Converted LT1 with DBW Monoblade Throttle Tuning

[Fast9C1]

This weekend, I finally got my EFI Connection 24x conversion running and am having a ball getting it sorted. One of the issues that I think is probably pretty unique is the fact that I am running a 2003 Corvette calibration with the associated TAC module, pedal and throttle servo on a monoblade throttlebody. Looks like this:


The MAF and idle tuning are coming along nicely, but the thing I don't understand is how to go about making this thing sane in the street. As you can imagine, the area profile is vastly different than the round hole throttlebodies pretty much everyone with a Gen3 PCM is using. The throttle is WAY jumpy just by touching the pedal. To the point where trying to drive around in parking lots is practically impossible without a lot of clutch work. Out on the road, where the throttle is more open, it is not bad at all.

I have been trying to read ahead and figure out what I need to change, but my head is spinning. Do I just start fudging the left side of the Desired Pedal Area table(s) against the very stern warning about rendering the PCM permanently inoperable? That sure seems like the logical place to start trying to tame this thing down.

EDIT: the one thing I forgot to post originally was that with the stockish 2003 Z06 calibration, it immediately threw the dreaded P1514 DTC any time I got the throttle over about 10% and it would shut down the whole system and stall. Doubling that entire table seemed to help :-)

[Fast9C1]

Alright, I mucked around for a few days, knocking the lower regions of the Pedal Desired Area tables down 2-3% at a time until it started acting less like a switch and a lot more like a progressive pedal It's actually not bad at the moment, but it's possible that I am still sort of compensating for it when I drive it. My Tahoe and LeSabre both feel really soggy right off idle

Anyways, now I am at that point of the learning curve where I have no idea how to solve a couple of issues. Attached are 3 logs from today using the TPS_Air.cfg from http://www.hptuners.com/forum/showpo...1&postcount=12:

• cold_start_01.hpl is what the name implies, a cold start...of course cold is relative, since it's well into the 80's (IAT registered 90 when I turned the key on)
• warm_start_01.hpl is pretty much turning the key off, waiting like 10 seconds and starting it back up
• drive_cycle_01.hpl is just a run around the block to show how it doesn't idle down until after a couple seconds of being stopped completely. When I first take off, it is a lot less likely to do this. As I drive longer, it is guaranteed. In fact, a couple times out recently, it will free rev well over 3k until after a stop...then it has all it can do to stay running. I get a lot of sideways glances at the stoplights
• Open_Loop_VE_Tuning-RTT.hpt is of course the current tune. It's not completely open loop at the moment, but does have the MAF disabled while I knock down the VE table. I also turned the long term trims back on trying to get the histograms to work properly.

Complicating my job is the fact that this is my first real tuning exercise with HP Tuners, my first ever DBW experience, a brand new setup (wired the 24x conversion from scratch) and I don't know of anyone that has a reference system to work from.

After spending the last few days trying to internalize idle tuning, I think I need to make some serious adjustments to the ETC Area Scalar but I have no idea which direction to even start heading. I can try to do some open area calculations in SciLab if need be (comparing round bore to oval per TPS).

I notice that my dynamic airflow is almost always double the Idle Desired Airflow, which I assume is another place to take a big swipe at my issues. Is it really as simple as just jacking the Base Running Airflow to meet those numbers?

[Wnts2Go10O]

u are a braver man than i..lol. on the cold start. ur tps is 3%, is there any way to lessen that so ur not getting as much air at idle?

[Fast9C1]

With DBW, you don't exactly control the TPS directly. It is a result of the PCM having commanded the servo to have the throttle blade that far open. There is no IAC, so all of the air needs to go through the throttle blade. The only time I have seen the TPS lower than that is during those wild rpm swings where the system is out of control. I have actually heard the blade snap shut a couple of times...then the TPS goes to zero

[Wnts2Go10O]

With DBW, you don't exactly control the TPS directly. It is a result of the PCM having commanded the servo to have the throttle blade that far open. There is no IAC, so all of the air needs to go through the throttle blade. The only time I have seen the TPS lower than that is during those wild rpm swings where the system is out of control. I have actually heard the blade snap shut a couple of times...then the TPS goes to zero

hmm. any luck on the idle so far?

[Fast9C1]

Actually, yes. Apparently, I was using the wrong .cfg file above and, after searching around, found the real Idle-Airflow.cfg and did the cold start with that. It pushed my Base Running Airflow table down quite a bit (like well over 20% in places) in the 32ºC and above cells. My cold start idle still hunts around and needs a lot of work, but at least the runaway hot idle issue is gone. Thanks Russ, that was too simple.

I still have quite a lot of work to do with cold start and smoothing out the idle, but the car is quite driveable and I am very happy. I just went on 4 of my driving loops, dialing in the MAF and adding a little timing here and there. Right now, if I am just rolling along at 1500 rpms, I can slam the pedal to the floor and it doesn't hesitate or buck at all. If I am in first gear, it's just a lot of

Throttle is still kind of touchy off idle and I still need to understand that ETC Area Scalar number since I haven't touched it yet. Do I just multiply by the percentage difference in open area between the monoblade and a stock LS1/LS6 throttlebody? I think it's 85mm (that is a plea for verification).

