Originally Posted by GMCVT

Guys, I'm just curious about something. 04 GTO with the cam shown in sig. I'm still tuning my trims and what not but today just for fun I logged a couple of WOT blasts just to look at the 02 v. I noticed that as I got around 6k and up the cell that the 02's were reporting in were dropping in KPa's. I went back and looked at the Dynamic Cylinder air PID and from 5212rpms it droppped from .73g/cyl to 63g/cyl at 6402. MAP readings go from 93 to 91 at those respected RPM's. Could this indicate a restriction in the induction or exhaust? This cam should make power till 6300-6500. I am running MAF'less right now. I still have the factory air tube and filter and was just wandering if maybe it was presenting a restriction. Or is this just a calibration issue with my PCM. I was thinking that if this cam generally makes power to 63-6500, then the measured amount of air should not be dropping right?? Help

Originally Posted by Silverhawk_02TA

I get the same thing with my setup. At WOT, when I hit 4800 RPM, the MAP values drop from the 85 kpa row into the 80 kpa row. My actual MAP values go from 86 kpa in the lower RPM's to 82 kpa close to the limiter. When I removed the MAF and stuck in a piece of straight pipe, the RPM at which the MAP dropped from the 85 kpa row into the 80 kpa row actually dropped to about 3600 RPM, with the actual MAP values going from 84 to 81 kpa near the limiter, which would seem to show that flow got worse. Go figure. I'm thinking that perhaps the MAP vs RPM drop is a little more complicated than simply the restrictiveness of the intake path. Perhaps as the air velocity increases, the MAP value drops? Maybe someone with more knowledge about airflow characteristics can shed some light on this.

Originally Posted by GMCVT

Glad to see I'm not just being stupid here. Good thought on the velocity. I would think though, that if the appratus that is carrying the air were large enought that the velcity of the incoming charge would no be able to create a vacuum. I'm sure I'm way out of my league so I'll shut up and let you guys explain this.

Originally Posted by Silverhawk_02TA

Well, the MAP value may be dropping as RPM's go up, but it's not creating a vacuum. We're still talking positive pressures here.

I went back to look at some old WOT logs, and here is what I found: at WOT, as the RPM's go up, MAP is steadily dropping. However, Dynamic Cylinder Air (and hence airflow overall) is steadily climbing. This shows that the amount of airflow is not directly proportional to MAP. We can see how this is possible if we look at the mass flow equation:

Mass flow = (VE * MAP * RPM * Displacement) / IAT

So, the MAP may be dropping, but the RPM is climbing. Displacement of course is not changing.

So, in your case GMCVT, not only is your MAP dropping, but also your Dynamic Cylinder Air. This may indeed be due to the restrictiveness of the stock intake path. However, keep in mind that the equation for mass flow (from which Dynamic Cylinder Air is derived) is also dependent on the VE table. If you have not tuned the WOT cells on your VE table, then you can take those Dynamic Cylinder Air values and throw them out the window right now. Have you tuned those WOT, high RPM VE cells?

Originally Posted by GMCVT

No, actually I have not. To be honest, I'm not sure I know how. I was under the impression that WOT tuning was done under the PE table. As you can see I'm still on a steep learning curve. I'm actually still tuning the Fuel Trims. I've noticed that when I go to WOT the values in the trim cells all go to 0. Not really sure how I'm going to tune that unless thos value come back with the MAF reconnected or I use a wideband. But no I have not and that is why I ask in my first post if this could be PCM calibration related since I know we have to change so many things when we introduce more air to the engine. Thank you for the help!

Originally Posted by Silverhawk_02TA

I describe the method I used in the VE tuning how-to I did that's in the big sticky in this forum. It's not actually WOT tuning per se, since I do it with PE disabled. All it is is tuning the VE table at high RPM's, including the WOT cells, using fuel trims just like the rest of the table. I disable PE because I don't want the PCM to go into PE mode and throw the trims off. Most people just tune thier VE tables up to 4000 RPM because they plan on using a MAF. Even some people that want to stay SD will only tune in the same area, and for WOT will just adjust the PE divisor until they get the AFR they're looking for. My goal was for my entire VE table to be correct, so that's the method I developed, and it worked very well for me. I won't go into detail here since it's in the sticky.

