xfactor_pitbulls

iTrader: (16)

My Z28 isnt a daily driver, and my other 2 cars run soley on 87 octane. I knew it was a matter of time before I dazed off and and started to fill up with the cheap stuff. So I realized what I was doing about 5 gallons into the fillup and stopped, went inside paid and got some off the shelf octane booster. Then put 5 more gallons of 93 in it. I probably had 3 or so gallons left in the tank before whole thing started. So I figure the overal octane rating would be around 91 or so when all was done. I know that isnt a huge deal, and the car drove just fine on the way home. When it took it out later that day it seemed a bit sluggish. I dont know if it was me being paranoid, but didnt seem to be running very well. Will the ECM pull timing if it sees a sudden change in the octane? Did I confuse it will the mix of all that crap? Or am I a jackass and imagining something that didnt happen?

Thanks

Brandon

HumpinSS

iTrader: (1)

If you are getting detonation because of the octane and heat yes it will pull timing. enough timing and you will see around 10 removed when you hit the low octane table.

samz28

yeah these cars were built (assuming stock tune) to run on the worst 85 octane of colorado or mexican(texas) 87 octane. Also if its -20F outside versus 100F outside, egr, PCV blowby oil, etc all affects the actual effective octane of your motor.

otherwise gm would have to buy you a new motor if you got a bad tank of gas.

even those turbo motors all run on 87 (or less) rather than self-destruct.

One must wonder if you were to do cruise control from point A to Point B (600 miles lets say) why not run 89 or 87 and keep the throttle light? Would the extra timing really offset the amount of gas used (20 cents more for 93). I've always wondered that. In theory alot of 80-90's cars were 10:1 with knock systems and very unsophisticated ecm's, that ran on cast pistons,junk motors, and 87 octane. They just ran the timing back. They got great gas mileage and didn't explode.

I would just drive the car lightly (ie no wot runs) until the gas is done and fill her back up with 93 and the octane scaled pid will move its way back up and come back to life.

Funny thing i heard at a vw dealer, car had a bad coilpack (recall with vw on 100000's of 1.8T) 170hp motors. They said just put 87 in. Oddly it helped alot of people. The car retarded the timing and i guess the reduced power output required less spark to prevent a boost-spark-blowout or soemthing along that lines .. and the cars would run. Then the whole coilpack would fail and the car would get towed in. lol.

marc_w

From what I noticed, it's pretty hard to get in the low octane table.

I had a lot of knock (8-9*) with my old cam due to false-knock, and the worst I'd see with the Knock Learn Factor was around 0.91. 0.00 being full low octane, 1.00 being full high octane.

It'd return up to the full 1.00 reading after about five minutes of no-knock.

I think your car is just fine, especially seeing as tuning (and more timing) hasn't been done yet.

FWIW: My truck calls for 91+. I've run 87 with no noticeable performance problems. One of these days I'll have to throw more in and scan it.

jimmyblue

iTrader: (11)

Anybody here ever tune for 87 octane straight up?
I would sure like to know whether there's any loss
of performance in doing so. Especially if running a
lower temp 'stat etc. Because 87 is supposed to
have a slightly higher energy content than 93,
seems like if you can avoid detonation you should
be ahead on power.

xfactor_pitbulls

iTrader: (16)

Well many thanks for the words guys. I think I have an idea of where I stand. I am hopefully getting tuned later this week and will see from a data standpoint what my computer is saying.

Thanks

Brandon