why is there the need for premium gas?

20

Asked by Jan 30, 2010 at 07:21 PM about the 2005 Subaru Outback 2.5 XT Limited Wagon

Question type: General

Looking at purchasing used 60k. want to know more details about gas requirements.

7 Answers

did your car come with a supercharger or turbo?

1 of 1 people found this helpful.
20

It is a turbo

2 of 2 people found this helpful.

thats why

20

OK. well thats not necessarily the answer that i was looking for. so i guess i will go and research why turbo engines ONLY run on premium gas. I will look up how it affects the performance and longevity of the engine. If I knew that car nerds on Cargurus like you were were assholes i could have started a thread somewhere else. Is this not a forum to get answers from people that know about cars? thanks.

com down. im not to get technical but a turbo engine has a higher compression ratio then a regular engine. higher compression more hp less dettination on 93 octane more heat and if not maintained right it can suck the engine dry. by the way im not a car nerd. im a delivery driver with 2.5 college to be a mechanic but couldnt get in. and also waich your pees and quus. the editer is waiching.

1 of 1 people found this helpful.
8,375

Turbo's force more air into the engine which is then compressed... You vehicle compresses based on teh engine geometry so say you have an 9:1 compression engine. So atmospheric pressure is ~14.7psi so pre-detonation the charge gets to ~132.3psi... Now say you have a turbo throwing another 7pounds of boost then you have ~21.7*9=195.3psi (This is greatly simplify things, but you get the point) the turbo increases the pressure on the charge prior to detonation. Now almost every fuel has a flash point and gas is no different. If the pressure and/or temperature get too high it'll detonate without the spark. Which mean the piston is firing before it should. This is known as predetonation or knock. This can damage an engine very quickly. The different grades of fuel are more resistant to this to varying degrees. Often the fuel grade is known as 'the anti-knock index' The higher the number the less likely you are to get pre-detonation. Contrary to popular belief the higher grade fuels do not contain more energy and will not be the best gas for every car. If you drive a naturally aspirated low compression engine then a lower grade gas may be more appropriate for you. However if there is any doubt about what grade is recommend then go with the higher grade. And always use a grade equal to or greater than the manufacturer recommendation.

8 of 8 people found this helpful.
20

thank you adam.

Your Answer

Add photo

Related Questions

Outback

Looking for a Used Outback in your area?

CarGurus has 40,752 nationwide Outback listings starting at $1,395.

ZIP:

Search Subaru Outback Questions

Subaru Outback Experts

#1 Markw1952
Markw1952
Reputation 7,370
#2 TheSubaruGuruBoston
TheSubaruGuruBoston
Reputation 2,300
#3 F_O_R
F_O_R
Reputation 2,030
View All

Related Models For Sale

Used Subaru Forester
414 Great Deals out of 32,510 listings starting at $995
Used Subaru Legacy
244 Great Deals out of 12,619 listings starting at $1,399
Used Subaru Impreza
216 Great Deals out of 19,037 listings starting at $1,100
Used Honda CR-V
982 Great Deals out of 57,314 listings starting at $1,000
Used Toyota RAV4
899 Great Deals out of 64,318 listings starting at $1,990
Used Toyota 4Runner
227 Great Deals out of 19,106 listings starting at $1,500
Used Toyota Highlander
376 Great Deals out of 26,278 listings starting at $2,500
Used Toyota Tacoma
518 Great Deals out of 43,167 listings starting at $1,995
Used Honda Pilot
394 Great Deals out of 23,467 listings starting at $995
Used Jeep Grand Cherokee
1,071 Great Deals out of 73,681 listings starting at $1,200
Used Honda Accord
1,048 Great Deals out of 68,868 listings starting at $1,000
Used Subaru Impreza WRX
66 Great Deals out of 1,367 listings starting at $3,500
Used Ford Escape
1,374 Great Deals out of 84,720 listings starting at $995

Used Cars For Sale

2017 Subaru Outback For Sale
42 Great Deals out of 30,024 listings starting at $20,965
2016 Subaru Outback For Sale
59 Great Deals out of 1,139 listings starting at $17,991
2015 Subaru Outback For Sale
76 Great Deals out of 1,678 listings starting at $10,499
2014 Subaru Outback For Sale
47 Great Deals out of 1,569 listings starting at $8,988
2013 Subaru Outback For Sale
36 Great Deals out of 971 listings starting at $7,988

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.