Interesting math work. I liked it. The one variable that may be missing, and I have NO idea how to calculate it, is the cam overlap. At low RPM, overlap affects cylinder pressure due to bleed off; a speed thing. At high RPM, the overlap gets the assistance of a ramming effect, so your pressure is now over the given 14.7. This is what my mind is telling me, but I've not gotten a full pot of coffee, and may be confused.
The overlap (as well as all other aspects of cam design) is baked into the VVE size and shape. So once the VVE is dialed in, overlap is irrelevant in terms of this math exercise.
Interesting, you point out the high part that is showing too much VE, which we can exceed 100% on a NA setup in rare occasions but 30% would be crazy. What gets me is the lower end is way too low, you are showing like 16% VE in an area that would normally be in the 40-50% range, so it is almost like the span is wrong. If it the total range from low to high was shrank a percentage to get the table from 114% span to 60% span I think the data would be a spot on representation of actual cylinder volumetric efficiency. Am I making sense? lol
Yes I get what you are saying and you are correct, I totally ignored the low spots! I think in the historical context VE% is only applicable at WOT and part throttle doesn't count, which is why my mind went there. In looking at my specific idle areas, the 'simple' chart shows 32% and the 'complex' one shows 37%. But here is where my mind went...this engine was rated at 415 crank hp from the factory, I think they normally chassis dyno'd at ~340 rwhp. A couple years ago mine dyno'd at 540 rwhp and that was BEFORE the better heads, more compression, better intake, larger TB...so I am 200+ rwhp now...****but on the same 376 cubic inches****.... 340 rwhp to 540 rwhp is a 58% increase (so perhaps 135% VE is not so far off)! I should probably throw the OEM VVE table on the spreadsheet to get a starting point, but that probably won't be too accurate for VVE in the WOT zones.
@@SilverSurfer77I think you're already onto this... but your built-engine-situation might be too different to apply normal "this is what I think VE should be" logic. Especially in the low load/rpm areas as it could be that your build/cammed engine has quite crap VE there, right? It would be great for you to redo this with a log and calibration from something completely stock. And perhaps something completely stock that has published VE numbers someplace as well to use as a check (if at all possible). Anyways, love the nerd-content and thank you for all that you do!
@@Scott02 the closest way to do this would be to find a motor that was physically the same and unchanged that was produced during both the Gen3 and Gen4 ECM era, and then you could compare GM's numbers for each. However, I don't think one exists since all Gen3's had cathedral port heads and Gen4 went to square ports. Otherwise I don't think there is a way to find published VE in percent values for a Gen4 motor. i guess another way would be if there was a standalone aftermarket ECU that uses VE% and we could compare to an identical build on a factory ECM...but that would be like finding a needle in a hay stack. Ultimately though, I am not concerned about VE at part throttle, WOT is the only VE% I am concerned with.
What is your stoich setting? Also, you can figure the engine is not 100% efficient at burning and using the energy of the fuel, so a amount of fuel is wasted. Compression, rings, chamber design, material, etc. play a factor in the amount of wasted fuel(heat).
So just looking and thinking about this? Wouldn't the computer be telling it self we could expect this amout of air, to calculate how much fuel should be used to get a close to stoich? Not that it is really that much air? Just a thought.
Yes exactly. As Kyle from Goat Rope says, "we don't tune fuel, we tune air", and once the ECM knows the air going in, it is a simple (stoich) ratio to determine the amount of fuel to spray.
This is exactly why I use the Dynamic Air channel (grams/sec) and multiply it by the fuel trim (%) to calculate the correct airflow into the engine. There is room for error, however, it eliminates a lot of other sources of error including user calibration of MAF and VVE, ECM modeling for ambient temperature, humidity, and pressure, injector characterization, as well as other sources of engine wear and vacuum leaks etc. This is also the method I use to tune the MAF and VVE itself (as demo'd here ua-cam.com/video/xRZaTblSQ_0/v-deo.htmlsi=hoWORg40lMFSHzC2).
@@davidwickboldt712 oh hahaha actually I never was into comics! SilverSurfer was just a name I used on the forums back in the day because all other user names were taken. So after the first forum, I decided to keep using it on the others so I didn't have to remember it (this was before browsers would remember your user/pass). The ball kept rolling into 2006 or whenever I created my youtube account....which I never thought I would start making videos. In hindsight I should have picked a different handle. Oh well!
No not at all. I am not sure if you are familiar with the rest of my work around tuning MAF and VVE using dynamic air calculations and the VVE Assistant tool I created...but rest assured I have spent a LONG time devising ways to properly tune my VVE. In fact, currently have my MAF failed and using speed density and the fueling is spot on at WOT. Keep in mind this engine is not stock and has a very healthy camshaft along with many other mods. However, disconnecting the MAF would also disconnect the IAT sensor which would not be good. No idea the impact of missing this input would have on the ECM's fueling algorithm.
Interesting math work. I liked it.
The one variable that may be missing, and I have NO idea how to calculate it, is the cam overlap. At low RPM, overlap affects cylinder pressure due to bleed off; a speed thing. At high RPM, the overlap gets the assistance of a ramming effect, so your pressure is now over the given 14.7.
This is what my mind is telling me, but I've not gotten a full pot of coffee, and may be confused.