[Fast9C1]

Feel like I am talking to myself here. Hope I give myself the right answers.

Based on a quick test, a bit of reading, some calculations and the TBresizing spreadsheet from 69lt1bird's site, it appears that everything here is wrong:

Throttle is still kind of touchy off idle and I still need to understand that ETC Area Scalar number since I haven't touched it yet. Do I just multiply by the percentage difference in open area between the monoblade and a stock LS1/LS6 throttlebody? I think it's 85mm (that is a plea for verification).

The result of that test was not pretty. Very easy to hang the idle, one restart resulted in 5000 rpm free rev, etc.

I would have bet money that the exposed area profile looked different for the monoblade than for a single round bore, but it turns out after spending WAY too much time calculating it, that they expose area at EXACTLY the same rate Good for calculations, though.

69lt1bird's spreadsheet shows the calculation as 100/total_area. The value that is in my base calibration was 0.0255 and it appears that the 2003 Corvette has a 73mm throttlebody. The math doesn't come out exact, so I did a little backing out of the throttle shaft area until I came up with the same number. The shaft at 3.6mm makes that happen. I don't have access to one to measure, but it seems an unlikely number. Maybe the 73mm bore is slightly smaller than 73mm.

If all THAT is true, then using the ACTUAL fully open area of the monoblade (bore minus area of 10mm shaft), I get 100/4942 which is 0.02023 and 26% more area. No effing wonder my driveability is all wacky. Looks like the neighbors are in for one more dose of desired area tuning in the morning. Good thing they all seem to like me.

[Wnts2Go10O]

Actually, yes. Apparently, I was using the wrong .cfg file above and, after searching around, found the real Idle-Airflow.cfg and did the cold start with that. It pushed my Base Running Airflow table down quite a bit (like well over 20% in places) in the 32ºC and above cells. My cold start idle still hunts around and needs a lot of work, but at least the runaway hot idle issue is gone. Thanks Russ, that was too simple.

I still have quite a lot of work to do with cold start and smoothing out the idle, but the car is quite driveable and I am very happy. I just went on 4 of my driving loops, dialing in the MAF and adding a little timing here and there. Right now, if I am just rolling along at 1500 rpms, I can slam the pedal to the floor and it doesn't hesitate or buck at all. If I am in first gear, it's just a lot of

Throttle is still kind of touchy off idle and I still need to understand that ETC Area Scalar number since I haven't touched it yet. Do I just multiply by the percentage difference in open area between the monoblade and a stock LS1/LS6 throttlebody? I think it's 85mm (that is a plea for verification).

sound engineer has an xls file for the scalar. pm him for it or search around. plug in size of tb and it spits out the new scalar number. that number should, i believe, go down with the increase in size of the tb, not up.

[WS6FirebirdTA00]

Yes, but that TB is not your typical size. No need to guess at the scalar value when you can log values and properly adjust for it.

[Fast9C1]

sound engineer has an xls file for the scalar. pm him for it or search around. plug in size of tb and it spits out the new scalar number. that number should, i believe, go down with the increase in size of the tb, not up.

I think I saw that one, but it only scales up based on a percentage difference between new and old. Until I understood what the number meant last night and how my monoblade is really just an 82mm roundbore, I had no idea what to do with it This is the one that gave me more useful info:
http://ls1tuningguide.com/files/free...TBresizing.xls

Yes, but that TB is not your typical size. No need to guess at the scalar value when you can log values and properly adjust for it.

Yes, but aren't we attempting to give the PCM good info through the tuning effort? If you threw an 82mm throttlebody on an otherwise stock Corvette, would you change the scalar or just fiddle with the rest of the airflow tables to compensate. It seems to me that it's a pretty critical piece of information for the PCM to have. Now that I understand what it means, it's not hard. Before last night, I was searching for answers about a badly misbehaving car that basically just needed the correct number there (and a couple of other tweaks).

[WS6FirebirdTA00]

Yes, that is why you tune the scalar value/effective area I said nothing about correcting for it with improper tables.

Idle desired airflow must equal actual airflow. If they do not, your scalar/effective area table is incorrect. The scalar is used to turn an IAC step to a TPS%, IIRC. Once you get a constant offset between the desired and actual airflow, the scalar will help bring it in line. On just about all ETC cars I have messed with the only thing needing adjustment is the scalar.

[Fast9C1]

Ah, sorry, I misunderstood what you were saying above. You meant to back into the scalar through logging as opposed to calculating it. No problem

[Japeatr]

your photo looks like your missing a intake manifold bolt

[WS6FirebirdTA00]

Yeah, doing it that way will help even more. It is easy enough to make a change, log it and then try again for the scalar itself.

[Fast9C1]

your photo looks like your missing a intake manifold bolt

It is, good eye That picture was taken during a mockup of the new stroker engine (which is currently back apart getting a new cam and some head work). The current reality is pretty horrible, but works like a charm:

Yeah, doing it that way will help even more. It is easy enough to make a change, log it and then try again for the scalar itself.

