Low/Mid RPM VPC Tuning

[Mike 99GSX]

Heres the question. I've got a pretty good handle now on what the timing curve should look like and how to factor in EGTs and everything else to dial in fuel up top but here's what I'm maybe having trouble with. Last night, I got out to the track with my new 50 trim and 660s. The problem I was having was that whenever I shifted into any gear, I would get a hesitation and the car kinda bogged down for a second. When you look at a datalog and see 3rd gear for example start at about 4000rpm, how do you know at that point if I'm starting out with too much fuel? I think timing started at about 9 and still gradually rose up to about 18. The car felt pretty good up top but the hestitation into each gear really screwed my time. I never had this problem with my 16g and 550s. We got rained out after 1 run so I didn't get to try anything else. Also, I was wondering if someone could explain to me the "response" knob on the VPC and how its exactly used. Right now mine is at 12 oclock. I used to have it at 3 o clock and the car used to hestitate when I putzed around town and by turning it back it seemed to help. I was wondering if maybe this was part of my problem at WOT and that it needs to be turned up during racing.

 

[jdmawd]

Originally posted by Mike 99GSX
, I was wondering if someone could explain to me the "response" knob on the VPC and how its exactly used. Right now mine is at 12 oclock. I used to have it at 3 o clock and the car used to hestitate when I putzed around town and by turning it back it seemed to help. I was wondering if maybe this was part of my problem at WOT and that it needs to be turned up during racing.

The response knob dictates how much fuel is added when the throttle plate is opened or tip in. from 12 to 6 clockwise is more fuel when the throttle is initially opened and 12-6 counter clockwise is less fuel when the throttle opens. its suggested to keep the response at around 5-6 o'clock

Depending on your setup its also a good idea to keep the gain knob at 12 and use the safc for everything else. the gain knob is best used as a global correction.

On a side note I found that with the vpc my 50 trim spooled so quickly and moved so much air between 35-4K the fuel correction in that rpm range was disproportionally rich because of how quickly and how much are was moved in that range. for example 1K was -30 2K -15 3K -8 4K -8 then back to -15 after 4K

 

[Mike 99GSX]

Originally posted by jdmawd


The response knob dictates how much fuel is added when the throttle plate is opened or tip in. from 12 to 6 clockwise is more fuel when the throttle is initially opened and 12-6 counter clockwise is less fuel when the throttle opens. its suggested to keep the response at around 5-6 o'clock

OK with that said, wouldn't you think that by turning it up to 5 or 6 oclock that that would dump even more fuel in after the shift making the hesitation even worse? I thought my hesitation was because I was initially dumping too much fuel. Am I wrong?

Depending on your setup its also a good idea to keep the gain knob at 12 and use the safc for everything else. the gain knob is best used as a global correction.

On a side note I found that with the vpc my 50 trim spooled so quickly and moved so much air between 35-4K the fuel correction in that rpm range was disproportionally rich because of how quickly and how much are was moved in that range. for example 1K was -30 2K -15 3K -8 4K -8 then back to -15 after 4K

Thats what I was going to try next. I have a GCC not an AFC but I was basically going to try to lean out the 2400 and 4000 RPM setting by about 2 or 3 notches, then the rain came!!

 

[jdmawd]

Originally posted by Mike 99GSX


Thats what I was going to try next. I have a GCC not an AFC but I was basically going to try to lean out the 2400 and 4000 RPM setting by about 2 or 3 notches, then the rain came!!

Also look at the logs where the car was bogging

 

[candela]

JDM pretty much hit it. I alsways had my VPC at about 5 o'clock and left it there all the time. The afc was usually enough to tune with, however I would haev liked to try an afc-2 as I bet that with the VPC woudl be one viscous combo. Anyhow when you go the track you should always adjust your driving style for that. When on the street, most dsm's seem to have a little tip in knock (depending on RPM, load and what not but the point remains the same), which will usually result in exactly what you described as a low timing shot then a gradual increase when the ECU realizes there isn't anything wrong. A gradual increase in the throttle will usually solve this...
however I know at the track you dont want to ####y foot it, so there is basically one option. Keep that pedal down at leist half throttle in between shifts, or if you are a nutt you can keep it mashed like some DSM'ers who like killing trannies and valves. This should also pretty much get rid of most of the timing loss and give much better shifting/boost responseAnyhow Im not saying that this cant be solved, but I cant give specific insight cause Ive never used a GCC (only seen them) on any car before. but if it does have pretty detailed inputs on it use it.... Good luck

Austin

 

[Mike 99GSX]

The car is bogging right into the next gear. The log read that the timing dropped to about 9 and then climbed up to about 18 at the top of 3rd gear. I'm not sure if not is too low coming off of a red line shift or if that is normal. Also, I placed that reply in the wrong section a post back about the response knob. Wouldn't turning it up to say 5oclock only make the bogging worse because I'd be dumping more fuel as I go into the next gear?

 

[candela]

I didnt really understand what you just said... if you could rephrase that a little about the shifting thing maybe I can pick up on it, but how do you know your running rich? Timing can be dropped to more than just runnign rich. Do not tune with the VPC! Use yoru GCC for that, thats why I said to set it at 5 then leave it alone period...jus ttune with whatever else you have.
Lets see some logs of it though so we know whats going on.