The overlap (as well as all other aspects of cam design) is baked into the VVE size and shape. So once the VVE is dialed in, overlap is irrelevant in terms of this math exercise.
Interesting, you point out the high part that is showing too much VE, which we can exceed 100% on a NA setup in rare occasions but 30% would be crazy. What gets me is the lower end is way too low, you are showing like 16% VE in an area that would normally be in the 40-50% range, so it is almost like the span is wrong. If it the total range from low to high was shrank a percentage to get the table from 114% span to 60% span I think the data would be a spot on representation of actual cylinder volumetric efficiency. Am I making sense? lol
Yes I get what you are saying and you are correct, I totally ignored the low spots! I think in the historical context VE% is only applicable at WOT and part throttle doesn't count, which is why my mind went there. In looking at my specific idle areas, the 'simple' chart shows 32% and the 'complex' one shows 37%.
But here is where my mind went...this engine was rated at 415 crank hp from the factory, I think they normally chassis dyno'd at ~340 rwhp. A couple years ago mine dyno'd at 540 rwhp and that was BEFORE the better heads, more compression, better intake, larger TB...so I am 200+ rwhp now...****but on the same 376 cubic inches****....
340 rwhp to 540 rwhp is a 58% increase (so perhaps 135% VE is not so far off)! I should probably throw the OEM VVE table on the spreadsheet to get a starting point, but that probably won't be too accurate for VVE in the WOT zones.
@@SilverSurfer77I think you're already onto this... but your built-engine-situation might be too different to apply normal "this is what I think VE should be" logic. Especially in the low load/rpm areas as it could be that your build/cammed engine has quite crap VE there, right? It would be great for you to redo this with a log and calibration from something completely stock. And perhaps something completely stock that has published VE numbers someplace as well to use as a check (if at all possible). Anyways, love the nerd-content and thank you for all that you do!
@@Scott02 the closest way to do this would be to find a motor that was physically the same and unchanged that was produced during both the Gen3 and Gen4 ECM era, and then you could compare GM's numbers for each. However, I don't think one exists since all Gen3's had cathedral port heads and Gen4 went to square ports. Otherwise I don't think there is a way to find published VE in percent values for a Gen4 motor. i guess another way would be if there was a standalone aftermarket ECU that uses VE% and we could compare to an identical build on a factory ECM...but that would be like finding a needle in a hay stack.
Ultimately though, I am not concerned about VE at part throttle, WOT is the only VE% I am concerned with.
What is your stoich setting? Also, you can figure the engine is not 100% efficient at burning and using the energy of the fuel, so a amount of fuel is wasted. Compression, rings, chamber design, material, etc. play a factor in the amount of wasted fuel(heat).
Not to mention tune/wb error, wb placement, eoit vs cam vs intake and port efficiency.
Yes lots of factors and room for errors, thanks for pointing those items out.
So just looking and thinking about this? Wouldn't the computer be telling it self we could expect this amout of air, to calculate how much fuel should be used to get a close to stoich? Not that it is really that much air? Just a thought.
Yes exactly. As Kyle from Goat Rope says, "we don't tune fuel, we tune air", and once the ECM knows the air going in, it is a simple (stoich) ratio to determine the amount of fuel to spray.
The problem is, there is no standard to compare to. Maf, map, o2, injector data, none are exact. Maf may be reporting to much air in that area.
This is exactly why I use the Dynamic Air channel (grams/sec) and multiply it by the fuel trim (%) to calculate the correct airflow into the engine. There is room for error, however, it eliminates a lot of other sources of error including user calibration of MAF and VVE, ECM modeling for ambient temperature, humidity, and pressure, injector characterization, as well as other sources of engine wear and vacuum leaks etc. This is also the method I use to tune the MAF and VVE itself (as demo'd here ua-cam.com/video/xRZaTblSQ_0/v-deo.htmlsi=hoWORg40lMFSHzC2).
@@SilverSurfer77 Hey thanks, that will be useful. Are you using Norrin Radd's power cosmic in tunning or just chem engineering? 😁
@@davidwickboldt712 I have no idea what you just said, so I am going with "no" lol
@@SilverSurfer77
@@davidwickboldt712 oh hahaha actually I never was into comics! SilverSurfer was just a name I used on the forums back in the day because all other user names were taken. So after the first forum, I decided to keep using it on the others so I didn't have to remember it (this was before browsers would remember your user/pass). The ball kept rolling into 2006 or whenever I created my youtube account....which I never thought I would start making videos. In hindsight I should have picked a different handle. Oh well!
What happens if you run the same calculations on the 3rd gen? How does it compare to its own VE %.
So according to your calculations if you disconect the maf and go WOT it should go stupid rich
No not at all. I am not sure if you are familiar with the rest of my work around tuning MAF and VVE using dynamic air calculations and the VVE Assistant tool I created...but rest assured I have spent a LONG time devising ways to properly tune my VVE. In fact, currently have my MAF failed and using speed density and the fueling is spot on at WOT. Keep in mind this engine is not stock and has a very healthy camshaft along with many other mods.
However, disconnecting the MAF would also disconnect the IAT sensor which would not be good. No idea the impact of missing this input would have on the ECM's fueling algorithm.