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Old 12-15-2013, 01:34 AM   #46
Signmaster
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Join Date: Jan 2007
Location: Virginia Beach, VA
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1995 SL1
Default Re: Fact or Fiction?: Premium Gasoline Delivers Premium Benefits to Your Car

Quote:
Originally Posted by satlite440 View Post
.also premum only engines have a lower comp ratio a regular moter is like 10 to 1 a preumum moter is like 8 to 1 for an example also you will find that pemum only engines are smaller in displacement.. for example out new ats is a 2.5L regular fuel naturaly asperated sidi engine with a 11 to 1 compression ratio while the trubo charged 2.0Lrunning premum is a 9&1/2 to 1 ratio...hth
Being that adding any compressor essentially makes the engine have variable compression pressures, it acts much the same under boost as if you had increased the compression ratio. That is the primary reason that boosted applications usually have a lower base compression ratio.

Compression is one of the major factors that often requires an engine to have a need for higher octane, with higher compression having a greater need for higher octane. In the case of a boosted application, the actual compression ratio remains the same, but the cylinders are filled beyond what a naturally aspirated intake system can achieve.

Timing control is another factor, and even engines designed with compression ratios low enough to run fine on 87 octane fuel may need higher octane when the timing tables are altered to be more aggressive. This is done on a regular basis for performance tunes.


There is more to the overall pictures than just the basics when it comes to a need for higher octane.

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