Modern Engine 101....Here is how it works on new vehicals with modern engine managment computers. If the computer senses knocking like some, but not all 87oct gas can do in the HEMI motor, it will retard the timing which will output less horsepower. Its that simple. This is what most chip upgrades do and require 91oct and above for the added hp they give. The OEM computer is mapped for 89oct or better grade 87oct. Humidity, elevation, and temp all play a role on if 87oct will cause knocking or detonation. 87oct may work for some climates in one area but not all. 89oct is the default oct rating. Will high oct gas like 94oct increase even more power than mid-grade gas? No, the engine managment will only advance its timing for 89oct. Any oct above 89 will not prduce more hp unless a aftermarket chip is in play. The days of wrenching hp gains have switched to computer mapping upgrades for that little edge in hp. Obviously there is no way Dodge can know the enviorment the HEMI motor is used in. This is why they state.. You can use 87oct but the 89oct may be better suited for your application. If they were to just draw a line and say, "use 89oct", it would eliminate a large enviorment where a good 87oct would not detonate and cause no adverse effects.

 

I stated this in the other forum over 89 octane. i filled my truck up on 87 for 3 months and the ECU retarded itself so that i only made 300hp not 345. DatNeggaDodge, if you're reading this...shape up or ship out, your Hemi wont be what ours are.

 

I just bought my 03 Ram QC Hemi with 60 000 kms., and I'm sure the previous owner ran 87 octane since it was new. If the ECU has retarded the timing to compensate for the lower octane, will it revert back to the stock setting if I switch to 89 octane or would it need to be reprogrammed? I would just hate to switch to 89 octane and not realize any potential benefit if something needs to be reprogrammed.

 

Good job making a new thread for this. Weedwacker.

 

Yes Tman I am pretty sure your ecu will not need cleared. On some cars disconecting the battrery terminals for 30 minutes will clear the ecu program but not errase service codes. In any case I would run a bottle of Techron fuel cleaner (for other reasons) through your tank on the next fill up of higher 89oct gas. I think alot of people see the word HEMI and think the old rules os muscle cars apply.
This could'nt be further from the trueth. The new HEMI is a hi-tech wonder motor that has more in common with the latest PC than a old musclecar motor.

 

I spot some bad info here.

Dealership told me the hemi will not clear with the 30 minute trick. Most vehicles are like this now. You have to plug them in to clear the codes and info stored. This is an emissions issue.

The computer is constantly learning so you do not have to even bother reseting the computer.

I am not going to run my mouth about my credentials, but I have past combustion engine design experience. The only time you will possibly need 89 is in very hot temperatures or very heavy loads. Even then 87 will work fine, the computer will compensate and you will loose some HP. Maybe 5%. Here in New England I would bet I never will need 89 unless I am towing.

All of the bad info on octanes is annoying.

 

I recently asked my dealership about the whole 89 octane issue and they said its true.

Running 93 won't gain you anything and 87 only retards your timing giving you less horsepower in the long run.

I had to argue with the secretary to let me speak with the mastertech.

 

....well, all I know is my truck runs very smoothly and throttle response very crisp since I started using 91 oct with my 87 superchips setting...

 

I have no problems using 87 oct. gasoline .When I pull my boat I blend in some 89 but not a full tank of it. I tried 89 a couple of times when I was low on gas but the mileage dropped so I put 87 back in. I pull a 5,000 boat with a loadrite four wheeler trailer and I haven't had a ping yet. I used to run a Octane testing lab for a major oil company and I think I know what's best for my engine. But remember, keep those injectors very clean. That's important.

 

My truck only has 3k miles, yours will never be what mine is. But I tell you what, as soon as my tank is empty, I'll fill up with 89 to see what happens.