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Unread 05-12-2014, 02:07 AM   #1
kaleo333
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Wj 85 in 4.7 high output?

Hi,

This is my first post in the WJ section...and I'm sure it won't be the last. I know there has been discussion of octane in the high output but this is more specific. Is it entirely okay to run 85 octane in the high output in colorado? I'm not saying I redline it all the time but if in the most extreme scenario, if I were to randomly WOT, would the high output be okay running 85? I know it would be less powerful, that's fine. I just don't want it to knock if I occasionally push it to the limit when it's running 85 octane....

Thanks in advance,

- Jordan

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Unread 05-12-2014, 02:25 AM   #2
jbaldry
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If this was the 4.7 Low Output, I might not respond, but I believe the High Output should never get that low octane of gas. Other people will show up with opinions, testimonials, and facts, but until then, take it from me and keep using high octane gas.
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Unread 05-12-2014, 04:05 AM   #3
veiri86
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All the ignition process in the HO engine was tuned by the manufacturer to run High RON, running low run engine will damage the engine on the long run. In the beginning you will notice a difference in the performance but in the long run you will notice that your engine will be damaged.
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Unread 05-12-2014, 04:30 AM   #4
kfxnando
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A slight different look

the HO has knock sensors
and once it detects knock/pinging/pre-ignition it should change the timing to avoid further knocking/pre ignition and damage and there should be no damage
loss in performance yes, damage doubtful

the low output has no knock sensor, and when using the Supachip mapping and the ch1t quality of our fuel I heard my 4.7 pinging/preigniting

hope this helps
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Unread 05-12-2014, 04:37 AM   #5
kaleo333
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Thanks you guys are really helpful and quick.

I was just confused with the weird way that Colorado gas works, where 87 is 85 a mile above sea level. Theoretically on 87 though, even when the engine is working hard it wouldn't ping at all right? I'm not planning on racing this thing, not even close, I'm just thinking worst case scenario, if I run the cheapest gas in Colorado (85) and then redline it, will I be damaging the high output engine or will the anti-knock keep it safe?

I don't intend to run 90+ octane ever due to price. I just want minimum octane to keep the engine safe at all RPM's
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Unread 05-12-2014, 04:47 AM   #6
kfxnando
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From my understanding the knock sensor and ECU should keep it safe
other wise why would there of been a knock sensor in the system if not to protect and optimiser the engine output

this is just how I understand it!!

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Unread 05-12-2014, 04:50 AM   #7
kaleo333
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Is the initial pinging to trigger the sensor and slow the ignition timing bad for the engine as well or unnoticeable?

and does anyone have mileage figures for different octanes? Maybe this is a whole different thread...
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Unread 05-12-2014, 07:50 AM   #8
lemiller
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Question: Does the owners manual say to run Premium Fuel? If so, and you don't EVER intend to run premium fuel, why would you buy a vehicle that requires you to do so?
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Unread 05-12-2014, 07:55 AM   #9
ezflip
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The 4.7 HO has dual knock sensors specifically for this purpose. It's perfectly okay to run lower octane fuel, you just miss out on some of the extra power over the non-HO. I've been running 85 in mine for about a year with no issues at all.

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Unread 05-12-2014, 07:57 AM   #10
ZJPunk98
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I have an h/o and I believe the owners manual recommends high octane but stats that 87 is usable. I run both fuels
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Unread 05-12-2014, 10:18 AM   #11
kaleo333
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Yeah I know the manual says premium if you want to match the dyno specs. But I just want mileage really and to not break it of course.

Good to hear that 85 is fine. I'll try to go easy on it when it's running anything less than 87.
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Unread 05-12-2014, 11:18 AM   #12
VestaviaPirate
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Quote:
Originally Posted by kaleo333 View Post
and does anyone have mileage figures for different octanes? Maybe this is a whole different thread...
This has been discussed at length, regarding specifically the 4.7 H.O. Pretty good facts and data to pour over.

There is also something to be said for using 87 Octane WITH 10% ethanol and using 87 Octane WITHOUT ethanol. I can attest that using ethanol-free octane makes a WORLD of difference in performance (feel) and mileage (my calculations).

Personally, I switch back and forth between 93 and 87 Octane, depending on what state I'm in. NC (home) is sometimes 30-50 cents more for 87 than SC (work) is for 93. I just depends on where I fill up. It's hard for me to swallow $10 more per fill up for lesser gas. That's why I try my damn-est to time my fill ups when I'm leaving work, instead of on the weekends.
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Unread 05-12-2014, 11:41 AM   #13
imaguy3
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Quote:
Originally Posted by kaleo333 View Post

I don't intend to run 90+ octane ever due to price. I just want minimum octane to keep the engine safe at all RPM's
Here there is only a $.30 difference per gallon bt 87/91... That works out to be a difference of $6.00 per tank.

When I run 87 I get much worse gas mileage, resulting in more fill ups and HIGHER cost in the long run over 91...
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Unread 05-12-2014, 02:43 PM   #14
kaleo333
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If I can afford 91 (highest octane in CO) I would love to run it because it seems like I could benefit from:
better mileage
more power!
would never ping
cleaner engine (meaning longer life for engine)

through my meager and quick calculations, it looks like a 2 mpg increase between 85 to 91 would be enough to make premium fuel "cheaper".
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Unread 05-12-2014, 03:13 PM   #15
imaguy3
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Quote:
Originally Posted by kaleo333 View Post
If I can afford 91 (highest octane in CO) I would love to run it because it seems like I could benefit from:
better mileage
more power!
would never ping
cleaner engine (meaning longer life for engine)

through my meager and quick calculations, it looks like a 2 mpg increase between 85 to 91 would be enough to make premium fuel "cheaper".
If you can't afford an extra few dollars at your fill-ups, then you should probably cut out fast food, buying pop, and other stupid **** you spend money on.
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