How did you improve your fuel economy on a 4ac?

hachipirate
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How did you improve your fuel economy on a 4ac?

Postby hachipirate » Thu Dec 24, 2015 9:10 am

It might be a moot question because most car guys will just say "that's the way it is", or "who cares about fuel economy". But this is a nice little 4 banger with potential and I'm interested in how any of you got the best fuel economy out of your 4ac motors. 91 octane and advanced the timing? Changing the air screw to non-factory settings? One turn out/in? Changing float height? Idle speed, or fast idle changes? I've read that the automagic transmission robs the engine of power and having a standard will help out. Whatever worked for you. And don't say put a 4age in, that's the lazy way.

I was recently calculating my MPGs and came to 21-23 miles per gallon, less than my WRX gets. I'm going to play with fuel settings soon, hopefully not run too lean, and run some tanks of gas to get a proper database.

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allencr
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Re: How did you improve your fuel economy on a 4ac?

Postby allencr » Fri Dec 25, 2015 1:34 am

Tire pressure, make sure the vacuum advance is working, also ease off the throttle & push into neutral(you don't even have to use the clutch) instead of charging up to a stop light or downshifting double clutching like a jr raceroo to wear the engine & drivetrain instead of the brakes.

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Re: How did you improve your fuel economy on a 4ac?

Postby ogdougynutty » Fri Dec 25, 2015 9:10 am

^ Hit it pretty good there. the biggest thing is not to use engine breaking a lot (i.e. off throttle in high RPMs). In a fuel injected car it can detect that and cut off or severely reduce the fuel supply. But with a carbureted car, off throttle will always deliver the same amount of fuel off throttle no matter the RPMs. So always try to keep the RPMs low. Coasting in neutral (when it is safe to) is one of the best things.

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Re: How did you improve your fuel economy on a 4ac?

Postby yoshimitsuspeed » Sun Dec 27, 2015 2:47 pm

The biggest thing you could do is max your compression ratio. Something like 10.5:1 would net a notable gain. Or even a little higher with a mild cam.
The next best thing would be switching to EFI.

Other than that you would be looking at small gains here or there. If you got a wideband you could probably tweak the carb in a little tighter and most likely a little leaner.
And yeah other than that just proper maintenance, tire pressure and driving style.

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hachipirate
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Re: How did you improve your fuel economy on a 4ac?

Postby hachipirate » Sun Dec 27, 2015 6:55 pm

Good stuff about driving habits. But none of you have found a gain with minor mechanical tweaks like I was wondering, huh? I'll find out soon enough it looks like with a little trial and error. Thanks for the input guys.

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Re: How did you improve your fuel economy on a 4ac?

Postby yoshimitsuspeed » Mon Dec 28, 2015 12:38 am

If there were gains to be had from easy little tweaks Toyota would have done it. You might get tiny gains from fine tuning fuel and timing but again you would really need a wideband to do fuel properly and OEM ignition timing is going to be damn close to perfect for the stock motor.

davew7
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Re: How did you improve your fuel economy on a 4ac?

Postby davew7 » Mon Dec 28, 2015 5:03 am

About the only easy change is the exhaust system. Look at headers and low restriction pipes and muffler. A better exhaust will reduce pumping losts. If the exhaust is custom, get anti-revrsion in the primary header tubes. You will probably have to adjust timing because of the improved scavenging. Dave W

aceforever
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Re: How did you improve your fuel economy on a 4ac?

Postby aceforever » Mon Dec 28, 2015 8:25 pm

davew7 wrote:About the only easy change is the exhaust system. Look at headers and low restriction pipes and muffler. A better exhaust will reduce pumping losts. If the exhaust is custom, get anti-revrsion in the primary header tubes. You will probably have to adjust timing because of the improved scavenging. Dave W


I'm curious. Is the exhaust really that restrictive on the 4ac? I keep on hearing the 4age headers and piping were designed well and can support a lot more HP. Not sure what the 4ac is like.

davew7
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Re: How did you improve your fuel economy on a 4ac?

Postby davew7 » Tue Dec 29, 2015 5:58 am

If you go to the AEU86 forum, and search exhaust "a post probably 5 or 6 years old" there was a member that did an A-B comparsion dyno pull, and posted the documents that showed a switch to a 20V stock header on a big port. There was a 5 HP improvement with just the header switch and an adjustment in timing allowed by the improved scavenging. And that was with the rest of the exhaust system stock. That would be pretty typical of most exhaust systems. Increasing the pipe Dia. and a low restriction muffler would add more. Dave W

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Re: How did you improve your fuel economy on a 4ac?

Postby aceforever » Tue Dec 29, 2015 7:18 pm

Interesting, thanks for the info.

Did torque change at all?

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