Timing
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Joined: Aug 2000
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From: San Jose, California, U.S.A.
Timing
I have the basic flip chip Superchip. 87 on one side and 91 on the other (for California gas). The other day I was going on a road trip and I bought a tank of 87. Its a regular trip, about 300 miles so I usually get a tank of 87 and by thetime I get back, its empty and I fill with 91 again. When I drive on the 91 setting I usually get a little better gas mileage than the 87 side. My driving style is the same on either side.
Well this latest time I forgot to flip the chip to the 87 octane side when I filled up with regular unleaded. I got on the highway and didn't hear any abnormal noises and didn't notice any lack of power.
That got me to wondering about the timing on the chip. Does anyone know what the base and final timing is on the 91 side of the superchip? Also at what rpm does the final timing come in at?
My theory is that I never got on it very hard and the timing on the chip was never causing any detonation due to the low rpm's? Does that sound like a valid explanation?
Now I don't plan on driving around the 91 chip setting with 87 gas or anything, just trying to get a feel as to why I got about the same mileage as I usually do with premeium and no audible pinging.
I would welcome all comments, and also if someone (Mike?) could answer the timing question. Thanks.
Jes
Well this latest time I forgot to flip the chip to the 87 octane side when I filled up with regular unleaded. I got on the highway and didn't hear any abnormal noises and didn't notice any lack of power.
That got me to wondering about the timing on the chip. Does anyone know what the base and final timing is on the 91 side of the superchip? Also at what rpm does the final timing come in at?
My theory is that I never got on it very hard and the timing on the chip was never causing any detonation due to the low rpm's? Does that sound like a valid explanation?
Now I don't plan on driving around the 91 chip setting with 87 gas or anything, just trying to get a feel as to why I got about the same mileage as I usually do with premeium and no audible pinging.
I would welcome all comments, and also if someone (Mike?) could answer the timing question. Thanks.
Jes
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Joined: Mar 1998
Posts: 13,385
Likes: 4
From: Virginia
Hi Jes,
You just got lucky, basically - this same question comes up anytime someone does the same thing you accidentally did - run 87 on the premium gas program - if they didn't hear *audible* detonation.
The reason you did not get any *audible* detonation is simply because these vehicles all have knock sensors & when the sound of detonation is picked up, the PCM yanks out timing to quell the detonation - and this happens so quickly that you as the driver never hear or notice it. You were just lucky that in *your* case, apparently the knock sensor system had enough effective compensation range so you didn't get *audible* detonation - but you werent "safe" or "OK" by any means.
You also weren't making the same power, you were down on power compared to if you had run the required premium, due to the knock sensor & different burn rate of the low octane fuel.
As you already know, you don't want to repeat that, as it's not just audible detonation that is the enemy in that situation - it's inaudible detonation and EGT's - the EGT's (exhaust gas temperatures) *were* elevated all during that time due to the much quicker light-off rate of lower octane fuel - so for many reasons, this is something you don't ever want to repeat, obviously - you already know all that, of course.
"Base" timing @ WOT in most of these truck V8 motors is about 8 degrees - what we use we don't publish publicly, as that is proprietary info of course - if we're in a *custom* program, then we release those specs to the individual vehicle owner privately. It's not the same amount of timing in every "standard" Superchips program for these vehicles, there is some variance based sometimes on code, or sometimes on octane (91 vs. 93, etc.). Figure that roughly, you can usually add anywhere from 4-8 degrees of timing, depending on how the vehicle will be used & local fuel supply, A/F's, etc. Now that is a *very* rough & wide range, but just to give you some FYI in general.........
You just got lucky, basically - this same question comes up anytime someone does the same thing you accidentally did - run 87 on the premium gas program - if they didn't hear *audible* detonation.
The reason you did not get any *audible* detonation is simply because these vehicles all have knock sensors & when the sound of detonation is picked up, the PCM yanks out timing to quell the detonation - and this happens so quickly that you as the driver never hear or notice it. You were just lucky that in *your* case, apparently the knock sensor system had enough effective compensation range so you didn't get *audible* detonation - but you werent "safe" or "OK" by any means.
You also weren't making the same power, you were down on power compared to if you had run the required premium, due to the knock sensor & different burn rate of the low octane fuel.
As you already know, you don't want to repeat that, as it's not just audible detonation that is the enemy in that situation - it's inaudible detonation and EGT's - the EGT's (exhaust gas temperatures) *were* elevated all during that time due to the much quicker light-off rate of lower octane fuel - so for many reasons, this is something you don't ever want to repeat, obviously - you already know all that, of course.
"Base" timing @ WOT in most of these truck V8 motors is about 8 degrees - what we use we don't publish publicly, as that is proprietary info of course - if we're in a *custom* program, then we release those specs to the individual vehicle owner privately. It's not the same amount of timing in every "standard" Superchips program for these vehicles, there is some variance based sometimes on code, or sometimes on octane (91 vs. 93, etc.). Figure that roughly, you can usually add anywhere from 4-8 degrees of timing, depending on how the vehicle will be used & local fuel supply, A/F's, etc. Now that is a *very* rough & wide range, but just to give you some FYI in general.........