Fuel for the STI (octanes)
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Fuel for the STI (octanes)
what is the recommended fuel in terms of octanes for the STI? What brand do you guys usually tank?
I have a Toyota right now and always cranking the highest octane fuel which is probably not necessary but it might keep the engine cleaner.
I have a Toyota right now and always cranking the highest octane fuel which is probably not necessary but it might keep the engine cleaner.
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STi will require something like 91 or higher. Here in the north east we get from 92-94 depending on where you go, but I seem to remember some of the guys on the west coast saying they only got 91.
As for other cars or octane, in general you only need to run what it listed in your owners manual, unless you are running higher compression, more turbo boost, or racing in an application where the engine sees high temps. The octane rating is basically an index of how easy the gas combusts or start to burn. The lower the number the easier. So, with a turbo motor running good boost you need higher octane (harder to combust) to aviod detenation, or the gas self combusting. Detonation being the air/fuel mixture begining to burn before a spark plug is fired. So, the STi being a highly tuned turbo motor with lots of boost, high octane will be a must. In general turbo cars benefit from higher octane, while non-turbo cars can actually be worse off with higher octane gas. (unless advancing timing but I'm trying to be real simple here and not go super in depth
) So I hope this helps you out, and if I missed something or got something wrong guys let me know.
Keith
As for other cars or octane, in general you only need to run what it listed in your owners manual, unless you are running higher compression, more turbo boost, or racing in an application where the engine sees high temps. The octane rating is basically an index of how easy the gas combusts or start to burn. The lower the number the easier. So, with a turbo motor running good boost you need higher octane (harder to combust) to aviod detenation, or the gas self combusting. Detonation being the air/fuel mixture begining to burn before a spark plug is fired. So, the STi being a highly tuned turbo motor with lots of boost, high octane will be a must. In general turbo cars benefit from higher octane, while non-turbo cars can actually be worse off with higher octane gas. (unless advancing timing but I'm trying to be real simple here and not go super in depth
) So I hope this helps you out, and if I missed something or got something wrong guys let me know. Keith
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Don't put higher octane in your car than is needed. Higher octane is not cleaner! Cleaner gas (ie, better quality) is cleaner
Without getting technical (mainly because I couldn't tell you the technical side) higher octane means it takes more to ignite the gas. 88 combusts before 91 which combusts before 100 does.
This is why if you put 88 in a car that needs 91, the gas will explode before the engine is ready, and you get knocking. VERY bad.
However, if a car expects 88 and you put 91, all that happens is the gas won't combust when the engine is ready. Either the ECU will compensate and will make the engine work harder to get the gas to combust or it won't combust enough and you'll make less power (I'm sure there are other scenarios here) ... either way, it's not helping the engine and in fact could be hurting the engine.
Now with high performance cars that want high octane, there can be some benefit in putting higher octane in... but only up to the point that the engine is made for. So yes, in an EVO or STi, by all means putting the highest octane will probably get some more power than 91.
However, normal cars like the ImprezaRS which want 88, will see no benefit out of 91 and may see some detriments.
Without getting technical (mainly because I couldn't tell you the technical side) higher octane means it takes more to ignite the gas. 88 combusts before 91 which combusts before 100 does.
This is why if you put 88 in a car that needs 91, the gas will explode before the engine is ready, and you get knocking. VERY bad.
However, if a car expects 88 and you put 91, all that happens is the gas won't combust when the engine is ready. Either the ECU will compensate and will make the engine work harder to get the gas to combust or it won't combust enough and you'll make less power (I'm sure there are other scenarios here) ... either way, it's not helping the engine and in fact could be hurting the engine.
Now with high performance cars that want high octane, there can be some benefit in putting higher octane in... but only up to the point that the engine is made for. So yes, in an EVO or STi, by all means putting the highest octane will probably get some more power than 91.
However, normal cars like the ImprezaRS which want 88, will see no benefit out of 91 and may see some detriments.
great
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I bet Subaru's quoted bhp numbers were derived on 93 RON gas (or better). The gas rating can be a big deal. Shiv at Vishnu recently dynoed an Evo VIII and found around 30 bhp less than Mitsu's quoted figures......Shiv's figures were obtained using 91 RON gas and Mitsu specifies 93 RON gas as the appropriate grade for the Evo.......smoke & mirrors on Mitsu's part, who knows ?
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BUT STi has a 2.5
that .5 alone will sure compensate for any loss of HP due to gas.
gas was always a concern for bringing in high boost rockets into the US.
thats prolly why STi cheated w/ the 2.5 liter engine
but we are the beneficiaries..
big thumb up to Subies.
when everyone expected a water downed STi, we actually got a cheater STi..
that .5 alone will sure compensate for any loss of HP due to gas.
gas was always a concern for bringing in high boost rockets into the US.
thats prolly why STi cheated w/ the 2.5 liter engine
but we are the beneficiaries..
big thumb up to Subies.
when everyone expected a water downed STi, we actually got a cheater STi..
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Originally posted by MTMS4
I bet Subaru's quoted bhp numbers were derived on 93 RON gas (or better). The gas rating can be a big deal. Shiv at Vishnu recently dynoed an Evo VIII and found around 30 bhp less than Mitsu's quoted figures......Shiv's figures were obtained using 91 RON gas and Mitsu specifies 93 RON gas as the appropriate grade for the Evo.......smoke & mirrors on Mitsu's part, who knows ?
I bet Subaru's quoted bhp numbers were derived on 93 RON gas (or better). The gas rating can be a big deal. Shiv at Vishnu recently dynoed an Evo VIII and found around 30 bhp less than Mitsu's quoted figures......Shiv's figures were obtained using 91 RON gas and Mitsu specifies 93 RON gas as the appropriate grade for the Evo.......smoke & mirrors on Mitsu's part, who knows ?
Keith
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Originally posted by RallyKeith
I don't know anything about Vishnu, or even wher they are located, but if they did there test on 91 RON then it is no surprise that they lost power. Gas in the US is not rated purely in RON. It's 2* (RON/MON). This has been covered in other threads so I won't go deeper, but that cool that they can put HP loss numbers to the lower octane gas
Keith
I don't know anything about Vishnu, or even wher they are located, but if they did there test on 91 RON then it is no surprise that they lost power. Gas in the US is not rated purely in RON. It's 2* (RON/MON). This has been covered in other threads so I won't go deeper, but that cool that they can put HP loss numbers to the lower octane gas
Keith
http://forums.evolutionm.net/showthr...threadid=16484
very insightful info..
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According to Shiv, The stock Evo gained about 8 bhp by switching from 91 octane to 93 octane. He also mentioned that the stock WRX does not benifit from switching to 93 octane because of the ECU.
So the real answer is...it depends on the individual car. We have no way of knowing how the STI will respond to better fuel until we dyno one.
So the real answer is...it depends on the individual car. We have no way of knowing how the STI will respond to better fuel until we dyno one.
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