Fixing Torque Dip

Hello I'm new to tuning, been doing it for about 3 months now trying to obsessively learn best I can. I signed up here because I love holycrapitsfast tuning guide (the best I've found), I also use the ones by Cobb and Badnoodle.

I have trying to figure out why I get a dip in torque and HP and how to fix it. I also get a count of knock or 2 if I give it WOT at 2000-2200 RPM. Having trouble figuring this out so I thought I would post up on here.

I have a 2016 STi

Mods are as follows:
Programmer:
Cobb Access Port
Laptop for realtime tuning and changes


Intake:
Cobb Intake
Cobb SF Airbox


Exhaust:
Cobb SS 3" Downpipe with High Flow Catalytic Converter
Killer B EL 4-1 Performance Holy Header/Up-Pipe combo


Fuel:
ia Performance Subaru GR Stumble Fuel Kit Fix (Fuel Pressure Regulator)
ID 1000cc Injectors
AEM 320 LPH Fuel Pump 50-1215
Cobb Subaru Flex Fuel Ethanol Sensor Kit
Cobb Subaru Fuel Pressure Sensor

Wideband:
PLX SM-AFR


Engine:
NGK (2309) LFR7AIX Iridium IX Spark Plugs
iag Performance Street Series Air Oil Seperator

Other:
Coolingmist Water/Methanol Injection Kit
Custom Water Injection Controller Designed and Programmed by Me


THIS IS ON E85


Logs:
Run 1
(Dip at about 4800 RPM)

Run 2 (Dip at about 5300 RPM)

Tables:
V2R16 Tables (Timing and Primary Open Loop Fueling - Let me know if you want other tables)

dynojet%20v2r15_v2r16.png
 
Last edited:

IGOTASTi

System Operator
Staff member
Welcome friend. ?

[MENTION=9]HolyCrapItsFast[/MENTION] you have a fan. ?

?Join us as Lifetime Platinum Member today!?
 

HolyCrapItsFast

Drinks beer!
Hiya @goldfingerfif!

I think you came to the right place and thank you for asking questions.

Before I answer your question directly I would like to just make some observations first with the dyno graph you provided. I see the two pulls and I note that one is showing AFRs to lean for my taste and the other is showing to rich for my taste. You want to try to get those to settle around 11.5 to 11.3 during a wot run after 4000 rpm and under boost. Not sure what would cause them to be so different.

So to answer your question directly, torque is a result of all three timing, fuel and boost and each can have profound effects. When a graph shows a dip you need to isolate the component that is causing the dip. Since your boost is very smooth, you can rule that out. The fuel is also smooth enough in that area to rule that out as well. That leaves timing. Timing is a total of several compensations so you need to look ate total timing before, during and after the dip to see what is going on. Then look at both the primary timing table and dynamic advance together in those areas to see where you need to add timing or take it away.

If timing is smooth then it could just be the nature of VirtualDyno and the conditions at the time you sample the pull. It is far from perfect so it is hard to really rely on what you are seeing at times. I recommend using the smoothest road surface on a calm day and on a very slight decline. I get good results when I sample a Dyno pull under those conditions. Wind conditions can have huge effects on the results. Also don't be afraid to use a smoothing factor of 2 for your pulls. You need to use the seat of your pants along with the dyno graph because if the car feels smooth and you don't physically feel the dip during the pull, then it is likely false.

As for the knock you are seeing, I would have to see a log to really know what is going on. What you described sounds like it could be a combination of timing and tip-in fuel
 
[MENTION=1]IGOTASTi[/MENTION]

Thank you for the warm welcome.

[MENTION=9]HolyCrapItsFast[/MENTION]

Thank you for the response. Makes a lot of sense, and well...while I don't "feel" the dip on VD, I do feel the "dip" in the stock turbo running out of breathe as it gets in the upper RPM range. This should be somewhat remedied soon with a EBCS and a ported/clipped VF48 turbo with a larger billet compressor wheel from Turbo Bay Performance just to hopefully give me a little more oomph to redline.

