increased vacuum with increased ig timing

[In-Tech]

Oy,
Whatever happened to giving an engine what it wants? What did you do before a wideband? What did you do before a vacuum gauge? You turned the screws on your carb till it was happy, and then figured out why it wasn't happy in gear and changed air bleeds cuz you spent the time to figure out what the engine wanted, not what you thought.

Every instrument in the world CAN lie to you if you don't understand what is happening around it. Plenty of times a large cam with alot of overlap can fool plenty of "tuners". Again, give it what it wants and forget the numbers. Stoich isn't Stoich many many times just because the sensor says so.

When I dyno tune, which is easily 3-4 days a week, I couldn't care less what the number is as long as I can make it bigger. I'm not just talking peak either. A good tune is tuning it for all conditions and of course takes time which is money.

Bottom line to the OP question, if you increase the efficiency you generally make more vacuum. Other conditions arise such as NOX emissions with increased timing which I assume is not part of this equation.

The bag test for CARB is tough and I have taken plenty of "off the showroom floor" brand new cars that wouldn't pass as stock, added a supercharger and bigger injectors and all the things to go with it and made it happen. It is not easy.

Carry on and Happy New Year Everyone.

[user-23911]

All instruments tell lies if they're not calibrated.

As far as giving it what it wants?
That doesn't work in a dyno test cell where you've got certain emission specs which have to be met.


So i that case you calibrate all the instruments, mass air flow, mass fuel flow, torque,5 gas exhaust emissions analyser, efficiency derived from torque and mass flow,efficiency derived from 5 gas, a WB that always reads different.

Not a job for a parts changer.


Back in the old days engines were always inefficient and dirty, getting a good tune was more by luck that anything else and drivability was always bad.

My first tuning tool was a "gunsons colourtune".....well actually I made a point of reading as many DV books as I could find first.
My next tuning tool was a vacuum gauge.
My third tuning tool was to replace the vacuum gauge with a VDO boost / vacuum gauge.
When you move forwards to electronic tools you expect them to work correctly but they rarely do.


How many vacuum gauges do you see where the needle doesn't sit on zero when it's "off"?
My 35 year old VDO does.
I've got 2 others which don't.
That's mechanical instruments, not even electronic.
If you've got an electronic vac gauge it probably uses a MAP sensor which references to vac so doesn't compensate for altitude. OK for sea level but if you're at 4000 feet it's going to read something else.


The result of that is different people talking different numbers for the same thing.

[In-Tech]

Hi Joe,

All instruments tell lies if they're not calibrated.
Calibrated by whom and what was the standard, pretty funny right?

As far as giving it what it wants?
That doesn't work in a dyno test cell where you've got certain emission specs which have to be met.
Everything can be made to work but everything doesn't work everywhere, hence closed loop

So i that case you calibrate all the instruments, mass air flow, mass fuel flow, torque,5 gas exhaust emissions analyser, efficiency derived from torque and mass flow,efficiency derived from 5 gas, a WB that always reads different.

Not a job for a parts changer.
Correct, I generally don't get my hands dirty.


Back in the old days engines were always inefficient and dirty, getting a good tune was more by luck that anything else and driveability was always bad.
I bet you didn't put up with that very long, lol. I sure didn't. Back in the 80's my 454 4300lb 3.42 geared Camino with a solid roller and the early round ex port L88 heads got 17mpg on the freeway and still run the quarter at near 130, et sucked cuz of traction, still got an 11.86 on the old N50/15's (remember those? )

My first tuning tool was a "gunsons colourtune".....well actually I made a point of reading as many DV books as I could find first.
My next tuning tool was a vacuum gauge.
My third tuning tool was to replace the vacuum gauge with a VDO boost / vacuum gauge.
When you move forwards to electronic tools you expect them to work correctly but they rarely do.
Man, I wish more people realized that.


How many vacuum gauges do you see where the needle doesn't sit on zero when it's "off"?
My 35 year old VDO does.
I've got 2 others which don't.
That's mechanical instruments, not even electronic.
If you've got an electronic vac gauge it probably uses a MAP sensor which references to vac so doesn't compensate for altitude. OK for sea level but if you're at 4000 feet it's going to read something else.


The result of that is different people talking different numbers for the same thing.
Numbers are comparisons and only if they are yours.

[In-Tech]

HeHaw, I definitely enjoyed those days when I didn't know shyte and today the more I learn the less I know.

