Blown Interceptor

iTrader: (5)

Still getting some bucking, I was hoping to raise my base spark tables in drive and park by 2 degrees accross the board. I just recently retuned my VE table, if I make the changes, will I have to redo the VE, or will I be ok?

Thanks,
Jason

ringram

Why not use bidirectional controls to adjust timing and fueling to make sure you are going in the right direction. Once you have it sorted write the changes.

High Octane spark changes can alter AFR yes. Base spark table changes should have a lesser effect.

macsperformance

iTrader: (2)

Jason your VE (Volumetric Efficiency) table is what is more commonly referred to as a base fuel table. Once the VE table is set correctly it will not have to be touched again until more modifications to the car have been made. This is the ECU's reference point in which to look at assuming a certain amount of air is in the cylinders at a given break point. Your spark timing is a different table all together and does not correlate in any way to the VE table.

Now if your A/F changes like if you make changes to an AE table or a target table it would necessitate readjustment of the spark table due to the A/F's being different. You would want to do this to optimize the map for the change in flame front travel speeds due to different A/F mixtures.



Chris Macellaro

ninobrn99

iTrader: (8)

the best way to determine if you need to make changes to the ve is log now and then log after you change the base spark and see if there is a big difference in your trims where you changed it. Besides, using that excel sheet i sent you should help out. stop being lazy :jk:

ringram

Hey I tweak my ve almost daily. 99% is not 100%.
Also messing with all the other tables causes minor changes.. Thats part of the fun.

Some say if your VE is within 10% of good, you are finished, return to closed loop and go to bed. As ninobrn99 says, thats just lazy.

Zeus

Plus or minus 10% for you BEN value is def OK, but if they're really talking about the VE table WOW. Ten percent is an enormous amount of error. I guess going back to closed loop with the MAF and O2 sensors it wouldn't be so bad, but I'm one of the perfectionists that would really be bothered if my tune was like that.

Black02SS

iTrader: (36)

From my experience if you change the timing table after you adjust the VE table, it can have an effect on the final AFR. Just from what I have seen.

ringram

Thats what I have found too Black02SS

A point to note is if your timing is too far out of whack and retarded you can be too late to burn everything and will run lean as unburnt air is going out the exhaust which make things look lean, whereas it might just be timing that sucks. Plus you will be dumping fuel as well.

So its best to get timing right first I think, then mess with fueling (& repeat till working nice)

Black02SS

iTrader: (36)

I couldn't agree more.

macsperformance

iTrader: (2)

Hello Black 02SS... yes this is possible when speaking of a piggyback or any software that allows you to manipulate MAF transfer function or scaling of signals. This is because when you adjust this above mentioned scaling the A/F and the timing change in an inverse proportion. An example would be when adjusted the A/F would lean out while the ignition advance would increase or while the A/F would richen the ignition advance would decrease.


But if we are talking about actual Volumetric Efficiency this is the amount of theoretical air that is in the cylinders at a given time. This table unless misadjusted to a point that the ECU can not correct for that great of a difference does not have anything to do with actual fueling or the target you are looking for. A VE table is used in the ECU's calculation (the number in that cell) is used to tell how much air is in the engine so the ecu can command the proper pulse width to try to achieve the proper A/F you have set in the target tables. This is why you have target tables to shoot for this is why in my first post I stated that once set you will not have to change the VE table. You can adjust the Target tables, AE, and MAF transfer to change the A/F's if desired. If you are getting large changes by adjusting the ve and you are not at your target A/F the ve table is to far out for ECU compensation.



Chris Macellaro

macsperformance

iTrader: (2)

Hello friend...

I could not agree more with the first part of your post. In most of my dyno and engine testing I have found late timing to do a couple things. The first being that late ignition timing obviously will increase EGT's due to the fact that your mixture is still burning out of the exhaust port like you stated above. On a side note in my findings the mixture will be completely burnt by the time the gas reaches the O2 sensor in all but the most extreme cases like 6500rpm and 2 degrees of total timing as an example. If the cylinder(s) experienced a misfire (fuel or spark) this would be the only way that the O2 would perceive a lean condition in what you are talking about. Think about the situation like this.

