So, I've had an issue on my car that I cannot tune out for the life of me ( running a Terminator X ). On every gear change, as RPM climbs and boost ramps up, the boost overshoots before settling flat. I have CO2 control, and I'm using a boost vs. dome control strategy (boost by speed). I've watched Joe Simpson's course on tuning boost with PID values, but nothing I've changed prevents this rise. It's not a spike, it's a gradual "hump" of sorts. The only thing I've noticed that is odd is when the hump occurs, dome pressure exceeds the commanded value by 1-3 PSI. That makes me wonder if exhaust pressure is cracking the wastegate open, compressing the spring slightly and raising the dome pressure. Yet the wastegate isn't flowing enough when it's slightly cracked to slow down the turbo, so it's a positive feedback loop that causes the boost to rise above commanded values. If I mess with the PID values, the hump never changes, but I have caused my boost to have a dip after the hump if I try to control it using "fast" PID values.

What if I were to change my "max boost allowed" curve to a value lower than dome pressure, but only at the MPH ranges where the "humps" occur? It seems to me, in theory at least, that it would make the vent solenoid dump more CO2 as RPM rises and maybe catch the rise before it happens. As far as I can tell, that's how the boost vs. dome control strategy functions. The only other fix I can think of is to install either a bigger wastegate or a second wastegate. Right now I have a VS Racing 44MM gate. Anybody have any ideas? By the way, if you're not aware, this is a stick shift car, so I let off the gas at every gear change.

 

Might be worth reaching out to Jay Blanchard (Jaywire, Grand Haven).

 

Weird that you say that, I was at the track tonight and saw a guy wearing a Jaywire T-shirt. I ended up having the opposite problem, and I'm scratching my head as to what is happening. 1st and 2nd gear, I got a bit of the rise in boost, but in 3rd and 4th, it went up to 16.5 PSI and flatlined. No overshoot at all. The problem is, I was commanding a rising boost curve all the way to 24 lbs. of dome pressure and it didn't raise the boost whatsoever. I'm wondering if I have a boost leak somewhere. Doesn't make sense that it's only in 3rd and 4th gear though, although 1st and 2nd don't seem completely right. See the datalog traces below to see what I'm talking about.

 

Jay was helping his buddy Brian with the gray Nova. Jay has a beard. Great guy, he's been one of my go-to guys.

 

I struggled with my dominator system with C02. Finally moved the dome sensor off the gate (I have 2 gates), updated to the fancy Holley solenoids and finally found a suggestion buried in a Holley forum post on how to tackle the PID settings.

I’m auto trans.

It’s my understanding that TermX has more sophisticated boost control than the Dominator. I guess the Dominator update is a year behind schedule….

 

If you are having CO2 pressure problems I would highly suggest temporarily setting up your dome pressure targets to be able to test and watch what is happening without the car running and making a pass. This way you can literally sit there and play with settings in your garage and verify it's doing what it's supposed to do be doing. Of course a lot depends on how you have it setup to begin with so without knowing any of that it's shooting in the dark.

 

I did just that Nic. I’m boost by time so it’s pretty easy using the strip chart to see Dome vs Commanded.

The OP is boost by speed so I’d assume he would need to set up boost by time to do the static test?

I used shop air and started with the PID values at 0

 

Yes, I'm boost by speed. I don't know how well the testing would work since setting it up with boost by time wouldn't simulate shift points where the throttle is shut and then I'm going WOT again. I've done a lot of testing with different PID settings and most of the time, changing them doesn't prevent the hump from occurring, but it does induce a downward drop in dome pressure after the hump. Where I have it now creates the most level pressure over a pass, aside from the humps. I do wonder if there's something mechanically wrong, however. If you look at the second datalog trace, 3rd and 4th gear are perfect. Normally they're not. I guess I'll have to do some inspection of my system to see if there's something going on.

 

I had this same characteristic with my last car, I would get a small spike on the 1-2 change but nothing on 3-4.
I was told it's just the nature of racing a stick shift car because the boost can't get out fast enough between the gear change if you're lifting while shifting.
Never gave me any issues so I just left it alone.

 

Do what RonSSNova did, change it to boost by time so you can do your testing to check your settings and adjust as necessary. You should be able to get it to nail the dome pressures and keep them in check. It's normal to have boost rise a little bit at the same dome pressure as load increases, but if your dome pressure rises it should bleed that off immediately with the correct settings. If your complaint is that actual manifold pressure rises with gear changes and not dome pressure then create an offset table for gear/dome to keep it steady. Actually seeing your settings and configuration would go a long ways to being able to make real suggestions though.

 

Try playing around with the Target Rate Limiter. Try going Down by 10 and make a pull and check the log

 

Hey Ron, good to see you post. Hope all has been well with you. I haven't been active in awhile. I'll have to catch up with you.
Yeah, seems like Holley has decided not to release a update for the Dominator for some reason.

 

Hey Rick. Doing ok. Just getting old. 😁