2g datalog question

[Mike 99GSX]

Hey guys. I'm new to the forum and have a tuning question. My mods are listed in my sig except that I just installed a set of 650 ball disk injectors. I did some 3rd gear pulls at 19psi on 94 pump gas and heres what I got. I've tuned for .92 o2s and have a steady timing advance starting at 7 degrees at 3700rpm and ending about 18 degrees at 7000. What I'm concerned about though is that mt EGTS are hitting over 1600 from about 5500rpm on. I'm not sure at this point what if anything I should change to bring the EGTs down? Should I tune for a lower or higher o2? Should I try changing base fuel pressure? (set @ 43 psi w/out vacuum) The other thing thats funny is that I didn't have to lean out anything on top with my VPC/GCC after I switched to the "bigger" 650s. I'm wondering now how accurately they flow test these compared to the RC550s that I had in there.

 

[umiami80]

I have teh same problem aith the same car, I have a AFPR and it is set at 43.5 PSI. Add more fuel, that .92 isn't accurate, you are getting knock and timing pull, i bet your car has a weak topend right?

Lower the boost, cut the fule, get a good run, add boost, add fuel, try to keep the timing.

 

[Mike 99GSX]

What do you mean exactly by .92 not being accurate. I thought anything higher than that would be too rich. I thought 18 degrees advance was pretty good for a 2g? Although I did try a .90 setting last night and my EGTs were even worse and my timing dropped to 15 at 7000 rpm so you may be right. I just thought that by going richer, I may bring the EGTs down, but I'll lose more power because I will be running too rich. I'm still puzzled as to why these new injectors aren't requiring me to lean anything out more than the 550s.

 

[whitegst97]

I'm on the same path of trying to tune the car, one problem though, im running a 20g with a walbro fuel pump and stock!! injectors, and i still have to lean the hell out of the AFC (-25) to get the 02's to .94. There has to be something going nuts here. Im getting at 3k, timing 17 and 02's at .90 then from 4k to 5k i lose timing to like 5 and the 02's go to .96 .98 but the from 6k and on i get timings around 16 17 and the 02's still at .96. Can someone help me out with these things, how come my 02's are the same at 4k-k5 and at 6k-7k but the timing is wack at 4k-5k.?? Any help will be greatly appreciated. Thanks

Yomny M

 

[Mike 99GSX]

Have you done a boost leek test yet? Thats where I would start. I'm guessing you've got a good size leek somehere which is why your showing so rich and your timing then takes a dive.

 

[Blk_99gst]

I am in a similar boat as you guys as I'm finding it a tad hard to tune my car. Got a big16g, walbro 255, 660cc, and pocketlogger.

I would NOT recommend tuning by O2 voltages at all. It's the last thing you should use because they are not very accurate unless you have a wideband o2 sensor ($$$). I think the most important things to tune by is knock (which us 2g's can't see), the timing advance, then egt temps, then o2 voltage.

You obviously want timing to increase from when boost hits to the top of the gear. (say from 10deg to 18, 19, or 20degs); and you never want timing to dip or go down. As log as you meet the above, then I would keep leaning it out until EGT's just touched 1600degF at the top of 3rd gear. I have seen too that my timing still seems to advance and o2 values can be .92 or .94, but my EGT's will be going well past 1600 and that's not acceptable in my opinion.

whitegst97 - There is no way you can be running a 20g and have the stock injectors backed out -25%. That may give you the lower o2 values, but I can guarantee you your egt temps have to be in the 1700 to 1800deg range; bye bye motor... Do you have an egt gauge at all?

 

[Mike 99GSX]

I understand the inaccuracy of the A/F gauge but I guess what I haven't understood is that the pocketlogger is inaccurate too because of the stock O2 sensor. So your saying that even though my pocketlogger reads .92, I'm really leaner then that because of the inaccurate O2 sensor. So its OK if I tune for .94 or even .96 if it keeps advancing my timing and it brings my EGTs back to right about 1600 at the top of 3rd?

 

[Blk_99gst]

Let's clarify a few things. First a blinky air fuel guage is useless to tune by because one green led could mean .92 and .94 but light the same LED. A pocketlogger is better because it reads the actual voltage from the o2 sensor unlike the blinky LED. The pocketlogger isn't inaccurate, it is just reading the value the ECU is seeing.

So when it comes to tuning, like I said before you've got the three values, timing, egt's, and o2 voltages. We know for a fact if timing is getting pulled, then the ecu is seeing something wrong and we know we have to fix it tuning wise. We also know for a fact that the danger zone of engine temps are 1650degF; above that and things start to melt. Now as far as O2 voltages, this is a grey area. Not all o2 sensors are the same, their values can change with age, they can be inaccurate, and we all think the o2 voltage sweet spot is .94; but this may not even be true and it may differ from car to car. It's not as definite as saying metal will start melting over 1650deg.

So to sum up, I would:
1) Tune for timing advance
2) Tune for EGT temps peaking at top of 3rd gear, but still under 1600degF
3) After the above, just see what your o2 voltage is. My guess is it would be around .94, or .96.

 

[Mike 99GSX]

Thanks alot. I think this is very good advice. I'll trying richening up across the board and see if my timing goes up and if the EGTs come down. I'll report back tomorrow after I hit the dragstrip tonight. Thanks again.

 

[dave99gst]

also- if you use o2 numbers from a datalogger -- ive noticed they are norm higher than an external gauge. for example if a external gauges reads .92 a log from the ECU may read .98 - 1.0v . point being- if you got .92 from a log that may be a tad low.

 

[Mike 99GSX]

I think that could definately be right as well. When I went to the track, I only got 2 runs. The first run I richened everything up(probably too much), I ran a 14.5 at 99MPH because I had a 2.6 60' time (please don't laugh, 1st time ever) My O2s were between .98 and 1.00 the whole time and my timing stayed between 20-24 but my EGTs only peeked at about 1400 so I figured this was a little too rich. For the next run, I leaned everything out a little too much I think. I ran a 13.5 at 100 MPH with a 1.9 60' time. I lost the connection to the log, but this setting before gave my the .92 with about 18 timing and over 1600 EGT. Obviously the 100 MPH is pretty slow for a 1.9 60' with my mods. I think I should have been somewhere in between the two settings and with a sub 2.0 60' then I would be around a 12.8-13-0 at around 103-105MPH. Does this seem about right?

 

[nine5raptor]

egt's are really worthless as well in terms of parts melting. you say the engine starts melting at about 1650, more like 3000F. egt's are indicative of timing. think about this, if you light the fire earlier (more timing advance), then more energy is expended pushing the piston farther and the fuel burns up earlier (in the cycle) then when the exhaust is pushed out it is cooler.

if you start the fire later, egt's will be higher b/c more energy will still be available (it's wasted)

when you see egt's skyrocket extremely fast, it is prob b/c timing is retarded so much that the a/f mix is still burning when it hits the egt probe.

tune for timing. #### a/f gauges and egt's

 

[nine5raptor]

for more about what I said, read this thread:
http://www.dsmtuners.com/forums/showthread.php?s=&threadid=41270