Jaraxle

I tuned my ecu such that 1st and 2nd gear are zero WGDC, and therefore wastegate is used (20-21psi) soley. For 3rd through 6th I have set the WGDC 5% low (from what is really required) so that boost correct is required to reach the target load. That is the only thing I have done in an attempt to prevent boost spikes when shifting from 2nd to 3rd, etc at WOT. Needless to say I am still spiking 30psi!
The actual target on a smooth non shifting pull is 25psi.

I am looking for some guidance on how to tune out boost spikes on TC-SST based EVOs.

My mods are below. The very fast spooling (9 blade TD05) 20G doesn't help this issue.


~Jaraxle

Hiboost

iTrader: (9)

The only 100% reliable way to eliminate the boost spikes is to intentionally swap in lower WGDC's above a certain RPM point. The way I've been doing this on customer cars as well as my own is moving the 7000 rpm data point to 6950 or whatever it rounds to and then 7500 becomes 7000. Then I'm placing the WGDC values that are similar or lower to what is in the 5000-5500 rpm range into the 7000 and 8000 rpm cells so that as soon as you upshift in the 7000+ rpm range it guarantees that the WGDC's will match what you want them to be as it engages the next higher gear with ZERO boost spikes. If you let your car autoshift you may only be able to run full WGDC to 6900 and then set your reduced WGDC's at 6950 in case it's not revving high enough. Personally I manually shift so that's never a problem for me.

The only real drawback to this technique is that your 7000-7600 rpm will now be slightly less boost than you may want but as long as you shift at or above 7000 the boost spikes are gone. You can move that rpm range higher if you had an 8000 redline so that you would use full WGDC values up to 7350 and then at 7400 it would be reduced. Another benefit is that it gives your car more time to complete a shift.

If you short shift and don't reach your lowered WGDC values it will still spike on the upshift but when done right it allows me to run 28 psi on my tune with no spikes instead of lowering my power to 25-26 psi to accommodate the spike. I'm pretty certain having 2-3 psi more boost from 5000-7000 rpm is better than being able to run a few psi more from 7000-7600 where in most cases you are shifting around 7200-7400 rpm anyways.

For certain it's a better bet on a road course when every upshift has no boost spike and much less stress on the clutchpacks. After doing this change I went from managing 20 minute sessions to getting full 30 minutes sessions with no overheat. This was with an AMS side mounted cooler and a Mocal medium water to trans oil cooler plumbed into my return line. Now the limiter is brakes and fuel again.

I'll be making a new post comparing logs and graphs showing the boost spike before and zero spike after using this technique, it really helps.

Jaraxle

Actually Chris I was hoping you would respond. There are so few people on the forums that actually have done and know what they are doing. I know that since I am running accesstuner I don't have PSI based WGDC control. So that left me to responding with OBTR based on load, which simply isn't fast enough. What you have proposed (and I am sure proven) sounds like the only way out, and I can live with that versus having my clutch packs open up and over-rev into a vented block. I appreciate your response.

What if you set the 7000+ RPM load target LOWER than your target WGDC will actually cause. This will cause a negative boost correction and when you shift I believe that negative boost correction will be in affect at FIRST and then within whatever time period you have your correct setup, and IF you have positive boost correction enabled you will get a correction back to what you wanted from 5krpm until your back to 7krpm. What are your thoughts on that?

So for instance right now I am targeting 255 load from 5k rpm and up. I would change the 7kpm or 7.5krpm to say 240. I would leave my target WGDC as is (which normally supports 255 load). The negative correction will kick in and I believe be sustained through the shift to the lower rpm that the engine settles at. Not sure exactly but probably 5.5k +/- 500 rpm.
Does that sound like something I should test?

Thanks!

~Jaraxle

Jaraxle

Chris,
I have not tried your method or my idea yet. I would like to know if you use the OBTR at all, or do you leave the over boost timing retard map all set to zero?

If my idea works, in theory: if your doing a clean pull say in 5th you will get the full boost targeted the entire time. If you shift above 7krpm in 4th then when 5th gear is caught your commanded WGDC should be lower than is required for a smooth pull through 5th. This would be due to the negative boost correction due to the lower target load for 7k and 7.5k rpm while you were in the top of 4th gear. Does any of this sound wack?

Thanks!
~Jaraxle

RazorLab

iTrader: (8)

You can also try running less negative timing in the lower bound table (which it uses during shifts). When I had my SST I would do about 2* or so less in that table and would never get much boost spikes during shifts

Hiboost

iTrader: (9)

Using lower WGDC than needed and then letting the WGDC drift back upward should indeed dump boost a few psi between shifts and start the next gear at lower than targeted boost levels. Depending on your Reactive Solenoid WGDC correction interval values it should get back up to targeted boost pretty quickly once fully in gear. In my experience I didn't really see the need for it as boost was flat between shifts but that could vary depending on turbo used and MIVEC settings among other things.

I know some tuners have had luck with increasing the Over Boost Timing Retard values to basically dump torque on upshifts but it does increase the EGT's which on a road course I tend to avoid doing unless necessary.

I usually run my lower bound timing table the same as my high tables for 100+ load and 4000+ rpm with good results, below that I have it taper off but it all depends on what kind of turbo you are running where boost spikes in the 3000-3500 range could be a problem if you short shifted an up shift and ended up in that area at full boost.

Jaraxle

Thanks guys for your inputs. I will post back what I ended up with, but it appears SOLVED.
I believe I went with a mix between what Chris suggested and my theory (using boost correction). I will circle back and post what I did if anyone wants the details.

~Jaraxle