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Engine / Re: The official mileage vs. compression thread
« Last post by kneedownnate on Today at 06:57:36 AM »
At what elevation?

Thanks.

Below 1000 feet
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Engine / Re: The official mileage vs. compression thread
« Last post by Lewis Hein on Today at 06:48:49 AM »
Or if you don't like approximations, use Boyles' law

P1     V2
--- = ---
P2     V1

V1 is the volume in the cylinder at BDC, V2 at TDC. P1 is local atmospheric pressure, P2 is pressure inside the cylinder at max compression (I.E, P2 is what we measure with a compression gauge).

V2/V1 is constant with respect to altitude, and therefore P1/P2 is, too. Thus, if your local atmospheric pressure is 75% of pressure at sea level, your compression readings will be 75% of what they would be at sea level, too.

So, if you are at 4000 feet elevation, air pressure is ~12.7 PSI rather than the ~14.7 at sea level. Your compression reading would go down from 171 to 147 PSI.

This is an approximation too, of course, because air is not an ideal gas.
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Engine / Re: The official mileage vs. compression thread
« Last post by Gnarly4X on Today at 06:32:33 AM »
For those interested.... to calculate for the difference in elevation when reading your compression, you can use a close estimated number of 5.25 PSI lower compression reading for every 1,000 feet rise in elevation from sea level.

In other words, if your engine  (1986 22R/RE) compression is spec'd at 171 psi, and it reads 171 PSI at sea level, and your actual elevation is 4,000 feet, your compression reading will be 4 x 5.25 lbs less, or 150 psi.

Another example.... if your reading at 3500 feet elevation is 152.6 PSI, your reading at sea level would be about 171 PSI.                                                                                                                                                 

Gnarls.
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Engine / Re: The official mileage vs. compression thread
« Last post by Lewis Hein on Today at 04:11:06 AM »
I will check my 91 when I can.  22re with nearly 284,000 miles, burns a bit of oil.  Very bad valve stem seals, fouls plugs quickly, but despite this it still had 185 psi minimum last time I checked

At what elevation?

Thanks.
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Engine / Re: The official mileage vs. compression thread
« Last post by Lewis Hein on Today at 04:09:00 AM »
Hope this thread doesn't die! I'm interested to see more information.

I really hope so too. Right now, I have two data points, yours and Nate's. That's not enough to draw any meaningful conclusions.
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Engine / Re: The official mileage vs. compression thread
« Last post by kneedownnate on Yesterday at 11:09:47 PM »
I will check my 91 when I can.  22re with nearly 284,000 miles, burns a bit of oil.  Very bad valve stem seals, fouls plugs quickly, but despite this it still had 185 psi minimum last time I checked
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New Member Check-In! / Re: Hello, this is my Pile: 1986 4Runner SR5
« Last post by BigBluePile on Yesterday at 09:18:01 PM »
So, that was fun

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Engine / Re: The official mileage vs. compression thread
« Last post by Toybrota on Yesterday at 08:44:26 PM »
Hope this thread doesn't die! I'm interested to see more information.

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1984-1988: How-To Guides / Re: Frame paint?
« Last post by Toybrota on Yesterday at 08:43:13 PM »
Thanks everyone for the kind words! I would've done POR15 but I just didn't have the time. I plan on getting a 3rd gen pickup bed at some point, and when that happens I'll POR15 for sure.

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Looking forward to this build, I've driven a few of the 6 speed Tacoma's, definitely on my wish list!

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