Your timing event starts to late past the point of peak cylinder pressure the mixture starts to burn and the Exhaust valve opens up directly after that. Well the mixture is still burning but the gases as they are being burned are traveling past the exhaust valve and into the exhaust port then into the exhaust. Like I said unless this is an extreme case the mixture will be burnt before it reaches the O2 sensor.



Chris Macellaro

ringram

Sounds good Chris.

Bottom line, sort your timing out first

oange ss

iTrader: (50)

so what 's the best way to attack timing, if it can even be done without a dyno

macsperformance

iTrader: (2)

A lot of people use logged data, track times, and just seat of the pants feel. But yes you are correct without quantifiable back to back controlled results from a dyno it would be hard to get the entire timing map optimal.




Chris Macellaro

TXNC5

I agree completely. I highly recommend a dyno like Dyno Dynamics or Dynapack for this type of testing. On any non-real time ECU (like the LS1), timing is a real bugger to get right. With a real time system and a good load dyno, it is not too difficult to work your way through the timing map. Timing curves are very interesting, and most people don't realize how close they are to knock utilizing the standard internet methodology. Why add any more timing if the additional timing doesn't make anymore power? This is very hard to tell on the street though.

I would also caution people reading this that are new to tuning. I would not recommend doing timing first. I would always recommend validating fuel first. Being 'lean' can be a very unforgiving situation, and often you will find that being lean once is one time too many. AFR is critical for thermal management.

I agree with Chris on what he has posted. It is funny how we talk about AFR. Even if the timing was very late and combustion was still occurring in the exhaust stream, did not the engine ingest the same amount of air and inject the same amount of fuel had timing been optimal? I have found very little affect on AFR based on 'reasonable' timing values, and much of the discrepancies can probably be attributed to all sorts of factors like the quality of the equipment (i.e. a $400 AFR meter vs a $5000 one). Also, remember that there is much more power to be found in timing modifications as compared to modifications to AFR. I see people always worried about running a few points richer (e.g. 12.7:1 instead of 12.9:1). I don't believe 1) that most people are using equipment that is this precise, and 2) that much power would be realized anyway. However, the difference between 22* and 24* degrees of timing can be sizable, and the difference between 28* and 30* can be detrimental if people don't know what they are doing.

I posted this in the Advanced forum a while back:
AFR is critical for thermal management, but not as important as people think in regards to HP output. Certainly, motors today are much more efficient and realize gains/losses from changes in AFR, but optimal timing will provide much bigger returns.

macsperformance

iTrader: (2)

TXNC5...

Me and you sir must have been on the same ship at one time or another lol. I could not agree with you more, well written and very informative. I am glad to see so many properly informed people on this forum. Great reading and I hope to share more with you and the other members of this forum in the future.






Chris Macellaro

MeentSS02

iTrader: (11)

So without a dyno (since many of us mess with tuning a lot, and don't have the money to do as many dynos as we do tunes), are you just looking to stay out of KR? I messed with my fuel first, as it was pretty far out of whack. I then tried adding some timing, but kept getting 1-2* of KR, so I backed it off. My car does not seem to like much timing at all (like 22-24 degrees max towards the end of a WOT run).

MeentSS02

iTrader: (11)

Oh, and would anyone like to post some pics of their current timing tables (3D view)? Chad?

ringram

efilive has a bidirectional timing control which allows realtime changes to be made (but not flashed until later)

Good info guys. I went quite a bit leaner from timing changes when my recorded afr read stoich. So I have experienced some actual variances from timing.

Timing definately makes all the difference compared to fueling for power.

Sounds like I need more time on the dyno. I look forward to more discussions going forward.