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Re: Getting high

To: MG list <>
Subject: Re: Getting high
From: James Howard <>
Date: Fri, 29 Jun 2001 13:02:10 -0700 (MST)
>As you get high you can actually use lower octane gas since the air is
>less dense.  I wouldn't sweat it though, the gas stations typically
>handle it for you.  if you use premium at sea-level and it is 91 octane,
> at 6000ft premium is only 89.  The regular will be 85.  

Here in Flagstaff (elevation 7000 ft) the premium is 91 and the regular is
87.  My 66 MGB needs premium in Phoenix (1500ft) but runs happily on the
cheap stuff up here.  

>It's gonna be slower though, there is nothing that you can do about
>that.  You will loose roughly 3% of your horsepower per 1000ft above
>sealevel, again, due to the lower density of the air.  Depending on how
>fast you make the change you may or may not notice right away, but be

The other cars (except the turbo ones) are slower too.  You can gain some
power back by advancing your timing a little, since the engine is less
likely to ping. 

>Also, you'll need to be leaning the HE@$ out of the jets.  If I
>remember I used somewhere between 1.25 and 1.75 flats per 1000ft.  Don't
>quote me on that, but it ought to be a good starting point. I think that
>I ended up going 8 or 10 flats leaner when I moved from sea- level to

I didn't even keep track, but that sounds right.  One thing I like about
the SUs is how easy it is to change the mixture.  On my other car I have
to take the carb apart and change the jet.


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