I can get you a log of the knock, I've had a tough time figuring out TIP-IN and getting it to respond accordingly. It's really odd how my fueling is pretty flat but either high or low from my commanded every time, not sure if it is this 20deg weather or maybe a vacuum leak (highly doubt) or some type of compensation I'm forgetting about. Maybe it's my laminar airflow promoter I 3D printed, but I doubt it, just something I was trying to experiment with as I will test out anything that make sense in my head. Some pictures here of it https://goo.gl/photos/SRvhFUH85ECfJDbq5

It could be fueling or timing I also have a tough time distinguishing what is needed especially with E85 as it has much different properties than gas. I've virtually eliminated all knock by retarding timing a little below a load of 1 and below about 3000rpms and then increasing it about 2 degrees across the board at a load of more than 1. Just this little bit is killing me in the 2200-2450 rpm range and a load of 1.2 - 1.4 area.

The next thing I'm trying to wrap my head around is AVCS with advancing the intake and retarding the exhaust. TD_D post about it having a profound effect on knock and I believe you state so in your tuning guide has scared me away until I get a better grasp on what is going on with it in my head and why you would want to advance or retard it and how it would effect knock.

Here's a chart of my run, nothing seems out of whack so I'm going to agree with it is the nature of the beast especially because of logging so many parameters.
https://docs.google.com/spreadsheet...eiXY/pubchart?oid=23431018&format=interactive
 
Thanks [MENTION=5388]Raven32[/MENTION], I've read that before I got my FPR and that is also where my boost source for the FPR is tapped off of.


As to issues with knock maybe [MENTION=9]HolyCrapItsFast[/MENTION] or someone can take a look over these logs and see if they notice anything out of whack

I made tabs at the bottom as per different revisions as I was changing things to either reduce or eliminate the knock and change things if it got worse, I think I'm about there but just need to fine tune something.

My knock logs
 

HolyCrapItsFast

Drinks beer!
I didn't know you were running ethanol. The AFR's make more sense now.

I doubt it has anything to do with the flow straightener you are using. I always see an improvement in stability when these are used and I have begun to use them on every build.

The knock in the log is marginal at best. If you are worried about it then take a degree of timing away from those areas. The knock sum in Cylinder 4 can probably be addressed by adding fuel to that cylinder. Maybe start by adding 5% to the entire cylinder trim table for cylinder 4
 
Thank you [MENTION=9]HolyCrapItsFast[/MENTION] I will try that.

I know it isn't much knock but still I don't know what amount is level for concern with stock block and internals, so I am just trying to keep it at 0 as best I can. Maybe I should see if it still does it when I turn on my water/alcohol injection as I have it off to get my base tune while learning. I'm thinking if it still does it then it might be a timing issue more than a fueling issue?

I know fueling and timing are kind of related as more fuel will burn slower so it will allow for more advance so you can either retard the timing or add fuel to fix things...but not always.

I'm still trying to figure out what makes more power and where as far as high timing with rich AFR or less timing and leaner.
 

HolyCrapItsFast

Drinks beer!
What I have found over the years is at low to mid level load, any knock below -2 is normal and perfectly acceptable as long as it is random but if it is excessive or occurs in the same spot all the time you might want to address it. In fact you kinda want to see this because this is just the ECU increasing timing to the threshold of knock which is desirable for fuel economy and drivability. At WOT is where you need to concern yourself but don't get hung up if it is -1.4. Finish optimizing your fuel strategy and then adjust for knock.

As for your fuel/timing strategy, when tuning on the street it is best to just go with the safe fuel strategy and then adjust timing to achieve the best power and torque curves. When tuning with out the benefit of a dyno, it is nearly impossible to know what is really effecting power and torque because virtual dyno is not consistent enough to determine the differences between runs on that fine a level.

When street tuning, I always just use a pre defined fuel table and just work around those AFR's. Then optimize timing till I just start seeing knock and then back off 2 degrees and call it a day. I have determined what is a good AFR for our cars over the years and I have found 11.5 in the mid RPM range tapering to 11.3 is an ideal general use AFR without any further tuning. For Ethanol I would start at 12.3 and taper to 12. This maintains a level of safety while providing good power and torque. In a street tune, boost is what is going to give you the best power results.

Regarding the use of water/alcohol injection while running E85. I wouldn't do that. You will get nothing from it. I would use that strategy when on 93.
 
So no benefit from using method on e85 or higher? There are big horse power turbo cars in DFW that use e98 and meth and say it is extra insurance for the motor.


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