Advancing Timing W/ Higher Octane Gas

Dank Xploidz · May 1, 2010

My truck calls for 0 degree base set timing. I've always been told that you can bump up the timing, and run higher octance gas for a little bit of more power. What would I want my new base setting to be if im running 91 octane? Is it worth the price difference between the octanes for the power? Will my gas milage change? Thanks

Nytemare · May 1, 2010

My truck calls for 0 degree base set timing. I've always been told that you can bump up the timing, and run higher octance gas for a little bit of more power. What would I want my new base setting to be if im running 91 octane? Is it worth the price difference between the octanes for the power? Will my gas milage change? Thanks

Your timing is ECM controlled....doesn't really matter what you do with your base timing...as long as its close to 0* the ECM will correct it to what the tables on the ECM say. Now you cant set it at like 30* and have the ECM correct...but a few degrees either side and it will just adjust accordingly.

Older vehicles you could do that...Computer controlled ones don't work like that however.

If you want to run 91 octane fuel you will need a Chip pre-programmed for 91 octane.

MaForrest · May 12, 2010

My truck calls for 0 degree base set timing. I've always been told that you can bump up the timing, and run higher octance gas for a little bit of more power. What would I want my new base setting to be if im running 91 octane? Is it worth the price difference between the octanes for the power? Will my gas milage change? Thanks

Your timing is ECM controlled....doesn't really matter what you do with your base timing...as long as its close to 0* the ECM will correct it to what the tables on the ECM say. Now you cant set it at like 30* and have the ECM correct...but a few degrees either side and it will just adjust accordingly.

Older vehicles you could do that...Computer controlled ones don't work like that however.

If you want to run 91 octane fuel you will need a Chip pre-programmed for 91 octane.

All I run in my truck is Shell V-power 91 oct. Unless Im a bit low and need fuel then I will get whatever but I always put in 91. Get a little less fuel for the same money but I get better milage. I was actually going to ask the same question because I want to advance my timing just a hair.

Nytemare · May 12, 2010

My truck calls for 0 degree base set timing. I've always been told that you can bump up the timing, and run higher octance gas for a little bit of more power. What would I want my new base setting to be if im running 91 octane? Is it worth the price difference between the octanes for the power? Will my gas milage change? Thanks

Your timing is ECM controlled....doesn't really matter what you do with your base timing...as long as its close to 0* the ECM will correct it to what the tables on the ECM say. Now you cant set it at like 30* and have the ECM correct...but a few degrees either side and it will just adjust accordingly.

Older vehicles you could do that...Computer controlled ones don't work like that however.

If you want to run 91 octane fuel you will need a Chip pre-programmed for 91 octane.

All I run in my truck is Shell V-power 91 oct. Unless Im a bit low and need fuel then I will get whatever but I always put in 91. Get a little less fuel for the same money but I get better milage. I was actually going to ask the same question because I want to advance my timing just a hair.

Your truck is a little different...you can tune yours using HP tuners of EFI Live...the OP has to use a Chip

MaForrest · May 13, 2010

My truck calls for 0 degree base set timing. I've always been told that you can bump up the timing, and run higher octance gas for a little bit of more power. What would I want my new base setting to be if im running 91 octane? Is it worth the price difference between the octanes for the power? Will my gas milage change? Thanks

Your timing is ECM controlled....doesn't really matter what you do with your base timing...as long as its close to 0* the ECM will correct it to what the tables on the ECM say. Now you cant set it at like 30* and have the ECM correct...but a few degrees either side and it will just adjust accordingly.

Older vehicles you could do that...Computer controlled ones don't work like that however.

If you want to run 91 octane fuel you will need a Chip pre-programmed for 91 octane.

All I run in my truck is Shell V-power 91 oct. Unless Im a bit low and need fuel then I will get whatever but I always put in 91. Get a little less fuel for the same money but I get better milage. I was actually going to ask the same question because I want to advance my timing just a hair.

Your truck is a little different...you can tune yours using HP tuners of EFI Live...the OP has to use a Chip

Ahhh, I see. So what would happen if you said screw technology, and ran hi octain anyways? I have also heard of people using the 454 TBI computers in the 5.0 and 5.7 TBI engines. Somthing about fuel curves and spark...i dont know.

