Go Back   Jeep Garage - Jeep Forum > Jeep Platform Discussion > Grand Cherokee - WK2 -

Join Jeep Garage Today
Reply
 
Thread Tools Display Modes
 
  #13  
Old 10-23-2010, 12:24 AM
Member
 
Join Date: Oct 2010
Posts: 138
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 1507
walterhudson is on a distinguished road
Re: Another Hemi Octane Thread

I own a 2007 Dodge Magnum hemi AWD and a 2008 Dodge Ram truck 1500 hemi. The owners manuals both state,"The routine use of 91 octane gasoline is not recommended. The use of premium gasoline will provide no benefit over high quality regular or mid-grade gasoline and may result in poorer performance". These engines are essential the same as the GC hemi. So why waste your hard earned money on 91 octane.
__________________

__________________
Reply With Quote
  #14  
Old 10-23-2010, 06:27 AM
Premium Member
 
Join Date: Sep 2010
Posts: 383
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 1775
bpmcgee is on a distinguished road
Re: Another Hemi Octane Thread

Quote:
Originally Posted by Bmwister View Post
...detonation being an uncontrolled explosion rather than a steady burn expansion...

Just a minor elaboration -- detonation is an uncontrolled explosion BEFORE the spark plug sparks -- i.e. a combustion event working against the rotation of the engine.

And +1 to RMac.

B
__________________

__________________
Reply With Quote
  #15  
Old 10-23-2010, 09:14 AM
Member
My Jeep: 2011 5.7L WK2
 
Join Date: Jan 2010
Location: Central NH
Posts: 674
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 2327
nek121328 is on a distinguished road
Re: Another Hemi Octane Thread

There's nothing to say you can't run a few tanks of 87 and the fill once or twice with 91 to blend the fuel to 89. We mix fuel all the time for small engines when 89 isn't available at the rural pumps.
__________________
Reply With Quote
  #16  
Old 10-23-2010, 09:28 AM
Jim Hef's Avatar
Member
My Jeep: 1999 4.7L WJ
 
Join Date: Aug 2010
Location: Yardley, PA
Posts: 816
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 2259
Jim Hef is on a distinguished road
Re: Another Hemi Octane Thread

Quote:
Originally Posted by robpp View Post
the higher the octane the more pure the fuel. so LESS DEPOSITS the higher the octane.
This is not my understanding at all! Generally, the higher the octane, the more additives that are present to boost the rating. I think you are confusing the old Mobil "clear" premium that they advertised as "pure". All fuels are colored, and the standard back then was red for premium, but at this point, I forget what the nomenclature was for that grade...wasn't known as premium. Mobil just didn't add the coloring pack.
__________________
Reply With Quote
  #17  
Old 10-24-2010, 12:50 AM
Bmwister's Avatar
Member
 
Join Date: Oct 2010
Posts: 543
Thanks: 11
Thanked 13 Times in 9 Posts
Rep Power: 1980
Bmwister has a reputation beyond reputeBmwister has a reputation beyond reputeBmwister has a reputation beyond reputeBmwister has a reputation beyond repute
Re: Another Hemi Octane Thread

Quote:
Originally Posted by bpmcgee View Post
Just a minor elaboration -- detonation is an uncontrolled explosion BEFORE the spark plug sparks -- i.e. a combustion event working against the rotation of the engine.

And +1 to RMac.

B
Nope...you are actually referring to pre-ignition (ignition before the spark); it's related, but I assure you NOT the same as detonation. The terms are commonly used interchangeably when they technically should not be.

Detonation is the uncontrolled explosion of pockets of fuel/air mix inside the combustion chamber during normal spark ignition that are a separate pressure front from the normal ignited mixture expansion. Pre-ignition (the worse of the two) is caused by ignition of the fuel/air mixture before the spark starts. Both can be initiated by similar things, hence their "relationship" and the fact that sometimes the noises they make are similar.

When pre-ignition occurs there is a heavy knocking/pounding along with a substantial loss of power while detonation makes the "ping" or "light rattle" noise. It is highly unlikely to find pre-ignition issues in a modern engine without a major defect or damage to the combustion chamber in the cylinder head or an obscene overheating condition.

EDIT: Forgot to add that when you get pre-ignition when the engine is running (not the run-on), you will likely experience component failure....engine failure...in short order. It isn't detectable until it happens.

I'm an old, long time engine builder and this subject along with "torque vs horsepower" discussions bristle me.
__________________
Reply With Quote
  #18  
Old 10-24-2010, 07:35 AM
Premium Member
 
Join Date: Sep 2010
Posts: 383
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 1775
bpmcgee is on a distinguished road
Re: Another Hemi Octane Thread

Hmm. Interesting info. Thanks for setting me straight -- I learn something new every day!

B
__________________
Reply With Quote
  #19  
Old 10-24-2010, 01:53 PM
whatevrworks's Avatar
Member
My Jeep: 2011 5.7L WK2
 
Join Date: Jul 2010
Location: Northern Virginia
Posts: 527
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 2581
whatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond reputewhatevrworks has a reputation beyond repute
Quote:
Originally Posted by Bmwister View Post
Nope...you are actually referring to pre-ignition (ignition before the spark); it's related, but I assure you NOT the same as detonation. The terms are commonly used interchangeably when they technically should not be.

