[flash]

take a look at this:



http://www.thorneymotorsport.co.uk/gcs_art...t%3D0%26toc%3D1

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[chris]

40hp difference?? Wow, that's crazy.

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[BMWRider]

Wow, that is something. I know there is a difference between European and American octane standards, but the moral seems to be, pay for the good stuff.

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[ds968]

10 minutes away from my house there is a station which sells 100 octane ( for about $ 6 /gallon) - this may turn out to be very expensive considering my car is a daily driver, but provided I REMEMBER to do it, I might just put in about 7 gallons with every fill up from now on.

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[Darryl]

I've tried a bottle of the "104 Octane Boost" and was definitely a bit peppier...it also seemed to burn a lot faster resulting in lower fuel economy, so probably not realistic every tank, but it's fun once in a while. I always run 93 as that's what's available here on the east coast. Didn't Shell used to have 94?



- Darryl

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[flash]

lol - the way the math works is that 1 pont raised in octane equals a 1% rise in horsepower - this is in traditional engines with traditional ignition systems - on our cars, it would equate to about 5hp going from 91 o 93



engines with the newer engine management systems might be able to manipulate things better and get more



turbos will certainly get more



our cars poop out after about 95 octane (RON+MON/2) in stock trim, and at about 93 with a good chip



my resoning behind this conclusion, beyond the dyno tests i did on this, is that we would need higher compression, and more ignition advance, or both, to take advantage of the higher energy fuel, and the setup as it stands maxes out there



the downside to higher octane is the increased heat it makes - i've watched my car run a full needle's width hotter with 95 than with 93, and no noticeable power increase



but, i thought it would make for interesting conversation

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[saxman]

Ideally, you want to run the lowest octane gas that'll allow for ignition to occur at peak cylinder pressure without knocking to occur. Going higher than that isn't going to necessarily bring more power to the equation, as the caloric value of higher octane gasses isn't going to bring much more to the table.



When you're running a car on lower octane gas than it's designed for, yes, you'll see huge power differences due to the ecu retarding ignition timing, etc. But if the car is already running close to ideal on the gas you're using, adding a higher octane gas isn't going to be the recipe for more power, without compression changes, etc to go with it.

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[flash]

how much it typically brings is above, but yes, it presumes you have the compression and ignition to accomodate the added energy - as i said, in our case, we seem to hit the ceiling as also mentioned above - after that, yes, it does indeed seem to be a waste, and worse, seems to heat things up

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[badberry68]

[quote name='flash' date='Oct 19 2006, 06:32 AM']how much it typically brings is above, but yes, it presumes you have the compression and ignition to accomodate the added energy - as i said, in our case, we seem to hit the ceiling as also mentioned above - after that, yes, it does indeed seem to be a waste, and worse, seems to heat things up

[right][post="26998"]<{POST_SNAPBACK}>[/post][/right][/quote]



Fuel can add power but not because of octane, it has to be oxigenated and that type of fuel can add 5% in power. Considering this type of fuel sells for $15 to $20 a gallon...forget it!

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[ether_joe]

round here it's Chevron 91 for me. . . if I could find 93 I'd buy it.



Gonna go for a run-rite treatment at some point though.

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[flash]

i have dyno tests that show otherwise, as do most chip manufacturers - within the limits of the compression and engine management, it is a approximately a 1% increase in power for each point of octane raised



i'll try to dig up the chemistry and math on that one - i found it a long time ago - i think it is even in one of my books - googling should turn it up pretty quickly again though

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[flash]

i did find a couple of interesting threads that basically say the same thing - i think we are all going at this from different directions, but getting the same answer - octane, by itself, does not increase power, regardless of higher energy content - it opens the door for the engine, and its management system to allow the engine to produce more power



now that we have computerized engine management systems, it seems that things are a bit different than they used to be - today engines are designed to achieve a particular power output, based on a minimum amount of energy from a fuel - the engine has the capacity for more power, but you have to manipulate things to get there if it does not have the capability to self adjust



this would explain why our cars acheive max power at 95 octane - that is where they set the maximums - it also explains why with a chip, the octane requirement goes down - the timing and such are manipulated to act as if the engine is at its max with 95



so, to sum up, a higher octane fuel will provide more power, as long as the compression and engine management can acccommodate it - with the compression we have now, 95 is the max for a stock chip, and somewhere around 93 seems to be the max for a good aftermarket chip - to be able to take advantage of the higher energy fuels (or more importantly, their anti-knock capability) we would need higher compression



here are the threads:



http://en.wikipedia.org/wiki/Octane_rating



http://www.hpt-sport.com/gasclass.htm



did that help?

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[badberry68]

http://www.factorypro.com/tech_tuning_proc...e_vs_power.html



I think that some power can be derived from a fuel that has a burn rate that matches an engines characteristics.

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[flash]

that also seems to agree with why i think i see temps climb when i use over 93 - with the chip already advancing the timing, and the slower burning higher octane fuel, everything sums to a higher net temp



lol - in the end, after all the bouncing around and dyno testing different combinations and such, i have found that using the factory specs for fuel work best - go figure

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[333pg333]

As you say Bob, turbo's are different. I use 100 oct (which I think is about the same as your 96-98?) that has 5% ethanol added and when I'm at the track I use an octane booster. Basically it's to avoid pre-detonation in our turbo cars. I'm not sure if it adds to performance but I guess it could allow some to turn up their boost if they were able?

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[KMR968Turbo]

Darn, I just bought my turbo. Guess I'll have to learn to live with it. <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" />

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