Boost spikes with PD blowers

[cc-rider]

On really hard shifts (m6 manual) I am occasionally getting a boost spike that causes KR every time. I'm running about 9.5 psi. And looking at my logs I see boost spike to 13-14 psi when doing something like a hard shift from 2nd to 3rd. These boost spikes are literally milliseconds long...but they are enough to trigger knock and make the KR go crazy.

It must have to do with a shift and resulting abrupt (and large) swings in the boost/vac/boost sequence from the bypass valve shutting and opening so quickly. It only happens on higher rpm shifts. The only way I can figure it is that the blower is spun up and really huffing some air and hits the engine with more boost than it can consume for a brief instant. And it's usually a 2-3 shift or a 3-4 shift (higher engine loads after the shift). Never seems to happen on a 1-2 shift. Maybe the engine can rev up and consume that boost as quick as it can come in lower engine load conditions...but at higher loads after the shift its causes a pile up of boost?

Anyone have any solutions on how to deal with this? I slowed my throttle blade opening rate down. But HP Tuners settings doesn't allow you that much control over the opening rate. I've also heard of people putting carb jets into the boost/vac line that controls the bypass valve. Anyone ever tried this?

Perhaps the next big leap in PD blower technology is the ability to have variable control of the bypass valve closing rate...

[GHuggins]

SS had this same problem with a Whipple. Seems to be on platforms running stock cams and or exhaust? Unfortunately the solutions you already stated are the only ones I know of to bandaid the problem for now?

[ttz06vette]

I had that problem in my twin turbo setup and fixed it by reducing gate pressure on my boost controller. Doesn't sound like there is a similar way to control how quickly boost builds on a blower...

[cc-rider]

Nope. And it seems like their should be. It's time to stop controlling the bypass valve with a single pre defined spring and give us something more adjustable.

[10_SS]

you give people enough time and they come around. . I whined about this forever when I first got the Whipple, in the end slowing the opening rate is perfect. I was at 3-4 for years, latey just ramped it up to 8. G has a good point, maybe stock cam/exhaust contributes. I thought about adding an oriface but that would also reduce its opening when you let off... a check valve may fix that. But I feel the opening rate is all control you need. What other settings do you feel are missing?

Regarding the Manifold Volume setting, using the fast AEM 0330 can wideband I was seeing lean tip in 28:1AFR just for a short blip, and now increasing it 50% from a ZL1 setting maybe reduced the max lean spike down to 18AFR, but it may be spread out longer... so i don't know what is better. Manifold Volume didn't fix it, just changed the way it behaves. This is above 4000rpm that I know transients behave completely different than below 4000rpm, in my opinion don't work above 4000rpm. 2010 E38 Camaro LS3 btw.

[cc-rider]

Yeah yeah...I'm with you bud. You were right 😄 Boost spikes are a bitch. The KR goes nuts. I'll have to go down to 5 or something on the throttle setting. I think I'm at 10 now.

But where I do disagree is that the transients don't work above 4K. I've been keen to look at this since you pointed this out. And I see transients up there above 4K. I'll try to post some datalogs later. Did you ever adjust you're VE table any further? That big dip you had in the 100-130 kpa range always made me wonder if your lack of transient fuel was coming from that VE table being referenced on throttle transients and that dip was pulling fuel.

[10_SS]

I just checked my file it is at 5 for opening rate, was 3, not 8 like I said. Do you have burst knock working? I still have that and it pulls allot and goes away fast, so I dont get knock. I did retune the VE tables more, but dont seem to help the lack of transient fuel above 4000... I'll also find some logs to post here, I get lots of tip in fuel below 4000, above it all goes away.

Here's one where there's some WOT below 3999rpm vs some above 4000rpm... you need to see the AEM WB data so the charts are attached hopefully that brings it in ok. This was right after I installed the new WB and have since dialed it wots much better. Zoom way in, you'll see lots of lean tip in above 4000rpm.

Good examples
2:09 through 2:29 are going WOT at just under 3900rpm and at 2:40 enter WOT at 4100rpm...
3:34 is a throttle blip at 3500rpm and nice and rich tip in, 3:36 goes WOT at 4100rpm, lean tip in
below 4000rpm is 6:10 then above 4000rpm is 6:15 but that RPM is farther apart.

You'll see anything going WOT below 3900rpm has this rich spike after the slight lean spike, and anything above 4000rpm still has the lean spike, then just kinda comes down slow. But slowing throttle opening with burst knock combined eliminated my knock so I'm not concerned anymore.

I can tell just from the shape of the beginning of the WOT Wideband curve if I was below or above 4000rpm, that's how pronounced it is.

You could try a test, go back and put opening rate above 10 and see if most if your lean tip in/knock was above 4000rpm?

126a First Drive 3900-4100rpm transients.hpl
Camaro.Charts.xml

[cc-rider]

Here is an example of the transients I am seeing above 4k rpm. I was doing a bit of a burnout here so I was on and off the throttle multiple times above 4k rpm. You can see in the injector pulsewidth (white line in the bottom chart) that there is a spike every time I get back into the throttle. Now it doesn't necessarily show up on the wideband (but you can see it a little bit). But to me...that injector pulsewidth chart clearly shows a transient shot. I think that the engines consume it so fast at higher rpms so you don't necessarily see it on a wideband like you would a transient at lower rpms.

I'll definitely slow the throttle rate down a bit more and see if that works.

I didn't turn burst knock back on yet. I tried to turn this on when I was running a speed density tune and it went nuts. Would just repeatedly trigger the burst knock. So I had to shut it back off. But now I'm running a MAF/dynamic tune. So maybe the burst knock function works off the MAF Air only and needs the MAF functional in the tune. So I'll have to give it a try again. I like the idea of burst knock....for exactly what we are talking about here. PD blowers could benefit from this because of how hard they hit the engines with boost.

transient.jpg

[10_SS]

All I can tell from that pic is your Fuel Pressure drops and your injectors go up but that's expected... and you have a small pressure spike but not bad.

But then there was all of this which basically says the "pump shot" stops working: http://www.hptuners.com/forum/showth...-above-3999rpm