I have it nailed now. I popped the 0.0202 in and re-scanned with Russ's Idle-Air.cfg to reset the desired air and it behaves exactly like it should. Idles down while coasting to a stop, starts up quickly (when hot) and idles smoothly right away and the throttle pedal has a much more smooth/linear relationship to the off-idle area. It's still more touchy than when it was a cable driven throttle with an LT1 PCM, but I am just going to call those the lazy days

Thanks for your help.

[WS6FirebirdTA00]

Cool, glad to hear.

[patooyee]

Just trying to learn for myself here, but what does EFIConnection have to say about it? I've been reading the Banish books and he has a large section about IAC's and why GM uses them and a lot of the reasons seem to be exactly what you are describing. (Incidentally, I've since found out that Banish still actually works for GM so he probably has some pretty good insight into it.)

In addition, I'm not sure what the actual area of that oblong opening is but it looks to be less than what the opening of the round ones on the newer engines for which DBW was designed. If that is the case you would expect that it would actually be less touchy than a round TB given the same anglular opening. I could be (and probably am) wrong but to me what you are describing is just a symptom of trying to make a part that was designed to take in mass quantities of air be accurate at delivering minute quantities of air. GM never intended that which is why they had the IAC. Is adding an IAC possible with that setup or does EFIConnection offer it?

Finally, I'm not even sure how the older TPI setups worked but how did they control idle? Did they have an IAC or was it all done through the TB? If TB, was it a direct cable linkage or was there a cam / lever that gave the pedal a mechanical advatage / caused the throttle actuation to be less than a 1:1 ratio? If there was no IAC and there was a cam / lever that could indicate how GM addressed the need to minutely control the throttle blade.

Again, I am trying to learn so if I am completely off base feel free to let me know. Please just be nice by telling me why / how I am off base.

J. J.

[Fast9C1]

Welcome patooyee, I am nowhere near a veteran here either, so I always hope that someone with more knowledge comes along to correct me when I am wrong. I am getting a pretty good understanding of DBW due to my immersion in this project, though

Welcome, by the way.

The IAC is how they controlled idle air when throttles had cables and there was no other (cheap, reliable) means of opening and closing the throttle blades quickly via computer control. With DBW, there is no IAC motor and all of the air control is done with the main throttle blade(s) by the throttle servo. Makes for kind of a confusing interface for the scanner and calibration editor since so many OS's could do either depending on the segment option. I even see a couple of IAC PIDs in the scanner for my DBW calibration.

No, you cannot add an IAC motor to the DBW setup.

As far as the area deal goes, it took some long calculations to show me something I already learned 20 years ago in college: the rate of change does not depend on the shape of the hole(s). I plotted single round, dual round, mono, square and even triangular profiles and the area vs angle curve looked exactly the same every time. I couldn't believe it at first, but then I was like "duh, I should have seen that from the formula".

Believe me, not having gone to DBW for this project would have GREATLY simplified my life. It's a labor of love and I am glad I did it.

[patooyee]

Welcome patooyee, I am nowhere near a veteran here either, so I always hope that someone with more knowledge comes along to correct me when I am wrong. I am getting a pretty good understanding of DBW due to my immersion in this project, though

Welcome, by the way.

The IAC is how they controlled idle air when throttles had cables and there was no other (cheap, reliable) means of opening and closing the throttle blades quickly via computer control. With DBW, there is no IAC motor and all of the air control is done with the main throttle blade(s) by the throttle servo. Makes for kind of a confusing interface for the scanner and calibration editor since so many OS's could do either depending on the segment option. I even see a couple of IAC PIDs in the scanner for my DBW calibration.

No, you cannot add an IAC motor to the DBW setup.

As far as the area deal goes, it took some long calculations to show me something I already learned 20 years ago in college: the rate of change does not depend on the shape of the hole(s). I plotted single round, dual round, mono, square and even triangular profiles and the area vs angle curve looked exactly the same every time. I couldn't believe it at first, but then I was like "duh, I should have seen that from the formula".

Believe me, not having gone to DBW for this project would have GREATLY simplified my life. It's a labor of love and I am glad I did it.

Then it appears that you are going about it correctly. How do you figure shape of opening doesn't affect air input though?

And actually, now that I think about it more an oblong port may actually take more air in at micro-throttle as the opening would be much longer. I don't know.

J. J.

[Fast9C1]

My intuition also told me that it was jumpy because of the shape of the bore (the evidence is in the first post of this thread), but when I ran the numbers I proved to myself that I was wrong.

Which is nice, because that means that the scalar applies to any shape bore. The fact that they used the word scalar in the description of that number makes perfect sense now, since scalars are dimensionless.

If you want to see my proof, I uploaded the spreadsheet I used:
http://spreadsheets.google.com/ccc?k...OWjdsbnc&hl=en


Note the column labeled Diff. It is currently the ratio of the monoblade area to the single round bore area and it never changes all the way down. I even did the way out there test of making the rectangle 1 high by 6122 wide and watched the values become exactly the same as the monoblade column.