[Belgian1979]

Oy,
Whatever happened to giving an engine what it wants? What did you do before a wideband? What did you do before a vacuum gauge? You turned the screws on your carb till it was happy, and then figured out why it wasn't happy in gear and changed air bleeds cuz you spent the time to figure out what the engine wanted, not what you thought.

Every instrument in the world CAN lie to you if you don't understand what is happening around it. Plenty of times a large cam with alot of overlap can fool plenty of "tuners". Again, give it what it wants and forget the numbers. Stoich isn't Stoich many many times just because the sensor says so.

When I dyno tune, which is easily 3-4 days a week, I couldn't care less what the number is as long as I can make it bigger. I'm not just talking peak either. A good tune is tuning it for all conditions and of course takes time which is money.

Bottom line to the OP question, if you increase the efficiency you generally make more vacuum. Other conditions arise such as NOX emissions with increased timing which I assume is not part of this equation.

The bag test for CARB is tough and I have taken plenty of "off the showroom floor" brand new cars that wouldn't pass as stock, added a supercharger and bigger injectors and all the things to go with it and made it happen. It is not easy.

Carry on and Happy New Year Everyone.

couple of questions :
- how do you know what an engine wants when it runs under several conditions quite well on a certain tune. Is that with 20°, 24° or 33° of timing at idle for instance.
- if you talk about efficiency increase, I assume you talk about increased burn efficiency. How does that effect vacuum then ?
- Let's assume that the O2's are lying to me, and it shows lean. Why then would it become richer with less ignition timing ?

[naukkis79]

- Let's assume that the O2's are lying to me, and it shows lean. Why then would it become richer with less ignition timing ?

O2 don't know if mixture is lean or rich. It's measured free oxygen on exhaust gases. With less ignition timing, which also means less intake vacuum burn is more complete so there's less free oxygen in exhaust gases which makes lambda signal to rise, even if mixture ratio stays exactly same.

[Belgian1979]

- Let's assume that the O2's are lying to me, and it shows lean. Why then would it become richer with less ignition timing ?

O2 don't know if mixture is lean or rich. It's measured free oxygen on exhaust gases. With less ignition timing, which also means less intake vacuum burn is more complete so there's less free oxygen in exhaust gases which makes lambda signal to rise, even if mixture ratio stays exactly same.

I understand the free oxygen but : I thought that time for a complete burn is reduced with less ignition timing...especially with a diluted mixture at idle from cam overlap

[In-Tech]

couple of questions :
- how do you know what an engine wants when it runs under several conditions quite well on a certain tune. Is that with 20°, 24° or 33° of timing at idle for instance.
- if you talk about efficiency increase, I assume you talk about increased burn efficiency. How does that effect vacuum then ?
- Let's assume that the O2's are lying to me, and it shows lean. Why then would it become richer with less ignition timing ?

One thing to try with EFI is to watch the IAC counts, if you make a change to the tune at idle and the IAC counts go up, it is less happy. If they go down, you are making it happy. Forget what the o2 is telling you. There isn't ONE timing number or o2 number that works on all situations, every combination is unique, especially at idle where the engine is least "happy".

The engine doesn't go lean with less timing, what's happened is your vacuum is less and now you are deeper into the map(higher KPA number) where you have more fuel in YOUR tune.

The overlap cycle can create quite a few "lies" at WOT in your observations due to over scavenging or under scavenging, carb or EFI, many times lying to you about VE too when on an engine dyno that has the fuel flow and laminar air flow being measured.

[naukkis79]

I understand the free oxygen but : I thought that time for a complete burn is reduced with less ignition timing...especially with a diluted mixture at idle from cam overlap

As there's not much clean air and lot's of exhaust gas big parts of fuel won't burn as they are mixed with too much exhaust gas. HC emissions will usually shoot up when increasing idle advance, so stock configurations have usually much less idle timing than ideal for max vacuum.

[Ed Wright]

MAP is Manifold Absolute Pressure, Manifold vacuum referenced to Baro. Therefore does correct for barometer/altitude.
So many guys I race, also running EFI cars, run them in "AlphaN" mode, which is pretty much throttle angle vs RPM. They have, for instance, a 1000' DA tune, a 2000' DA tune, etc. they have to load a different calibration in their ECU for different conditions, or Density Altitudes.

