what to look for when increasing boost

[MyBeatGSX]

Just wondering, when you turn up the boost and don't have a wideband around, what's the first effected area on a log?

The thing is, I already creep up to 25psi so I'm wondering why I shouldn't just set it there all the time... Its currently set at about 21-22psi (temperature and mood of the MBC dependant). I'm gussing it would be the lower and midrange running lean since higher RPM is already seeing 25psi. Here's the latest log. Now that I'm running the NOS octane booster all the time, the logs are very consistant and pretty much all look just like this one regardless of weather, day or night, etc.

FYI, increasing from 20psi to 22psi picked me up about 2lb/min across the board, execpt where creep starts obviously, that stayed the same.

The odd thing is that the WB on the dyno showed me running lean (12-13:1) at under 4,400rpm, but the second 4,400rpm hit, it dropped down into the low 11's and held there.WTF The odd thing is that my SAFC correction factor is the exact opposite of that. At 4,400rpm it drips way negative (-20%). I had to bring the SAFC into the -9% range at lower RPM to keep the AFR in the 11.5 range.WTF

FOR THE MODS: This is not a log analysis, that's why it's not in that section. I'm just oosting it up to help answer the original question. Please don't move the thread.

RPM Timing Airflow
3224 7 12.51
3460 4 17.87
3828 5 19.33
4048 7 21.07
4304 8 21.59
4468 8 22.42
4804 9 24.37
5012 10 25.76
5252 12 25.44
5604 12 26.56
5636 13 27.68
5932 14 27.87
6036 14 28.75
6252 16 29.04
6344 16 29.29
6528 14 30.15
6676 16 29.26
6868 17 29.09
7148 20 28.19

I'd love to know why my airflow drops off up high too, the correction factor stays the same from 6k up (-17%). There's always one spot up high were airflow peaks and timing drops a degree or 2 (higher map switch maybe?). But that isn't really relevant to the original question because boost will do what it wants up there anyway. I'm just worried about turning it up without a wideband and I don't feel like paying another $85 to rerun on the dyno just to check the AFR.

 

[daren_p]

Since you can't log knock the first thing affected would be timing. You will see timing being pulled when the car starts to knock. Your timing will begin high then will dip down on the onset of boost, the amount of dip will depend on how much air you are flowing, the more air, the larger the dip. After the initial dip the timing should progressivly increase to the redline. A dip in timing during the increase after this initial dip would indicate knock. It is best if you start the log at a slightly lower rpm. From what you have posted it looks like you are knocking up top, starting ~ 6500. This is probably true as you said you have boost creep, so your creep is putting you over your safe boost limit. With the safc you can't directly play with timing, so I would try to richen from low 6000's up abit & see what happens. There is no reason you can't turn the boost to 25 if it is already creeping to 25, IF you don't have knock issues and you have proper supporting mods (head studs defently a good idea if you don't already have them).

The airflow that you have posted is this lb/min? You are reading this directly from the SAFC? I don't use the SAFC so I can't tell you exactly how to do it but don't you have to calculate in your correction factor somehow to give you your "true" lb/min? This may be why you are seeing less airflow up top?

As a side note what octane are you running as 25 is really pushing it for an evoIII on pump? Granted you will be able to run abit more boost compared to someone with cams (being your VE isn't as great) but most seem to get away with about 22 max on straight pump (by this I mean without water injection). I know it says you run octane booster but octane booster is sort of a scam. I don't know the exact number but for example it may say will raise your octane 10 octane points. So you would think, I run sunoco 94 so this would make my gas 104? this is incorrect. Its something like 10 octane points make 1 octane so your 94 would be 95, its abit missleading.

 

[MyBeatGSX]

Yes the airflow is in lb/min, and the SAFC corrected airflow. However, the correction factor from 6k up is the same, so the numbers are all relative at that point.

Actual airflow is:

6528 -- 35.27
6676 -- 34.23
6868 -- 34.03
7148 -- 32.98

I find that kind of odd. Power drops off in proportion, so maybe I'm just reaching the flow limit of something.


As for the point of timing drop. I'm wondering if that's not just the ECU moving to a different timing map or whatever it does, because the timing does continue to climb after that, and no matter how rich I go I can't get rid of that drop spot (I spent 2 hours on the dyno trying), but the rest of the curve is always perfect. I'm already in the 10.8-11.0 range right there. As a matter of fact, richer made it drop more timing earlier. Seeing as how richer means the ECU sees more airflow, I thought that supported my higher timing map idea so I just left it at a safe AFR that was a few HP below what it could have made and kept the rest of the map looking good.


Are head studs nessesary? I know that guy 99GST just made well over 400hp on stock bolts and even a stock head gasket (I have an MLS with stock bolts). So this brings up something else I've been wondering. Is it normal cylinder pressure that causes them to fail (which would be indicated by a torque number I would assume), is it a certain amount of boost pressure (I don't see how this is possible, a lot of boost and no power is still no power), or is it just detonation (which would explain how 99GST and other get away with it on a good tune).

