Cooler Inlet Air & Gas Mileage


OH, OK .......Now I get it
Dec 6, 2018
Hello everybody,
As some may know, I came to this forum with a unique vehicle. I have an '84 Hot Air with a 700R4 tranny in my '75 Jeep CJ5. I have learned a lot thru you guy's & have done a lot of maintenance improvements to this 17K mile, 36 Year old engine. New chip from Eric, exhaust headers dye checked & welded, new vacuum lines, wires . BLM's at 132 , TPS at .412, FP at 38 line off, 42 line on, ect ect.
It runs very well cold & warm. I can even spin the rears from a standstill with the 3:73 gears. That's good enough for me, it's not for racing anyway. I'm very please at the work I've done.
My question is : the air intake is the stock air horn & it points toward the DS exhaust manifold, about 10" away. If I install a cold air kit toward the front , could that help with improving my gas mileage ? I know it's a Jeep , running 31 X 10.5 tires & the gears are what they are, but I am only getting 10-12 MPG running 93 pump gas , as a DD, to & from work. If I go on the Hi-Way , it does better at around 60 MPH...... I'll get it up to 18 MPG . my other questions would be, what could I do to improve the DD, around town, MPG ?
Thanks in advance.... for all & any replies . I need some guidance & advice. :cool:
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So.......I also ran two tankfuls with BG44. .Along with it now being a much cooler ambient temp ( High's in the low 60's ) , My mileage has improved ~ 3 MPG . :cool: I'm now on the determination that my HA needs a cold air kit . I'm also going to make sure I'm running a 160 T stat. Not 100% sure , 'till I see for myself this weekend.
A cold air intake will always improve performance and mpg. That is always one of the main goals for us Hot Air owners. Good luck!
Thanks , Brother........ It's always amazing how long it takes this stubborn old Irishman to get anything new thru this thick head ! Think I'm going with G-Bodys kit , so I can customize it ,,,,,, to my custom Rig.
Since heat turns the tires, lowing the cylinder temps would lower your MPGs. Based on physics.

The only time lowering the cylinder temps help is when you're so hot you've exceeded the detonation threshold due to heat.
Thanks for the Physics info. May I ask why you think I'm noticing an improvement ever since our average outside Temperature has lowered by ~ 30 degrees ? Am I thinking wrongly that a remote cold air intake would be better than my stock' ' 84 air horn which is presently ~ 10 " away my DS exhaust manifold ?
There's more oxygen per cubic foot of air when it's colder. If you were running a little rich before, the denser air will lean out your mixture a little and could stretch your mileage a little. Or you were 'right' and now you've got a leaner burn...

There's a million different reasons for you mileage to change.
Thanks , again, for the lesson. I do appreciate you tak'n time to reply for me. I do agree with you about the million reasons . One could be proper inflation in the Tires I use. ;) Oh Yeah, the higher heat range NGK UR 4 Plugs , gaped @ .25 have made a difference too.
For that rig and tires I think you're doing ok at 12mpg. It's prob heavier than most people think. If you're fuel injected and it's running right the only way to really improve mileage is to drive like Gramma. Low n slow.
Yes Sir.....she's only 2800 #'s . Not bad for a " Brick " with big tires , though . I've been looking at smaller ones....... every little bit will help.Thanks for the support with this. BTW..... I'm very pleased with her capabilities off road , that's her main job going into the near future , + the fuel injection & auto tranny beats the hell out of other's performance.
Thanks again , everyone.
As stated:
The laws of physics cant be fooled. For a given AFR, more oxygen = more fuel.

With a HA, you will see a typical 140-145F intake charge temp with a 75-100F ambient / inlet air temperature. Around 40F ambient / inlet air the idle intake charge temp will drop to around 130F. 30-40F drop in inlet air temp in a HA will result in an added 2-3 psi detonation cushion.

You can run a HA at 55 mph around 15.5-16.3:1 (flat road with Buick wind resistance and close to stock tires) if looking for better fuel economy. Slighly learner can be done but you will notice that more throttle may needed to maintain the same speed. (Diminishing returns)