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....
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.
2000 Jeep Grand Cherokee Limited, Quadradrive, 4.7 V8
Living life mod by mod
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.
01' 4.7 Limited WJ 5" lifted, Rubicon Express 4.5" coil springs with IRO critical path setup and Bilstien 5100 shocks all around, JKS adjustable Trackbar (KOR bushings), JKS HD tie rod (MOOG problem solver Ends), JKS HD drag link (Moog Probel solver Ends), 4.56 Yukon ring and pinion, Moog HD SSD107 Steering Stabilizer, IRO Front drive shaft conversion, Stillen slotted rotors all around with Stillen brake pads, IRO adjustable A-Arm, 3" all the way Kolak Exhaust with High flow Magnaflow Cat. Converter and Flowmaster Super 50 Muffler, 285/70R17 AT Kumho (33") on 17" BlackWheel rims 909B, K&N Cold air intake, Four nozzles Bosch injectors, and Flashpaq 3780.
03' 4.7 H.O WJ 3" lifted, OME HD with 0.5" Coil spacers and Bilstien 5100 shocks all around, JKS adjustable Trackbar (KOR bushings), Moog Problem solver TRE's, IRO Front drive shaft conversion, IRO adjustable A-Arm, High flow magnaflow mini cats, high flow magnaflow cat, Flowmaster Super 44 muffler, 265/65R17 AT Yokohama on 17" Rays rims, and Flashpaq 3780
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
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
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.
Sent from inside my dinosoar head.
2002 Overland - 4.7 HO, "Select-Drive", 4" RC long arms, TAG front winch bumper, 32" BFG KM's, 3" exhaust, Magnaflow hi-flow cat, Flowmaster 50 series
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.