So I was thinking that I could help tune my compressor surge out of my new GT30 turbo with some electronic throttle adjustments. Right now 1st-4th gears are fine but in 5th gear if I go WOT at 2000-3000 RPM's I'll hit 20 psi by 3600 and get compressor surge until 3900 where it clears up and then jumps to my 26 psi I have set for my boost levels.

I'll have to do some logging to figure out what throttle positon builds only 20 psi of boost in the 3600-3900 RPM range in 5th but possibly if I limit throttle below 4000 to say 70% or whatever that number ends up being I can still hammer the pedal and avoid having to back off the throttle when it surges. Since I won't build more than 20 psi of boost in other gears below 4000 rpm's it "shoudln't" effect my acceleration at all but it's something that would be worth testing.

So I'm assuming that in order to do this I would just max out the values to 70% if that ends up being the magic number and not even have 100% in the tables for those lower RPM ranges? I supose I could just change the 3500-4000 range but maybe it would be more controllable boost or spool off the line not having the throttle plate fully open anyways?

This could also be a nice way of limiting torque on the MR's in order to save their trannies. I don't want to have to lower boost to get rid of the surge as that would effect the 4k+ range and I want the flexibility of using the Dual setting MBC and change boost as I see fit.

 

Why dont you just address the boost tables so that your 4/5 gears have lower DC up until 3500rpm?

 

Because I'm lazy and want to just use my MBC toggle switch between 2 boost levels.

I was thinking I could make a triple switch where one was ECU controlled and the 2 other settings were MBC controlled but then only the ECU controlled boost setting would have the Compressor Surge eliminated in 5th gear.

So the question is would limited throttle from 3500-4000 work for me assuming I find a throttle % that will just barely support 20 psi? Is throttle opening angle "wasted" when you aren't churning out full boost out of the turbo? I might just have to test it and report back.

 

dunno - any throttle map changes you make will affect ALL gears.. so I am not sure its all that useful to you.

just run ECU boost

 

Well keep in mind that my boost is something like this on the GT30:

1st - 20 psi by 4700?
2nd - 20 psi by 4400?
3rd - 20 psi by 4100
4th - 20 psi by 3800
5th - 20 psi by 3600

When racing I would never drop below 5500 rpm's anyways so the only time it might reduce performance for a split second is in 1st gear where likely I can't hold the power to the road when boost hits anyways. On the road course I might see myself dip down to 4th gear at 3500 in certain situations but having slightly less torque for a few hundred RPM's seems worth it to avoid having to manually lift when going WOT in 5th.

 

I don't know what to say other than limiting it to 50% throttle between 3500 and 4000 I still built 22 psi of boost and had compressor surge in that range. Next I tried to modulate the throttle right before surge kicked in and I was closer to 40% throttle at 17-18 psi. My next flash will reduce throttle to 40% and see where that gets me as from what I'm seeing if I get right on the edge of the surge line it will be "faster" through that RPM range than exceeding it and sending reverse flow back at the compressor wheel. This is all to cure surge in 5th gear but how will it effect other gears?

I also compared two 3rd gear pulls that had similar boost levels set to see if I would lose airflow, boost, or acceleration. What I found was very interesting, first set is reduced throttle and second set of data is allowing full throttle:

3000 -- 76 g/s - 66.3% TPS - 118% Load - 5.2 psi --- 67 g/s - 87.1% TPS - 105% Load - 2.5 psi
3250 -- 98 g/s - 60.4% TPS - 138% Load - 8.2 psi --- 87 g/s - 87.1% TPS - 127% Load - 5.8 psi
3500 - 120 g/s - 49.8% TPS - 160% Load - 11.3 psi --- 112 g/s - 87.1% TPS - 149% Load - 9.4 psi
3750 - 154 g/s - 49.8% TPS - 189% Load - 15.1 psi --- 143 g/s - 87.1% TPS - 178% Load - 13.8 psi
4000 - 187 g/s - 54.1% TPS - 218% Load - 19.3 psi --- 187 g/s - 87.1% TPS - 218% Load - 18.8 psi
4250 - 230 g/s - 72.5% TPS - 250% Load - 23.6 psi --- 227 g/s - 87.1% TPS - 252% Load - 23.5 psi
4500 - 249 g/s - 87.1% TPS - 249% Load - 25.2 psi --- 246 g/s - 87.1% TPS - 245% Load - 25.4 psi
4750 - 255 g/s - 87.1% TPS - 244% Load - 25.0 psi --- 246 g/s - 87.1% TPS - 239% Load - 24.9 psi
5000 - 266 g/s - 87.1% TPS - 241% Load - 24.7 psi --- 260 g/s - 87.1% TPS - 238% Load - 24.8 psi

