LX Forums Forum banner
1 - 18 of 18 Posts

·
LX Newbie
Joined
·
73 Posts
Discussion Starter · #1 ·
I have always used Premium for my 5.7L Hemi on my 300c, is it necessary because I have read on other forums that you should not cuz the block may crack ect.......

What do all you HEMI owners use.....
 

·
~~~~~~~~~
Joined
·
962 Posts
YOUNG_G said:
I have always used Premium for my 5.7L Hemi on my 300c, is it necessary because I have read on other forums that you should not cuz the block may crack ect.......

What do all you HEMI owners use.....
Chrysler owners manual specifically says not to use 91.
Where do you read that 91 octane will crack the block?

The reason I am curious is that the Superchips Flashpaq 91 tune requires 91 octane. I have been curious how Flashpaq negates the long-term negative implications, if any, of running 91 octane.
 

·
MAG V
Joined
·
2,163 Posts
My .02 Cents...

Using higher than needed octane fuel will not crack the block. It can however, cause excessive emissions resulting in a clogged catalytic converter. I say this lightly, as this is possible but not likely.

Truth is, with computer controlled cars, your timing is set based on the programming, which is preset based on the expected fuel. Using higher than needed octane will result in no power improvements, nothing at all. The result MAY be that the car will run slightly better but it is not a direct result of the higher octane, but rather, the addition of detergents or just in general BETTER gas. But the octane itself will not make any difference and will not help or hurt performance.

SUPERCHIPS, among other things, advances the timing, meaning now the car is EXPECTING the higher octane fuel. The timing will be as such that emissions are no higher (in a perfect world) than before, just that the car can now take advantage of the higher octane. Using superchips to advance the timing, but continuing to use lower octane, will result likely in pinging or other issues, in which the car will then retard timing, in the end producing even less power than before, and possibly damaging other systems.

OK, long story short. Summary.

Factory the car is set to run on mid grade, using higher does not help performance but may help because you end up using a better fuel, but in the long term it MAY result in emissions (CAT, O2 sensors, etc) issues... Using Lower (Low grade) fuel can result in pinging or knocking, and will further reduce power.

Superchips performance tune now sets the car to expect premium, likewise as before, using higher or lower octane will result in un-desired reults.

Bottom line, use good quality with octane matched to the programming of the car (Stock = mid grade, superchips = Premium).
 

·
Speed on... Hell ain't half full
Joined
·
24,673 Posts
^ amen
 

·
LX Newbie
Joined
·
73 Posts
Discussion Starter · #7 ·

·
Survived 2017 ... 2020 or Bust ...
Joined
·
5,309 Posts
It's very hard for me to believe, anyone on this forum actually believes what salesmen say.

Some were selling other brands of cars or washing machines the week before.
 

·
The member formerly known as Jleilich
Joined
·
533 Posts
higher octane cracking the block..? thats a new one.
 

·
MAG V
Joined
·
2,163 Posts
MomsR/T said:
are you positive higher octane = higher emissions?
It isnt an exact equal...

You have the possibility that without the advanced timing to accomodate the higher octane, that you will have more unburned fuel, or in other words, it is possible to run richer... Now with that being said, I have seen and heard of many people running higher octane without running into emissions issues or clogged cats... Also since we have the trailing spark plug, the scenario is even less likely, but it is still possible...

For me, if I get no performance gain, then why spend the extra money.... Once superchips, or in other words, a timing advance was available, I was one of the first to jump on it and start taking advantage of premium fuel.
 

·
Builders of the 500rwhp 426's
Joined
·
5,341 Posts
i wasn't looking as to WHY someone would run 91-93 with no advantage, however I was taught that the higher octanes actually burned more completely.

I would assume that a more complete burn lead to lower emissions........

Just wondering
 

·
Movin and shakin
Joined
·
1,900 Posts
Higher octane fuel is less likely to preignite from compression - no? Does higher octane burn at a higher temp?

I, too, believe that salesman is abusing a controlled substance.
 

·
MAG V
Joined
·
2,163 Posts
MomsR/T said:
i wasn't looking as to WHY someone would run 91-93 with no advantage, however I was taught that the higher octanes actually burned more completely.

I would assume that a more complete burn lead to lower emissions........

Just wondering
hmmm, not sure... I am thinking higher octanes do burn more completely, but only when timing is such that can take advantage of it... Like I said before, just my .02 cents... but I think we can all agree any salesman that passes along information about higher octane fuel cracking a block should be avoided at all cost.
 

·
LX Guru
Joined
·
14,153 Posts
I run premium fuel tunes in both of my hemi's with 89 octane and no detonation what so ever.
 

·
LX Padiwan
Joined
·
2,163 Posts
Octane has no bearing on "how complete" the mixture burns. Octane is simply the resistance to detonation. If the octane rating is above the level a given engine can adjust itself for, it does ABSOLUTELY nothing for you.
 
1 - 18 of 18 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top