I have to admit that I'm not real certain I ever experienced much improvement in my mpg's with my EAT chip. I took it out months ago when premium hit above $3.00 per gallon here in Kentucky and haven't put it back in since. It's bad enough paying $2.60 a gallon now for regular 87 octane.

After reading some of the above posts, I did some math. Here's what I found. Assuming a 21 gallon tank, if you filled it with 87 octane at $2.50 per gallon (without EAT chip installed) and drove all highway miles and got 23 mpg (which is pretty consistent for me), you'd be able to go 483 miles. That calculates out to $.1087 per mile.

If you put 21 gallons of 91 octane at $2.70 per gallon (with EAT chip installed) and drove all highway miles and got 25 mpg (which I can't say I ever got 25...maybe 24 at 60 mph), then you could go 525 miles. That calculates out to $.108 per mile.

So the real issue is whether you actually get better mpg's with the EAT chip. If you don't, then it will certainly cost more overall to have to purchase high octane fuel. Frankly, I've had my EAT chip out for a few months and I don't miss the performance. I do however like saving $4-5.00 per fillup. I suppose it all comes down to what you want to spend your money on.

Grace and peace,

Robert K
1991 535i