different octanes on dyno...

[Tyler]

would i dyno better numbers on 93 octane rather than 87 octane?


just curious..

this is for an NA dyno

[BLUE]

No. Unless you advance the timing also to benefit on using 93 octane.

[camaroincal]

Could you please elaborate on this BLUE? I'm still a bit confused as to the definate octane to use in the 3.8

[Tyler]

our cars are made to run on 87.


what he's saying is that you wont get any gains by throwing in 93 octane.. unless you advance the timing some.

which i understand. if you advance the timing on 87, you may get some ping

[speedy-v6-camaro]

Higher Octane at the same timing will get you less power. Lower octane actually burns hotter and produces more power unless you adjust the timing.

[Devilsy2k]

I think you would get better numbers with 93 because ECU will advance the timing, like it does when the car is cold or hot.

[speedy-v6-camaro]

<blockquote>quote:</font><hr>Originally posted by Devilsy2k:
I think you would get better numbers with 93 because ECU will advance the timing, like it does when the car is cold or hot.<hr></blockquote>

The ECU doesn't...that's what a JETChip does.

[Darknight]

Just put a 4.7k or 10k resistor in the IAT sensor, and have fun making more power from higher octanes. If you're running boost or NOS, though, it's not a good idea, since it fixes the timing in one position. That would make it more prone to knocking if the intake air temp was significantly higher than that indicated by the resistor. If memory serves me well, I think the 4.7k imitates a 57 degree reading, while the 10k imitates a 32 degree reading.

DK

[ July 06, 2003: Message edited by: Darknight ]</p>

[Magnus]

The PCM may learn a more agressive spark curve if you put in 93 due to the fact that it may knock on 87... and if you drive the car hard, you definatley want 93 in there.

I tried 89 in my car once.. it didn't like it at all.. the PCM adjusted my timing to high with the 93 and was going nuts with the lower octain.

My vote is 93 if you drive it hard!!!

89 if you are a granny.

87 only if you don't go WOT.

[BigCutlass]

ok so you are tellin me that if i put 93 in my car(93 cutlass ciera), it will actually hurt its performance more than help it? am i understanding correctly?

[speedy-v6-camaro]

<blockquote>quote:</font><hr>Originally posted by BigCutlass:
ok so you are tellin me that if i put 93 in my car(93 cutlass ciera), it will actually hurt its performance more than help it? am i understanding correctly?<hr></blockquote>

Possibly. Unless your PCM advances timing and can retard it when it detects knock then you are not getting the most out of it. You should choose which ever fuel will make your engine run without knock.

[black34v6]

<blockquote>quote:</font><hr>Originally posted by Magnus:
The PCM may learn a more agressive spark curve if you put in 93 due to the fact that it may knock on 87... and if you drive the car hard, you definatley want 93 in there.

I tried 89 in my car once.. it didn't like it at all.. the PCM adjusted my timing to high with the 93 and was going nuts with the lower octain.

My vote is 93 if you drive it hard!!!

89 if you are a granny.

87 only if you don't go WOT.<hr></blockquote>


not sure if this relates or not but interesting story - used to only put 89 in my car..all the time. drove it that way since i got it. two years later im driving down the road and actually ran out of gas, called AAA and they came with 2 gallons to get me to the gas station.

filled it up, i asked him what it was and he said 87. i didnt pay any attention to it cause the cars are built to run on 87 octane.

so i drive a block, come to a stop sign and stop..and the car idles up and then dies. just straight out stalled. i had the clutch to the floor too (its a manual). couldnt understand it. started it back up, drove to the next red light and stopped where the engine did the same - stall. so when i got to the gas station i filled up with 89 again and did a couple of WOT runs (light to light) to use up all the 87. since then i dont put anything less than 89 in the car..

(of course it could have been an early sign of the crank walk - but it only did it that one time..cause i never put 87 octane in it again)

-R

[Magnus]

<blockquote>quote:</font><hr>Originally posted by BigCutlass:
ok so you are tellin me that if i put 93 in my car(93 cutlass ciera), it will actually hurt its performance more than help it? am i understanding correctly?<hr></blockquote>

In this case, most likely. A cutlass cierra probably doesn't have agressive timing curves so you should be fine with 89 or even possibly 87.

If you drive your car hard, and you have it modded for performance, and its a V6 f-body, you will want to run 93. The octain will allow your PCM to learn a more agressive spark map and thus you will go faster. ;)

[Mikael]

<blockquote>quote:</font><hr>Originally posted by Magnus:


In this case, most likely. A cutlass cierra probably doesn't have agressive timing curves so you should be fine with 89 or even possibly 87.

If you drive your car hard, and you have it modded for performance, and its a V6 f-body, you will want to run 93. The octain will allow your PCM to learn a more agressive spark map and thus you will go faster. ;) <hr></blockquote>

I'm sorry but this is horrible advice/misinformation. All GM PCMs have spark and fuel tables- preset values that it follows- and knock sensors to adjust timing when necessary. It does not just start learning new curves- like increasing the spark consistantly until there is knock then backing off. It will make and store corrections for idle/part throttle fuel, but that's it. You will never go beyond the max spark that is programmed into the PCM from the factory. The LS1 has two tables, one for high and one for low octane. When too much knock is recorded, it'll default to the lower table. It won't make its own custom table though.

If the car is made for 87, run 87. With hot plugs, a hot day, and a lot of WOT runs, it still should not detonate. And you can't hear 3-4 degrees- you can only hear like 5+, so i'd trust a logger over your ear.

[ July 07, 2003: Message edited by: Mikael ]</p>

[Magnus]

OMG.. You are going to teach ME about PCM's? get the F out of here. You have to be kidding me. I have PCM source disassemblies in front of me at this very moment as well as hundreds and hundreds of megs of docs on my computers regarding PCM's, programming, and how they work.

Do you even KNOW how high the timing table is in the 3.8? do you KNOW that I was pushing 29 degrees of timing with STOCK TUNING.. Hmm.. 29 degrees of timing and 87 octain.. BAD IDEA. I also know of a 3.8 that was pushing 31 degrees of timing STOCK TUNING. yea, he was on 87 octain.. riiiiiiiiiiiiight. :rolleyes:

The PCM DOES learn what it can do.. it won't up the max timing however it WILL learn a correction factor of how much lower it should be.. In a best case scenaro with no behind the scenes timing retard you should see 31 degrees at WOT @ 5900 rpm's.. bet you didn't know that.

Running a 3.8 with hot plugs, hot engine temps in hot weather with 87 octain.. yea.. expect ~22 degrees of timing. Good luck seeing 26+ on 87.