Nytemare · May 13, 2010

My truck calls for 0 degree base set timing. I've always been told that you can bump up the timing, and run higher octance gas for a little bit of more power. What would I want my new base setting to be if im running 91 octane? Is it worth the price difference between the octanes for the power? Will my gas milage change? Thanks

Your timing is ECM controlled....doesn't really matter what you do with your base timing...as long as its close to 0* the ECM will correct it to what the tables on the ECM say. Now you cant set it at like 30* and have the ECM correct...but a few degrees either side and it will just adjust accordingly.

Older vehicles you could do that...Computer controlled ones don't work like that however.

If you want to run 91 octane fuel you will need a Chip pre-programmed for 91 octane.

All I run in my truck is Shell V-power 91 oct. Unless Im a bit low and need fuel then I will get whatever but I always put in 91. Get a little less fuel for the same money but I get better milage. I was actually going to ask the same question because I want to advance my timing just a hair.

Your truck is a little different...you can tune yours using HP tuners of EFI Live...the OP has to use a Chip

Ahhh, I see. So what would happen if you said screw technology, and ran hi octain anyways? I have also heard of people using the 454 TBI computers in the 5.0 and 5.7 TBI engines. Somthing about fuel curves and spark...i dont know.

Your knock sensor would auto correct for the increase in octane...but it would take about 3 tanks of fuel and some highway miles at a steady cruse 65-70MPH. It would slightly advance the timing and you may see a slight power gain and fuel economy increase...or you may not.

I have heard of the same thing...also guys using the 454SS pickup ECM on MPFI trucks. Apparently the theory is that 4 MPFI injectors have the same electronic load as 1 TBI injector, so your ECM fires the MPFI like a TBI....Kind of acting like a mechanical injection system in a Mercedes or VW...Heard of guys doing it...never been in one or seen one...and I have no idea if it works well or not.

Badass69 · May 13, 2010

You can easily use the 7427 ECM from a TBI truck to batch fire four injectors instead of cycling two. Check out over a fullsizechevy.com as there are a few members with tuned port and other setups driven by TBI ECM's. That computer came in 94 and 95 trucks... not 454SS's. Regardless of the engine all that changed was the chip from application to application. You can run a 4.3 or a 454 with the same ECM, just tune accordingly.

Advancing a distributor is a method of increasing the maximum amount of timing without tuning. The reason the spec is zero degrees is because that is a neutral point of reference for the ECM to advance and retard from. If you bump to 4 degrees as the base point the ECM will simply start from there. So if the computer was calling for 30 degrees of advance it would really be giving you 34. The computer in the TBI trucks relies on you setting base timing as it has no cam or crank sensor to reference actual distributor position. Bumping the base position fools it into adding more advance. It will still retard if the truck knocks and will continue to work within its normal window of advance and retard otherwise. Even with the distributor bumped it will just continue retarding the timing until the knock disappears. This is unless you set the base timing so far advanced it couldn't but in the 4-8 degree window it will run just fine.

I used to add 4-8 degrees to my TBI trucks...... 4 is probably max on 87 octane fuel. If you go too far you just mess up the curve too badly and lose the ability to properly compensate for knock. 8 degrees ran fine on my modded 92's 350 with premium fuel.

A proper custom tune will do wonders beyond any of this fooling stuff however.........

Nytemare · May 13, 2010

You can easily use the 7427 ECM from a TBI truck to batch fire four injectors instead of cycling two. Check out over a fullsizechevy.com as there are a few members with tuned port and other setups driven by TBI ECM's. That computer came in 94 and 95 trucks... not 454SS's. Regardless of the engine all that changed was the chip from application to application. You can run a 4.3 or a 454 with the same ECM, just tune accordingly.

Advancing a distributor is a method of increasing the maximum amount of timing without tuning. The reason the spec is zero degrees is because that is a neutral point of reference for the ECM to advance and retard from. If you bump to 4 degrees as the base point the ECM will simply start from there. So if the computer was calling for 30 degrees of advance it would really be giving you 34. The computer in the TBI trucks relies on you setting base timing as it has no cam or crank sensor to reference actual distributor position. Bumping the base position fools it into adding more advance. It will still retard if the truck knocks and will continue to work within its normal window of advance and retard otherwise. Even with the distributor bumped it will just continue retarding the timing until the knock disappears. This is unless you set the base timing so far advanced it couldn't but in the 4-8 degree window it will run just fine.