Detonation is the uncontrolled explosion of pockets of fuel/air mix inside the combustion chamber during normal spark ignition that are a separate pressure front from the normal ignited mixture expansion. Pre-ignition (the worse of the two) is caused by ignition of the fuel/air mixture before the spark starts. Both can be initiated by similar things, hence their "relationship" and the fact that sometimes the noises they make are similar.

When pre-ignition occurs there is a heavy knocking/pounding along with a substantial loss of power while detonation makes the "ping" or "light rattle" noise. It is highly unlikely to find pre-ignition issues in a modern engine without a major defect or damage to the combustion chamber in the cylinder head or an obscene overheating condition.

EDIT: Forgot to add that when you get pre-ignition when the engine is running (not the run-on), you will likely experience component failure....engine failure...in short order. It isn't detectable until it happens.

I'm an old, long time engine builder and this subject along with "torque vs horsepower" discussions bristle me.
So in your opinion what is the reason for higher octane not be recommended? We know 89 is recommended to avoid knocking and to get full performance out of engine.
__________________
2011 WK2: Limited, 4x4, Hemi, 730n, Class IV Tow, Brilliant Black. 30% Ceramic Tint, Lockpick, LED DRL, LED License Plate, LED Backup, LED Liftgate (all), Axle/Transfer Case OEM add-on skid plates, Sharkfin Antenna.:thumbsup:
Reply With Quote
  #20  
Old 10-24-2010, 06:30 PM
Bmwister's Avatar
Member
 
Join Date: Oct 2010
Posts: 543
Thanks: 11
Thanked 13 Times in 9 Posts
Rep Power: 1980
Bmwister has a reputation beyond reputeBmwister has a reputation beyond reputeBmwister has a reputation beyond reputeBmwister has a reputation beyond repute
Re: Another Hemi Octane Thread

Quote:
Originally Posted by whatevrworks View Post
So in your opinion what is the reason for higher octane not be recommended? We know 89 is recommended to avoid knocking and to get full performance out of engine.
My guess is balancing the fuel energy content with detonation resistance; the higher the octane rating, the lower the fuel's BTU (energy) content. Chrysler/Mercedes probably found that 89 worked best for their design parameters and ran with it. I do find it odd being that 89 is an inexact mix of 87 and 91/93 made at-the-pump by blending the two during fueling. Perhaps they discovered that to utilize 87 (or 91/93) and still meet power and EPA fuel economy goals it would require an expensive ECO (engineering change order) or retooling. I would expect a spec to read, say, "89 or better octane fuel only" rather than eschewing the 91/93. Mercedes and VW/Audi have always been anal about fuel and oil requirements (i.e. "You must use THIS, not THAT because we only designed it for THIS.") so that's some that food for thought.
__________________
Reply With Quote
  #21  
Old 10-24-2010, 08:04 PM
jonesark's Avatar
Premium Member
 
Join Date: Sep 2010
Location: The South
Posts: 593
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 1985
jonesark is on a distinguished road
Cool Re: Another Hemi Octane Thread

Quote:
Originally Posted by Bmwister View Post
My guess is balancing the fuel energy content with detonation resistance; the higher the octane rating, the lower the fuel's BTU (energy) content. Chrysler/Mercedes probably found that 89 worked best for their design parameters and ran with it. I do find it odd being that 89 is an inexact mix of 87 and 91/93 made at-the-pump by blending the two during fueling. Perhaps they discovered that to utilize 87 (or 91/93) and still meet power and EPA fuel economy goals it would require an expensive ECO (engineering change order) or retooling. I would expect a spec to read, say, "89 or better octane fuel only" rather than eschewing the 91/93. Mercedes and VW/Audi have always been anal about fuel and oil requirements (i.e. "You must use THIS, not THAT because we only designed it for THIS.") so that's some that food for thought.
what he said.......
__________________

__________________
2011 Jeep Grand Cherokee
Overland 4x4 Hemi
Stone White, Saddle, ACC Package
Ordered Sep 21st 2010
VIN assigned Oct 25th 2010
D1 Dec 10th 2010
Estimated Delivery Jan 7th 2011
Delivered Jan 12th 2011
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
*****WK2*****2011-??? Grand Cherokee pricing and info thread discussion THREAD!!!! White WK Swagga Grand Cherokee - WK2 - 136 12-13-2010 12:52 AM
Hemi Owners - Gas Octane Question? boarderman23 Grand Cherokee - WK2 - 19 10-03-2010 10:35 AM
Question re Octane jrb1 Engine Performance/Intakes/Exhausts 9 09-22-2010 10:15 PM
Difference in GC Hemi and Ram Hemi?? HemiDawg Grand Cherokee - WK 12 05-13-2010 11:52 AM
What grade of gasoline octane do you use & Why? Also state what size motor? White WK Swagga Performance Modifications 49 08-07-2009 08:24 PM

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 02:30 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright 2012 - JeepGarage.Org
The Jeep Grand Cherokee Owners Community