5.7L V8 Magnum Needs 89 Octane?

[oldyellr]

But still, when it comes to fill up, paying $50 instead of $70 (in Canada) does make a difference.

But this is not about ultimate gas mileage, or we'd be driving something totally different. Are you paying another $5 extra to fill up with 89 octane because you believe it will save you $5 on the tankful because it's more efficient or because you feel regular gas will "damage" your engine. If it makes no difference, I'd rather spend the extra $5 bread and milk or something. I don't care if 89 octane will get me a tenth at the dragstrip unless I;m actually going to the dragstrip.

[Geoff of NV]

OK, 20 gallons at $2,79 US is $55.80. Your costs may vary.
20 gallons at $2.89 US is $57.80
Difference of $2.00
I just don't think it's significant. If you do, buy regular and I think I'll bow out of this conversation now.

[oldyellr]

Yeah, Iwasn't really debating economy, just whether using 87 is harmful.

[jkelly16]

Page 246 of the owners manual. It can be downloaded at the Dodge site.

3.5L and 5.7L Engines
The 3.5L and 5.7L engines are designed to
meet all emissions regulations and provide
satisfactory fuel economy and performance
when using high-quality unleaded
gasoline with an octane rating of 87 to 89.
The manufacturer recommends the use of
89-octane for optimum performance. The routine use of
premium gasoline is not recommended. The use of
premium gasoline will provide no benefit over high quality
regular gasoline or mid-grade gasoline and in
some circumstances may result in poorer performance.

Now what you possibly get into using the lower octane or cheap gas is the chance of LTSK (long term spark knock) which will be stored in the PCM and in the end will pull timing all the time which will hurt both power & gas mileage.

[oldyellr]

Okay, now I understand. It will run fine on 87 because the spark will get retarded, but that's not a good thing because it reduces power, so I'll end up using more gas, negating any savings, so I may as well use 89 in the first place and get marginally better performance as well.