Seems like the lower TPS didn't reduce flow through the engine in 3rd gear at 25 psi for 3rd gear pulls! In fact it may have even spooled ever so slightly faster. Once it hits 4500+ they are both back to 87.1% TPS and seem to be every close.

 

Can you check what fuel pressure you run at the surge point?

 

I don't have any fuel pressure gauges hooked up on my car so I'm not sure.

I do have an AEM AFR gauge that I also have recorded in the logs.

The throttle reduced run was 13.5 AFR @ 3000 rpm tapering to 12's as it spooled then 11.9 AFR when it reached 20 psi and settling at 11.3 AFR just beyond that.

The full throttle run was around 13.3 AFR @ 3000 rpm tapering to 12's as it spooled then 11.7 AFR when it reached 20 psi and settling at low 11's after that. Seems like it was slightly richer during the spoolup area so that could account for the slightly slower spool at first.

 

A little OT...but somewhat relevant...

Quick question about the TPS, is it possible that the ECU can be reading the position of the throttle incorrectly?

I'm having issues with my car making way less power than it should after the battery was disconnected...I guess my main question is after a battery disconnect, does the throttle need to be recalibrated? My tuner tried changing the throttle position using ECUFlash and it didn't seem to affect anything...so I'm thinking maybe the TPS is reading wrong.

I know this is a fairly broad question, but more curious to see if the TPS need to re-learn it's position after a battery disconnect or ECU swap.

 

Shouldn't ever effect the throttle plate with a battery reset. The reading in OBD2 programs usually is around 87% though which seems odd but is normal.

I tested 40% at 3500 and 4000 rpm points and now surge is gone in 5th completely. Likely I can move the 4000 RPM point back to 45%, maybe 50% as it allows a little more boost as RPM's go up.

The part throttle BOV fluttering is still annoying though, going up hills at 5 psi and letting off slightly or even trying to hold speed it can start acting up. I may look into those Synapse Synchronic BOV's as a possible option so that the flutter evens out more and doesn't jerk the car around.

 

Is that log with you modulating the throttle or changing the table ??

I think you guys have the idea wrong .. the throttle tables doesn't seem to work this way ..

The table seem to be used only on closing / shifting ..
If you log the parameters .. they are always at max values unless there's a shift or liftoff ..

 

Those logs are straight from EvoScan and are from me changing the table. My foot was to the floor on both runs! The reason the TPS is lower on the left side log is that I entered in lower values in all the throttle tables as a test to see what would happen. This might be good or bad news but these tables are indeed maxxing out the throttle position at the throttle body.

I started with just trying to elminate compressor surge when my car hits 20 psi at 3600 instead of lifting manually until 4000 I figured I would make it idiot proof. I also figured that if I kept flow just below the surge line it would at least be similar acceleration if not slightly better since you aren't surging and stalling the turbo as it tries to spool before the engine can consume all the airflow.

My latest change was to adjust the 3000 RPM point to 3500 and top out that line at 40% throttle. I also changed the 3500 line to 3900 and topped that out to 48%. The reason I did this was to isolate the RPM's I was getting surge in 5th gear and make everything else normal. I tested this by spooling at 3000 in 5th and it felt like it was right at the edge of surge then went 100% throttle right at 4000 and moved pretty good. My stupid work laptop is locking up when it vibrates in my car and needs a new system board so datalogging will have to wait until the middle of next week but it is promising.

