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Old 03-09-2005, 09:29 PM   #1
svek
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Default will 91 octane hurt my poor 2.2L?

im just wondering if filling up on 91 octane would hurt my naturally aspirated bare stock 99 2.2L
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Old 03-09-2005, 09:35 PM   #2
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No, its just a waste of money. Do it if it makes you feel good.
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Old 03-09-2005, 09:40 PM   #3
Caplin 2.5
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yea check up one of my threads about if 91 octane is any good in this forum. We all concluded that 89 is the way to go for a naturally aspirated motor ...
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Old 03-09-2005, 09:47 PM   #4
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so no damage but is there any benefit? and i cant find ur thread btw. i hate the search thingy for this site
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Old 03-09-2005, 09:56 PM   #5
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The thread in question basically "demonstrated" some minor benefits with 89 octane. However, we have no idea how crappy the 87 it was tested against really was to begin with.
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Old 03-09-2005, 09:57 PM   #6
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There is no benefit from the higher octane and there are three potential disadvantages from using high test. First is the cost. Second, high octane fuel burns more slowly than regular unleaded, which is why high test is better at preventing knocking. Your ECU is programmed for the faster burning regular unleaded, so using high test makes your car operate outside its optimum design parameters, hurting your performance. Third, regular unleaded burns faster and hotter, making your engine less likely to form carbon deposits, or so I've been told.
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Old 03-09-2005, 10:02 PM   #7
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The octane rating is only the anti-detonation rating of the fuel. the higher the octane the more it resists detonation. Detonation can and will destroy a motor very quickly. Factors that increase the possibility of detonation are; high intake temps, super/turbocharging, high compression, running at peak EGTs, and a few others. With a STOCK NA motor if you run any octane higher that the factory recommended it will not produce any benefit, just cost more. Hope this answers your question.
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Old 03-09-2005, 10:04 PM   #8
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but it does kinda make sense if you have some mods done to your car to go with 89. If you have done minor upgrades like intake, full exhaust and an Ecu, but if it is all stock i think 87 would be fine.... i just run 89 for the sake of it cause its in the middle. if higher is too much and lower is too little i'd just stay righ tin between haha.
oh yea plus i have increased power over stock so i think i need some better quality gas

Last edited by Caplin 2.5; 03-09-2005 at 10:14 PM.
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Old 03-09-2005, 10:13 PM   #9
svek
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wow thx for the input
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Old 03-09-2005, 10:22 PM   #10
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how do you get 91 octane?

do you mix 87 and 93 or something?
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Old 03-09-2005, 10:27 PM   #11
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how do we get 91??? well in the wonderful state of California someone decided that it would be a good idea to sell crappy 91 as the highest octane rating, not 93. We can find 100 from the pump, but it's like $5 a gallon and only a very few stations have it. So, be happy texas sells 93......
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Old 03-09-2005, 10:28 PM   #12
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man, that stinks, I guess that kind of forces you guys to have conservative tunes
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Old 03-09-2005, 10:47 PM   #13
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yeah, now you know why COBB has maps specifically for the CA 91 Octane gas. It's very conservative.
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Old 03-10-2005, 08:41 AM   #14
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Quote:
Originally Posted by Caplin 2.5
...oh yea plus i have increased power over stock so i think i need some better quality gas
High test isn't necessarily higher quality than regular, it is just more resistant to detonation. Whether your modified motor prefers one over the other is anybody's guess.
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Old 03-10-2005, 10:00 AM   #15
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Quote:
Originally Posted by OneOBS
No, its just a waste of money. Do it if it makes you feel good.
Tests have concluded that there is no benefit to using a higher octane level than recommended by your owners manua (unless your boosted)l. My RS asks for 87 octane, so I put in 87. It's cheaper than 89, and 91 (other 2 main types they have here in Utah) and the extra octane simply increases the resistance to detonation, which unless you have a change in engine internals, or boost, won't make much difference in the performance.

However, my porsche does require 91 octane, or better. So, my best recommendation is to read through your owner's manual. It may sound stupid, but you'll learn a lot about your car that you may never have to use everyday, and you'll have a greater understanding of your vehicle than most people. It's really rare to find someone who reads through their owner's manual when they purchase a car (when I bought my RS, it didn't come with an Owner's Manual, so I found and bought one off Ebay).

David
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Old 03-10-2005, 10:16 AM   #16
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Car & Driver mag. ran some tests on several cars that recomended 87 octain gas. The test had them dyno or measure power output using higher octane vs the recomended 87. No car did better on the higher octane and several produced less horsepower. Their conclusion is use what is recomended by the manufacture.
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