There is no reason you can't turn the boost to 25 if it is already creeping to 25, IF you don't have knock issues

Exactly. But with that boost onset timing dip you were talking about, I'm worried that the knock will be hiding in that area (since that also happens to be peak IDC rpm and peak torque rpm too). How can I tell if I'm knocking if the timing is dropping already?

 

[daren_p]

Hmm that seems kinds strange, that you can't seem to get rid of that dip at that point even by richening it up. As long as the ecu see's I believe its 2.1 gm/rev, it will stay on the "peak performance" timing curve & with running that kind of boost on the evoIII, I doubt you should be dipping below this point. (by any chance can you log your gm/rev? to be sure). If anything I would think you would see a jump in timing as less airflow would put you on a timing map with more advance, so doubt this is your issue. Have you tried "free reving" the motor just to make sure it isn't mechanical? What about mid throttle pulls etc, does it still knock at the same point? I know NB O2's are pretty useless (to compare one setup to another, but they are pretty repeatable on your own setup) but what do they look like are they constant through the pull or do you have any spikes or dips? If it is just knocking in that one spot it will take the dip then continue to climb once the knock is gone, so you can't just assume its okay.

Its normal for gm/rev to drop off at higher rpms since its rpm/time dependent but lb/min doesn't normally drop off like that, well not that I've seen anyways especially since you say your boost is actually creping up in the higher rpms, if anything you would think this showing your boost dropping off.

As for head studs yes you can probably run the stockers since you have the 6bolt (slightly larger diameter vs 2g) but you are pushing the limits at that kind of boost & you are unsure of your tune which defently doesn't help. I would just get some ARP fastners so you know your not going to stretch the bolts & be done with it. If anything its usually the bolts that are the weaker link as people seem to run higher boost with stock HG & ARP studs vs the other way around.

With the initial onset of boost dip, if the dip seems to remain & not start to increase again as fast as it did before the boost increase (flatlines or increases & dips) this should indicate that it is knocking when you have turned it up to the constant 25. Usually at these lower rpms where this occurs you aren't at peak cylinder pressure so the chances of knock aren't as high. I believe our peak cylinder pressure is somewhere around the 5000's.

 

[CanadianTSi]

Airflow will fall off up top with the stock cams and a "smaller" turbo.

Other than that your tune looks pretty spot on.

 

[pneumo]

I notice you have 550 injectors. Could you log in duty cycle and see if they're going over 100%? I've seen knock start just as the injectors approach 100% DC.

Timing does not jump between maps as airflow goes up and down. If the airflow ammount puts you in between different load levels then the ecu will extrapolate the difference between the timing of those two map levels. That way the timing changes smoothly as airflow changes.

 

[CanadianTSi]

Can't log Duty Cycle on a 2G without DSMLink.

 

[pneumo]

Awww.... so you can't log inj pulsewidth either?
anyway, I'd assume since you're pushing high boost on pumpgas you're probably maxing the injectors.

 

[daren_p]

Airflow will fall off up top with the stock cams and a "smaller" turbo.

Other than that your tune looks pretty spot on.

He's running the evoIII & I know when I had stock cams my flow wouldn't drop off like that with boost set at 18-22, yes it would basically flaten out but defently not drop a couple lb/min. I don't even think my t25 dropped like that but then again I probably didn't log it over ~6500 rpms as it was out of steam long before that.

Good point pneumo, didn't even check what injectors he was running. With the evoIII @ 25 on pump and 550 injectors he's probably pretty much maxed, which could explain why trying to richen up the SAFC didn't help him any. Looks like you are also running Precision injectors, which if their like the rest of their injectors, they are tested at elevated pressure compared to the industry std of 43.5 psi, so you actually have less fuel then you would suspect. Have you tried bumping the base fuel pressure to squeeze abit more fuel out of those injectors?

 

[MyBeatGSX]

Looks like you are also running Precision injectors, which if their like the rest of their injectors, they are tested at elevated pressure compared to the industry std of 43.5 psi, so you actually have less fuel then you would suspect.

Out frickin standing.... Wish I had known that before I bought them.

Well here's the odd thing. Riching it up definatly made it do what I wanted, it just had to be pretty rich (-9%). But up higher when I'm flowing more air and also hitting max torque/max IDC (which you said was ~5,000rpm) is also when I have the most negative AFC settings (-19%) and I'm hitting low 11 AFR's with no problem. That's kind of confusing. Seems like if I was running out of fuel it would be at peak torque and not way low.

The airflow drop could be my horrible exhaust which I (and everyone else) love to blame things on. Or maybe I need to watch my boost more carefully. I noticed on a few dyno pulls it started coming back closer to the set point after 6,700rpm. But its hard to see this on the road when I'm trying to watch the tach at the same time.