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      02-11-2018, 02:40 PM   #1
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MHD tuning fuel

Hey guys,

I'm looking at putting an MHD tune on my N54. However, I live in Portland, Oregon and the only gas that seems to be available is 87, 89, and 92 octane. If I recall correctly all the MHD stage 1 tunes require 91 or 93 octane. Any ideas here? Thanks for the help.
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      02-11-2018, 03:25 PM   #2
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Originally Posted by Colinoscopy View Post
Hey guys,

I'm looking at putting an MHD tune on my N54. However, I live in Portland, Oregon and the only gas that seems to be available is 87, 89, and 92 octane. If I recall correctly all the MHD stage 1 tunes require 91 or 93 octane. Any ideas here? Thanks for the help.
I see that this is your first post, welcome to the forums! And you're going to want to use the 91oct tune.
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      02-11-2018, 03:30 PM   #3
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Originally Posted by asiflicious View Post
I see that this is your first post, welcome to the forums! And you're going to want to use the 91oct tune.
Thank ya kindly. Ok, so a 91 octane tune should be fine running 92 octane?
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      02-11-2018, 03:31 PM   #4
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Quote:
Originally Posted by Colinoscopy View Post
Quote:
Originally Posted by asiflicious View Post
I see that this is your first post, welcome to the forums! And you're going to want to use the 91oct tune.
Thank ya kindly. Ok, so a 91 octane tune should be fine running 92 octane?
Yeah that's what I do. It's arguably even safer for the car
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      02-11-2018, 05:14 PM   #5
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Originally Posted by asiflicious View Post
Yeah that's what I do. It's arguably even safer for the car
Ahh, good to hear. Why is it safer? Thanks btw
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      02-11-2018, 10:06 PM   #6
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A point or 2 will make no appreciable difference.
They are not full on race, extract the most power at all cost, tunes. They are fun and pretty safe. And what they don't catch the DME will adjust for pretty quickly.
That does not mean you want to push it hard right away. Work up to it and take logs each time to verify the car is acting correct.
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      02-12-2018, 03:50 PM   #7
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Quote:
Originally Posted by Colinoscopy View Post
Ahh, good to hear. Why is it safer? Thanks btw
Octane is a measure of a fuel's resistance to autoignition, commonly known as knock. A higher octane means the fuel can withstand higher temperatures and pressures before knocking. This allows a custom tuner to advance the ignition timing to increase power. Running a tune designed for a lower octane rating means that the tune has been designed not to knock (for the most part) with the low octane, so a higher octane will be even less likely to cause knocking.
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      02-12-2018, 08:17 PM   #8
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Quote:
Originally Posted by Colinoscopy View Post
Ahh, good to hear. Why is it safer? Thanks btw
Octane is a measure of a fuel's resistance to autoignition, commonly known as knock. A higher octane means the fuel can withstand higher temperatures and pressures before knocking. This allows a custom tuner to advance the ignition timing to increase power. Running a tune designed for a lower octane rating means that the tune has been designed not to knock (for the most part) with the low octane, so a higher octane will be even less likely to cause knocking.
Exactly. Your fueling has more headroom and you won't be asking it to do more than it's capable of
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      02-12-2018, 09:47 PM   #9
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Quote:
Originally Posted by BimmerAg View Post
Octane is a measure of a fuel's resistance to autoignition, commonly known as knock. A higher octane means the fuel can withstand higher temperatures and pressures before knocking. This allows a custom tuner to advance the ignition timing to increase power. Running a tune designed for a lower octane rating means that the tune has been designed not to knock (for the most part) with the low octane, so a higher octane will be even less likely to cause knocking.
This just really bugs me.

Autoignition is the temperature at which the fuel self ignites. This is how a diesel engine works.
Knock is unstable or unpredicted burn rate, much faster than expected. This is generally due to improper fuel to air mixture, not necessarily quantity or equivalency ratio, in combination to ignition advance.
They are separate conditions and should never be confused.

I challenge anyone to find reliable data about Gasoline Octane ratings and different autoignition temps. If you find them post them.
*hint, you'll have a hard time if you do good research
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      02-13-2018, 04:01 PM   #10
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Quote:
Originally Posted by iminhell1 View Post
This just really bugs me.

Autoignition is the temperature at which the fuel self ignites. This is how a diesel engine works.
Knock is unstable or unpredicted burn rate, much faster than expected. This is generally due to improper fuel to air mixture, not necessarily quantity or equivalency ratio, in combination to ignition advance.
They are separate conditions and should never be confused.

I challenge anyone to find reliable data about Gasoline Octane ratings and different autoignition temps. If you find them post them.
*hint, you'll have a hard time if you do good research
The burn rate is much faster than expected because the local temperature rises high enough to reach the autoignition temperature of the fuel at that point. This can be caused by a number of factors, but the most common are hot deposits on the piston or cylinder head, or overly advanced ignition timing. Advanced ignition timing releases heat earlier in the compression stroke and as the flame front travels, the temperature and pressure in the cylinder increases. If the timing is advanced far enough, that temperature can reach the autoignition point of the unburned fuel in the cylinder before the flame front arrives, causing a sudden release of energy. The sudden energy release creates a pressure pulse which is then audibly heard as knock.

University of Washington study of autoignition temperature of different octane gasoline: Fluid sprayed on a recessed stainless steel plate.
87 octane: 1135-1225°F
89 octane: 1240-1445°F
http://depts.washington.edu/vehfire/...sults.html#gas

That being said, octane is not always a great measure of a fuel's anti-knock properties. Much research has been done on the Low Speed Pre-Ignition (LSPI) phenomenon that can occur in high compression, boosted engines, and has found that in testing multiple fuels with the exact same octane rating, some may knock and others may not. The test for octane rating is likely a bit outdated, as it is performed on a carbureted, low compression engine designed in the 1920s.
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      02-13-2018, 09:23 PM   #11
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Looking at the same table, Gasoline of any grade can be from 1,100*F to 1,520*F. Which is what I was saying. It's just not a good measure because there isn't uniform results. That is a very broad range. And on top of that it could vary cycle o cycle.
AND it does not take into account dilution by residual gasses or crank case vapors.

Perhaps the most interesting is that E85 has a lower temp than the high end of Gasoline. But in real world we know this to not be completely true. But that's due in part to the Latent heating value.
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      07-02-2019, 05:48 AM   #12
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Quote:
Originally Posted by iminhell1 View Post
This just really bugs me.

Autoignition is the temperature at which the fuel self ignites. This is how a diesel engine works.
Knock is unstable or unpredicted burn rate, much faster than expected. This is generally due to improper fuel to air mixture, not necessarily quantity or equivalency ratio, in combination to ignition advance.
They are separate conditions and should never be confused.

I challenge anyone to find reliable data about Gasoline Octane ratings and different autoignition temps. If you find them post them.
*hint, you'll have a hard time if you do good research
For example i run my 435i mhd stage 1 93 oct to icar today with 91 oct gas and i make 13.1 sec 1/4 mile. I refill the tank with 94 oct and i made 12.6 sec 1/4 mile.
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      07-02-2019, 05:04 PM   #13
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This type of question belongs on the MHD Facebook Group. It's too embarrassing for this forum.
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