After what Todd said during the last podcast and what Ian posted over at gbmini, I thought I would do a little experimentation, you know, to help you, the faithful dbmini.us reader and wrr podcast listener.

This morning when I filled up with gas, I put in regular unleaded.

DISCLAIMER – My MINI is about 45K miles out of warranty. The owners manual and your dealer’s service dept. will all say that’s a huge no-no. I’m sure my SA would tell me the same thing. I highly recommend not doing it. That being said…

I’m going to give it 2 tankfuls. So far I can tell a difference in the idle with the A/C running at a stop light. Oddly enough, it’s not quite so rough after only 60 miles on this tank.

The problem that I have is when the A/C is on and I come to a stop, the cooling fan kicks in. When that happens, I get a big shudder until she almost stalls (drops to about 500 RPM), then she sputters back to normal. I’m running the latest greatest software for the MC, but it still will not go away, no matter what is done.

I will also be checking gas mileage and hope to get an idea of power loss, if any. I’m not going to get any dyno results, but I should still be able to tell.

I’ll post an update after cruising around more today and tomorrow.

4 replies on “Experimentation”

  1. Regular = 87?
    Two things should happen – first the engine will need to do some re-learning (that is of course why I and you do two tanks of experimentation).
    Second, reducing that far you might get some pre-ignition; the engines response to that should worsen your mpg.
    With the intelligent engines we all have today, there won’t be any risk of damage … it will be interesting to see what the results are, once the re-learning period is over (200+ miles?)

  2. Oh yea, regular unleaded is 87 octane. I should have maybe tried midgrade, but oh well. Maybe next time if these test don’t produce the results I’m hoping for. I am saving about $3 a tank at least, and it will only be for 2 tanks.

    Already getting the pre-ignition a little. But only from a dead-stop.

    I would expect this tank’s mileage to be a little higher, but the next should work back to around normal.

    And 200 miles is about right for mine to relearn stuff, or 2 days of normal driving. I should have some solid information in a couple of days. The idle, however, is already starting to smooth out.

  3. The MC doesn’t have too high of a compression ratio, I think you’ll be fine. The MCS however has a rather high compression ratio, so I wouldn’t try anything but premium in it, though I have done 89 octane for a tank without any problems.

  4. about 160 miles so far. I can’t say the shudder has gone altogether, but it is not as bad oddly enough. I have, however, noticed a drop in power. This too was expected. And, as far as I can tell, gas mileage hasn’t been affected either. OBC is still telling me 400 miles out of this tank.

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