How do I trim 30% of my fuel w/out spending $500?

douglas vincent · Post by **douglas vincent** » Wed Dec 22, 2004 6:33 am

So I have the 370 CC injectors instead of the 270 cc injectors. Running way rich (but happy at boost). So if I could concievably cut 30% of the fuel off boost, I would have the fuel economy and power as a normal (or as normal as mine could be) NA motor.

How can I do this without just spending the $500 for some piggyback/standalone unit?

91White-T · Post by **91White-T** » Wed Dec 22, 2004 6:45 am

A used AFC should be nowhere near that, a new one is only like 250$ I think,

THAWA · Post by **THAWA** » Wed Dec 22, 2004 6:49 am

vrg3 gave you a good suggestion in the other thread.

douglas vincent · Post by **douglas vincent** » Wed Dec 22, 2004 6:54 am

I'm reading that thread but didnt want to confuse it with other ideas.

Thanks

vrg3 · Post by **vrg3** » Wed Dec 22, 2004 6:57 am

Only when off boost?

Maybe a little circuit to ramp the MAF sensor signal downwards when you're off boost. You'll get more timing advance than usual, but when you're not on boost that might work okay given that you're running premium fuel.

You have the Hitachi MAF sensor; you can scale down its voltage to achieve a pretty good scaling down of airflow readings. This is the graph I made a while back of it:

http://www.graphics.cornell.edu/~v/pics ... visors.png

So 370cc/270cc is about 1.4. If you wanted to divide airflow by 1.4, you'd need to divide the voltage by about maybe 1.16.

But the trick is getting it to only happen when you're off boost. Maybe get a MAP sensor from a car in the junkyard and use its signal to trigger the switchover?

Does this sound like the kind of thing you want to do?

douglas vincent · Post by **douglas vincent** » Wed Dec 22, 2004 7:03 am

Yes, if messing with the MAF lowers the period the injectors are open, then thats what I want. And since I am running premium fuel, the advanced spark might even help some.

vrg3 · Post by **vrg3** » Wed Dec 22, 2004 7:06 am

Okay. Let me draw up a schematic for what I'm talking about.

douglas vincent · Post by **douglas vincent** » Wed Dec 22, 2004 7:08 am

Thanks

vrg3 · Post by **vrg3** » Wed Dec 22, 2004 7:22 am

Okay, this is the basic idea:

http://www.graphics.cornell.edu/~v/pics/fueldealie.png

The 20K pot would adjust how much the MAF signal is ramped down when off boost.
The 10K pot would adjust when the circuit would transition from "off boost" to "on boost."

Pretty much any MAP sensor from a non-turbo car should do.

If you'd like me to walk you through the circuit I can try.

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How do I trim 30% of my fuel w/out spending $500?

How do I trim 30% of my fuel w/out spending $500?