 

[Mike 99GSX]

Thanks for the patience. I don't know how to print the log in table form like everyone else does so I'll try to summarize. Basically once I leave the line and the clutch catches, the timing starts at about 9 and climbs to about 22 in 1st, then when I shift theres some junk numbers, and when the car starts accelerating again the timing starts at 9 and goes to about 20. Shift to 3rd and same thing. I do lift my foot off of the gas when I shift. When I let out the clutch and go back on the gas, the car basically does not respond to the pedal until about one second. Thats what I'm describing as hesitation or bogging. Hope this clears it up a little. Thanks for the help.

Mike

 

[candela]

Thats exactly what I though you were saying... try what I suggested!

 

[nowayout]

that's kind of funny.
My car does the Same thing I finally got tuned out.

I needed to add fuel . My response knoe is at 2 o'clock.
I have a VPC and AFR combo.
Add fuel in between 3k4.5k my turbo move soo much air when it spooled up that I was getting seven to 10 knock count,

Here my log.
Time RPM Knock Timing O2 Airflow Inj P/W Air Temp TPS
00:39.4 3125 0 30 0.82 479 6.41 67 65
00:39.6 3281 0 29 0.92 523 7.179 67 79
00:39.9 3469 0 29 0.9 567 7.436 67 82
00:40.1 3656 0 28 0.88 617 7.436 67 84
00:40.3 3875 0 27 0.88 706 8.718 67 85
00:40.6 4125 0 26 0.88 882 11.282 67 86
00:40.8 4406 0 24 0.88 1121 13.846 67 86
00:41.0 4625 0 21 0.88 1304 15.385 67 86
00:41.2 4844 0 22 0.88 1361 15.128 67 86
00:41.4 5219 0 23 0.88 1474 15.897 67 86
00:41.6 5438 0 23 0.88 1588 17.179 67 86
00:41.7 5625 0 23 0.88 1607 17.436 67 86
00:41.9 5812 0 24 0.88 1607 17.436 67 86
00:42.0 6125 0 25 0.88 1607 17.692 67 86
00:42.2 6188 0 23 0.88 1607 17.436 67 86
00:42.4 6469 0 20 0.88 1607 17.179 67 86
00:42.5 6438 0 21 0.88 1607 16.923 67 86
00:42.7 6562 0 21 0.88 1607 16.923 67 86
00:42.9 6812 0 21 0.86 1607 16.154 67 10
00:43.1 6438 0 39 0.88 290 2.051 67 10
00:43.3 5719 0 45 0.8 239 5.641 67 83
00:43.5 5094 0 27 0.88 901 10.256 67 93
00:43.8 4656 3 25 0.88 1103 13.59 67 94
00:44.0 4781 3 20 0.88 1310 15.128 67 95
00:44.2 4875 2 21 0.88 1329 15.128 67 96
00:44.3 5000 2 21 0.88 1367 15.128 67 96
00:44.6 5094 2 22 0.88 1418 15.385 67 96
00:44.8 5250 1 22 0.88 1468 15.897 67 97
00:45.0 5344 1 21 0.88 1512 16.41 67 97
00:45.1 5469 1 22 0.88 1562 16.667 67 98
00:45.3 5500 0 22 0.88 1607 16.923 67 99
00:45.4 5562 0 23 0.88 1607 17.179 67 99
00:45.6 5719 0 23 0.88 1607 17.436 67 99
00:45.7 5781 0 24 0.88 1607 17.436 67 99
00:45.9 5844 0 24 0.88 1607 17.436 67 99
00:46.1 5906 0 24 0.88 1607 17.436 67 99
00:46.2 5906 0 25 0.88 1607 17.179 67 99
00:46.4 6031 0 24 0.88 1607 17.179 67 99
00:46.5 6188 0 25 0.88 1607 17.179 67 99
00:46.7 6219 0 24 0.88 1607 17.179 67 99
00:46.8 6156 0 22 0.88 1607 16.923 67 99
00:47.0 6438 0 22 0.88 1607 16.923 67 99
00:47.2 6250 1 21 0.88 1607 16.667 67 99
00:47.3 6500 1 21 0.88 1607 16.667 67 99
00:47.5 6469 1 22 0.88 1607 16.667 67 99
00:47.7 6625 0 22 0.88 1607 16.41 67 99
00:47.8 6656 1 21 0.88 1607 16.154 67 70
00:48.1 6656 1 27 0.86 1027 2.308 67 10

 

[jdmawd]

nice log man but your o2 number looks a litte flat do you know if your 02 sensor is grounded. i used to show .88 no matter how rich the car was. I think the spool up lean condition is pretty common with the vpc. it drove me nuts until a friend told me it was normal with a quick spooling turbo. Also the air temp data is a dummy number it will never change from 67* is that log from your old turbo or the new one?

 

[Mike 99GSX]

Thanks guys for all the input. I'll try turning up the response, adding fuel in the midband and not completely lifting the throttle during shifts.

 

[nowayout]

My O2 is grounded. That is from my new turbo.

 

[candela]

How do you like your Kit? Satisfied with the performance and drivability of that turbo?

 

[nowayout]

Very satisfied. I used to big turbos. The boost comes on very smooth. I have no problem driving it around at all.