Your trims go to 0 at WOT because the PCM is going into PE mode.

Originally Posted by Silverhawk_02TA

I describe the method I used in the VE tuning how-to I did that's in the big sticky in this forum. It's not actually WOT tuning per se, since I do it with PE disabled. All it is is tuning the VE table at high RPM's, including the WOT cells, using fuel trims just like the rest of the table. I disable PE because I don't want the PCM to go into PE mode and throw the trims off. Most people just tune thier VE tables up to 4000 RPM because they plan on using a MAF. Even some people that want to stay SD will only tune in the same area, and for WOT will just adjust the PE divisor until they get the AFR they're looking for. My goal was for my entire VE table to be correct, so that's the method I developed, and it worked very well for me. I won't go into detail here since it's in the sticky.

Your trims go to 0 at WOT because the PCM is going into PE mode.

Originally Posted by Bink

ummm......

At constant throttle (constant orifice) as the RPMs increase there is an increased airflow through the throttle/orifice and a vacuum does develope - relative to atmospheric pressure. So, if atm is ~ 101.4 kPa then it will drop towards 20 kPa.

Volumetric Efficiency tables drop after Peak Torque, typically (NA). Actually it's the VE creating that Torque. HP continues upward due to increasing RPMs.

Here's an excellent overview (from an aviation author ...highly applicable tho) of the internal combustion engine and performance ->>

http://www.eaa1000.av.org/technicl/engemp/engemp1.htm

Hope this helps some.

Originally Posted by Silverhawk_02TA

You are misunderstanding me. While the engine is running, the pressure inside the intake manifold will always be less than atmospheric (unless running FI). In this sense, the air accelerating through the throttle body results in a vacuum effect. However, the pressure inside the intake is still positive, so it's not a true vacuum. This is the point I was trying to make.



The only reason I disable PE is so I can tune the cells in the VE table close to and including WOT using fuel trims. If I didn't do this, PE mode would kick in when I hit those cells and skew my fuel trims. Once I finished that, I re-enabled PE mode. After using this method to tune my WOT VE values, I can command a solid AFR in the PE table, and all my O2 readings are within .005 mv of eachother during a logged WOT run, which shows that my VE values are dead on.



VE is representative of the TQ curve, but not necessarily DCA. As Bink said, VE tends to be max where the TQ peak is, and fall off after that. My max VE is 101 at 5200 RPM (my TQ peak) and drops off to 97 at 6200 RPM, where my rev limiter is set at. After my TQ peak, both my VE and MAP are falling, but my DCA is still going up. Looking at the mass flow equation, VE and RPM are their raw values, and MAP is in bars. As such, the mass flow output of the equation is most heavily affected by RPM, since both VE and MAP are much smaller numbers. Hence, as long as RPM is rising, only VE and/or MAP falling off considerably should cause a decrease in DCA. My DCA at 5200 RPM is .68 g/cyl, while at 6200 RPM it's at .70 g/cyl, despite my VE dropping from 101 to 97, and my MAP dropping from 83 to 81 kpa. If I logged up past 6200 RPM, my VE and MAP would probably fall to the point that my DCA would start dropping before I hit 7000 RPM.

Also, keep in mind that DCA is a calculated and not measured value, so it's only as good as the data going in. If your VE values are incorrect, your DCA values don't mean squat. It being a calculated and not measured value also means that it cannot be used in and of itself to show the efficiency of the intake/exhaust regardless. It's the VE table which does this.

Originally Posted by gtodoug

I believe (like Bink said earlier) the dyn cyl air is representative of your tq curve. It doens't follow it exactly but is pretty darn close from my scanned dyno runs vs. dyno charts. Dyn cly air is the highest at .84 for me @5625rpms. I was under the impression that it's natural to fall off at or slightly after tq peak and should not be viewed as some sort of cork in the intake/exhaust system.

Originally Posted by GMCVT

O.K. That makes sense, thank you for the explanation. Cat3 was asking how you disable PE. I assume you change the 15 value to like 110 or 115 in the PE tab, is that correct?