I run mine in Speed Density Mode, so it corrects for different air. I data log a run each day to verify everything is correct. While developing the tuning, I just correct each cel in the V.E. table it is using. 500 RPM incrementals one way, 3KPA increments the other. Different elevation tracks around here, it runs off different rows as per the Baro there. It also corrects for MAT.
Never had to make any corrections last season. Corrects itself. Some guys run theirs in Closed Loop @ WOT, but I found the corrections too slow in 1st gear. I just run in Open Loop.
MAP does a pretty good job of correcting for altitude changes.

[Belgian1979]

MAP is Manifold Absolute Pressure, Manifold vacuum referenced to Baro. Therefore does correct for barometer/altitude.
So many guys I race, also running EFI cars, run them in "AlphaN" mode, which is pretty much throttle angle vs RPM. They have, for instance, a 1000' DA tune, a 2000' DA tune, etc. they have to load a different calibration in their ECU for different conditions, or Density Altitudes.

I run mine in Speed Density Mode, so it corrects for different air. I data log a run each day to verify everything is correct. While developing the tuning, I just correct each cel in the V.E. table it is using. 500 RPM incrementals one way, 3KPA increments the other. Different elevation tracks around here, it runs off different rows as per the Baro there. It also corrects for MAT.
Never had to make any corrections last season. Corrects itself. Some guys run theirs in Closed Loop @ WOT, but I found the corrections too slow in 1st gear. I just run in Open Loop.
MAP does a pretty good job of correcting for altitude changes.

Mine runs in ITB mode, which is a mix of both map and AN. Lower throttle openings is more map, higher throttle angles is more AN. This corrects for the lack of resolution at lower rpm when in AN and for the same lack of resolution at higher TP where map is virtually useless.
We have an extra curve that lets you correct additionally (extra on top of the normal baro density correction) for altitude changes to account for the differences some setups seem to have (due to among others different intakes and exhaust combinations which also has an effect on the influence of baro). This last one seems to be a bit of a hit and miss type of deal with a lot of testing required. Luckily where I level I'm maximum 50 m above sea level and the highest point is +- 600 m above sea level. So I just left it alone.

[Belgian1979]

couple of questions :
- how do you know what an engine wants when it runs under several conditions quite well on a certain tune. Is that with 20°, 24° or 33° of timing at idle for instance.
- if you talk about efficiency increase, I assume you talk about increased burn efficiency. How does that effect vacuum then ?
- Let's assume that the O2's are lying to me, and it shows lean. Why then would it become richer with less ignition timing ?

One thing to try with EFI is to watch the IAC counts, if you make a change to the tune at idle and the IAC counts go up, it is less happy. If they go down, you are making it happy. Forget what the o2 is telling you. There isn't ONE timing number or o2 number that works on all situations, every combination is unique, especially at idle where the engine is least "happy".

The engine doesn't go lean with less timing, what's happened is your vacuum is less and now you are deeper into the map(higher KPA number) where you have more fuel in YOUR tune.

The overlap cycle can create quite a few "lies" at WOT in your observations due to over scavenging or under scavenging, carb or EFI, many times lying to you about VE too when on an engine dyno that has the fuel flow and laminar air flow being measured.

I agree to the approach you suggested, however it seems to keep going down in IAC counts all the way up to 36° of timing which is what I would consider a locked timing (as per old hei setup). Not sure if that's right as I notice it running 'heavy'.
"Happy running" is quite relative as a tuning method of course.

I think I'm going to set idle a bit higher, 1200 rpm as opposed to my usually setting of 1100 as this seems to give the best amount of idle vacuum and smooth running so far. At that point I'm using around 26-27° of advance.

BTW : As I run individual widebands in each cyl, I can see quite well when it's lean misfiring, which is evident by violent swings in the wideband reading.

[Ed Wright]

If it likes that much timing (36 deg) at idle, you could very well be (probably are) too rich. With race cams (lots of overlap) don't believe your wide bands at idle. Mine thinks it is idling over 15-1.
My 350" LT1 has a 280-284 ".050" cam, stock compression, it likes 26 degrees @ idle (1200).

[naukkis79]

BTW : As I run individual widebands in each cyl, I can see quite well when it's lean misfiring, which is evident by violent swings in the wideband reading.

There's not violent swing in lambda when lean misfiring as it's very lean all time.

[Belgian1979]

BTW : As I run individual widebands in each cyl, I can see quite well when it's lean misfiring, which is evident by violent swings in the wideband reading.

There's not violent swing in lambda when lean misfiring as it's very lean all time.

On a single or maybe a double WB this might be correct.

If it was something else, it would be very strange that increasing fuel cured the problem on that specific cyl.