in 5k miles due to this or not, I don't honestly care (good excuse to do the SOHC 5sp swap). I modded the car, am seeing amazing results, and I couldn't be happier.

I'm happier if I get some of these results and possibly modding my wife's car too.. haha