I used to add 4-8 degrees to my TBI trucks...... 4 is probably max on 87 octane fuel. If you go too far you just mess up the curve too badly and lose the ability to properly compensate for knock. 8 degrees ran fine on my modded 92's 350 with premium fuel.

A proper custom tune will do wonders beyond any of this fooling stuff however.........

Very Odd...I have read many things about this, and it says that the ECM just auto corrects back to base timing...if you advance by 4* and the ECM calls for 30* it will only advance you by 26*....

I know for sure the 96 and newer trucks have both Crank and Cam sensors.

Badass69 · May 13, 2010

Vortecs can sorta........... they pop a P1345 code if you don't have the distributor in the correct position. They can judge the base reference point as they use both a crank sensor in the timing cover and a cam position in the distributor itself. If you twist a distributor on a Vortec truck it just buggers it up and sets a code.

TBI is not even close to that sophisticated. It has no point of reference other than assuming you set the distributor to 0 degrees. It infers cam position based off that. Unlike a Vortec that can reference its crank sensor to know true camshaft position. TBI have no crankshaft position reference so the ECM has no idea where base is if its not zero. Like mentioned if you set it to 4 advance and the ECM calls for -4 degrees you really would have 0. Same all the way through the scale. You have a window of advance and retard and all you do is move the scale up and down but don't change the window. Think of it that way. TBI ECM's are dumb or blind, whichever you want and rely on the end user disconecting the brown and black stripe wire and setting the base timing to 0 degrees ( factory reference) or whatever you want. It has no way of knowing as it has no sensors to reference timing from.

Dank Xploidz · May 13, 2010

So whould I get any gain from it?

Badass69 · May 13, 2010

Not enough to be bothered in my experience on a relatively stock truck.. Get a decent custom burnt chip or just leave it stock........

Nytemare · May 14, 2010

Vortecs can sorta........... they pop a P1345 code if you don't have the distributor in the correct position. They can judge the base reference point as they use both a crank sensor in the timing cover and a cam position in the distributor itself. If you twist a distributor on a Vortec truck it just buggers it up and sets a code.

TBI is not even close to that sophisticated. It has no point of reference other than assuming you set the distributor to 0 degrees. It infers cam position based off that. Unlike a Vortec that can reference its crank sensor to know true camshaft position. TBI have no crankshaft position reference so the ECM has no idea where base is if its not zero. Like mentioned if you set it to 4 advance and the ECM calls for -4 degrees you really would have 0. Same all the way through the scale. You have a window of advance and retard and all you do is move the scale up and down but don't change the window. Think of it that way. TBI ECM's are dumb or blind, whichever you want and rely on the end user disconecting the brown and black stripe wire and setting the base timing to 0 degrees ( factory reference) or whatever you want. It has no way of knowing as it has no sensors to reference timing from.

Cool man....

Like I said...it reads like it just backs it off if it was advanced...Good to know

grampadirt · May 14, 2010

Sorry to jump in here but I've been reading this thread and it let's me believe my thoughts might be correct....I have a '95 TBI 454 and have the base timing advanced six degrees(base timing,brown wire disconnected).Can I assume the ECM is controlling the advancing rather than the vacuum advance pod that used to be attached to the dist.? I've had 454s before and I know they won't run at factory timing,they need at least four degrees advanced base timing

Just curious

Nytemare · May 14, 2010

Sorry to jump in here but I've been reading this thread and it let's me believe my thoughts might be correct....I have a '95 TBI 454 and have the base timing advanced six degrees(base timing,brown wire disconnected).Can I assume the ECM is controlling the advancing rather than the vacuum advance pod that used to be attached to the dist.? I've had 454s before and I know they won't run at factory timing,they need at least four degrees advanced base timing

Just curious

Yeah the EMC controls advance on anything that does not have a vacuum advance pod....for the most part...unless its mechanical advance....but it would likely not have an ECM than either.