Background:
Car is boosted with GTM Stage 2, made 514whp @11 psi. Car is now running Blitz Dual SBC Spec S boost controller. Settings 1-3 hold boost great with set gain at 5 and Duty cycle @ 22% (7.5psi), 30% (8.75psi), 38% (10.25ish psi). As soon as I turn it to 39% or 40% it jumps beyond my safe limit of around 11ish psi.

Now, in the instructions, it states that only the Spec R system should be used in a Twin or sequential turbo setup because of the capacity of the solenoid. It is a simple design with a two-wire input and IN/OUT/BLEED ports. I think what is happening is the solenoid sold with the Spec S is reaching its maximum capacity of airflow and is not able to keep up with the turbos past a certain point. The Input port on the solenoid is sourced from the passenger side cold pipe only. We are not reading both cold pipes for the boost source, which should not be an issue.

I'm thinking about switching out the solenoid for a MAC 30-2400 which seems more durable and capable of much higher boost pressures and is also uses a two wire elec. input and similar boost line routing. The car is externally gated with 5.80lb springs.When Jon tuned the car it had a Greddy Profec B Spec 2 controller which uses the same solenoid I'm looking at getting.

Shouldn't this work fine? Its a cheap experiment ($37) to test my boost control issue past 38%. Do you guys think the MAC solenoid will work with the Blitz head unit. The only difference between the Spec S and Spec R is the boost solenoid according to the U.S. Representative for Blitz. I'm pretty sure the Duty Cycle on the Head Unit controls the voltage the solenoid sees up to 12 volts base on the wastegate duty cycle.

Thoughts? I just want to run 11.0 psi with steady control. I'm fine with a little spike as long as it settles back down at 11.0 psi.

Thanks in advance.
Jay

 

a solenoid is a solenoid.

You aren't maxing the solenoid out. When that happens you can't hold boost, IE: it will drop down towards wastegate spring pressure.

On some boost controllers there is no rhyme or reason to the percentage numbers. They do not directly correlate with the rise in boost. So Just going from 38% up to 40% might be a whole 1psi in boost or maybe 2psi. It's hard to tell.

Chances are it's just a boost spike as it tries to control it to the set psi. Mine spikes up and down a little bit around the set boost.

You are already seeing 10.25psi so going up to 11psi probably won't yield enough gain to mess with anyways.

 

Which controller do you use?

 

haltech.

i run closed loop tuning based on wheel speed to keep traction. One of the many benefits of a nice stand alone

I know a few people on here with aem true boost that have had the same issue you have. They move it 1% and get small changes in some areas then other areas 1% is a huge change in boost pressure.

 

OK, thanks for the info. The AEM True boost uses the same solenoid that I was looking at so if people are having similar issues it may not be a remedy.

 

well it's not a problem with the boost controller, it's a problem with "open loop" boost control in general.

Pressure on that wastegate isn't linear so trying to get a linear response from a duty cycle percentage with a solenoid is almost impossible.

when i have mine set based on open loop it will do funky things like that. As the boost goes up it generally requires more and more duty cycle to get the desired increase. Where this fails can be certain duty cycles the solenoid is more efficient or the exhaust pulses are different. It's really hard to tell.

if i watch the output of my closed loop duty cycle some pulls it might be at 26% to hold a boost number and other times it might be at 25% and other times it's at 27% so it varies up and down a little. It does that to target a specific boost level. Now if it was just set at say 26% then i would be seeing changes in boost pressure instead of a constant boost with varying duty cycle.

It varies by RPM as well. I'd say try it at 39% and see if that 11psi is just a temporary spike or if it actually holds boost higher. If 11psi is truthfully your "danger" zone then i wouldn't recommend it though. 10.25 is already too close to danger. My "danger" zone is 29psi and i run 22psi so i have plenty of room to overboost without damage.

 

You should just sell that boost controller and buy this easier to use HKS EVC VI

https://my350z.com/forum/turbos-nitr...ml#post9528489

 

Hi 08NismoZ, the Blitz unit is very simple to operate. That is not the issue. I think I will stick with it. Also Jeff, I understand boost will vary with outdoor weather conditions, especially barometric pressure since pressure is what we are talking about. I used to adjust my Profec B Spec 2 constantly based on weather conditions. My car is tuned at 11psi so I just dont want to run much beyond that, say 12psi for example. Thanks for all of the feedback and assistance Jeff.

 

no problem. like i said, put it at 1% greater and do a few logs and see what it does.

just some of the normal pitfalls of static duty cycle boost controllers (open loop)