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Ok so first off i have K-pro and im making a 7 hour road trip tomorrow on short notice due to a family death. I have seen graphs that indicate our K3 motors (EP3) will burn the least amount of gas cruising at about 15.5-15.7 AFR . That being said im going to go out in a bit here on the highway to retune a new KAL for fuel economy for the trip tomorrow.

A big question i have is does anyone know FOR SURE if i would get better MPG if i raised the vtec point to say 3500 so its only on 12 valves while cruising at highway speeds aswell as burning at 15.5ish AFR. Would that be potentially unsafe due to heat buildup holding it out running like that for an entire 7 hour highway run? I just want to get the best economical tune i possibly can as im a little short on cash and would rather keep it for bills rather than filling my tank 4 times to get there and back.

Thanks in advance to anyone with personal experiance with this (didnt find much with a search)

*edit*
Forgot to add i have no cat either so it is not an issue to have a bunch of NOx or w/e happens

will i need to force open loop to cruise higher than 14.7? (i will find out when i try in a little but just incase someone sees this first) ;p
 

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I'd say just upload a stock map if your engine is unmodified Honda's oem tune is pretty safe and if you are cruising your car won't be making too much power so 14.7:1 is what the computer is going to try to set your AFR at close loop and will adjust it with the short term fuel trim according to your driving style. so in cruising mode light partial throttle you should be ok if the engine is untouched.
 

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please report back ur gas mileage. :cool::up:
 

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Hey bud,

Yes you will need to either disable closed loop or adjust the target air fuel ratio's in area you will be cruising to your desired ratio(recommended vs the other way). I wouldn't go much past 15.4ish for efficiency reasons.

And as for weather or not you will get better gas mileage, you will most likely from the difference in fuel input, but if you take too much out, you will be forced to use more load for the same power requirement during cruising. This would of course negate your goals.

Heat shouldn't really be an issue at highway speeds, the workload on your radiator should be minimal, and the key for the valves is that they will have a consistently hot temperature vs. a radically changing environment. The only reason this is possible is because you will be at very low loads when your cruising. Good luck and let us know! :up:
 

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Honestly, I'd disable vtec altogether, and run the car at around 16:1.. You're not going to hurt the motor, especially without a catalyst to retain all that heat..
 
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