Using vacuum to tune a timing table??????

Using vacuum to tune a timing table??????

I have been lurking around this site for the last couple of months trying to familiarize myself with the knowledge and tools necessary to tune a computer controlled motor. Mostly I am trying to figure out if I can ever grasp enough understanding of the process to possibly learn how to do my own tuning someday.

In my case I have a Jeep with 350 (vortec heads) TBI conversion running headers and link suspension with several heim joints and I was originally told this would cause a lot of false knock issues if I ran a knock sensor, therefore it was recommended that it be deleted. I now realize it may have been good to have left it on if for nothing else to activate it just for tuning proposes (timing table).

Since I don’t I have a knock sensor I got to thinking would it be possible to use vacuum data to aid in the tuning of the timing table. Since in most cases the best timing develops the highest vacuum and when pre-detonation occurs it will lowering the vacuum, I felt this might be a good alternative to the knock sensor for tuning purposes.

My question, is it possible make a vacuum history table this may not be correct but for example something like this (map Vs. rpm Vs. TPS %) and use it to help fine tune timing? I was thinking after recording a data log, I could pull the vacuum history find the cells with high count numbers than adjust the timing in those areas until the highest vacuum can be achieved, than just smooth out the low count cells to blend with the fine-tuned high count cells.

I hope all of this made sense and I don't sound like a complete idiot.

Sounds feasible. Don't need vacuum though, you have MAP kpa which is manifold pressure/vacuum.

I've done several rigs like yours without false knock issues, then had to turn off knock sensor because of off roading. Rock crawling in paticular, hit a rock on frame and get knock counts, loose timing and engine stability at idle. Not a good thing when rock crawling.

False knock from noise is always a possibility, but usually not vibration, usually a bang. Some good examples were a Third Gen Camaro with a rear axle control arm bushing and a pick up truck with things banging in bed.

Some things to remember with knock sensors is knock sensor has to match ESC module which matches engine CID. Knock sensor is installed with a torque setting, to tight, false knock. Can make it a little less sensitive for header noise with about 6 wraps of teflon tape, can also put it in a brass elbow. If the sensor was ever over tightened it's shot and always over sensitive.

There's a point where to much timing does not help and is hard to notice without a dyno, will cause detonation without knock, causes piston heat and failed rod bearings. There's a slope to MBT and you want to be on the up side to top not going down. For a street rig off roader there's way to many varibles to try and get this accurate, fuel from station to station, tempreture, humidity. If you get MBT and back off 4-6 degrees you'll have a long lasting safe spark table.

If your going to push this hard always run highest octane...

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Originally Posted by EagleMark

Sounds feasible. Don't need vacuum though, you have MAP kpa which is manifold pressure/vacuum.

I've done several rigs like yours without false knock issues, then had to turn off knock sensor because of off roading. Rock crawling in paticular, hit a rock on frame and get knock counts, loose timing and engine stability at idle. Not a good thing when rock crawling.

False knock from noise is always a possibility, but usually not vibration, usually a bang. Some good examples were a Third Gen Camaro with a rear axle control arm bushing and a pick up truck with things banging in bed.

Some things to remember with knock sensors is knock sensor has to match ESC module which matches engine CID. Knock sensor is installed with a torque setting, to tight, false knock. Can make it a little less sensitive for header noise with about 6 wraps of teflon tape, can also put it in a brass elbow. If the sensor was ever over tightened it's shot and always over sensitive.

There's a point where to much timing does not help and is hard to notice without a dyno, will cause detonation without knock, causes piston heat and failed rod bearings. There's a slope to MBT and you want to be on the up side to top not going down. For a street rig off roader there's way to many varibles to try and get this accurate, fuel from station to station, tempreture, humidity. If you get MBT and back off 4-6 degrees you'll have a long lasting safe spark table.

If your going to push this hard always run highest octane...

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Thanks Mark,
I believe I was In the process of editing (rewording my question when you posted).

I am just curious if there is a way to use some of the data available to help develop a timing table without the aid of the knock sensor.

I do not hammer all that hard on this rig it is just an all-around trail rig that I need to be dependable. One weekend I might be in Clayton OK doing some pretty hard core rock crawling (for me hardcore) and every other year or so I might get to spend 2 weeks in Silverton CO for vacation where it will be drove almost every day hitting trails and highways.

I agree with you as for backing the timing off 4 to 6 deg for a safety margin I just need to find out were that limit is that I need to backing up from .

I thought Dave was doing a chip for you? He knows what Vortec head spark needs are, POOF your done. Then apply your techniques and learn to fine tune.

Quote:

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Originally Posted by EagleMark

I thought Dave was doing a chip for you? He knows what Vortec head spark needs are, POOF your done. Then apply your techniques and learn to fine tune.

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Your right, He is!

I am just trying to learn something, so that maybe I can fine tune or at least have a better understanding.

Your thinking good!

If you search around here you'll find a 1998 Vortec Spark Advance spreadsheet Dave made with all the numbers that can be interpolated into your spark table. Then learn to use the smooth tool. This thread goes over reasoning.
http://www.gearhead-efi.com/Fuel-Inj...4-7747-ve1-ve2