I've noticed a strange thing tonight though after the latest change though... If I go WOT at 2500 (which is rare normally) I'm now making 20 psi by 3200-3300 rpms in 5th and started getting surge much earlier than before. I think the 60F air might be assisting the better spool but it's possible the lower throttle % is somehow effecting this. Since I shifted my tables slightly it was tapering throttle from 87% at 2500 down to 40% at 3500 so my next test is to cap 2500 RPM point to 40% and see if it removes the surge at 3300. This is obviously going to take some tweaking but is an interesting test none the less. It will take some work to compare AFR's, timing, spool/boost, and airflow numbers to see what is going on here.

It could be that Cams and intake manifold will allow the engine to flow more air for this size compressor wheel and it won't be needed but being able to tune it out with the side effect of making the car more responsive for spool is keeping me interested.

 

This is what I'm trying to say ..

The X axis output is maxed out all the time until you lift off/or accelerate. .. then it outputs a value that is taken and reflected on the table you guys changed .. its a single point value output ..

This trigger signal comes from another table .. which tephra assume is throttle plate .. and I think its torque computation (similiar in logic but probably different in values) ..

I have seen your results without even changing the tables .. so maybe what you're changing is not a direct result of the tables??

There are 5 tables .. of this, 3 tables are used only if coolant temperature is less than 60 degrees .. and 1 table is double used .. so which table did you change to have this effect ??

I'm not doubting you .. I need to understand this table slightly better .. I have seen totally irrelevant results from changing small things due to environmentals ..

Are all the tests totally repeatable ?? Are the values / results always the same ??

Thanks

 

1) Table #3 is the one you want to use for regular driving, the others are unused OR under coolant temp threshold.

2) The X-Axis for the throttle maps comes from MANY sources, HOWEVER for normal driving you can pretty much be sure that the 3d maps I posted before are the input to the X-axis on the throttle maps.

3) This table, *could* be some sort of requested torque.

4) The X-Axis for these tables IS NOT a straight APP input, it varies slightly, so there could be another process going on.

Modifying the Throttle Maps to fix boost problems is not the right way to go, if it works for a specific scenario then that's fine, but I wouldn't advertise it as a fix for most people

I dont think I need todo any more disasm in the throttle maps area, I wanted to understand how they worked and I think I understand enough now, I particularly wanted to find out if smoothing the maps across to 100% of the X-Axis was a good idea - its not...

Anyways...

 

I ended up changing all 5 tables since I didn't know which one would kick in at any one particular situation.

All the results are very repeatable assuming you remove all the values above your target throttle % all the way accross the chart for that RPM entry as I didn't know exactly where on the X axis it would be landing.

Ok it's good to know that the #3 is the main chart, I'm assuming altering the others just in case isn't going to be bad assuming they are similar changes. From what I could gather if you stretched the charts out past the peak values in the original ROM charts that you might not even reach 87.1% throttle when going WOT if the value in the X axxis is constantly changing.

I would also agree that modifying these tables to control boost is not the best way to go either. However in my particular situation where I want to retain my adjustable MBC setup that can be changed from the driver's seat on the fly it was the next best thing. Basically instead of modulating throttle with my foot to avoid the compressor surge in 5th gear I'm just limiting the max throttle input in the tables so i don't go about tearing my turbo apart by accident. I'll have more data once I get my laptop repaired, apparently the USB bus on the system board is what was causing the lockups. I want to verify that by adjusting the throttle so that airflow is right along the surge line it ends up being similar if not quicker acceleration through that RPM range. Trust me when I tell you that compressor surge at WOT is a very uncomfortable feeling when you are not expecting it.

This is really all just a work around to account for the Compressor surge of my larger turbo and anyone using a stock turbo would never have to do any of these tweaks. The only other possible application would be an alternate method of limiting how much power is applied on a paddle shifting MR although using the factory boost solenoids to reduce boost would also be more conventional.