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#1
04-07-2003, 08:42 PM
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At a higher altitude do you need a higher or lower octane gas as oposed to like sea level. The reason i ask is some one told me i could run 91 octane on 12.5:1 compression in Colorado. Is that guy right or wrong. Any input would greatly help.
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#2
04-07-2003, 08:42 PM
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At a higher altitude do you need a higher or lower octane gas as oposed to like sea level. The reason i ask is some one told me i could run 91 octane on 12.5:1 compression in Colorado. Is that guy right or wrong. Any input would greatly help.
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#3
04-07-2003, 08:59 PM
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At higher altitudes the air is thinner. This effectively lowers the engine's compression allowing you to get by on lower octane than you could at sea-level.
Let's go racing! www.outlawpontiacs.com/members/B-Man2.php www.outlawpontiacs.com/members/B-Man.php
__________________
1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
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#4
04-07-2003, 10:16 PM
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so then i should be fine with 91 octane or should i run a race gas?
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#5
04-08-2003, 01:02 PM
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Dish pistons and pump premium forever!
 BIGGERISBETTER-15 yrs in NHRA tech ret. 400 .030 1977, RPM E-Take, Q-jet, 6X, TH350, 8.5 3.73 spool, 3650#, 78 Catalina, 14.50's. Check it out, www.nhra.com.
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NHRA tech. "Its just a 412, I swear it". Pontiac tip of the year, quit those damn cigarettes. 
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#6
04-08-2003, 01:32 PM
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I would think you need at least 100 octane for a 12.5:1 engine even at higher altitude. I would be scared to try 91 anywhere at that compression.
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74 LEMANS GT 350 4SPD MAROON |
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#7
04-08-2003, 04:22 PM
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<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Tyes68gto:
so then i should be fine with 91 octane or should i run a race gas?<HR></BLOCKQUOTE> I have seen aluminum-head engines here in CA near sea-level getting away with 91 octane with around 11:1, most had long-duration (over 250@.050") roller cams. I really can't say your engine would be fine on 91 anywhere in CO. Only where it is at least a mile high would I even want to chance 12.5:1 on 91 octane, and only with aluminum heads and a big cam. Whoever told you that you could run 91 in a 12.5:1 engine at high altitude might be right, and might be wrong. A lot depends on the engine itself, and things like ignition timing and carb jetting. If it were my engine I would at least mix race gas with 91 at 50/50.
__________________
1964 Tempest Coupe LS3/4L70E/3.42 1964 Le Mans Convertible 421 HO/TH350/2.56 2002 WS6 Convertible LS1/4L60E/3.23 |
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