Gas Mileage - How much can tuning get you?

[74NovaMan]

Hey Guys,

I've got an 86 Trans Am with a 350, TPI, 700R4, and a 2.43 posi. I am in the process of putting it back together and have never actually driven it so I have no first hand experience with actual gas mileage for this combo. http://www.fueleconomy.gov/ says the car was rated for 17-25 mpg in stock form with a 305. I am thinking about a mild performance cam, and an adjustable pressure regulator as the car was originally a 305. I would imagine that it would run fine with the stock computer and chip but that seems so boring. I'd love to find an excuse to play around with a megasquirt setup.

Here's the questions:

If I tune for mileage how far can I push this combo if performace is secondary? (If I could get a consistent 25-28mpg on my 80 mile per day commute I could drive this in the summer and not my 95 Ford Aspire.)

If I tune for mileage, do I have to stay out of the gas all the time or is the mega squirt flexible enough to run a mileage tune at anything under half throttle and something more fun over half throttle?

Any help is appreciated.

[squirrel]

Wild guess is that your driving habits will have much more affect on mileage, than the tune of the injection will.

[TheSilverBuick]

If I tune for mileage, do I have to stay out of the gas all the time or is the mega squirt flexible enough to run a mileage tune at anything under half throttle and something more fun over half throttle?


I don't know yet, but I hope so. I "plan" on running as lean as possible at low throttle and let the fuel pour at higher throttle. The MS allows automatic fuel cut off while coasting, not sure if the OEM's did that in the 80's, but I don't think so. Cam, compression and timing will still be large parts. Oh yeah, Driving habits are still the biggest mpg factor.

[74NovaMan]

If it's any indication, I always seem to be at the high end of the MPG range for the cars I drive on that commute. Arguably, they have all been gutless wonders for the most part. My driving habits are largely dictated by traffic conditions.

[dieselgeek]

You won't gain but maybne a percent or two when trying to "tune lean" and it takes a lot of time to cut back slowly on "accel enrichments" which are a big factor (think of it as a "pump shot" for a carb), however the Overrun Fuel Cut that SilverBuick is talking about, is generally a big benefit, on the order of 10% or more.

You won't need separate maps for mileage versus power though, you just set up your fuel and spark maps so the WOT, high load high rpm areas are "aggressive" (or however you want them) and then you set the low rpm, higher vacuum areas (cruising) as lean and with as much timing as you can put in.

Really, tuning for best power and best economy are about the same thing. You want to tune for maximum vacuum at all possible load combinations...

-scott

[Brian Lohnes]

Ya know Scott, every once in a while, you give me the impression that you know what you're talking
about.

;D

Learning is fun.

Brian