Big boost spike during shift - Must fix due to stock charge pipe!

[bradsm87]

I've tried lots of things that all made very little difference. I really need to get rid of this as I have a stock charge pipe haha!

Any ideas on how to fix?

http://datazap.me/u/bradsm87/rev36?l...2&zoom=226-309

[DirtKurt]

Boost is spiking because the throttle plate is closing when you shift and the stock diverters can't keep up. Get a charge pipe/bov

[bradsm87]

Boost is spiking because the throttle plate is closing when you shift and the stock diverters can't keep up. Get a charge pipe/bov

The throttle is closing because of the spike, which yes, does make it worse before the throttle. I want the spike to not happen in the first place. Stock diverters are the fastest reacting BOVs of them all. The Australian dollar is rubbish and there's no way I'm spending a week's pay on a glorified aluminium bend.

[bradsm87]

The annoying thing is that my boost target tapers down a bit from 6400 onwards which I want but the problem is when revs start to drop at the beginning of the shift, the boost target goes back up because the revs are lower. I'd like to be able to have a slight boost taper without the boost target hump during a shift. If the boost target hump wasn't there, the P and D factor would be a lot more aggressive with lowering WGDC when the spike starts.

[trebila]

lower your vanos settings up top (intake and exhaust), it will help a lot.

[bradsm87]

lower your vanos settings up top (intake and exhaust), it will help a lot.

Thanks!

The only thing is, I'd be worried I'd lose performance up top as a result.

Hopefully I'm dyno tuning the VANOS next week so I'll know for sure then!

[hydra]

I did some dyno sweeps a few months back and saw absolutely no change in performance up top between 112, 116, and 120 FWIW Running upgraded twins & FBO...

[bradsm87]

I did some dyno sweeps a few months back and saw absolutely no change in performance up top between 112, 116, and 120 FWIW Running upgraded twins & FBO...

Interesting. What mods and what about down load and midrange? When is the best RPM to transition into the more retarded intake cam timing?

[bradsm87]

Edit: Oops. Saw you already posted mods. I'm very keen to hear how you went with the rest of the RPM range.

[hydra]

A good place to start IMO would be the stock VANOS table settings @ 150 load give or take, I can post a screenshot of my tables if you like

[bradsm87]

A good place to start IMO would be the stock VANOS table settings @ 150 load give or take, I can post a screenshot of my tables if you like

That'd be great if you could!

[hydra]

[V8Bait]

Looks like you took my advice, you ever get that 6mt swap ghost fixed @hydra?

[bradsm87]

Well I got it a little better.

- I advanced the intake cam from 116 to 115.2. Probably nowhere near enough to make a difference haha.
- Increased D-Factor values on the negative (left) side of the table back up to stock values. This makes it drop WGDC harder when boost is rising compared to the target curve.
- Changed the last breakpoint on the D-Factor multiplier table from 5500rpm to 6000rpm and increased the value in the last cell for more aggressive D-Factor at 6000rpm and above.
- Decreased "Threshold (Major throttle closure)" from 0.980 to 0.977 so that the throttle doesn't close as hard and cause as much of a spike. I may further reduce this but I do remember not really liking 0.970 back in the day as you can feel the slight delay when coming off the throttle.

I guess a 3psi spike before the throttle when the throttle closes is a pretty fair expectation and can't do much better than that.

[hydra]

Looks like you took my advice, you ever get that 6mt swap ghost fixed @hydra?

No sadly, still chasing ghosts, in addition to fighting massive traction issues to boot

[bradsm87]

@hydra

Very interesting findings. So that VANOS curve across all RPM are a result of back-to-back dyno runs?

I've always ran somewhere between stock and Cobb eg. at 4500RPM in the highest load cell, stock intake is 98.4, Cobb is 112, I run 106. You run 95.2, less than stock. So you came to that from dyno comparisons? Maybe most of us have been running way too retarded intake cam timing!

[hydra]

Keep in mind I'm running GC Lite Turbos with larger hotsides than stock, therefore I should have a more favorable boost/backpressure ratio than most, allowing for more advance. With that said, my dyno testing showed that power/torque was largely insensitive to intake lobe centerline in the 100-112 range above 4000rpm so I ended up going with settings close to stock @ stock boost...

[mfish]

I'm no expert but have you tried increasing d factor multiplier in the higher rpm columns?

I've had that problem with overshoots on upshifts and raising d factor multiplier a lot up there helps beat down / mitigate that overshoot quickly. Raising the multiplier in the lower and mid RPM's gave me oscillations but raising it up top doesn't seem to have that unwanted side effect.

I'm using 0.75 in the 4500 RPM column, 0.781 @ 5,000 RPMs, and 0.813 @5,500 RPMs.

[bradsm87]

I'm no expert but have you tried increasing d factor multiplier in the higher rpm columns?

I've had that problem with overshoots on upshifts and raising d factor multiplier a lot up there helps beat down / mitigate that overshoot quickly. Raising the multiplier in the lower and mid RPM's gave me oscillations but raising it up top doesn't seem to have that unwanted side effect.

I'm using 0.75 in the 4500 RPM column, 0.781 @ 5,000 RPMs, and 0.813 @5,500 RPMs.

Well I got it a little better.

- I advanced the intake cam from 116 to 115.2. Probably nowhere near enough to make a difference haha.
- Increased D-Factor values on the negative (left) side of the table back up to stock values. This makes it drop WGDC harder when boost is rising compared to the target curve.
- Changed the last breakpoint on the D-Factor multiplier table from 5500rpm to 6000rpm and increased the value in the last cell for more aggressive D-Factor at 6000rpm and above.
- Decreased "Threshold (Major throttle closure)" from 0.980 to 0.977 so that the throttle doesn't close as hard and cause as much of a spike. I may further reduce this but I do remember not really liking 0.970 back in the day as you can feel the slight delay when coming off the throttle.

I guess a 3psi spike before the throttle when the throttle closes is a pretty fair expectation and can't do much better than that.

Yep that did help a bit. Thanks for sharing that it worked for you. I might further increase mine and see how it goes!

I think it's probably about as good as it's going to get. With upgraded turbos at 7000rpm and all the air momentum still very much wanting to flow and a hard change in RPM from the transmission is going to have a bit of a boost spike which is made worse by the throttle closing. I think a 3psi boost mean spike in that scenario is pretty much to be expected.

[europav]

get an ER charge pipe. Mine fits perfect

[bradsm87]

get an ER charge pipe. Mine fits perfect

Nah I'll give spending AU$500 on a piece of pipe (a little under a week's pay) a miss. Having a stock charge pipe keeps me from the temptation of running more boost and running into PCV and turbo issues anyway.