Octane requirement?

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L31MaxExpress

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With the blackbox, mine ALWAYS pulled 4 degrees of timing WOT regardless of tune or fuel bone stock.
Some of the earlier PCMs had more aggressive timing mapping than the later ones. My 97 van had as much as 6° more timing programmed into it than my 99 Tahoe did stock for stock. The Tahoe ran fine on 87 but was an absolute dog on stock tune. Then again the Tahoe had other factors that made it worse. Small exhaust tubing to the muffler(van was dual 3"), smaller cats and a throttle body lip that was twice as wide as the one on the van. 99 Tahoe had the same TB as my brothers 4.3L S10. Almost like GM was trying to neuter the 99 to make sure that people wanted the newer 5.3L when they came out.
 

Supercharged111

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Some of the earlier PCMs had more aggressive timing mapping than the later ones. My 97 van had as much as 6° more timing programmed into it than my 99 Tahoe did stock for stock. The Tahoe ran fine on 87 but was an absolute dog on stock tune. Then again the Tahoe had other factors that made it worse. Small exhaust tubing to the muffler(van was dual 3"), smaller cats and a throttle body lip that was twice as wide as the one on the van. 99 Tahoe had the same TB as my brothers 4.3L S10. Almost like GM was trying to neuter the 99 to make sure that people wanted the newer 5.3L when they came out.

I suspect it was an issue with the knock module as I pulled timing from the stock map and it did the exact same thing. With that in mind, I proceeded to advance the timing to which the truck responded favorably. I couldn't go too far though without the knock sensor reference, part of why the 411 woke the truck up so much.
 

0xDEADBEEF

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While what you are saying is true, that does not mean that the engine is making as much power as it can. If you eliminate the knock retard with higher octane the engine will make more power. Even the old black box had octane based learning that allowed it to advance the timing more for high octane fuel. The Gen3 LS based controllers like the 0411 and the P59 I run my 383 on have dual timing maps. The 0411 could pull enough timing on its own to prevent knock retard however it ran like a dog with less timing.

I don't need to be making all the power all the time. 25 ft-lbs or whatever isn't going to change my life.

I had an old Jetta GTI that had a bad knock sensor and that ECM would pull so much timing you could barely drive it when it happened. That was dangerous and got fixed.
 

L31MaxExpress

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I suspect it was an issue with the knock module as I pulled timing from the stock map and it did the exact same thing. With that in mind, I proceeded to advance the timing to which the truck responded favorably. I couldn't go too far though without the knock sensor reference, part of why the 411 woke the truck up so much.
I have buddy thats 95 TBI truck did the same. 4° retard anytime the knock sensor was on and would go into low octane mode which pulled 5° of timing across the board. Going down the road it would pull 9° of timing all together. That 350 ended up spinning eating a rod bearing or two. Always felt the knock sensor was likely picking up the looseness of the bearing on that ~200K 350.

0411 woke mine up too even compared to a tuned black box.
 

Pinger

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While what you are saying is true, that does not mean that the engine is making as much power as it can. If you eliminate the knock retard with higher octane the engine will make more power. Even the old black box had octane based learning that allowed it to advance the timing more for high octane fuel. The Gen3 LS based controllers like the 0411 and the P59 I run my 383 on have dual timing maps. The 0411 could pull enough timing on its own to prevent knock retard however it ran like a dog with less timing.
The 'old black box' you are referring to - as per 1999 L31?
 

L31MaxExpress

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I don't need to be making all the power all the time. 25 ft-lbs or whatever isn't going to change my life.

I had an old Jetta GTI that had a bad knock sensor and that ECM would pull so much timing you could barely drive it when it happened. That was dangerous and got fixed.
I found mine more economical to run with higher octane. The fuel economy gains especially around town were worth burning higher octane as it offset the cost while making more power.
The 'old black box' you are referring to - as per 1999 L31?
Yes up through the 2000 model year.
 

0xDEADBEEF

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I found mine more economical to run with higher octane. The fuel economy gains especially around town were worth burning higher octane as it offset the cost while making more power.

To me the ROI isn't there, but I salute your efforts. Sometimes it's just fun to tinker.
 

Pinger

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Yes up through the 2000 model year.
That's good news for me given I'm running on LPG (propane) with a (UK) octane rating of 100+ (regular here is 95, premium 98).

My (turbo) smart had the same adaptive function. For years I ran it on (UK) 95 due to availability but changed to 98 when I moved to another district. No immediate change then after the third tankful it became a lot more responsive and gained 5+ mpg (45 to 50 minimum). I'd never believed the 'it takes a few tankfuls' line - until I had it happen that way. IMO, if the engine can configure itself for higher octane it is well worthwhile using it. But only if it can exploit it.
 

Supercharged111

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That's good news for me given I'm running on LPG (propane) with a (UK) octane rating of 100+ (regular here is 95, premium 98).

My (turbo) smart had the same adaptive function. For years I ran it on (UK) 95 due to availability but changed to 98 when I moved to another district. No immediate change then after the third tankful it became a lot more responsive and gained 5+ mpg (45 to 50 minimum). I'd never believed the 'it takes a few tankfuls' line - until I had it happen that way. IMO, if the engine can configure itself for higher octane it is well worthwhile using it. But only if it can exploit it.

You guys don't do (R+M)/2 for octane, do you?
 

Pinger

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You guys don't do (R+M)/2 for octane, do you?
No, it's RON all the way here. Took me a while to figure that you guys have fuel as good as ours - just the numbers are different.
LPG has the highest octane of all the available fuels and is currently around one third the price of diesel. If I was running a diesel here, I'd have to get 39 mp(Imp)g (32 mp(US)g) to be as cost effective. I'll take my L31 over any diesel any day of any week. And, there isn't any diesel engine that could return those figures when in a Suburban.
 
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