What does the Mopar PCM do when using 91 octane gas?

[Shannon Whitehead]

#176823

I would not be running 91 octane with a PCM calibrated for 93. Granted you will have knock retard as soon as you get detonation, but that’s after the fact. Knock sensors can only “save” you from further damage, they dont prevent the detonation. So the damage may already be done by the time they step in and start pulling out ignition advance.

I would not strap the car to the dyno and run 91 on your current PCM. I would sell the controller, and have yourself a custom HP tune done for 91 oct. Just my .02

If you must, an octane booster at minimum, but that’s a band-aid.

[Shannon Whitehead]

#176939

Seriously? I’ve run to Colorado numerous times in my car and octane goes as low as 89 max in some places (Raton Pass). Never noticed a difference. But I’m not driving spirited either at that time.

[Shannon Whitehead]

#176941

I thought this was mentioned in one of the recent Gen V Arrow ECU threads but I havent been able to find it yet.

[Shannon Whitehead]

#177406

MtnBiker said:
Seriously? I've run to Colorado numerous times in my car and octane goes as low as 89 max in some places (Raton Pass). Never noticed a difference. But I'm not driving spirited either at that time.

John there’s a big difference between being able to run on lower octane, and running 6000rpm+ WOT on lower octane than you’re tuned for.

She’ll run on 87 all day if you’re putting about, no worries. I was saying that I wouldn’t run my car on a load bearing dyno at 6000rpm+ with low octane gas, as that is a recipe for detonation and damage.

[Shannon Whitehead]

#177466

That’s kind of what I thought Alex. Wasn’t sure though.

[Dajerseyviper]

#177519

I would guess pull a shitload of timing…I dont know about the Viper PCM or the Mopar Perfomance one, but conventional PCM’s will have multiple timing and AF maps for different octane and load conditions. They will put the car into a low timing map if they pick up knock (detonation), but the Perfomance PCM may not have low octane maps in it and may be solely programmed for performance and higher 93+octane and be unable to pull the timing when the car detonates. Some one like Dan Lesser would be able to answer that question for sure, you could call him and ask.

But my guess is the car would not run to its full potential and possibly cause harm to the engine, keep in mind you would be prone to detonation not only at 6000 rpms but most likely ate Peak TQ levels where cylinder pressures are the highest, which on a viper is most likely around 3500 rpms my guess.. I wouldnt run 91 octane in my Hyundai…

[Shannon Whitehead]

#17357

TIA – Moved from Iowa to Phoenix and 93 octane gas is not readily available – matter of fact, haven’t found 1 station in the area that carries 93.

I have the Mopar PCM (which I understand is optimized for 93) along with head/intake work, and headers/full exhaust with a single high flow cat.

Just wondering how much I’m losing by using 91 and if it would be worth the hassle of using some type of octane booster? I was planning to dyno in a week – so any insight appreciated!

[Author]

Posts